How Children Develop [6th Canadian ed.] 9781319269678

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How Children DEVELOP CANADIAN SIXTH EDITION

How Children DEVELOP CANADIAN SIXTH EDITION Robert Siegler Teachers College, Columbia University Jenny R. Saffran University of Wisconsin–Madison Susan Graham University of Calgary Elizabeth T. Gershoff The University of Texas at Austin Nancy Eisenberg Arizona State University and Campbell Leaper University of California, Santa Cruz Author of Chapter 15: Gender Development

This is dedicated to the ones we love

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About the Authors

ROBERT SIEGLER is the Schiff Foundations Professor of Psychology and Education at Teachers College, Columbia University. His research focuses on how children learn mathematics. He is author of the cognitive development textbook Children’s Thinking and has written or edited several additional books on child development. His

books have been translated into Japanese, Chinese, Korean, German, Spanish, French, Greek, Hebrew, and Portuguese. He has presented keynote addresses at the conventions of the Cognitive Development Society, the Japanese Psychological Association, the German Psychological Association, the American Psychological Society, and the Conference on Human Development. He also has served as Associate Editor of the journal Developmental Psychology, co-edited the cognitive development volume of the 1998 and 2006 editions of the Handbook of Child Psychology, and served on the National Mathematics Advisory Panel from 2006 to 2008. Dr. Siegler received the American Psychological Association’s Distinguished Scientific Contribution Award in 2005, was elected to the National Academy of Education in 2010, was named Director of the Siegler Center for Innovative Learning at Beijing Normal University in 2012, and was elected to the Society of Experimental Psychologists in 2016.

JENNY R. SAFFRAN is the Vilas Distinguished Achievement Professor and College of Letters & Science Distinguished Professor of Psychology at the University of Wisconsin–Madison, and is an investigator at the Waisman Center. Her research is focused on learning in infancy and early childhood, with a particular emphasis on language. Dr. Saffran’s research has been continually funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development for over 20 years. She has received numerous awards for her research and teaching, including the Boyd McCandless Award from the American Psychological Association for early career contributions to developmental psychology and the Presidential Early Career Award for Scientists and Engineers from the National Science Foundation. In 2015, she was elected to the American Academy of Arts and Sciences.

SUSAN GRAHAM is a Professor in the Department of Psychology at the University of Calgary and the Director of the Owerko Centre at the Alberta Children’s Hospital Research Institute. She is a fellow of the Association for Psychological Science and Canadian Society for Brain, Behaviour, and Cognitive Science. She has received a number of awards for her research and mentorship, including a Canada Research Chair, the Killam Annual Professor Award, and the Izzak Walton Killam Award for Graduate Supervision and Mentoring. She is currently the Editor-in-Chief for the Journal of Cognition and Development. After completing her undergraduate degree at the University of Manitoba, she moved to Concordia University to complete her graduate studies. She received her PhD in Clinical Psychology in 1996. Her research program focuses on language and

cognitive development during the infancy and preschool years and has been continuously funded by the Natural Sciences and Engineering Research Council of Canada and the Social Sciences and Humanities Research Council of Canada.

ELIZABETH T. GERSHOFF is the Amy Johnson McLaughlin Centennial Professor of Human Development and Family Sciences and Associate Director of the Population Research Center, both at the University of Texas at Austin. Her research focuses on how parental and school discipline affect child and youth development and on how parent education and early childhood education programs, such as the federal Head Start program, can improve the lives of at-risk

children. Dr. Gershoff has been awarded numerous federal grants from the Centers for Disease Control and Prevention, the National Institute for Child Health and Human Development, the National Institute for Mental Health, and the National Science Foundation to support her research. She was lead author of the volume Societal Contexts of Child Development, which won the 2014 Society for Research on Adolescence Social Policy Award for Best Edited Book, and of a new book, Ending the Physical Punishment of Children: A Guide for Clinicians and Practitioners. She was an Associate Editor at the journal Developmental Psychology and is President-Elect of the Society for Child and Family Policy and Practice, which is Division 37 of the American Psychological Association. She is an internationally recognized expert on the effects of physical punishment on children, and her research on the topic has been recognized with a Lifetime Legacy Achievement Award from the Center for the Human Rights of Children at Loyola University Chicago and the Nicholas Hobbs Award from Division 37 of the American Psychological Association. NANCY EISENBERG is Regents’ Professor of Psychology at Arizona State University. Her research interests include social, emotional, and moral development, as well as socialization influences, especially in the areas of self-regulation and adjustment. She has published numerous empirical studies, as well as books and chapters on these topics. She has also been editor of Psychological Bulletin and the Handbook of Child Psychology and was the founding editor of the Society for Research in Child Development journal Child Development

Perspectives. Dr. Eisenberg has been a recipient of Research Scientist Development Awards and a Research Scientist Award from the National Institutes of Health (NICHD and NIMH). She has served as President of the Western Psychological Association and of Division 7 of the American Psychological Association and is president-elect of the Association for Psychological Science. She is the 2007 recipient of the Ernest R. Hilgard Award for a Career Contribution to General Psychology, Division 1, American Psychological Association; the 2008 recipient of the International Society for the Study of Behavioral Development Distinguished Scientific Contribution Award; the 2009 recipient of the G. Stanley Hall Award for Distinguished Contribution to Developmental Psychology, Division 7, American Psychological Association; and the 2011 recipient of the William James Fellow Award for Career Contributions in the Basic Science of Psychology from the Association for Psychological Science.

Brief Contents Preface 1 An Introduction to Child Development 2 Prenatal Development and the Newborn Period 3 Biology and Behaviour 4 Theories of Cognitive Development 5 Perception, Action, and Learning in Infancy 6 Development of Language and Symbol Use 7 Conceptual Development 8 Intelligence and Academic Achievement 9 Theories of Social Development 10 Emotional Development 11 Attachment to Others and Development of the Self 12 The Family 13 Peer Relationships 14 Moral Development 15 Gender Development 16 Conclusions

Glossary References Name Index Subject Index

Contents Preface

CHAPTER 1 An Introduction to Child Development Reasons to Learn About Child Development Raising Children Choosing Social Policies

BOX 1.1 A Closer Look: The Romanian Adoption Study Understanding Human Nature Historical Foundations of the Study of Child Development Early Philosophers’ Views of Children’s Development Social Reform Movements Darwin’s Theory of Evolution Enduring Themes in Child Development 1. Nature and Nurture: How Do Nature and Nurture Together Shape Development? 2. The Active Child: How Do Children Shape Their Own Development? 3. Continuity/Discontinuity: In What Ways Is Development Continuous, and in What Ways Is It Discontinuous? 4. Mechanisms of Change: How Does Change Occur? 5. The Sociocultural Context: How Does the Sociocultural Context Influence Development? 6. Individual Differences: How Do Children Become So Different from One Another? 7. Research and Children’s Welfare: How Can Research Promote Children’s Well-Being? Methods for Studying Child Development The Scientific Method BOX 1.2 Individual Differences: Can Children Learn to

Be More Intelligent? Contexts for Gathering Data About Children Correlation and Causation Research Designs for Examining Children’s Development Ethical Issues in Child-Development Research CHAPTER SUMMARY

CHAPTER 2 Prenatal Development and the Newborn Period Prenatal Development BOX 2.1 A Closer Look: Beng Beginnings Conception BOX 2.2 Individual Differences: Do Girls Outnumber Boys? Developmental Processes

Early Development An Illustrated Summary of Prenatal Development Fetal Experience and Behaviour Fetal Learning Hazards to Prenatal Development Teratogens BOX 2.3 Applications: Sudden Infant Death Syndrome Maternal Factors The Birth Experience Diversity of Childbirth Practices The Newborn Infant State of Arousal Negative Outcomes at Birth CHAPTER SUMMARY

CHAPTER 3 Biology and Behaviour Nature and Nurture Genetic and Environmental Forces BOX 3.1 Applications: Genetic Testing Behaviour Genetics Quantitative Genetics Research Designs Heritability Molecular Genetics Research Designs BOX 3.2 Individual Differences: Genetically Transmitted Developmental Disorders Environmental Effects Brain Development The Neuron

The Cortex Developmental Processes BOX 3.3 A Closer Look: Mapping the Mind The Importance of Experience The Body: Physical Growth and Development Growth and Maturation Nutritional Behaviour BOX 3.4 A Closer Look: Poverty and Health Disparities Vaccines CHAPTER SUMMARY

CHAPTER 4 Theories of Cognitive Development Piaget’s Theory View of Children’s Nature Central Developmental Issues BOX 4.1 Applications: Educational Applications of Piaget’s Theory Piaget’s Legacy Information-Processing Theories View of Children’s Nature Central Developmental Issues The Development of Problem Solving BOX 4.2 Applications: Educational Applications of Information-Processing Theories Core-Knowledge Theories View of Children’s Nature Central Developmental Issue: Nativism Versus Constructivism BOX 4.3 Applications: Educational Applications of CoreKnowledge Theories Sociocultural Theories View of Children’s Nature: Vygotsky’s Theory Central Developmental Issues BOX 4.4 Applications: Educational Applications of Sociocultural Theories

Dynamic-Systems Theories View of Children’s Nature Central Developmental Issues BOX 4.5 Applications: Educational Applications of Dynamic-Systems Theories CHAPTER SUMMARY

CHAPTER 5 Perception, Action, and Learning in Infancy Perception

Vision BOX 5.1 A Closer Look: Infants’ Face Perception Auditory Perception BOX 5.2 A Closer Look: Picture Perception Taste and Smell Touch Intermodal Perception Motor Development Reflexes Motor Milestones Modern Views of Motor Development The Expanding World of the Infant BOX 5.3 A Closer Look: “The Case of the Disappearing Reflex” BOX 5.4 A Closer Look: “Gangway—I’m Coming Down” Learning and Memory Habituation Statistical Learning Classical Conditioning Instrumental Conditioning Observational Learning/Imitation Rational Learning Active Learning Memory

CHAPTER SUMMARY

CHAPTER 6 Development of Language and Symbol Use Language Development The Components of Language What Is Required for Language? BOX 6.1 Applications: Two Languages Are Better Than One The Process of Language Acquisition Speech Perception Word Segmentation Preparation for Production First Words BOX 6.2 Individual Differences: Language Development

and Socioeconomic Status BOX 6.3 Applications: iBabies: Technology and Language Learning Putting Words Together Conversational Skills Later Development Theoretical Issues in Language Development Chomsky and the Nativist View Ongoing Debates in Language Development BOX 6.4 A Closer Look: “I Just Can’t Talk Without My Hands”: What Gestures Tell Us About Language BOX 6.5 Individual Differences: Developmental Language Disorders Nonlinguistic Symbols and Development Using Symbols as Information Drawing and Writing CHAPTER SUMMARY

CHAPTER 7 Conceptual Development Understanding Who or What Dividing Objects into Categories Understanding Oneself and Other People BOX 7.1 Individual Differences: Children with Autism Spectrum Disorders (ASD) Knowledge of Living Things BOX 7.2 Individual Differences: Imaginary Companions Understanding Why, Where, When, and How Many Causality BOX 7.3 A Closer Look: Magical Thinking and Fantasy

Space BOX 7.4 Individual Differences: Development of Spatial Concepts in Blind and Visually Impaired People Time Number Relations Among Understanding of Space, Time, and Number CHAPTER SUMMARY

CHAPTER 8 Intelligence and Academic Achievement What Is Intelligence? Intelligence as a Single Trait Intelligence as a Few Basic Abilities Intelligence as Numerous Cognitive Processes A Proposed Resolution Measuring Intelligence

The Contents of Intelligence Tests The Intelligence Quotient (IQ) Continuity of IQ Scores IQ Scores as Predictors of Important Outcomes Other Predictors of Success Genes, Environment, and the Development of Intelligence Qualities of the Child Influence of the Immediate Environment Influence of Society BOX 8.1 Applications: Highly Successful Early Interventions: Better Beginnings, Better Futures (BBBF) and the Carolina Abecedarian Project Alternative Perspectives on Intelligence Gardner’s Theory Sternberg’s Theory Acquisition of Academic Skills: Reading, Writing, and Mathematics Reading BOX 8.2 Individual Differences: Dyslexia Writing Mathematics BOX 8.3 Applications: Mathematics Disabilities CHAPTER SUMMARY

CHAPTER 9 Theories of Social Development Psychoanalytic Theories Freud’s Theory of Psychosexual Development Erikson’s Theory of Psychosocial Development Current Perspectives Learning Theories Watson’s Behaviourism Skinner’s Operant Conditioning Social-Learning Theory Current Perspectives BOX 9.1 A Closer Look: Bandura and Bobo Theories of Social Cognition Selman’s Stage Theory of Role Taking Dodge’s Information-Processing Theory of Social Problem Solving

Dweck’s Theory of Self-Attributions and Achievement Motivation Current Perspectives BOX 9.2 A Closer Look: Developmental Social Neuroscience Ecological Theories Ethological and Evolutionary Theories The Bioecological Model BOX 9.3 Individual Differences: Attention-Deficit Hyperactivity Disorder Current Perspectives CHAPTER SUMMARY

CHAPTER 10 Emotional Development The Development of Emotions

Theories on the Nature and Emergence of Emotion The Emergence of Emotions BOX 10.1 A Closer Look: Basic Emotional Expressions in Infants Understanding Emotions Identifying the Emotions of Others Understanding Real and False Emotions BOX 10.2 A Closer Look: Emotional Intelligence Emotion Regulation The Development of Emotion Regulation The Relation of Emotion Regulation to Social Competence and Adjustment The Role of Family in Emotional Development Parents’ Expression of Emotion Parents’ Socialization of Children’s Emotional Responses Temperament Measuring Temperament Determinants of Temperament How Temperament Fits with Environment Mental Health, Stress, and Internalizing Mental Disorders Stress BOX 10.3 Applications: Toxic Stress and Adverse Childhood Experiences Internalizing Mental Disorders

BOX 10.4 Individual Differences: Gender Differences in Adolescent Depression CHAPTER SUMMARY

CHAPTER 11 Attachment to Others and Development of the Self The Caregiver–Child Attachment Relationship Attachment Theory Measurement of Attachment Security BOX 11.1 A Closer Look: Does Childcare Interfere with Attachment?

Sources of Individual Differences in Attachment Styles BOX 11.2 Applications: Interventions to Improve Attachment Attachment and Social-Emotional Development The Self Self-Concept BOX 11.3 Individual Differences: Development of SelfAwareness Amongst Autistic Children Self-Esteem BOX 11.4 A Closer Look: Is Too Much Praise Bad for SelfEsteem? Identity CHAPTER SUMMARY

CHAPTER 12 The Family Family Structure Changes in Family Structure in Canada BOX 12.1 Individual Differences: Teenagers as Parents Same-Sex Parents Divorced Parents Stepparents Family Dynamics Parenting BOX 12.2 Applications: Should Parents Spank Their Children? Differences in Mothers’ and Fathers’ Interactions with Their Children The Child’s Influence on Parenting Sibling Relationships Child Maltreatment Risks for Maltreatment Consequences of Maltreatment Box 12.3 Applications: Preventing Child Maltreatment Family Socioeconomic Context Cultural Contexts Economic Contexts BOX 12.4 A Closer Look: Homelessness Parents’ Work Contexts

Childcare Contexts BOX 12.5 Applications: Family-Leave Policies CHAPTER SUMMARY

CHAPTER 13 Peer Relationships Play Box 13.1 Individual Differences: The Development of Children’s Social Play Friendships Children’s Choice of Friends BOX 13.2 Individual Differences: Culture and Children’s Peer Experience Developmental Changes in Friendship The Role of Technology in Friendships Effects of Friendships on Psychological Functioning and Behaviour BOX 13.3 A Closer Look: Cyberbullying Gender Differences in the Functions of Friendships

Status in the Peer Group Measurement of Peer Status BOX 13.4 Applications: Fostering Children’s Peer Acceptance Cross-Cultural Similarities and Differences in Factors Related to Peer Status The Role of Parents in Children’s Peer Relationships Relations Between Attachment and Competence with Peers BOX 13.5 A Closer Look: Parents’ Strategies for Shaping Peer Relationships Quality of Ongoing Parent–Child Interactions and Peer Relationships CHAPTER SUMMARY

CHAPTER 14 Moral Development

Moral Judgment Piaget’s Theory of Moral Judgment Kohlberg’s Theory of Moral Reasoning Social Domain Theory of Moral Development The Development of Conscience Prosocial Behaviour The Development of Prosocial Behaviour The Origins of Individual Differences in Prosocial Behaviour BOX 14.1 A Closer Look: Cultural Contributions to Children’s Prosocial Tendencies BOX 14.2 Applications: School-Based Interventions for Promoting Prosocial Behaviour Antisocial Behaviour The Development of Antisocial Behaviours BOX 14.3 A Closer Look: Oppositional Defiant Disorder and Conduct Disorder The Origins of Aggression and Antisocial Behaviour Interventions for Aggressive and Antisocial Children BOX 14.4 Applications: Positive Youth Development and Service Learning CHAPTER SUMMARY

CHAPTER 15 Gender Development Sex and Gender Box 15.1 A Closer Look: Challenges to the Gender Binary Comparisons of Girls and Boys Theoretical Approaches to Gender Development Biological Influences Cognitive and Motivational Influences BOX 15.2 Applications: Where Are Spongesally Squarepants and Curious Jane? Cultural Influences Milestones in Gender Development Infancy and Toddlerhood Preschool Years Middle Childhood Adolescence Patterns of Gender Development Physical Growth: Prenatal Development Through

Adolescence Cognitive Abilities and Academic Achievement Interpersonal Goals and Communication Aggressive Behaviour BOX 15.3 Applications: Sexual Harassment and Dating Violence CHAPTER SUMMARY

CHAPTER 16 Conclusions Theme 1: Nature and Nurture: All Interactions, All the Time Nature and Nurture Begin Interacting Before Birth Infants’ Nature Elicits Nurture Timing Matters Nature Does Not Reveal Itself All at Once

Everything Influences Everything Theme 2: Children Play Active Roles in Their Own Development Self-Initiated Activity Active Interpretation of Experience Self-Regulation Eliciting Reactions from Other People Theme 3: Development Is Both Continuous and Discontinuous Continuity/Discontinuity of Individual Differences Continuity/Discontinuity of Overall Development: The Question of Stages Theme 4: Mechanisms of Developmental Change Biological Change Mechanisms Behavioural Change Mechanisms Cognitive Change Mechanisms Change Mechanisms Work Together Theme 5: The Sociocultural Context Shapes Development Growing Up in Societies with Different Practices and Values Growing Up in Different Times and Places Growing Up in Different Circumstances Within a Society Theme 6: Individual Differences Breadth of Individual Differences at a Given Time

Stability Over Time Predicting Future Individual Differences on Other Dimensions Determinants of Individual Differences Theme 7: Child-Development Research Can Improve Children’s Lives Implications for Parenting Implications for Education Implications for Helping Children at Risk Improving Social Policy Glossary References Name Index Subject Index

Preface This is an exciting time in the field of child development. Recent years have brought new theories, new ways of thinking, new areas of research, and innumerable new findings. We originally wrote How Children Develop to describe this ever-improving body of knowledge of children and their development and to convey our excitement about the progress that is being made in understanding the developmental process. We are pleased to continue this endeavour with the publication of the Canadian sixth edition of How Children Develop. As teachers of child development courses, we appreciate the challenge that instructors face in trying to present these advances and discoveries—as well as the major older ideas and findings—in a one-semester course. Therefore, rather than aim at encyclopedic coverage, we focus on identifying the most important developmental phenomena and describing them in sufficient depth to make them meaningful and memorable to students. In short, our goal has been to write a textbook that makes the child development course coherent and enjoyable for students and teachers alike.

Classic Themes

The basic premise of the book is that all areas of child development are unified by a small set of enduring themes. These themes can be stated in the form of questions that child-development research tries to answer: 1. How do nature and nurture together shape development? 2. How do children shape their own development? 3. In what ways is development continuous, and in what ways is it discontinuous? 4. How does change occur? 5. How does the sociocultural context influence development? 6. How do children become so different from one another? 7. How can research promote children’s well-being? These seven themes provide the core structure of the book. They are introduced and illustrated in Chapter 1; highlighted repeatedly, where relevant, in the subsequent 14 content chapters; and utilized in the final chapter as a framework for integrating findings relevant to each theme from all areas of development. The continuing coverage of these themes allows us to tell a story that has a beginning (the introduction of the themes), a middle (discussion of specific findings relevant to them), and an ending (the overview of what students have learned about the themes). We believe that this thematic emphasis and structure will not only help students understand enduring questions about child development but will also leave them with a greater sense of satisfaction and completion at the end of the course.

Contemporary Perspective The goal of providing a thoroughly contemporary perspective on how children develop has influenced the organization of our book as well as its contents. Whole new areas and perspectives have emerged that barely existed when most of today’s child-development textbooks were originally written. The organization of How Children Develop is designed to present these new topics and approaches in the context of the field as it currently stands, rather than trying to shoehorn them into organizations that once fit the field but no longer do. Consider the case of Piaget’s theory and current research relevant to it. Piaget’s theory often is presented in its own chapter, most of which describes the theory in full detail and the rest of which offers contemporary research that demonstrates problems with the theory. This approach often leaves students wondering why so much time was spent on Piaget’s theory if modern research shows it to be wrong in so many ways. The fact is that the line of research that began more than 50 years ago as an effort to challenge Piaget’s theory has emerged since then as a vital area in its own right—the area of conceptual development. Research in conceptual development provides extensive information on children’s understanding of such fascinating topics as human beings, plants and animals, and the physical universe. As with other research areas, most studies in this field are aimed primarily at

uncovering evidence relevant to current claims, not those of Piaget. We adapted to this changing intellectual landscape in two ways. First, our chapter “Theories of Cognitive Development” (Chapter 4) describes the fundamental aspects of Piaget’s theory in depth and honours his legacy by focusing on the aspects of his work that have proven to be the most enduring. Second, a first-of-its-kind chapter called “Conceptual Development” (Chapter 7) addresses the types of issues that inspired Piaget’s theory but concentrates on modern perspectives and findings regarding those issues. This approach allows us to tell students about the numerous intriguing proposals and observations that are being made in this field, without the artificiality of classifying the findings as “pro-Piagetian” or “antiPiagetian.” The opportunity to create a textbook based on current understanding also led us to assign prominent positions to such rapidly emerging areas as epigenetics, behavioural genetics, brain development, prenatal learning, infant cognition, acquisition of academic skills, emotional development, prosocial behaviour, and friendship patterns. All these areas have seen major breakthroughs in recent years, and their growing prominence has led to even greater emphasis on them in this edition.

Getting Right to the Point

Our desire to offer a contemporary, streamlined approach led to other departures from the traditional organization. It is our experience that today’s students take child-development courses for a variety of practical reasons and are eager to learn about children. Traditionally, however, they have had to wait two or three or even four chapters—on the history of the field, on major theories, on research methods, on genetics—before actually getting to the study of children. We wanted to build on their initial motivation from the start. Rather than beginning the book, then, with an extensive examination of the history of the field, we include in Chapter 1 a brief overview of the social and intellectual context in which the scientific study of children arose and provide historical background wherever it is pertinent in subsequent chapters. Rather than have an early chapter of “blockbuster” theories that covers all the major cognitive and social theories at once (at a point far removed from the content chapters to which the theories apply), we present a chapter on cognitive developmental theories just before the chapters that focus on specific aspects of cognitive development, and we similarly present a chapter on social developmental theories just before the chapters that focus on specific aspects of social development. Likewise, rather than have a separate chapter on genetics, we include basic aspects of genetics as part of Chapter 3, “Biology and Behaviour,” and then discuss the contributions of genetics to some of

the differences amongst individuals throughout the book. When we originally chose this organization, we hoped that it would allow us, from the first weeks of the course, to kindle students’ enthusiasm for finding out how children develop. Judging by the overwhelmingly positive response we have received from students and instructors alike, it has.

Features The most important feature of this book is the exposition, which we have tried to make as clear and compelling as possible. As in previous editions, we have given extra attention to making it accessible to a broad range of students. To further enhance the appeal and accessibility of the text, we have retained three types of discussion boxes that explore topics of special interest: “Applications” boxes focus on how child development research can be used to promote children’s well-being. Amongst the applications that are summed up in these boxes are genetic testing, which probes the depths of an individual’s genetic makeup; board-game procedures for improving preschoolers’ understanding of numbers; the Better Beginnings, Better Futures program; interventions to reduce child abuse; programs, such as PATHS, for helping rejected children gain acceptance from their peers; and Positive Youth Development and Service Learning

Programs, which seek to reduce problem behaviours and increase positive behaviours. “Individual Differences” boxes focus on populations that differ from the norm with regard to the specific topic under consideration, or on variations amongst children in the general population. Some of these boxes highlight developmental problems such as autism, ADHD, dyslexia, specific language impairment, visual impairments, and conduct disorder, whereas others focus on differences in the development of children that centre on attachment status, gender, socioeconomic status, and cultural differences. “A Closer Look” boxes examine important and interesting research in greater depth than would otherwise be possible: the areas examined range from brain-mapping techniques to explorations of gender nonbinary identity to the developmental impact of homelessness and disparities between poverty and health. In place of the brief section summaries used in previous editions, we cap each major section with a thought-provoking Review Question. These prompts serve the dual purpose of encouraging deeper thinking about the material and of forcing the student to pause before diving ahead in the chapter. We have also retained a number of other features intended to improve students’ learning. These features include boldfacing key terms and supplying definitions both within the immediate text and in marginal glossaries; extensive, bulleted Summaries at the end of

each chapter; Test Yourself quizzes for students to quickly test their comprehension and understanding of the material in preparation for exams or simply as a way to review; and Critical Thinking Questions intended to promote deeper consideration of essential topics.

The Canadian Edition Our goal in writing this Canadian edition was to create a textbook that retains the essential and updated coverage of the American edition, but would also engage Canadian students by situating the content in Canadian and international contexts, highlighting the remarkable scientific accomplishments of Canadian developmental scientists, drawing on Canadian issues, and including current Canadian data and statistics whenever possible. We integrate discussion of research conducted with Canadian children and families throughout the chapters, highlighting the research conducted at universities across Canada. Finally, we have included photographs and figures that reflect the Canadian context and Canadian research. To illustrate how we have incorporated a Canadian perspective, we highlight below some of the specific information included across different chapters. Please note that this is by no means an exhaustive list of the Canadian content incorporated in each chapter!

Chapter 1

We have included recent statistics about the prevalence of spanking in Canada, recent developments in practices regarding legal interviews of and testimony from children in Canada, and recent rates of child poverty in Canada. We also incorporate findings from the study of children who were adopted from Romanian orphanages to families in Canada. We include a description of the Tri-Council Policy Statement: Ethical Conduct for Research Involving Humans, which governs research involving human subjects in Canada.

Chapter 2 We incorporate Canadian statistics about maternal smoking, the use of alcohol and drugs during pregnancy, fetal alcohol syndrome (FAS), sudden infant death syndrome (SIDS), the rate of teenage pregnancies, infant mortality rates (including comparison of rates across some provinces and territories, with a focus on the north), newborns with low birth weight, and multiple births. We also discuss recent developments related to environmental pollutants affecting Inuit communities and the Grassy Narrows and White Dog First Nations people. We present research from studies conducted in Alberta investigating the effects of maternal prenatal depression on children’s brain structure. We present data on hospitalization rates for First Nation and Inuit infants compared to non-Indigenous infants in a discussion of structural racism.

Chapter 3 We discuss recent research from the University of Toronto on genetic mutations that may lead to autism, findings from the Quebec Newborn Twin Study, information about mandated daily physical activity in schools, and McMaster University’s Early Development Inventory and other interventions to address issues related to the effects of poverty on children’s health and wellbeing.

Chapter 5 We highlight research by Canadian researchers including Kang Lee, who looked at other-race effect (ORE) in children; Sarah Laurence, Daphne Maurer, and Catherine Mondloch, who study face perception of infants; Laurel Trainor, Sandra Trehub, and Glen Schellenberg, who study infants’ responses to music; and Diane Poulin-Dubois, who researches infants’ observational learning and imitation.

Chapter 6 We cite research from McGill University that provides insight into language and the brain, comparing brain activation in the left hemisphere for hearing speakers of English and deaf signers of American Sign Language (ASL) and Langue des Signes Québécoise (LSQ). We also describe research from Canadian researchers such as

Laurel Trainor (McMaster University), Janet Werker (University of British Columbia), Diane Poulin-Dubois (Concordia University), and Geoff Hall (University of British Columbia), whose research has shaped our understanding of language development. The discussion of bilingualism includes details specific to the Canadian context.

Chapter 7 We present a multi-country study from J. Bradley Wigger about the prevalence of imaginary companions, as well as research from the Angus Reid Institute on beliefs in fantasy and the supernatural.

Chapter 8 We describe results of the Better Beginnings, Better Futures program in Ontario and of the Aboriginal Head Start Program in Urban and Northern Communities, as well as Canadian studies on gifted children and the development of reading abilities. We also discuss Canadian research on how reading at home affects the development of reading skills, as well as a recent Canadian study on children’s use of invented spelling.

Chapter 9 We present data on the prevalence of ADHD diagnoses among

Canadian children. We discuss screen time rates among children in Alberta, and present recommendations from the Canadian Pediatric Society. We also discuss social media trends among Canadian adolescents.

Chapter 10 We discuss the Roots of Empathy program, originally developed in Toronto, which aims to encourage prosocial behaviour and decrease aggressive behaviour, and the Alberta Family Wellness Initiative, which works to develop practices and policy related to mental health. We present a new study conducted in Alberta exploring the intergenerational effects of Adverse Childhood Experiences (ACEs). We present findings on access to mental health care across Canada, and we offer data on the prevalence of mood disorders among Canadian children.

Chapter 11 We highlight Canadian research on paternal and maternal attachment, bicultural integration and ethnic identity, and sexual-minority adolescents, including a discussion of the impact of Gay Straight Alliances in Canadian schools.

Chapter 12

This chapter has been heavily revised to present recent changes to the Canadian family structure, including statistics related to lone parents, first-time parents, adolescent parents, grandparents raising children, same-sex parents, teen parents, and divorced and stepparent families, with supporting graphs detailing various family structures by child’s age and province. We discuss child maltreatment in the context of the Public Health Agency of Canada’s description of various forms of abuse, and present recent data from Ontario on rates of abuse. Within the discussion of the economic context, we present data and research on child poverty and homelessness in Canada. We reference research on Canadian family-leave policies and the effects and availability of childcare, including a detailed presentation of the Alberta Child Care Accreditation Standards.

Chapter 13 This chapter includes discussion of Canadian research on peer relations, including studies by researchers such as Hildy Ross, Bill Bukowski, François Poulin, Sara Pedersen, Frank Vitaro, Shelley Hymel, Robert Coplan, and Wendy Craig. We include statistics from Canadian studies on time spent with friends, adolescents’ use of technology, bullying, and cyberbullying.

Chapter 14 This chapter includes Canadian studies on the relationship

between cultural and socioeconomic differences and morality, temperament and prosocial behaviour, aggression, the connection between socioeconomic status and antisocial behaviour, and the prevalence of Oppositional Defiance Disorder. We discuss community service projects in Ontario and other provinces. This chapter opens with a discussion of the tragic murder of Canadian soldier Captain Nathan Cirillo.

Chapter 15 This chapter highlights Canadian research on academic achievement, including degree attainment by women in STEMrelated fields, gender bias in observed aggressive behaviour, and sexual harassment and physical aggression in dating relationships.

New and Expanded Coverage In every edition, we endeavour to address new developments in the field and bring in fresh examples drawn from current events. In addition to the Canadian focus just described, we have expanded our coverage of a number of research areas that have become increasingly important in recent years for both the students of child development and the instructors who teach it. We have sought in this Canadian sixth edition to balance the inclusion of this new material

with judicious cuts and consolidation of coverage. We have worked to remove outdated and less relevant material, eliminate overlapping coverage across chapters, and present core concepts in a more concise manner. The result is a leaner, more visually appealing text that delivers the same wealth of coverage found in prior editions, but in a manner that we hope you, and more importantly your students, will find more manageable and digestible. In the following paragraphs, we outline some of the most significant highlights of the Canadian sixth edition. We hope you find it to be useful and appealing.

Chapter 1 Updated presentation of long-term consequences and later findings in Box 1.1: The Romanian Adoption Study. Updates and revisions made throughout the presentation section on Enduring Themes in Child Development, notably in Theme 2: The Active Child (expanded discussion of play), Theme 4: Mechanisms of Change (additional examples and recent research added), and Theme 5: The Sociocultural Context (updated discussion of SES).

Chapter 2 Exposition updated and tightened throughout, most notably in the discussions of conception, early and prenatal development,

teratogens, infant sleep, and crying. Updated the subsection on Fetal Experience, including a new discussion of prenatal visual preferences and of phylogenetic continuity. Updates to the discussion of Drugs and Maternal Factors in the section on Teratogens, including a significant revision of the section on Maternal Emotional State. Updated and revised subsection on Intervention Programs included in the section on Negative Outcomes at Birth.

Chapter 3 Significant reorganization and update to the discussion of heredity in the section on Parents’ Genotype–Child’s Genotype. Updated (and reduced length of) Box 3.1: Genetic Testing, with new content covering non-invasive prenatal testing. Expanded and updated discussion of methylation, including a new figure, and epigenetic effects. In the section on Behavioural Genetics, revised and updated the discussion of Heritability, particularly the discussion of misconceptions, and expanded and updated the discussion of molecular genetics research design with new coverage of candidate gene studies. In the section on Brain Development, added new figures and expanded discussions of arborization, neurogenesis, and synapse production and elimination. New subsection on Vaccines added to section on Physical Growth and Development.

Chapter 4 Opening section discussing Piaget’s Theory of Cognitive Development has been shortened for a more concise presentation. Presentation of Sociocultural Theories has been restructured and shortened. New research added to the discussion of executive functioning in the section on Information-Processing Theories.

Chapter 5 Section on Cognition has been eliminated, with topics distributed to other sections in the chapter (as well as to Chapter 7). Section on Learning has been retitled Learning and Memory, and a corresponding subsection on Memory has been added. Expanded and updated discussion of Taste and Smell. New Table 5.1 charting Infant Reflexes has been added to this section.

Chapter 6 All Boxes shortened and updated with current research. Section on Components of Language has been revised to be more concise.

Chapter 7

Expanded discussion of causal understanding now includes a discussion of object knowledge (adapted from material previously found in Chapter 5). Expanded discussion of Naïve Psychology in Infancy, with additional material previously found in Chapter 5, now adapted and updated for this section.

Chapter 8 Updated discussion of the impact of technology, such as video games, on fluid intelligence. Updated discussion of the effects of poverty on measures of intelligence and academic achievement, including a new figure showing current poverty rates across several countries. Discussion of intervention programs updated to reflect recent findings. Revamped and shortened presentation of Gardner’s theory of multiple intelligences and Sternberg’s theory of successful intelligence. Updates throughout the section on Acquisition of Academic Skills, including new coverage of the simple view of reading and new research on math achievement and math anxiety.

Chapter 9 Each section covering a major theoretical approach has been streamlined for a more concise presentation. Updated discussion of Parental Leave, including a new figure

plotting the length of maternity leave in a sampling of countries. Subsection SES and development has been cut from the chapter, and the subsection on child maltreatment has been moved from this chapter to Chapter 12, to allow for an expanded and updated subsection on Children and the Media.

Chapter 10 Coverage has been streamlined and updated throughout, most notably to the sections on Understanding Emotions and Emotion Regulation. New research added throughout the sections on the Emergence of Emotions. Relocation and restructuring of the sections on the Role of Family and on Temperament, for better flow through the chapter.

Chapter 11 Coverage has been streamlined and updated throughout, particularly in the coverage of Attachment Theory in the opening section and in the section on The Self. New research included in the discussions of parenting and attachment styles and on genetic influences on attachment styles. Significant revisions and updates throughout the discussion of Identity, including new research added on acculturation in the context of children of immigrants, and new survey data related to

sexual-minority youth.

Chapter 12 Substantial updates to the section on Family Structure. Section on Child Maltreatment added to this chapter, expanding and updating material previously found in Chapter 9. Box 12.3: Preventing Child Abuse, previously included in Chapter 9, has been updated and reworked to focus on strategies recommended by the Centers for Disease Control and Prevention. Substantial revisions and updates to Box 12.5: Family Leave Policies.

Chapter 13 Significant streamlining of material throughout chapter to make for a more concise presentation. New major section on Play opens the chapter, with a new Box 13.1: The Development of Children’s Social Play. Box 13.2: Culture and Children’s Peer Experience has been substantially revised. Subsection on Cyberbullying has been thoroughly updated.

Chapter 14 Discussion of Piaget’s Theory of Moral Judgment and Kohlberg’s Theory of Moral Reasoning have been reworked for a more

concise treatment. Heavily revised coverage of Social Domain Theory of moral development, including the introduction of several new key terms. New research added to the discussion of Cultural and Socioeconomic Differences in moral reasoning, including a series of new figures based on a study done on charitable giving. Updated and streamlined section on Prosocial Behaviours for a more concise presentation; discussion of Hamlin’s helper/hinderer study added from Chapter 5. Updated and streamlined section on Antisocial and Aggressive Behaviours, including the addition of a new subsection on Interventions for Aggressive and Antisocial Children.

Chapter 15 Extensive updating and restructuring throughout the chapter, including a focus on issues and research related to transgender and gender-nonbinary populations, where applicable. New opening section on Sex and Gender, including the introduction of several new key terms; discussion of major gender differences across several dimensions, including new Box 15.1: Challenges to the Gender Binary; Table 15.1: Summary of Average Gender Differences has also been moved from later in the chapter to this opening section. Section on Theoretical Approaches to Gender Development has been updated and restructured, with a new discussion of Integrative Theoretical Approaches, including a new figure

diagramming the gender self-socialization model. Revised and updated section on Milestones in Gender Development, including a new discussion of ambivalent sexism in the discussion of development during adolescence. Final section Patterns of Gender Development has been updated and reorganized with a new subsection on STEM-Related Skills.

Supplements How Children Develop, Canadian Sixth Edition, features a wide array of multimedia tools that are designed for the individual needs of students and teachers. For more information about any of the items listed below, please visit the online catalog at www.macmillanlearning.com.

LaunchPad with LearningCurve Quizzing

Description The title bar reads, LaunchPad, Macmillan Learning, followed by the student’s name, Help drop-down menu, and a Feedback button. The window is divided into two vertical panels: on the left is the Menu panel listing various options including eBook, Gradebook, Calendar, Resources, Welcome Center, Instructor Console, and Preview as Student. The right panel is divided into two horizontal sections. The top section has a header with text, ‘Siegler et al., How children Develop 6e Canadian Edition,’ followed by a search bar and search icon. The header is followed by text reading, ‘You have 2 assignments due in the next 7 days.’ Below the text is a list of assignments displaying the chapter number, title of the chapter, and the due date. The bottom section lists the unassigned chapters displaying the chapter number, title of the chapter, and a date.

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How Children Develop, Canadian Sixth Edition, and LaunchPad can be ordered together with ISBN-10: 1-319-34650-2 / ISBN-13: 978-1-31934650-8. LaunchPad for How Children Develop, Canadian Sixth Edition, includes the following resources: The LearningCurve quizzing system was designed based on the latest findings from learning and memory research. It combines adaptive question selection, immediate and valuable feedback, and a game-like interface to engage students in a learning experience that is unique to them. Each LearningCurve quiz is fully integrated with other resources in LaunchPad through the Personalized Study Plan, so students will be able to review with Worth’s extensive library of videos and activities. And state-ofthe-art question analysis reports allow instructors to track the progress of individual students, as well as their class as a whole.

Description The title bar reads, LearningCurve, on the left and has a button on the extreme left reading, End Student Preview. The title bar is followed by text reading, ‘3. Biology and Behaviour.’ Below the heading, on the left, is the ‘Target score progress’ scale; the scale reads, ‘You have: 225 points, Target: 750,’ followed by a button reading ‘LearningCurve tips for success.’ The right panel displays the personalized plan. The text on the top reads, ‘Your personalized study plan’; it is followed by data reading, ‘Genetic and Environmental Forces: 100 percentage accuracy,’ ‘Behaviour Genetics: 69 percentage accuracy. Below the genetics is a list of study plan suggestions.

An interactive e-book allows students to highlight, bookmark, and make their own notes, just as they would with a printed textbook. Digital enhancements include full-text search and intext glossary definitions. Student Video Activities include more than 100 engaging video modules that instructors can easily assign for student assessment. Videos cover classic experiments, current news footage, and cutting-edge research, all of which are sure to spark discussion and encourage critical thinking. Deep integration is available between LaunchPad products and most learning management systems, including Blackboard, Brightspace by D2L, Canvas, and Moodle. These deep integrations offer educators single sign-on and gradebook sync, now with auto refresh. These best-in-class integrations offer deep linking to all Macmillan digital content at the chapter and asset levels, giving professors maximum flexibility within their LMS.

Presentation and Faculty Support Presentation Slides Presentation slides are available in two formats that can be used as they are or can be customized. One set includes all the textbook’s illustrations and tables. The second set consists of lecture slides that focus on key themes and terms in the book and include text illustrations and tables. Both of these prebuilt PowerPoint

presentations are available through LaunchPad at launchpadworks.com.

Presentation Videos Worth’s video clips for developmental psychology span the full range of topics for the child development course. With hundreds of clips to choose from, this premium collection includes research and news footage on topics ranging from prenatal development to the experience of child soldiers to empathy in adolescence. These clips are made available to instructors for lecturing in the classroom and also through LaunchPad.

Instructor’s Resource Manual Written by Lynne Baker-Ward of North Carolina State University, and revised by Barinder Bhavra, this innovative Instructor’s Resource Manual includes handouts for student projects, reading lists of journal articles, course-planning suggestions, and supplementary readings, in addition to lecture guides, chapter overviews, and learning objectives. The Instructor’s Resource Manual can be downloaded in LaunchPad at launchpadworks.com.

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Acknowledgments So many people have contributed (directly and indirectly) to this textbook that it is impossible to know where to start or where to stop in thanking them. All of us have been given exceptional support by our spouses and significant others—Jerry Harris, Xiaodong Lin, Seth Pollak, John Gerlach, and Andrew Gershoff—and by our children— Benjamin Clore; Michael Harris; Todd, Beth, and Aaron Siegler;

Avianna McGhee; Eli and Nell Pollak; Sam and Madeline Gerlach; and Noah and Ella Gershoff—as well as by our parents, relatives, friends, and other loved ones. Our advisors in college and graduate school, Richard Aslin, Ann Brown, Les Cohen, Ted Dix, Harry Hake, George Holden, Robert Liebert, Jim Morgan, Paul Mussen, Elissa Newport, Jim Pate, and Diane Poulin-Dubois, helped to launch our careers and taught us how to recognize and appreciate good research. We also have all benefited from collaborators who shared our quest for understanding child development and from a great many exceptionally helpful and generous colleagues, including Larry Aber, Karen Adolph, Martha Alibali, Renee Baillargeon, Sharon Carver, Craig Chambers, Zhe Chen, Robert Crosnoe, Suzanne Curtin, Richard Fabes, Cindy Fisher, Susan Gelman, Geoff Hall, Aletha Huston, Andrew Grogan-Kaylor, Melanie Jones, David Klahr, Patrick Lemaire, Casey Lew-Williams, Angeline Lillard, Liz Nilsen, John Opfer, Penny Pexman, Elizabeth Planalp, Karl Rosengren, Kristin Shutts, Tracy Spinrad, David Uttal, Carlos Valiente, and Erica Wojcik. We owe special thanks to our assistants, Sheri Towe and Theresa Treasure, who helped in innumerable ways in preparing the book, and to Shanting Chen and Kathleen Holloway for their thorough work reviewing the video library that accompanies this edition. We would also like to thank the many reviewers who contributed to this and previous editions. For the Canadian edition, we thank Alba Agostino, Ryerson University; Daniel Ansari, University of Western Ontario; Christina Besner, Champlain College Lennoxville; Ann

Bigelow, St. Francis Xavier University; Tanya Broesch, Simon Fraser University; Tina Bonnett, Fanshawe College; Carie M. Buchanan, St. Thomas More College–University of Sakatchewan; Arloene Burak, University of Victoria; Jeremy Carpendale, Simon Fraser University; Kyle Danielson, University of British Columbia; Kelly Dean Schwartz, University of Calgary; Cass Foursha-Stevenson, Mount Royal University; Kathleen Hughes, University of Calgary; Jacqueline Kampman, Thompson Rivers University; Padmapriya Kandhadai, University of British Columbia; Elizabeth Kelley, Queen’s University; Cheryl Kier, Athabasca University; Tru Kwong, Mount Royal University; Danielle Labossière, Grenfell Campus, Memorial University of Newfoundland; Linda Langevin, Medicine Hat College; Vivian Li, University of British Columbia; Tina Malti, University of Toronto; Anna Matejka, University of Toronto Mississauga; Lillian May, University of British Columbia; Nancy Ogden, Mount Royal University; Gene Ouellette, Mount Allison University; Angelina Paolozza, University of Toronto; Alissa Pencer, Dalhousie University; Jocelyn Proulx, University of Manitoba; Danielle Quigley, Douglas College; Valerie San Juan, University of Calgary; Daniel Séguin, Mount Saint Vincent University; Veronica Smith, University of Alberta; Christina Starmans, University of Toronto; Alexandra Twyman, University of Western Ontario; Tara Vongpaisal, MacEwan University; Kelly Warren, Grenfell Campus, Memorial University of Newfoundland; Janet F. Werker, University of British Columbia; Sandra Wiebe, University of Alberta; Lynne Zarbatany, University of Western Ontario.

For the American edition: Daisuke Akiba, Queens College, City University of New York; Kimberly Alkins, Queens College, City University of New York; Hiram Allen, College of New Rochelle; Dina Anselmi, Trinity College; Lynne Baker-Ward, North Carolina State University; Hilary Barth, Wesleyan University; Christie Bartholomew, Kent State University; Christopher Beevers, University of Texas at Austin; Martha Bell, Virginia Tech; Cynthia Berg, University of Utah; Rebecca Bigler, University of Texas at Austin; Margaret Borkowski, Saginaw Valley State University; Lyn Boulter, Catawba College; Renia Brown-Cobb, Virginia State University; Eric Buhs, University of Nebraska–Lincoln; G. Leonard Burns, Washington State University; Allison Butler, Bryant University; Wendy Carlson, Shenandoah University; Erik W. Cheries, University of Massachusetts Amherst; Mel Joseph Ciena, University of San Francisco; Kristi Cordell-McNulty, Angelo State University; Myra Cox, Harold Washington College; Maria Crisafi, Columbia University; Kimberly Cuevas, University of Connecticut; Emily Davidson, Texas A&M University–Main Campus; Peggy DeCooke, The State University of New York at Purchase; Ed de St. Aubin, Marquette University; Marissa Diener, University of Utah; Julie Earles, Wilkes Honors College, Florida Atlantic University; Sharon Eaves, Shawnee State University; Jessica Espinosa, Miami Dade College; Guadalupe Espinoza, California State University, Fullerton; Elisa Esposito, Widener University; Urminda Firlan, Grand Rapids Community College; Dorothy Fragaszy, University of Georgia; Jeffery Gagne, University of Texas–Arlington; Jennifer Ganger, University of Pittsburgh; Alice Ganzel, Cornell College;

Catherine Gaze, Elmhurst College; Janet Gebelt, Westfield State University; Peter Gerhardstein, Binghamton University; Melissa Ghera, St. John Fisher College; Helana Girgis, Hartwick College; Susan Graham, University of Calgary; Andrea Greenhoot, University of Kansas; Jessica Greenlee, Virginia Commonwealth University; Shelia Greenlee, Christopher Newport University; Frederick Grote, Western Washington University; John Gruszkos, Reynolds University; Hanna Gustafsson, University of North Carolina; Alma Guyse, Midland College; Louise Hainline, Brooklyn College; Lauren Harris, Michigan State University; Sybil Hart, Texas Tech University; Karen Hartlep, California State University–Bakersfield; Patricia Hawley, University of Kansas–Main; Joan Henley, Arkansas State University; Susan Hespos, Northwestern University; Doris Hiatt, Monmouth University; Aline Hitti, University of San Francisco; Susan Holt, Central Connecticut State University; Wendy Jung, Tulane University; Lana Karasik, The College of Staten Island; Lisa Huffman, Ball State University; Kathryn Kipp, University of Georgia; Rosemary Krawczyk, Minnesota State University; Amber Kreischer, University of Texas at Austin; Raymond Krukovsky, Union County College; Tara Kuther, Western Connecticut State University; Martin Lampert, Holy Names University; Richard Lanthier, George Washington University; Elida Laski, Boston College; Kathryn Lemery, Arizona State University; Barbara Licht, Florida State University; Jeffrey Liew, Texas A&M University; Angeline Lillard, University of Virginia; Lori Markson, Washington University in St. Louis; Marsha J. McCartney, University of Kansas; Wayne McMillin, Northwestern State University; Martha Mendez-Baldwin, Manhattan

College; Scott Miller, University of Florida; Keith Nelson, Pennsylvania State University–Main Campus; Paul Nicodemus, Austin Peay State University; Tracy Nishida, Arizona State University; Katherine O’Doherty, Vanderbilt University; Christin Ogle, American University; John Opfer, The Ohio State University; Beverly Pead, Springfield Technical Community College; Ann Repp, University of Texas at Austin; Nicole Rivera, North Central College; Shannon Ross-Sheehy, University of Tennessee; Sarah Sanborn, Clemson University; Leigh A. Shaw, Weber State University; Jennifer Simonds, Westminster College; Rebekah Smith, University of Texas– San Antonio; Tara Stoppa, Eastern University; Mark Strauss, University of Pittsburgh–Main; Spencer Thompson, University of Texas–Permian Basin; Marisel Torres-Crespo, Hood College; Lisa Travis, University of Illinois Urbana–Champaign; Roger Webb, University of Arkansas–Little Rock; Keri Weed, University of South Carolina–Aiken; Sherri Widen, Boston College; Fei Xu, The University of California, Berkeley. We would especially like to thank Campbell Leaper, University of California, Santa Cruz, for his major contributions to the revision of our chapter on gender development (Chapter 15). We are indebted to Campbell for bringing to the Canadian sixth edition his expertise and keen insight in this important area. Thanks are particularly due to our friends and collaborators at Worth Publishers. As Executive Program Manager for Psychology, Daniel DeBonis provided exceptional support and any number of excellent

suggestions. We would also like to thank Marge Byers, who nurtured our first edition from its inception and helped us to realize our vision. Peter Deane, our development editor for the first four editions, is in a class by himself in both skill and dedication. Peter’s creative thinking and firm understanding of the field enhanced the content of the book in innumerable ways. We are deeply grateful to him. Special thanks go to the development editor for the latest two editions, Andrew Sylvester, who provided consistently outstanding help throughout the process, as well as to assistant editor Anna Munroe, senior content project manager Vivien Weiss, director of content management enhancement Tracey Kuehn, art manager Matthew McAdams, cover designer John Callahan, interior designer Victoria Tomaselli, design manager Natasha Wolfe, executive permissions editor Cecilia Varas, photo researcher Jennifer Atkins, senior workflow project manager Paul Rohloff, and compositor Lumina Datamatics, and Subramaniam Vengatakrishnan and Prasanna Kalyanaram in particular, for their excellent work. They have helped create a book that we hope you will find a pleasure to look at as well as to read. Executive marketing manager Katherine Nurre provided outstanding promotional materials to inform professors about the book. Associate media editor Stephanie Matamoros managed the superb package of ancillary material. We also want to thank the Canadian marketing and sales teams led by Jen Cawsey. The enthusiasm and support provided by Jen, as well as Kasia Bulgarski, Jennifer Mills, Kiyo Monteith, Kate Nicoll, Robbie Patterson, Jordan Scholefield, and Katy Turenne, are greatly appreciated!

CHAPTER 1

An Introduction to Child Development

Water Baby and the Moon

Reasons to Learn About Child Development Historical Foundations of the Study of Child Development Enduring Themes in Child Development Methods for Studying Child Development

THEMES NATURE AND NURTURE THE ACTIVE CHILD CONTINUITY/DISCONTINUITY MECHANISMS OF CHANGE THE SOCIOCULTURAL CONTEXT INDIVIDUAL DIFFERENCES RESEARCH AND CHILDREN’S WELFARE

In 1955, a group of child-development researchers began a unique study. Their goal, like that of many developmental researchers, was to find out how biological and environmental factors influence children’s intellectual, social, and emotional growth. What made their study unique was that they examined these diverse aspects of development for all 698 children born that year on the Hawaiian island of Kauai and continued studying the children’s development for 40 years. With the parents’ consent, the research team, headed by Emmy Werner, collected many types of data about the children. To learn about possible complications during the prenatal period and birth, they examined physicians’ records. To learn about family interactions

and the children’s behaviour at home, they arranged for nurses and social workers to observe the families and to interview the children’s mothers when the children were 1 year old and again when they were 10 years old. The researchers also interviewed teachers about the children’s academic performance and classroom behaviour during the elementary school years and examined police, family court, and social service records that involved the children, either as victims or perpetrators. Finally, the researchers administered standardized intelligence and personality tests to the participants when they were 10 and 18 years old and interviewed them at ages 18, 32, and 40 to find out how they saw their own development (Werner, 2005). Results from this study illustrated some of the many ways in which biological and environmental factors combine to produce child development. For example, children who experienced prenatal or birth complications were more likely than others to develop physical handicaps, mental illness, and learning difficulties. But whether they developed such problems—and if so, to what degree—depended a great deal on their home environment. Parents’ income, education, and mental health, together with the quality of the relationship between the parents, especially influenced children’s development. By age 2, toddlers who had experienced severe prenatal or birth problems but who lived in harmonious middle-income families were nearly as advanced in language and motor skills as were children who had not experienced early problems. By the time the children were 10-year-olds, prenatal and birth problems were consistently related to

psychological difficulties only if the children also grew up in poor rearing conditions. What of children who faced both biological and environmental challenges—prenatal or birth complications and adverse family circumstances? The majority of these children developed serious learning or behaviour problems by age 10. By age 18, most had acquired a police record, had experienced mental health problems, or had become an unmarried parent. However, one-third of such atrisk children showed impressive resilience, growing up into young adults who, in the words of Werner, “loved well, worked well, and played well” (1989, p. 108D). Michael was one such resilient child. Born prematurely, with low birth weight, to teenage parents, he spent the first 3 weeks of his life in a hospital, separated from his mother. By his 8th birthday, Michael’s parents were divorced, his mother had deserted the family, and he and his three brothers and sisters were being raised by their father, with the help of their elderly grandparents. Yet by age 18, Michael was successful in school, had high self-esteem, was popular with his peers, and was a caring young man with a positive attitude toward life. The fact that there are many children like Michael— children who show great resilience in the face of adversity—is among the most heartening findings of research on child development.

This family has lived in a one-room tent for approximately 2 years. Will these children be resilient enough to overcome their disadvantaged environment? The answer will depend in large part on how many risk factors they face, their personal characteristics, and the nature of the parenting they receive.

Reading this chapter will increase your understanding of these and other basic questions about child development. It will also introduce you to some historical perspectives on these fundamental questions, as well as to the perspectives and methods that modern researchers use to address them. But first, we would like you to consider a basic question for those taking this course: Why study child development?

Reasons to Learn About Child Development For us, as both parents and researchers, the sheer enjoyment of watching children and trying to understand them is reason enough for studying child development. What could be more fascinating than the development of a child? But there are also practical and intellectual reasons for studying child development. Understanding how children develop can improve child rearing, promote the adoption of wiser social policies regarding children’s welfare, and answer basic questions about human nature. We examine each of these reasons in the following sections.

Raising Children Trying to be a good parent raises endless questions. If I drink wine occasionally while I’m pregnant, will it harm my baby even before she’s born? Once she’s born, is it okay to take her outside in the cold weather? Should I raise my son at home for his first few years, or would going to day care be better for his development? My daughter is 3 years old and not speaking yet—should I worry, and is there some way to help her? Should I try to teach my 5-year-old to read early, or will she learn when she’s ready? How can I help my kindergartner deal with her anger? My teenager seems lonely and says that no one likes him; how can I help?

Child-development research can help answer such questions. For example, one problem that confronts almost all parents is how to help their children control their anger. One tempting reaction is to spank children who express anger in inappropriate ways, such as fighting, name-calling, and talking back. In Canada, about 25% of parents report spanking their children (Fréchette & Romano, 2015; Perron et al., 2014). Research shows, however, that spanking makes problem behaviours worse, and the effects are long-lasting. One large-scale study showed that the more often parents spanked their kindergartners, the more often the same children argued, fought, and acted inappropriately at school when they were 3rd-graders. This relation has held true for children from various backgrounds, and it has held true above and beyond the effects of other relevant factors, such as parents’ income and education (Gershoff et al., 2012). Fortunately, research suggests several effective alternatives to spanking (Denham, 1998, 2006). One is expressing sympathy: when parents respond to their children’s anger with sympathy, the children are better able to cope with the situation causing the distress. Another effective approach is helping angry children find positive alternatives to expressing their feelings. For example, encouraging them to do something they enjoy helps them cope with their hostility. These strategies and similar ones, such as time-outs, can also be used effectively by others who contribute to raising children, such as daycare personnel and teachers. One demonstration of this was provided by a special curriculum devised for helping preschoolers (3- and 4-

year-olds) who were angry and out of control (Denham & Burton, 1996). This curriculum encourages preschool teachers to help children recognize their own and other children’s emotions, as well as to teach children techniques for controlling their anger and peaceably resolving conflicts with other children. One approach that children were taught for coping with anger was the “turtle technique.” When children felt themselves becoming angry, they were to move away from other children and retreat into their “turtle shell,” where they could think through the situation until they were ready to emerge from the shell.

Posters like this are used in the turtle technique to remind children of ways to control anger.

The curriculum was quite successful. Children who participated in it became more skillful in recognizing and regulating anger when they experienced it. For example, one boy, who had regularly gotten into fights when angry, told the teacher after a dispute with another child, “See, I used my words, not my hands” (Denham, 1998, p. 219). The benefits of this program can be long term. In one test, positive effects

were still evident as long as 4 or 5 years after children completed the curriculum (Jennings & Greenberg, 2009). As this example suggests, knowledge of child-development research can be helpful to everyone involved in the care of children.

Choosing Social Policies Another reason to learn about child development is to be able to make informed decisions about the wide variety of social-policy questions that affect children in general. For example, does playing violent video games increase aggressive behaviour? How much trust should judges and juries place in preschoolers’ testimony in childabuse cases? Should children who struggle in school be held back, or should they be promoted to the next grade so that they can be with children of the same age? Consider the issue of whether playing violent video games makes children and adolescents more aggressive. This issue has been hotly contested by politicians, advocacy groups, and researchers, with some arguing that such games are sufficiently harmful that their sale to minors should be forbidden. The Entertainment Software Association of Canada is responsible for rating video games in terms of age-appropriateness, content, and interactive features, and most retailers in Canada, using this rating system, require age verification for the purchase of games rated M (mature) (Entertainment Software

Rating Board, n.d.). To provide a thorough evaluation of the evidence, Ferguson (2015; also see Furuya-Kanamori & Doi, 2016) reviewed findings from 101 studies conducted on the topic. He used a statistical technique known as meta-analysis, a method for combining the results from independent studies to reach conclusions based on all of them. This meta-analysis indicated that the effect of playing violent video games on children’s and adolescents’ aggression was minimal. Minimal is not the same as nonexistent—playing violent video games did appear to increase aggressive behaviour by a small amount—but the metaanalysis contradicted claims that violent video games are a major cause of children’s and adolescents’ aggression. Such quantitative analyses of the impact of various activities on children’s behaviour are useful evidence in deciding whether the benefits of preventing potentially harmful activities outweigh the costs of impinging on people’s freedom to do what they want. meta-analysis a method for combining the results from independent studies to reach conclusions based on all of them

Another issue of social policy in which child-development research has played an important role concerns how much trust to put in preschoolers’ courtroom testimony. Research suggests that tens of thousands of children testify in legal cases in Canada about crimes they either experienced or witnessed (Cunningham & Stevens, 2011).

Many of these children are very young: in 2012, about 40% of children who were victims of sexual offences in Canada were 11 years of age or younger (Statistics Canada, 2014). Many of these children face the prospect of testifying in court. The stakes are extremely high in such cases. If juries believe children who falsely testify that they were abused, innocent people may spend years in jail. If juries do not believe children who accurately report abuse, the perpetrators will go free and probably abuse other children. What can be done to promote reliable testimony from young children and to avoid leading them to report experiences that never occurred? Psychological research has helped answer such questions. In one experiment, researchers tested whether biased questioning affects the accuracy of young children’s memory for events involving touching one’s own and other people’s bodies. The researchers began by having 3- to 6-year-olds play a game, similar to “Simon Says,” in which the children were told to touch various parts of their body and those of other children. A month later, a social worker was sent to interview the children about their experiences during the game (Ceci & Bruck, 1998). Before the social worker conducted the interviews, she was given a description of each child’s experiences. However, unknown to her, the description she heard included inaccuracies. The social worker was given instructions much like those in a court case: “Find out what the child remembers.”

In courtrooms such as this one, asking questions that will help children to testify accurately is of the utmost importance.

As it turned out, the version of events that the social worker had heard often influenced her questions to children. If, for example, children’s accounts of an event contradicted what the social worker believed to be the case, she tended to question the children repeatedly about the event (“Are you sure you touched his foot? Is it possible you touched some other part of his body?”). In response to the social worker’s questions, children often changed their responses, with 34% of 3- and 4-year-olds eventually corroborating at least one of the social workers’ incorrect beliefs. Children were led to

“remember” not only plausible events that never happened but also implausible ones that the social worker had been told about. For instance, some children “recalled” their knee being licked and a marble being inserted in their ear. Studies of this type have yielded a number of conclusions regarding children’s testimony in legal proceedings. One important finding is that when 3- to 5-year-olds are not asked leading questions, their testimony is usually accurate as far as it goes, though they leave out a great deal of information (Bruck, Ceci, & Principe, 2006; Howe & Courage, 1997). However, when prompted by leading questions, young children’s testimony is often inaccurate, especially when the leading questions are asked repeatedly. The younger the children are, the more their recall tends to reflect the biases of the interviewer’s questions (Otgaar et al., 2018). In addition, realistic props, such as anatomically correct dolls and drawings, which are often used in judicial cases in the hopes of improving recall of sexual abuse, turn out not to improve recall of events that occurred but to actually increase the number of inaccurate claims, perhaps by blurring the line between fantasy and reality (Poole, Bruck, & Pipe, 2011). Research on child eyewitness testimony has had a large practical effect: In various jurisdictions in Canada, multidisciplinary guidelines have been developed to assist police, child welfare workers, physicians, and other professionals in interviewing children and preparing them for court (see the Canadian Child Abuse Association for examples of these guidelines). Training programs have been

developed by researchers at Wilfrid Laurier University and the University of Regina to improve how police and social workers conduct investigative interviews with children (Price & Roberts, 2011). In addition to helping courts obtain more accurate testimony from young children, such research-based conclusions illustrate how knowledge of child development can inform social policies more generally.

Understanding Human Nature A third reason to study child development is to better understand human nature. Many of the most intriguing questions regarding human nature focus on infancy and childhood. For example, does learning start only after children are born, or can it occur in the womb? Can later upbringing in a loving home overcome the detrimental effects of early rearing in a loveless institutional setting? Do children vary in personality and intellect from the day they are born, or are they similar at birth, with differences arising only because they have different experiences? Studying infants and young children offers an opportunity to learn what people are like before they are affected by the innumerable influences of family and society. One major group of contemporary philosophers and psychologists, known as nativists, argues that evolution has created many remarkable capabilities that are present

even in early infancy, particularly in areas of special importance, such as understanding basic properties of physical objects, plants and animals, and other people. Another major group of philosophers and psychologists, known as empiricists, has argued that infants possess general learning mechanisms that allow them to learn a great deal quite quickly, but that infants and young children lack the specialized capabilities that nativists attribute to them. Until recently, people could only speculate about questions regarding human nature. Now, however, developmental scientists have methods that enable us to observe, describe, and explain the process of development, and thus to deepen our understanding of how we become who we are. Box 1.1 provides one fascinating example of the questions that these methods can address.

BOX 1.1 A CLOSER LOOK The Romanian Adoption Study A particularly poignant illustration of the way in which scientific research can increase understanding of human nature comes from studies of how children’s ability to overcome the effects of early maltreatment is affected by its timing, that is, by when in the child’s life the maltreatment begins and ends. This research examines children whose early life was spent in horribly inadequate orphanages in Romania in the late 1980s and early 1990s (McCall et al., 2011; Nelson et al., 2007; Rutter, O’Connor, & The English and Romanian Adoptees Study Team, 2004). Children in these orphanages had almost no contact with any caregiver. For reasons that remain unknown, the brutal Communist dictatorship of that era demanded that staff workers not interact with the children, even when giving

them their bottles. Staff members provided the infants with so little physical contact that the crown of many infants’ heads became flattened from the babies’ lying on their backs for 18 to 20 hours per day. Shortly after the collapse of Communist rule in Romania, a number of these children were adopted by families around the world, including Canada and Great Britain. When these children arrived in their adoptive homes, most were severely malnourished, with more than half being in the lowest 3% of children their age in terms of height, weight, and head circumference. Most also showed varying degrees of intellectual disability and were socially immature. The parents who adopted them knew of their deprived backgrounds and were highly motivated to provide loving homes that would help the children recover from the damaging effects of their early mistreatment. To evaluate the long-term effects of their early deprivation, the physical, intellectual, and social development of about 150 of the Romanian-born children adopted into homes in Great Britain were examined at age 6 years. To provide a basis of comparison, the researchers also followed the development of a group of British-born children who had been adopted into loving British families before they were 6 months of age. Simply put, the question was whether human nature is sufficiently flexible that the Romanian-born children could overcome the extreme deprivation of their early experience. By age 6 years, the physical development of the Romanian-born children had improved considerably, both in absolute terms and in relation to the British-born comparison group. However, the Romanian children’s early experience of deprivation continued to influence their physical development, with the extent of negative effects depending on how long the children had been institutionalized. Romanian-born children who were adopted by British families before age 6 months, and who had therefore spent the smallest portion of their early lives in the orphanages, weighed about the same as British-born children when both were 6year-olds. However, Romanian-born children adopted between the ages of 6 and 24 months, and who therefore had spent more of their early lives in the

orphanages, weighed less; and those adopted between the ages of 24 and 42 months weighed even less (Rutter et al., 2004). Intellectual development at age 6 years showed a similar pattern. The Romanianborn children who had been adopted before age 6 months demonstrated levels of intellectual competence comparable with those of the British-born group. Those who had been adopted between ages 6 and 24 months did somewhat less well, and those adopted between ages 24 and 42 months did even more poorly (Rutter et al., 2004). The intellectual deficits of the Romanian children adopted after age 6 months were just as great when the children were retested at age 11, indicating that the negative effects of the early deprivation persisted for many years after they were adopted into the loving homes (Beckett et al., 2006; Kreppner et al., 2007). However, by the time the children had become young adults (22- to 25-yearolds), their intellect was in the normal range (Sonuga-Barke et al., 2017). The early experience in the orphanages had even more prolonged damaging effects on the children’s social development (Kreppner et al., 2007). Almost 20% of the Romanian-born children who were adopted after age 6 months showed extremely abnormal social behaviour at age 6 years, such as not looking at their parents in anxiety-provoking situations and willingly going off with strangers (versus 3% of the British-born comparison group who did so). Even in early adulthood, many had difficulty controlling their emotions and forming friendships (Rutter et al., 2009). Unlike with intellectual development, these negative effects on social and emotional development persisted into adulthood (Sonuga-Barke et al., 2017), with children from the Romanian orphanages having far greater rates of using mental health services than those in the control group (43% versus 10%). In contrast to the differences in intellectual development, which diminished over time, the differences in mental health problems increased between ages 15 and 23 years. This atypical social development was accompanied by abnormal brain activity. Brain scans obtained when the children were 8 years old showed that those adopted after living for a substantial period in the orphanages had unusually low

levels of neural activity in the amygdala, a brain area involved in emotional reactions (Chugani et al., 2001). Subsequent studies have identified similar brain abnormalities among children who spent their early lives in poor-quality orphanages in Russia and East Asia (Nelson et al., 2011; Tottenham et al., 2010). amygdala an area of the brain that is involved in emotional reactions These findings reflect a basic principle of child development that is relevant to many aspects of human nature: The timing of experiences influences their effects. In the present case, children were sufficiently flexible to overcome the effects of living in the Romanian institutions if the deprivation ended by age 6 months; living in the institutions until older ages, however, had effects that were rarely overcome completely, even when children spent many subsequent years in loving and stimulating environments. The adoptive families clearly made a huge positive difference in their children’s lives, but the later the age of adoption, the greater the long-term harmful effects of early deprivation.

This infant is one of the children adopted from a Romanian orphanage in the 1990s. How successfully he was likely to develop depended not only on the quality of caregiving he received in his adoptive home but also on the amount of time he spent in the orphanage and the age at which he was adopted.

REVIEW QUESTIONS In addition to the examples discussed in this section, can you think of other situations where a better understanding of child development may benefit society? What reasons do you have for studying child development?

Historical Foundations of the Study of Child Development From ancient Greece to the early years of the twentieth century, a number of profound thinkers observed and wrote about children. Their goals were like those of contemporary researchers: to help people become better parents, to improve children’s well-being, and to understand human nature. Unlike contemporary researchers, however, these early philosophers usually based their conclusions on general beliefs and informal observations of only a few children. Beginning in the early twentieth century, when the benefits of using the scientific method had become evident in medicine and many other areas, psychologists began to apply the scientific method to analyzing human behaviour. Still, the issues the early thinkers raised are sufficiently important, and their insights sufficiently deep, that their views continue to influence contemporary thinking about child development.

Early Philosophers’ Views of Children’s Development The classic Greek philosophers Plato and Aristotle, who lived in the fourth century B . C ., proposed some of the earliest recorded and most

influential ideas about children’s development. They were particularly interested in how children are influenced by their nature and by the nurture they receive. Both philosophers believed that the long-term welfare of society depended on the proper raising of children. Careful upbringing was essential because children’s basic nature would otherwise lead to their becoming rebellious and unruly. Plato viewed the rearing of boys as a particular challenge: Now of all wild things, a boy is the most difficult to handle. Just because he more than any other has a fount of intelligence in him which has not yet “run clear,” he is the craftiest, most mischievous, and unruliest of brutes. (The Laws, bk. 7, 1961, p. 1379)

Consistent with this view, Plato emphasized self-control and discipline as the most important goals of education (Borstelmann, 1983). Aristotle agreed with Plato that discipline was necessary, but he was more concerned with fitting child rearing to the needs of the individual child. In his words: It would seem … that a study of individual character is the best way of making education perfect, for then each [child] has a better chance of receiving the treatment that suits him. (Nicomachean Ethics, bk. 10, chap. 9, p. 1180)

Plato and Aristotle differed considerably in their views of how

children acquire knowledge. Plato believed that children have innate knowledge. For example, he believed that children are born with a concept of “animal” that, from birth onward, automatically allows them to recognize that dogs, cats, and other creatures they encounter are animals. In contrast, Aristotle believed that all knowledge comes from experience and that the mind of an infant is like a blackboard on which nothing has yet been written. Roughly 2000 years later, the English philosopher John Locke (1632– 1704) and the French philosopher Jean-Jacques Rousseau (1712–1778) refocused attention on the question of how parents and society in general can best promote children’s development. Locke, like Aristotle, viewed the child as a tabula rasa, or blank slate, whose development largely reflects the nurture provided by the child’s parents and the broader society. He believed that the most important goal of child rearing is the growth of character. To build children’s character, parents need to set good examples of honesty, stability, and gentleness. They also need to avoid indulging the child, especially early in life. However, once discipline and reason have been instilled, Locke believed that authority should be relaxed as fast as their age, discretion, and good behavior could allow it…. The sooner you treat him as a man, the sooner he will begin to be one. (Cited in Borstelmann, 1983, p. 20)

In contrast to Locke’s advocating discipline before freedom,

Rousseau believed that parents and society should give children maximum freedom from the beginning. Rousseau claimed that children learn primarily from their own spontaneous interactions with objects and other people, rather than through instruction by parents or teachers. He even argued that children should not receive any formal education until about age 12, when they reach “the age of reason” and can judge for themselves the worth of what they are told. Before then, they should be allowed the freedom to explore whatever interests them. Although formulated long ago, these and other philosophical questions continue to underlie many contemporary debates about human nature. However, the contemporary debates are based to a much greater extent on the results of carefully conducted research. For example, after reviewing many research studies, Kagan (2000) concluded that children have an innate moral sense, encompassing five abilities that even our closest primate relatives lack. These include the ability to infer the thoughts and feelings of others, to apply the concepts of good and bad to one’s own behaviour, to reflect on past actions, to understand that negative consequences could have been avoided, and to understand one’s own and others’ motives and emotions. A great deal of evidence relevant to these and other issues about human nature will be presented in the chapters that follow.

Social Reform Movements

The contemporary field of child psychology also has roots in early social reform movements that were devoted to improving children’s lives by changing the conditions in which they lived. During the Industrial Revolution of the 1700s, 1800s, and early 1900s, a great many children in Europe and the United States worked as poorly paid labourers with few if any legal protections. Some were as young as 5 and 6 years; many worked up to 12 hours a day in factories or mines, often in extremely hazardous circumstances. These harsh conditions worried a number of social reformers, who began to study how such circumstances affected the children’s development. For example, in a speech before the British House of Commons in 1843, the Earl of Shaftesbury noted that the narrow tunnels where children dug out coal had very insufficient drainage [and] are so low that only little boys can work in them, which they do naked, and often in mud and water, dragging sledgetubs by the girdle and chain…. Children of amiable temper and conduct, at 7 years of age, often return next season from the collieries greatly corrupted … with most hellish dispositions. (Quoted in Kessen, 1965, pp. 46–50)

The Earl of Shaftesbury’s effort at social reform brought partial success—a law forbidding employment of girls and of boys younger than 10. In addition to bringing about the first child labour laws, this and other early social reform movements established a legacy of research conducted for the benefit of children and provided some of the earliest recorded descriptions of the adverse effects that harsh

environments can have on children.

During the eighteenth, nineteenth, and early twentieth centuries, many young children worked in coal mines and factories. Their hours were long, and the work was often unhealthy and dangerous. Concern over the well-being of such children led to some of the earliest research on child development.

Darwin’s Theory of Evolution Later in the nineteenth century, Charles Darwin’s work on evolution inspired a number of scientists to propose that intensive study of children’s development might lead to important insights into human nature. Darwin himself was interested in child development, and in

1877 he published an article in which he presented his careful observations of the growth of his infant son, William. Darwin’s “baby biography”—a systematic description of William’s day-to-day development—represented one of the first methods for studying children. Such intensive studies of individual children’s growth continue to be a distinctive feature of the modern field of child development. Darwin’s evolutionary theory, which employs variation, natural selection, and inheritance as its fundamental concepts, also continues to influence the thinking of modern developmentalists on a wide range of topics: infants’ attachment to their mothers (Bowlby, 1969), innate fear of natural dangers such as spiders and snakes (Hoehl et al., 2017), sex differences (Geary, 2010a), aggression and altruism (Tooby & Cosmides, 2005), and learning mechanisms (Siegler, 1996).

REVIEW QUESTION Throughout history, philosophers and researchers such as Plato, Darwin, and Kagan have sought to understand what makes people different from even our closest primate relatives. In what ways other than their moral sense do you think human children differ most from the animals most similar to us?

Enduring Themes in Child Development The modern study of child development begins with a set of fundamental questions. Everything else—theories, concepts, research methods, data, and so on—is part of the effort to answer these questions. Although experts in the field might choose different particular questions as the most important, there is widespread agreement that the seven questions in Table 1.1 are among the most important. These questions form a set of themes that we will highlight throughout the book as we examine specific aspects of child development. In this section, we introduce and briefly discuss each question and the theme that corresponds to it.

TABLE 1.1 Basic Questions About Child Development 1. How do nature and nurture together shape development? (Nature and nurture) 2. How do children shape their own development? (The active child) 3. In what ways is development continuous, and in what ways is it discontinuous? (Continuity/discontinuity) 4. How does change occur? (Mechanisms of change) 5. How does the sociocultural context influence development? (The sociocultural context) 6. How do children become so different from one another? (Individual differences) 7. How can research promote children’s well-being? (Research and children’s welfare)

1. Nature and Nurture: How Do Nature and Nurture Together Shape Development? The most basic question about child development is how nature and nurture interact to shape the developmental process. Nature refers to our biological endowment, in particular, the genes we receive from our parents. This genetic inheritance influences every aspect of our makeup, from broad characteristics such as physical appearance, personality, intellect, and mental health to specific preferences, such as political attitudes and propensity for thrill-seeking (Plomin et al., 2012). Nurture refers to the wide range of environments, both physical and social, that influence our development, including the womb in which we spend the prenatal period, the homes in which we grow up, the schools that we attend, the broader communities in which we live, and the many people with whom we interact. nature our biological endowment; the genes we receive from our parents nurture the environments, both physical and social, that influence our development

Popular depictions often present the nature–nurture question as an either/or proposition: “What determines how a person develops, heredity or environment?” However, this either/or phrasing is misleading. All human characteristics—our intellect, our personality,

our physical appearance, our emotions—develop through the joint workings of nature and nurture, that is, through the constant interaction of our biology and our environment. Accordingly, rather than asking whether nature or nurture is more important, developmentalists ask how nature and nurture work together to shape development. That this is the right question to ask is vividly illustrated by findings on the development of schizophrenia. Schizophrenia is a label for a family of serious mental illnesses, often characterized by hallucinations, delusions, confusion, and irrational behaviour. There is an obvious genetic component to this disease. Children who have a schizophrenic parent have a much higher probability than other children of developing the illness later in life, even when they are adopted as infants and therefore are not exposed to their parents’ schizophrenic behaviour (Kety et al., 1994). Among identical twins— that is, twins whose genes are identical—if one twin has schizophrenia, the other has a roughly 40% to 50% chance of also having schizophrenia, as opposed to the roughly 1% probability for the general population (see Figure 1.1; Cardno & Gottesman, 2000; Gejman, Sanders, & Duan, 2010; Gottesman, 1991).

FIGURE 1.1 Genetic relatedness and schizophrenia The closer the biological relation, the stronger the probability that relatives of a person with schizophrenia will have the same mental illness. (Data from Gottesman, 1991)

Description This histogram shows the percentage of risk for schizophrenia based on the closeness of the relationship to a schizophrenic patient. The data follows. Specific numbers are not provided, so percentages are approximate. General population 1% First cousin 2% Uncle/aunt 2.5% Nephew/niece 5% Grandchild 6% Half sibling 7%

Parent 7% Sibling 9.5% Child 13% Fraternal twin 18% Identical twin 48%

At the same time, the environment is also clearly influential, since roughly 50% to 60% of children who have an identical twin with schizophrenia do not become schizophrenic themselves; and children who grow up in troubled homes are more likely to become schizophrenic than are children raised in a stable household. Most important, however, is the interaction of genes and environment. A study of adopted children, some of whose biological parents were schizophrenic, indicated that the only children who had any substantial likelihood of becoming schizophrenic were those who had a schizophrenic parent and who also were adopted into a troubled family (Tienari, Wahlberg, & Wynne, 2006).

How do you think nature and nurture together led Justin Trudeau, son of former Canadian prime minister Pierre Trudeau, to become prime minister himself in 2015?

A remarkable recent series of studies has revealed some of the biological mechanisms through which nature and nurture interact. These studies show that just as the genome—each person’s complete set of hereditary information—influences behaviours and experiences, behaviours and experiences influence the genome (Meaney, 2010; Slavich & Cole, 2013). This might seem impossible, given that each person’s DNA is constant throughout life. However, the genome includes not only DNA but also proteins that regulate gene expression by turning gene activity on and off. These proteins change in response to experience and, without structurally altering

DNA, can produce enduring changes in cognition, emotion, and behaviour. This discovery has given rise to a new field called epigenetics, the study of stable changes in gene expression that are mediated by the environment. Stated simply, epigenetics examines how experience gets under the skin. genome each person’s complete set of hereditary information epigenetics the study of stable changes in gene expression that are mediated by the environment

Evidence for the enduring epigenetic impact of early experiences and behaviours comes from research on methylation, a biochemical process that reduces expression of a variety of genes and is involved in regulating reactions to stress (Lam, Hastie et al., 2012). One study showed that the amount of stress that mothers reported experiencing during their children’s infancy was related to the amount of methylation in the children’s genomes 15 years later (Essex et al., 2013). Other studies showed increased methylation in the cord-blood DNA of newborns of depressed mothers (Oberlander et al., 2008) and in adults who were abused as children (McGowan et al., 2009), leading researchers to speculate that such children are at heightened risk for depression as adults (Rutten & Mill, 2009). methylation a biochemical process that influences behaviour by suppressing gene activity and expression

As these examples illustrate, developmental outcomes emerge from the constant bidirectional interaction of nature and nurture. To say that one is more important than the other, or even that the two are equally important, drastically oversimplifies the developmental process.

2. The Active Child: How Do Children Shape Their Own Development? Children’s own actions also contribute to their development. Even in infancy and early childhood, this contribution can be seen in a multitude of areas, including attention, language use, and play.

One of the earliest ways children shape their own development is through their choice of where to look. From the first month of life, seeing Mom is a high priority.

Infants shape their own development through selective attention. Even newborns attend more to objects that move and make sounds than to other objects. This preference helps them learn about important parts of the world, such as people, other animals, and inanimate moving objects, including cars and trucks. When looking at people, infants’ attention is particularly drawn to faces, especially

their mother’s face; given a choice of looking at a stranger’s face or their mother’s, even 1-month-olds choose to look at Mom (Bartrip, Morton, & de Schonen, 2001). At first, infants’ attention to their mother’s face is not accompanied by any visible emotion, but by the end of the second month, infants smile and coo more when focusing intently on their mother’s face than at other times. This smiling and cooing by the infant elicits smiling and talking by the mother, which elicits further cooing and smiling by the infant, and so on (Lavelli & Fogel, 2005). In this way, infants’ preference for attending to their mother’s face leads to social interactions that can strengthen the mother–infant bond. Once children begin to speak, usually between 9 and 15 months of age, their contribution to their own development becomes more evident. For example, toddlers (1- and 2-year-olds) often talk when they are alone in a room. Only if children were internally motivated to learn language would they practice talking when no one was present to react to what they are saying. This “crib speech” is entirely normal, and the practice probably helps toddlers learn language.

Play contributes to children’s development in many ways, including the spatial understanding and attention to detail required to complete puzzles.

Young children’s play provides many other examples of how their internally motivated activity contributes to their development. Children play by themselves for the sheer joy of doing so, but they also learn a great deal in the process. Anyone who has seen a baby bang a spoon against the tray of a high chair or intentionally drop food on the floor would agree that, for the baby, the activity is its own reward. At the same time, the baby is learning about the noises made by colliding objects, about the speed at which objects fall, and about the limits of his or her parents’ patience. Young children’s fantasy play seems to make an especially large contribution to their knowledge of themselves and other people. Starting at around age 2 years, children sometimes pretend to be

different people in make-believe dramas. For example, they may pretend to be superheroes doing battle with monsters or play the role of parents taking care of babies. The particular play activities vary across cultures, but the existence of play and its developmental pattern are similar, even in cultures that actively discourage playing (Carlson, Taylor, & Levin, 1998). In addition to being inherently enjoyable, play teaches children valuable lessons, including how to cope with fears, resolve disputes, and interact with others (Lillard, 2017). Older children’s play, which typically is more organized and rule-bound, promotes additional useful capabilities, such as the self-control needed for turn-taking, adhering to rules, and controlling one’s emotions in the face of setbacks (Hirsh-Pasek, Zosh et al., 2015). As we discuss later in the chapter, children’s contributions to their own development strengthen and broaden as they grow older and become increasingly able to choose and shape their environments.

3. Continuity/Discontinuity: In What Ways Is Development Continuous, and in What Ways Is It Discontinuous? Some scientists envision children’s development as a continuous process of small changes, like that of a pine tree growing taller and taller. Others see the process as a series of occasional, sudden,

discontinuous changes, like the transition from caterpillar to cocoon to butterfly (Figure 1.2). The debate over which of these views best describes child development has continued for decades. continuous development the idea that changes with age occur gradually, in small increments, like that of a pine tree growing taller and taller discontinuous development the idea that changes with age include occasional large shifts, like the transition from caterpillar to cocoon to butterfly

FIGURE 1.2 Continuous and discontinuous development Some researchers see development as a continuous, gradual process, akin to a tree’s growing taller with each passing year. Others see it as a discontinuous process, involving sudden dramatic changes, such as the transition from caterpillar to cocoon to butterfly. Each view fits some aspects of child development.

Researchers who view development as discontinuous start from a common observation: children of different ages seem qualitatively

different. A 4-year-old and a 6-year-old, for example, seem to differ not only in how much they know but in the way they think about the world. To appreciate these differences, consider two conversations between Beth, the daughter of one of the authors, and Beth’s mother. The first conversation took place when Beth was 4 years old; the second, when she was 6. Both conversations occurred after Beth had watched her mother pour all the water from a typical drinking glass into a taller, narrower glass. Here is the conversation that occurred when Beth was 4: Mother: Is there still the same amount of water? Beth: No. Mother: Was there more water before, or is there more now? Beth: There’s more now. Mother: What makes you think so? Beth: The water is higher; you can see it’s more. Mother: Now I’ll pour the water back into the regular glass. Is there the same amount of water as when the water was in the same glass before? Beth: Yes. Mother: Now I’ll pour all the water again into the tall thin glass. Does the amount of water stay the same? Beth: No, I already told you, there’s more water when it’s in the tall glass.

Two years later, Beth responded to the same problem quite differently: Mother: Is there still the same amount of water? Beth: Of course!

Children’s behaviour on Piaget’s conservation-of-liquid-quantity problem is often

used to exemplify the idea that development is discontinuous. The child first sees equal amounts of liquid in similarly shaped glasses and an empty, differently shaped glass. Then, the child sees the liquid from one glass poured into the differently shaped glass. Finally, the child is asked whether the amount of liquid remains the same or whether one glass has more. Young children, like this girl, are unshakable in their belief that the glass with the taller liquid column has more liquid. A year or two later, they are equally unshakable in their belief that the amount of liquid in each glass is the same.

What accounts for this change in Beth’s thinking? Her everyday observations of liquids being poured cannot have been the reason for it; Beth had seen liquids poured on a great number of occasions before she was 4, yet she failed to develop the understanding that the volume of liquid remains constant. Experience with the specific task could not explain the change either, because Beth had no further exposure to the task between the first and second conversation. Then why as a 4-year-old would Beth be so confident that pouring the water into the taller, narrower glass increased the amount, and then as a 6year-old be so confident that it did not?

Cognitive Development in Childhood: Conservation-of-Liquid Task

This conservation-of-liquid-quantity problem is actually a classic technique designed to test children’s level of thinking. It has been used with thousands of children around the world, and virtually all the children studied, no matter what their culture, have shown the same type of change in reasoning as Beth did (though usually at somewhat older ages). Furthermore, such age-related differences in understanding pervade children’s thinking. Consider two letters sent to the host of the children’s television show Mr. Rogers’ Neighborhood, one by a 4-year-old and one by a 5-year-old (Rogers, 1996, pp. 10–11): Dear Mr. Rogers,

I would like to know how you get in the TV. (Robby, age 4) Dear Mr. Rogers, I wish you accidentally stepped out of the TV into my house so I could play with you. (Josiah, age 5)

Clearly, these are not ideas that an older child would entertain. As with Beth’s case, we have to ask, “What is it about 4- and 5-year-olds that leads them to form such improbable beliefs, and what changes occur that make such notions laughable to 6- and 7-year-olds?” One common approach to answering these questions comes from stage theories, which propose that development occurs in a progression of distinct age-related stages, much like the butterfly example in Figure 1.2b. According to these theories, a child’s entry into a new stage involves relatively sudden, qualitative changes that affect the child’s thinking or behaviour in broadly unified ways and move the child from one coherent way of experiencing the world to a different coherent way of experiencing it. stage theories approaches proposing that development involves a series of large, discontinuous, agerelated phases

Cognitive Development: The Balance-Scale Problem

Among the best-known stage theories is Jean Piaget’s theory of cognitive development, the development of thinking and reasoning. This theory holds that between birth and adolescence, children go through four stages of cognitive growth, each characterized by distinct intellectual abilities and ways of understanding the world. For example, according to Piaget’s theory, 2- to 5-year-olds are in a stage of development in which they can focus on only one aspect of an event, or one type of information, at a time. By age 7, children enter a different stage, in which they can simultaneously focus on and coordinate two or more aspects of an event and can do so on many different tasks.

cognitive development the development of thinking and reasoning

According to this view, when confronted with a problem like the one that Beth’s mother presented to her, most 4- and 5-year-olds focus on the single dimension of height and therefore perceive the taller, narrower glass as having more water. In contrast, most 7- and 8-yearolds consider both relevant dimensions of the problem simultaneously. This allows them to realize that although the column of water in the taller glass is higher, the column also is narrower, and the two differences offset each other. In the course of reading this book, you will encounter a number of other stage theories, including Sigmund Freud’s theory of psychosexual development, Erik Erikson’s theory of psychosocial development, and Lawrence Kohlberg’s theory of moral development. Each of these stage theories proposes that children of a given age show broad similarities across many situations and that children of different ages tend to behave very differently. Although such stage theories have been highly influential, in the past 20 years, many researchers have concluded that most developmental changes are gradual rather than sudden, and that development occurs skill by skill rather than in a broadly unified way (Munakata, Snyder, & Chatham, 2012; Thelen & Smith, 2006). This view of development is less dramatic than that of stage theories, but a great deal of evidence supports it. One such piece of evidence is the fact

that a child often will behave in accord with one proposed stage on some tasks but in accord with a different proposed stage on other tasks (Fischer & Bidell, 2006). This variable level of reasoning makes it difficult to view the child as being “in” either stage. Much of the difficulty in deciding whether development is continuous or discontinuous is that the same facts can look very different, depending on one’s perspective. A classic study by Tanner (1961) addressed the seemingly simple question of whether children’s height increases continuously or discontinuously. Figure 1.3a shows a boy’s height, measured yearly from birth to age 18. When one looks at the boy’s height at each age, development seems smooth and continuous, with growth occurring rapidly early in life and then slowing down.

FIGURE 1.3 Continuous and discontinuous growth Depending on how it is viewed, changes in height can be regarded as either continuous or discontinuous. (a) Examining a boy’s height in absolute terms from birth to 18 years makes the growth look gradual and continuous. (b) Examining the increases in the same boy’s height from one year to the next over the same period shows rapid growth during the first 2½ years, then slower growth, then a growth spurt in adolescence, then a rapid decrease in growth; viewed this way, growth seems discontinuous. (Data from Tanner, 1961)

Description The graph labeled (a) shows continuous growth. It has its horizontal axis labeled Age (years) with values ranging from Birth to 18, at an increment of 2 years and its vertical axis labeled Height (centimeter) with values ranging from 60 to 210, at an increment of 30 units. The data in the graph are as follows: The graph starts at (Birth, below 60 centimeter) and passing through points (2, 88), (4, 100), and reaches (17, 180). The data given is approximate. The graph labeled (b) shows discontinuous growth. It has its horizontal axis labeled Age with values ranging from Birth to 18, at an increment of 2 years and vertical axis labeled, Height gain (cm/year) with values ranging from 2 to 22 at an increment of 4 units. The data in the graph are as follows: The graph starts at (Birth, 21) and steeply declines to (3, 7). It thereon passes through a steady growth and reaches (12, 4) and then steadily increase to a peak (15, 12). It further declines to (17, 1).

However, when you look at Figure 1.3b, a different picture emerges. This graph illustrates the same boy’s growth, but it depicts the amount of growth from one year to the next. The boy grew every year, but he grew most during two periods: from birth to age 2½ and from ages 13 to 15. These are the kinds of data that lead people to talk about discontinuous growth and about a separate stage of adolescence that includes a physical growth spurt. So, is development fundamentally continuous or fundamentally discontinuous? The most reasonable answer seems to be, “It depends on how you look at it and how often you look.” Imagine the difference between the perspective of an uncle who sees his niece every 2 or 3 years and that of the niece’s parents, who see her every day. The uncle will almost always be struck with the huge changes in his niece since he last saw her. The niece will be so different that it will seem that she progressed to a higher stage of development. In contrast, the parents will most often be struck by the continuity of her development; to them, she just seems to grow up steadily. Throughout this book, we will consider the changes, large and small, sudden and gradual, that have led some researchers to emphasize the continuities in development while others emphasize the discontinuities.

4. Mechanisms of Change: How Does

Change Occur? Perhaps the deepest mystery about children’s development is expressed by the question “How does change occur?” In other words, what are the mechanisms that produce the remarkable changes that children undergo with age and experience? Different developmentalists use the term “mechanisms” in somewhat different ways, but all attempts to specify mechanisms share the goal of producing increasingly precise accounts of the processes that produce an outcome of interest. Developmental mechanisms can be behavioural, neural, or genetic. Thus, mathematical development has been explained through the behavioural mechanism of improved strategies (Siegler, 2016), the neural mechanism of increased interconnection between the frontal cortex and the intraparietal sulcus (Rosenberg-Lee, Barth, & Menon, 2011), and the genetic mechanism of the presence or absence of specific alleles (Davis et al., 2014). One particularly interesting analysis of mechanisms of developmental change involves the roles of brain activity, genes, and learning experiences in the development of effortful attention (e.g., Rothbart, Sheese, & Posner, 2007). Effortful attention involves voluntary control of one’s emotions and thoughts. It includes processes such as inhibiting impulses (e.g., obeying requests to put all of one’s toys away, as opposed to putting some away but then getting distracted and playing with the remaining ones); controlling

emotions (e.g., not crying when failing to get one’s way); and focusing attention (e.g., concentrating on one’s homework despite the inviting sounds of other children playing outside). Difficulty in exerting effortful attention is associated with behavioural problems, weak math and reading skills, and mental illness (Blair, 2016; Diamond & Lee, 2011). To specify the physiological mechanisms underlying effortful control, researchers have examined brain activity of people as they performed tasks that require such control. These studies have shown that when people are controlling thoughts and emotions, brain activity is especially intense in connections between the limbic area— a part of the brain that plays a large role in emotional reactions—and the anterior cingulate and prefrontal cortex—brain structures involved in setting and attending to goals (Gazzaniga, Ivry, & Mangun, 2013). Connections among these brain areas develop considerably during childhood, and their development appears to be one mechanism that underlies improving effortful attention during childhood. As we might predict, based on our understanding of nature and nurture, development of these areas reflects environmental circumstances as well as genetics. For example, spending one’s childhood in poverty has a negative effect on the brain activity needed to suppress negative emotions and improve effortful attention many years later in adulthood (Kim, Evans et al., 2013). Other studies have examined the genetic mechanisms that influence brain activity during effortful attention and the way in which those

genetic mechanisms influence the effects of parenting. Specific genes have been found to influence the production of key neurotransmitters—chemicals involved in communication among brain cells. Variations in these genes among children are associated with variations in the quality of performance on tasks that require effortful attention (Canli et al., 2005; Diamond et al., 2004). These genetic influences do not occur in a vacuum. Infants with a particular form of one of the genes in question show differences in effortful attention related to the quality of parenting they receive; lowerquality parenting is associated with lower ability to regulate attention (Sheese et al., 2007). Among children who do not have that form of the gene, quality of parenting has less effect on effortful attention. neurotransmitters chemicals involved in communication among brain cells

Learning can change the wiring of the brain system that produces effortful attention. Rueda and colleagues (2005) presented 6-year-olds with a 5-day training program that used computerized exercises to improve capacity for effortful attention. Examination of electrical activity in the anterior cingulate indicated that those 6-year-olds who had completed the computerized exercises showed improved effortful attention. These children also showed improved performance on intelligence tests, which makes sense given the sustained effortful attention required by such tests. Thus, the experiences that children encounter influence their brain processes and gene expression, just as brain processes and genes influence

children’s reactions to their experiences. More generally, a full understanding of the mechanisms that produce developmental change requires specifying how genes, brain structures and processes, and experiences interact. Another illustration of developmental mechanisms involves the changing role of sleep in promoting learning and generalization (Gómez & Edgin, 2015). Infants spend a great deal of their lives sleeping; for example, 6-month-olds average 14–15 hours of sleep per day (Ohayon et al., 2004). This prolonged sleep serves an important function in promoting learning (Diekelmann & Born, 2010). However, the type of learning that it promotes changes with the maturation of the hippocampus, a brain structure that is particularly important for learning and remembering. During the first 18 months following birth, sleep appears to promote learning of general, frequently encountered patterns but not learning of the specifics of material presented only once or twice (Gómez, Bootzin, & Nadel, 2006). In contrast, after age 24 months, children tend to show the opposite pattern: when tested shortly after napping, they often remember the specifics of what they learned better than peers who did not nap during that period, but their memory for general patterns is no better than those of peers who did not nap (Kurdziel, Duclos, & Spencer, 2013). Werchan and Gómez (2014) described mechanisms that could underlie this change from infancy to the preschool period. Their

explanation was based on a major theory of memory, called Active Systems Consolidation Theory (McClelland, McNaughton, & O’Reilly, 1995), which posits that two interconnected brain areas, the hippocampus and the cortex, simultaneously encode new information during learning (see Figure 1.4). The hippocampus can learn details of new information after one or two experiences; the cortex produces abstraction of general patterns over many experiences. The theory posits that in older children and adults, hippocampal memories are replayed during sleep, which allows opportunities for the cortex to extract general patterns from the specific memories stored in the hippocampus. The mechanism works in the opposite direction as well; learning general patterns improves the retention of details of new experiences of the same type (Mullally & Maguire, 2014).

FIGURE 1.4 The human cortex The four main lobes of the cortex: frontal, parietal, occipital, and temporal. The hippocampus, which is also shown, is deeper inside the brain than it appears in this figure, whereas the cortex covers outer portions of the brain.

These findings and theories led Werchan and Gómez (2014) to hypothesize that the benefits of sleep on infants’ memory for general patterns reflect functioning of the cortex, whereas the benefits of sleep on preschoolers’ memory for specific experiences reflect functioning of the hippocampus. They proposed that prior to 18 to 24 months of age, the hippocampus is too immature to enable the rapid learning of the details of specific experiences; therefore, sleeping does not benefit memory for these specifics. However, the cortex is mature enough at this age to extract general patterns. Considerable

evidence supports this claim (Edgin et al., 2015; Friedrich et al., 2015). Thus, sleep is not a waste of time; it is essential for learning and for healthy development in general.

5. The Sociocultural Context: How Does the Sociocultural Context Influence Development? Children grow up in a particular set of physical and social environments, in a particular culture, under particular economic circumstances, at a particular time in history. Together, these physical, social, cultural, economic, and historical circumstances constitute the sociocultural context of a child’s life—which influences every aspect of children’s development. sociocultural context the physical, social, cultural, economic, and historical circumstances that make up any child’s environment

A classic depiction of the components of the sociocultural context is Urie Bronfenbrenner’s (1979) bioecological model (discussed in depth in Chapter 9). The most obviously important components of children’s sociocultural contexts are the people with whom they interact—parents, grandparents, brothers, sisters, day-care providers, teachers, friends, and classmates—and the physical environment in which they live—their house, childcare centre, school,

neighbourhood, and so on. Another important but less tangible component of the sociocultural context is the institutions that influence children’s lives, including educational systems, religious institutions, sports leagues, social organizations, and others. Yet another important set of influences are the general characteristics of the child’s society: its economic and technological advancement; its values, attitudes, beliefs, and traditions; its laws and political structure; and so on. For example, the simple fact that most toddlers and preschoolers growing up in Canada today go to childcare outside their homes reflects a number of these less tangible sociocultural factors, including the historical era (50 years ago, far fewer children in Canada attended childcare centres); the economic structure (there are far more opportunities today for women to work outside the home); cultural beliefs (e.g., that receiving childcare outside the home does not harm children); and cultural values (e.g., the value that mothers of young children should be able to work outside the home if they wish). Attendance at childcare centres, in turn, partly determines the people children meet and the activities in which they engage. One method that developmentalists use to understand the influence of the sociocultural context is to compare the lives of children who grow up in different cultures. Such cross-cultural comparisons often reveal that practices that are rare or nonexistent in one culture are common in others. The following comparison of young children’s

sleeping arrangements in different societies illustrates the value of such cross-cultural research. In most families in Canada and the United States, newborn infants sleep in their parents’ bedroom, either in a crib or in the same bed. However, when infants are 2 to 6 months old, parents usually move them to another bedroom where they sleep alone (Greenfield, Suzuki, & Rothstein-Fisch, 2006). This seems natural to most people raised in North America because it is how they and others whom they know were raised. From a worldwide perspective, however, such sleeping arrangements are unusual. In most other societies, including nations such as Italy, Japan, and South Korea, young children almost always sleep in the same bed as their mother for the first few years, and somewhat older children also sleep in the same room as their mother, sometimes in the same bed (e.g., Nelson, Schiefenhoevel, & Haimerl, 2000; Whiting & Edwards, 1988).

In many countries, including Denmark, the country in which this mother and child live, mothers and children sleep together for the first several years of the child’s life. This sociocultural pattern is in sharp contrast to the Canadian practice of having infants sleep separately from their parents soon after birth.

How do these differences in sleeping arrangements affect children? To find out, Morelli and colleagues (1992) interviewed mothers in middle-class U.S. families in Salt Lake City, Utah, and in rural Mayan families in Guatemala. These interviews revealed that by age 6 months, the large majority of the U.S. children had begun sleeping in their own bedroom. As the children grew out of infancy, the nightly separation of child and parents became a complex ritual, surrounded by activities intended to comfort the child, such as telling stories, reading children’s books, singing songs, and so on. About half the

children were reported as taking a comfort object, such as a blanket or teddy bear, to bed with them. In contrast, interviews with the Mayan mothers indicated that their children typically slept in the same bed with them until the age of 2 or 3 years and continued to sleep in the same room with them for years thereafter. The children usually went to sleep at the same time as their parents. None of the Mayan parents reported bedtime rituals, and almost none reported their children taking comfort objects, such as dolls or stuffed animals, to bed with them. Why do sleeping arrangements differ across cultures? Interviews with the Mayan and U.S. parents indicated that cultural values were foremost. Mayan culture prizes interdependence among people. The Mayan parents expressed the belief that having a young child sleep with the mother is important for developing a good parent–child relationship, for avoiding the child’s becoming distressed at being alone, and for helping parents spot any problems the child is having. They often expressed shock and pity when told that infants in the United States typically sleep separately from their parents (Greenfield et al., 2006). In contrast, U.S. culture prizes independence and selfreliance, and the U.S. mothers expressed the belief that having babies and young children sleep alone promotes these values, as well as allowing intimacy between husbands and wives (Morelli et al., 1992). These differences illustrate both how practices that strike us as natural may differ greatly across cultures and how the simple conventions of everyday life often reflect deeper values.

Contexts of development differ not just between cultures but also within them. In modern multicultural societies, many contextual differences are related to ethnicity, race, and socioeconomic status (SES)—a measure of social class that is based on income and education. Virtually all aspects of children’s lives—from the food they eat to the parental discipline they receive to the games they play— vary with ethnicity, race, and SES. socioeconomic status (SES) a measure of social class based on income and education

The socioeconomic context exerts a particularly large influence on children’s lives. In economically advanced societies, including Canada, most children grow up in reasonably comfortable circumstances, but millions of other children do not. In 2017 in Canada, 9% of children lived below the poverty level; in absolute numbers, that figure represents approximately 622,000 children, down from 11% in 2016 (see Table 1.2; Statistics Canada, 2019). Although declining in Canada, poverty rates are especially high for Indigenous children in Canada (MacDonald & Wilson, 2016).

TABLE 1.2 Child Poverty in Canada (Persons under 18 years), 2013 to 2017 Child Poverty Rate

Total Number of Children Living in Poverty (in thousands)

2013

14.5%

974

2014

12.4

836

2015

13.3

900

2016

11.0

755

2017

9.0

622

Data from Statistics Canada, 2019.

As documented in a report to the Royal Society of Canada, children from economically disadvantaged families tend to do less well than other children in many ways, and these effects can be long-lasting (Boivin & Hertzman, 2012). In infancy, they are more likely to have serious health problems. Beginning at age 3 years and continuing through at least age 20, their brains, on average, have less surface area, especially in areas that support spoken language, reading, and spatial skills (Noble et al., 2015). Throughout childhood and adolescence, they tend to have more emotional problems, smaller vocabularies, lower IQs, and lower math and reading scores on standardized achievement tests (Evans, Li, & Whipple, 2013). In adolescence, they are more likely to have a baby or drop out of school (Penman-Aguilar et al., 2013). These negative outcomes are not surprising when we consider the huge array of challenges that poor children face. Compared with children who grow up in more affluent circumstances, they are more likely to live in dangerous neighbourhoods, to attend lower-quality childcare centres and schools, and to be exposed to high levels of air and water pollution (Bell & Ebisu, 2012). In addition, their parents

read to them less, provide fewer books in the home, and are less involved in their schooling (Hart & Risley, 2003). Children in lowincome families also are more likely than children from more affluent families to grow up in single-parent homes or to be raised by neither biological parent. The accumulation of these disadvantages over years of development, often termed cumulative risk, seems to be the greatest obstacle to poor children’s successful development (Evans & Cassells, 2014; Morales & Guerra, 2006). cumulative risk the accumulation of disadvantages over years of development

Yet, as we saw in Werner’s study of the children of Kauai, described at the beginning of the chapter, many children do overcome the obstacles that poverty presents. Such resilient children are more likely than others to have three characteristics: (1) positive personal qualities, such as high intelligence, an easygoing personality, and an optimistic outlook on the future; (2) a close relationship with at least one parent; and (3) a close relationship with at least one adult other than their parents, such as a grandparent, teacher, coach, or family friend (Chen & Miller, 2012; Masten, 2007). As these characteristics suggest, children’s resilience reflects not just their personal qualities but also the interactions they have with other people (Masten, 2014).

6. Individual Differences: How Do Children Become So Different from

One Another? Everyone who has experience with children is struck by their uniqueness—their differences not only in physical appearance but in everything from activity level and temperament to intelligence, persistence, and emotionality. These differences among children emerge quickly. Some infants in their first year are shy, others outgoing. Some infants play with or look at objects for prolonged periods; others rapidly shift from activity to activity. Even children in the same family often differ substantially, as you probably already know if you have siblings. Scarr (1992) identified four factors that can lead children from a single family (as well as children from different families) to turn out very different from one another: 1. 2. 3. 4.

Genetic differences Differences in treatment by parents and others Differences in reactions to similar experiences Different choices of environments

Different children, even ones within the same family, often react to the same experience, such as this roller coaster ride, in completely different ways.

The most obvious reason for differences among children is that every individual is genetically unique. This is true even of so-called “identical twins.” At conception, the genomes of these children are identical, but mutations or copying errors result in several hundred gene differences being present, on average, even before birth (Li et al., 2014). The genomes of all other children are much more different from each other; for example, other siblings, including fraternal twins, differ in 50% of the genes on which people differ (the vast majority of genes are identical for all humans; they’re what make us human). A second major source of variation among children is differences in

the treatment they receive from parents and other people. This differential treatment is often associated with preexisting differences in the children’s characteristics. For instance, parents tend to provide more sensitive care to easygoing infants than to difficult ones; by the second year, parents of difficult children are often angry with them, even when the children have done nothing wrong in the immediate situation (van den Boom & Hoeksma, 1994). Teachers likewise tend to provide positive attention and encouragement to pupils who are learning well and are well behaved, but with pupils who are doing poorly and are disruptive, they tend to be openly critical and to deny the pupils’ requests for special help (Good & Brophy, 1996). In addition to being shaped by objective differences in the treatment they receive, children also are influenced by their subjective interpretations of their treatment. A classic example occurs when each of a pair of siblings feels that their parents favour the other. Siblings also often react differently to events that affect the whole family. In one study, 69% of negative events, such as parents’ being laid off or fired, elicited fundamentally different reactions from siblings (Beardsall & Dunn, 1992). Some children were very concerned at a parent’s loss of a job; others were sure that everything would be okay. A fourth major source of differences among children relates to the previously discussed theme of the active child: as children grow older, they increasingly choose activities and friends for themselves and

thus influence their own subsequent development. They may also accept or choose niches for themselves: within a family, one child may become “the smart one,” another “the popular one,” another “the naughty one,” and so on. A child labelled by family members as “the nice one” may strive to live up to the label; so, unfortunately, may a child labelled “the troublemaker.”

Adolescents who participate in sports and other extracurricular activities are more likely to complete high school, and less likely to get into trouble, than peers who are not engaged in these activities. This is another example of how individuals make choices that influence their development.

As discussed in the sections on nature and nurture and on mechanisms of development, differences in biology and experience

interact in complex ways to create the infinite diversity of human beings. A study of 11- to 17-year-olds found that the grades of children who were highly engaged with school changed in more positive directions than would have been predicted by their genetic background or family environments alone (Johnson, McGue, & Iacono, 2006). The same study revealed that children of high intelligence were less negatively affected by adverse family environments than were other children. Thus, children’s genes, their treatment by other people, their subjective reactions to their experiences, and their choice of environments interact in ways that make each child unique.

7. Research and Children’s Welfare: How Can Research Promote Children’s Well-Being? Improved research-based understanding of child development often leads to practical benefits. Several examples have already been described, including the program for helping children deal with their anger and the recommendations for fostering valid eyewitness testimony from young children. Another type of practical benefit arising from child-development research involves educational innovations. Children’s reasoning, remembering, conceptualizing, and problem solving is inherently

related to education; throughout the book, especially in Chapters 4 and 8, we review many examples of educational innovations stemming from child-development research. One fascinating example comes from studies of children’s differing beliefs about intelligence and how those differing beliefs influence their learning (see Box 1.2).

BOX 1.2 INDIVIDUAL DIFFERENCES Can Children Learn to Be More Intelligent? Carol Dweck and her colleagues (Dweck, 2012; Yeager & Dweck, 2012) have found that some children (and adults) believe that intelligence is a fixed entity. They see each person as having a certain amount of intelligence that is set at birth and cannot be changed by experience. Other children (and adults) believe intelligence is a changeable characteristic that increases with learning and that the time and effort people put into learning is the key determinant of their intelligence. People who believe that intelligence increases with learning tend to react to failure in more effective ways (Dweck, 2006). When they fail to solve a problem, they more often persist on the task and try harder. Such persistence in the face of failure is an important quality. As the great British Prime Minister Winston Churchill once said, “Success is the ability to go from one failure to another with no loss of enthusiasm.” In contrast, people who believe that intelligence is a fixed entity tend to give up when they fail. Building on this research regarding the relation between beliefs about intelligence and persistence in the face of difficulty, Blackwell, Trzesniewski, and Dweck (2007) devised an effective educational program for middle school students from lowincome backgrounds. They presented randomly selected students with research findings about how learning alters the brain in ways that improve subsequent

learning and thus “makes you smarter.” Other randomly selected students from the same classrooms were presented with research findings about how memory works. The investigators predicted that the students who were told about how learning affects the brain would change their beliefs about intelligence in ways that would help them persevere in the face of failure. In particular, the changed beliefs were expected to improve students’ learning of mathematics, an area in which children often experience initial failure.

Screenshot from Brainology, a commercially available educational program based on the findings of Blackwell, Trzesniewski, and Dweck (2007). The software, like the research study, emphasizes that learning makes children smarter by building new connections within the brain.

The researchers’ prediction was borne out. Children who were presented information about how learning changes the brain and enhances intelligence subsequently improved their math grades, whereas the other children did not. Children who initially believed that intelligence was an inborn, unchanging quality, but who came to believe that intelligence reflected learning, showed especially large improvements. Perhaps most striking was that when the children’s teachers (who did not know which type of information each child had received) were asked

if any of their students had shown unusual improvement in motivation or performance, the teachers cited more than three times as many students who had been given information about how learning builds intelligence. Subsequent reviews of research on mindset instruction indicate that such effects are real, though they often are small (Burnette et al., 2012; Sisk et al., 2018). Providing children with information about how learning changes the brain and thus builds intelligence is, of course, not the only way to increase their motivation to learn. Another effective method involves presentation of struggle stories, which relate how famous or notable people—for example, great scientists such as Albert Einstein and Marie Curie—needed to overcome failures and difficult life circumstances on the way to success. Studies conducted in the United States and in China have shown that hearing such struggle stories improves children’s science learning (Hong & Lin-Siegler, 2012; Lin-Siegler et al., 2016).

Interview with Carol Dweck

REVIEW QUESTION Which of the seven fundamental questions about child development most interests you? Why?

Methods for Studying Child Development As illustrated in the preceding section, modern scientific research has advanced understanding of fundamental questions about child development well beyond that of the ancient Greek philosophers who first raised the questions. This progress reflects the successful application of the scientific method to the study of child development. In this section, we describe the scientific method and examine how its use has advanced our understanding of child development.

The Scientific Method The basic assumption of the scientific method is that all beliefs, no matter how probable they seem and no matter how many people share them, may be wrong. Therefore, until beliefs have been repeatedly tested, they must be viewed as hypotheses, that is, as testable predictions of the presence or absence of phenomena or relations rather than as truth. If a hypothesis is tested, and the evidence repeatedly does not support it, the hypothesis must be abandoned no matter how reasonable it seems. scientific method an approach to testing beliefs that involves choosing a question, formulating a hypothesis, testing the hypothesis, and drawing a conclusion

hypotheses testable predictions of the presence or absence of phenomena or relations

Use of the scientific method involves four basic steps: 1. 2. 3. 4.

Choosing a question to be answered Formulating a hypothesis regarding the question Developing a method for testing the hypothesis Using the resulting data to draw a conclusion regarding the hypothesis

To illustrate these steps, let’s make the question to be answered “What abilities predict which children will become good readers?” A reasonable hypothesis might be “Kindergartners who can identify the separate sounds within words will become better readers than those who cannot.” A straightforward method for testing this hypothesis would be to select a group of kindergartners, test their ability to identify the separate sounds within words, and then, several years later, test the reading skills of the same children. Research has, in fact, shown that kindergartners who are aware of the component sounds within words later tend to read more skillfully than their peers who lacked this ability as kindergartners. This pattern holds true regardless of whether the children are learning English, Norwegian, or Swedish (Furnes & Samuelsson, 2011). The pattern also holds whether children are learning Canadian-English as a first or second language (Chiappe & Siegel, 1999). These results support the conclusion that kindergartners’ ability to identify sounds within

words predicts their later reading skill. The first, second, and fourth of these steps are not unique to the scientific method. Great thinkers of the past also asked questions, formulated hypotheses, and drew conclusions that were reasonable, given the evidence available to them. What distinguishes scientific research from nonscientific approaches is the third step: the methods used to test the hypotheses. When rigorously employed, these research methods yield high-quality evidence that allows investigators to progress beyond their initial hypotheses to draw firmly grounded conclusions.

The Importance of Appropriate Measurement For the scientific method to work, researchers must use measures that are directly relevant to the hypotheses being tested. Even measures that initially seem reasonable sometimes turn out to be less informative than originally thought. For example, a researcher who hypothesized that a supplemental food program would help children suffering from malnutrition might evaluate the program on the basis of weight gain from just before the program to just after it. However, weight is an inadequate measure of nutrition: providing unlimited doughnuts would probably produce weight gain but would not improve nutrition; many people who consume large amounts of junk food are obese yet malnourished (Via, 2012).

Regardless of the particular measure used, many of the same criteria determine whether a measure is a good one. One key criterion has already been noted—the measure must be directly relevant to the hypothesis. Two other qualities that good measures must possess are reliability and validity.

Reliability The degree to which independent measurements of a behaviour under study are consistent is referred to as reliability. One important type of consistency, interrater reliability, indicates how much agreement there is in the observations of different raters who witness the same behaviour. Sometimes the observations are qualitative, as when raters classify a baby’s attachment to her mother as “secure” or “insecure.” Other times, the observations are quantitative, as when raters score on a scale of 1 to 10 how upset babies become when they are presented with an unfamiliar noisy toy or a boisterous stranger. In both cases, interrater reliability is attained when the raters’ evaluations are in close agreement—as when, for example, Baby A in a group being observed for a particular behaviour gets a 6 or 7 from all the raters, Baby B gets a 3 or 4 from all of them, Baby C consistently gets an 8 or 9, and so on. Without such agreement, one cannot have confidence in the research findings because there is no way to tell which (if any) of the ratings were accurate. reliability the degree to which independent measurements of a given behaviour are consistent

interrater reliability the amount of agreement in the observations of different raters who witness the same behaviour

A second important type of consistency is test–retest reliability. This type of reliability is attained when measures of a child’s performance on the same test, administered under the same conditions, are similar on two or more occasions. Suppose, for example, that researchers presented a vocabulary test to a group of children on two separate occasions, one week apart. If the test is reliable, the children who scored highest on the first testing should also score highest on the second because none of the children’s vocabularies would have changed much over such a short period. As in the example of interrater reliability, a lack of test–retest reliability would make it impossible to know which result (if either) accurately reflected each child’s status. test–retest reliability the degree of similarity of a participant’s performance on two or more occasions

Validity The validity of a test or experiment refers to the degree to which it measures what it is intended to measure. Researchers strive for two types of validity: internal and external. Internal validity refers to whether effects observed within experiments can be attributed with confidence to the factor that the researcher is testing. For instance, suppose that a researcher tests the effectiveness of a type of

psychotherapy for depression by administering it to a number of depressed adolescents. If, three months later, many of the adolescents are no longer depressed, can it be concluded that this type of psychotherapy caused the improvement? No, because the students’ recovery may have been due to the mere passage of time. Moods fluctuate, and many people who are depressed at any given time will be happier at a later date even without psychotherapy. In this example, the passage of time is a source of internal invalidity because the factor believed to cause the improvement (the psychotherapy) may have had no effect. validity the degree to which a test measures what it is intended to measure internal validity the degree to which effects observed within experiments can be attributed to the factor that the researcher is testing

External validity, in contrast, refers to the ability to generalize research findings beyond the particulars of the research in question. Studies of child development are almost never intended to apply only to the particular children and research methods involved in a given study. Rather, the goal is to draw conclusions that apply to children more generally. Thus, the findings of a single experiment are only the first step in determining the external validity of the results. Additional studies with participants from different backgrounds and with research methods that vary in their particulars are invariably needed to establish the external validity of the findings. (Table 1.3 summarizes the key properties of behavioural measures.)

external validity the degree to which results can be generalized beyond the particulars of the research

TABLE 1.3 Key Properties of Behavioural Measures Property

Question of Interest

Relevance to hypotheses

Do the hypotheses predict in a straightforward way what should happen on these measures?

Interrater reliability

Do different raters who observe the same behaviour classify or score it the same way?

Test–retest reliability

Do children who score higher on a measure at one time also score higher on the measure at other times?

Internal validity

Can effects within the experiment be attributed to the variables that the researcher intentionally manipulated?

External validity

How widely can the findings be generalized to different children in different places at different times?

External validity, internal validity, and reliability are related in important ways. An unreliable measure, one in which the ratings of different people are not strongly related, cannot be valid because there is no way to tell which rater, if any, is accurately assessing the behaviour being rated. Similarly, measures that are invalid with the original sample and experimental situation provide no reason to believe that the measures would be valid for different samples or situations. Thus, reliability is necessary for internal validity, and both are necessary for external validity.

Contexts for Gathering Data About Children Researchers obtain data about children in three main contexts: interviews, naturalistic observation, and structured observation. In the following sections, we consider how gathering data in each context can help answer different questions about children.

Interviews and Questionnaires The most obvious way to collect data about children is to go straight to the source and ask the children themselves about their lives. Structured interviews, sets of predetermined questions administered to participants, are especially useful when the goal is to collect selfreports on the same topics from everyone being studied. structured interview a research procedure in which all participants are asked to answer the same questions

One-on-one clinical interviews like this one can elicit unique in-depth information about a child.

With young children, the questions are usually presented orally; however, with children of reading age, printed questionnaires are usually used. Such questionnaires make it easier for researchers to obtain data from many children simultaneously. Both oral interviews and printed questionnaires provide a quick and straightforward way for researchers to learn about children’s feelings, beliefs, and behaviours. questionnaire a method that allows researchers to gather information from a large number of participants simultaneously by presenting them a uniform set of printed questions

A second type of interview, the clinical interview, is especially useful for obtaining in-depth information about an individual child. In this approach, the interviewer begins with a set of prepared questions, but if the child says something intriguing, the interviewer can depart from the script to follow up on the child’s lead. clinical interview a procedure in which questions are adjusted in accord with the answers the interviewee provides

The usefulness of clinical interviews can be seen in the case of Bobby, a 10-year-old child who was assessed for symptoms of depression (Schwartz & Johnson, 1985). When the interviewer asked him about school, Bobby said that he did not like it because the other children disliked him and he was bad at sports. As he put it, “I’m not really very good at anything” (p. 214). To explore the source of this sad selfdescription, the interviewer asked Bobby what he would wish for if three wishes could be granted. Bobby replied, “I would wish that I was the type of boy my mother and father want, I would wish that I could have friends, and I would wish that I wouldn’t feel sad so much” (p. 214). Such heartrending comments provide a sense of the painful subjective experience of this depressed child, one that would be impossible to obtain from methods that were not tailored to the individual. As with all contexts for collecting data, interviews have both strengths and weaknesses. On the positive side, they can yield a great

deal of data quickly and provide in-depth information about individual children. On the negative side, answers to interview questions often are biased. Children (like adults) often avoid disclosing facts that show them in a bad light, misremember the way that events happened, and fail to understand their own motivations (Wilson & Dunn, 2004). These limitations have led many researchers to use observational methods that allow them to witness the behaviour of interest for themselves.

Naturalistic Observation When the primary research goal is to describe how children behave in their usual environments—homes, schools, playgrounds, and so on —naturalistic observation is the method of choice for gathering data. In this approach, observers station themselves unobtrusively in the background of the chosen setting, allowing them to see the relevant behaviours while minimizing the chances that their presence will influence those behaviours. naturalistic observation examination of ongoing behaviour in an environment not controlled by the researcher

A classic example of naturalistic observation is Gerald Patterson’s (1982) comparative study of family dynamics in “troubled” and “typical” families. The troubled families were defined by the presence of at least one child who had been labelled “out of control” and

referred for treatment by a school, court, or mental health professional. The typical families were defined by the fact that none of the children in them showed signs of serious behavioural difficulties. Income levels and children’s ages were similar for the troubled and typical families. To observe the frequency with which children and parents engaged in negative behaviours—teasing, yelling, whining, criticizing, and so on—research assistants repeatedly observed dinnertime interactions in both troubled and typical homes, always staying silent in the background. The researchers found that the behaviours and attitudes of both parents and children in the troubled families differed strikingly from those of their counterparts in the typical families. Parents in the troubled families were more self-absorbed and less responsive to their children than were parents in the typical households. Children in the troubled families responded to parental punishment by becoming more aggressive, whereas children in the typical households responded to punishment by becoming less aggressive. In the troubled families, interactions often fell into a vicious cycle in which the child acted in a hostile or aggressive manner, the parent reacted angrily, the child escalated the level of hostility, the parent ratcheted up the aggression even further, and so on. As Patterson’s study suggests, naturalistic observations are particularly useful for illuminating everyday social interactions, such as those between children and parents.

Psychologists sometimes observe family interactions around the dinner table, because mealtime comments can evoke strong emotions.

Although naturalistic observation can yield detailed information about certain aspects of children’s everyday lives, it also has important limitations. One is that naturally occurring contexts vary on many dimensions, so it is often hard to know which ones influenced the behaviour of interest. For example, it was clear in the Patterson study that the interactions of troubled families differed from those of the more harmonious families, but the interactions and family histories differed in so many ways that it was impossible to specify how the current situation arose. A second limitation of naturalistic studies is that many behaviours of interest occur only occasionally in the everyday environment, which reduces

researchers’ opportunities to observe them. A means for overcoming both limitations is the method known as structured observation.

Structured Observation When using structured observation, researchers design a situation that will elicit behaviour that is relevant to a hypothesis and then observe how different children behave in that situation. The researchers then relate the behaviours to characteristics of the child, such as age, sex, or personality, and to the child’s behaviour in other situations that are also observed. structured observation a method that involves presenting an identical situation to each participant and recording the participant’s behaviour

Temptation is everywhere, but children who are generally compliant with their mother’s requests when she is present are also more likely to resist temptation when she is absent (like this boy, the nephew of one of the authors, whose reach, despite appearances, stopped just short of the cake).

In one such study, Kochanska, Coy, and Murray (2001) investigated the links between 2- and 3-year-olds’ compliance with their mother’s requests to forego appealing activities and their compliance with her requests that they participate in unappealing ones. Mothers brought their toddlers to a laboratory room that had a number of especially

attractive toys sitting on a shelf and a great many less attractive toys scattered around the room. The experimenter asked each mother to tell her child that he or she could play with any of the toys except the ones on the shelf. Raters observed the children through a one-way mirror over the next few minutes and classified them as complying with their mother’s request wholeheartedly, grudgingly, or not at all. Then the experimenter asked the mother to leave the room and observed whether the child played with the “forbidden” toys in the mother’s absence. The researchers found that children who had complied wholeheartedly in the first instance tended to avoid playing with the forbidden toys for a longer time in the second. Moreover, these children were also more likely to comply with their mother’s request that they put away the many toys on the floor after she left the room. When retested near their 4th birthday, most children showed the same type of compliance as they had as toddlers. Overall, the results indicated that the quality of young children’s compliance with their mother’s requests is a somewhat stable, general property of the mother–child relationship. This type of structured observation offers an important advantage over naturalistic observation: it ensures that all the children being studied encounter identical situations. This allows direct comparisons of different children’s behaviour in a given situation and, as in the research just discussed, also makes it possible to

establish the generality of each child’s behaviour across different situations. On the other hand, structured observation does not provide as extensive information about individual children’s subjective experience as do interviews, nor can it provide the openended, everyday kind of data that naturalistic observation can yield. As these examples suggest, which data-gathering approach is best depends on the goals of the research. (Table 1.4 summarizes the advantages and disadvantages of interviews, naturalistic observation, and structured observation as contexts for gathering data.)

TABLE 1.4 Advantages and Disadvantages of Three Contexts for Gathering Data Data-Gathering

Features

Advantages

Disadvantages

Children answer

Can reveal children’s

Reports are often

questions asked

subjective experience.

biased to reflect

Situation Interview/questionnaire

either in person or on a questionnaire.

favourably on Structured interviews are

interviewee.

inexpensive means for collecting in-depth data

Memories of

about individuals.

interviewees are often inaccurate

Clinical interviews allow

and incomplete.

flexibility for following up on unexpected

Prediction of

comments.

future behaviours often is inaccurate.

Naturalistic observation

Children’s activities

Useful for describing

Difficult to know

in one or more

behaviour in everyday

which aspects of

everyday settings

settings.

situation are

are observed.

most influential. Helps illuminate social interaction processes.

Limited value for studying infrequent behaviours.

Structured observation

Children are

Ensures that all children’s

Context is less

brought to

behaviours are observed

natural than in

laboratory and

in same context.

naturalistic

presented prearranged tasks.

observation. Allows controlled comparison of children’s

Reveals less

behaviour in different

about subjective

situations.

experience than interviews.

Correlation and Causation People differ along an infinite number of variables, that is, attributes that vary across individuals and situations, such as age, sex, activity level, socioeconomic status, particular experiences, and so on. A major goal of child-development research is to determine how these and other major characteristics of children and influences on them are related to one another, both in terms of associations and in terms of cause–effect relations. In the following sections, we consider the research designs that are used to examine each type of relation.

variables attributes that vary across individuals and situations, such as age, sex, and popularity

Correlational Designs The primary goal of studies that use correlational designs is to determine whether children who differ in one variable also differ in predictable ways in other variables. For example, a researcher might examine whether toddlers’ aggressiveness is related to the number of hours they spend in day care or whether adolescents’ popularity is related to their self-control. correlational designs studies intended to indicate how two variables are related to each other

The association between two variables is known as their correlation. When variables are strongly correlated, knowing a child’s score on either variable allows accurate prediction of the child’s score on the other. For instance, the number of hours per week that children spend reading correlates highly with their reading-test scores (Guthrie et al., 1999); this means a child’s reading-test score can be accurately predicted if one knows how much time the child spends reading. It also means that the number of hours the child spends reading can be predicted if one knows the child’s reading-test score. correlation the association between two variables

Correlations range from 1.00, the strongest positive correlation, to – 1.00, the strongest negative correlation. The direction is positive when high values of one variable are associated with high values of the other, and when low values of one are associated with low values of the other; the direction is negative when high values of one variable are associated with low values of the other. Thus, the correlation between time spent reading and reading-test scores is positive because children who spend high amounts of time reading also tend to have high reading-test scores; the correlation between obesity and amount of exercise that a child gets is negative because more obese children tend to exercise less.

Correlation Does Not Equal Causation When two variables are strongly correlated and there is a plausible cause–effect relation between them, it often is tempting to infer that one causes the other. However, correlations do not justify inferences about causal relations between the variables. This is true for two reasons. The first is the direction-of-causation problem: a correlation does not indicate which variable is the cause and which variable is the effect. In the preceding example, greater time spent reading might cause increased reading achievement, but the cause– effect relation could run in the opposite direction: greater reading skill might cause children to spend more time reading, because reading faster and with greater comprehension makes reading more fun.

direction-of-causation problem the concept that a correlation between two variables does not indicate which, if either, variable is the cause of the other

The second reason why correlation does not imply causation is the third-variable problem: the correlation between two variables may actually be the result of some third, unspecified variable. In the reading example, for instance, rather than greater reading achievement being caused by greater reading time, or vice versa, both of these aspects of reading could be caused by growing up in a family that values and rewards knowledge and intelligence. third-variable problem the concept that a correlation between two variables may stem from both being influenced by some third variable

Recognizing that correlation does not imply causation is crucial for interpreting research results. Even findings published in prestigious research journals can easily be misinterpreted. For example, based on a correlation between children younger than 2 years sleeping with a nightlight and their later becoming nearsighted, an article in the prestigious journal Nature concluded that the light was harmful to visual development (Quinn et al., 1999). Not surprisingly, the claim received considerable publicity in the popular media (e.g., Torassa, 2000). Subsequent research, however, showed that the inference about causation was wrong. The nearsighted children generally had nearsighted parents, and the nearsighted parents, for unknown reasons, more often placed nightlights in their infants’ rooms

(Gwiazda et al., 2000; Zadnik et al., 2000). Thus, inheritance of genes that predispose children to become nearsighted, rather than the use of nightlights, might have been the cause that led to the correlation. As the example illustrates, even seemingly straightforward inferences of causation, based on correlational evidence, frequently prove to be wrong. If correlation does not imply causation, why do researchers often use correlational designs? One major reason is that the influence of many variables of interest—age, sex, race, and social class among them— cannot be studied experimentally (see the next section) because researchers cannot manipulate them; that is, they cannot assign participants to one sex or another, to one SES or another, and so on. Consequently, these variables can be studied only through correlational methods. Correlational designs are also valuable when the goal is to describe relations among variables rather than to identify cause–effect relations among them. If, for example, the research goal is to discover how moral reasoning, empathy, anxiety, and popularity are related to one another, correlational designs would almost certainly be employed.

Experimental Designs If correlational designs are insufficient to indicate cause–effect relations, what type of approach is sufficient? The answer is experimental designs. The logic of experimental designs can be

summarized quite simply: if children in one group are exposed to a particular experience and subsequently behave differently from a comparable group of children who were not exposed to the experience or were exposed to a different experience, then the subsequent differences in behaviour must have resulted from the differing experiences. experimental designs a group of approaches that allow inferences about causes and effects to be drawn

Two techniques are crucial to experimental designs: random assignment of participants to groups, and experimental control. Random assignment involves assigning participants to one experimental group or another according to chance, so that the groups are comparable at the outset. In the same way that flipping a coin many times results in a roughly 50-50 distribution of heads and tails, assigning many children to experimental groups by a random process results in groups whose members are equivalent on all or almost all variables. This comparability is crucial for being able to infer that it was the varying experiences to which the groups were exposed in the experiment that caused the later differences between them. Otherwise, those differences might have arisen from some preexisting difference between the people in the groups. random assignment a procedure in which each participant has an equal chance of being assigned to each group within an experiment

Say, for instance, that researchers wanted to compare the effectiveness of two interventions for helping depressed mothers improve their relationship with their infant—namely, providing the mothers with home visits from trained therapists versus providing them with supportive phone calls from such therapists. If the researchers provided the home visits to families in one neighbourhood and the supportive phone calls to families in another neighbourhood, it would be unclear whether any differences in mother–infant relationships following the experiment were caused by differences between the effectiveness of the two types of support or by differences between the families in the two areas. Depressed mothers in one neighbourhood might suffer from less severe forms of depression than mothers in the other, or they might have greater access to other support, such as close families, mental health centres, or parenting programs. In contrast, when groups are created through random assignment and include a reasonably large number of participants (typically 30 or more per group), initial differences between the groups tend to be minimal. For example, if 100 families with mothers who suffer from depression are divided randomly into two experimental groups, each group is likely to include a few mothers who are extremely depressed, a few with mild forms of depression, and many in between, as well as a few infants who have been severely affected by their mother’s depression, a few who have been minimally affected, and many in between. The logic implies that groups created through random assignment should be comparable on all variables except the

different treatment that people in the experimental groups encounter during the experiment. The second essential characteristic of an experimental design, experimental control, refers to the ability of the researcher to determine the specific experiences that children in each group encounter during the study. In the simplest experimental design, one with two conditions, the groups are often referred to as the “experimental group” and the “control group.” Children in the experimental group are presented the experience of interest; children in the control group are treated identically except that they are not presented the experience of interest or are presented with a different experience that is expected to have less effect on the variables being tested. experimental control the ability of researchers to determine the specific experiences of participants during the course of an experiment experimental group the group of participants in an experimental design who are presented the experience of interest control group the group of participants in an experimental design who are not presented the experience of interest but in other ways are treated similarly

The experience that children in the experimental group receive, and that children in the control group do not receive, is referred to as the independent variable. The behaviour that is hypothesized to be affected by exposure to the independent variable is referred to as the

dependent variable. Thus, if a researcher hypothesized that showing schoolchildren an anti-bullying video would reduce school bullying, the researcher might randomly assign some children in a school to view the video and other children in the same school to view an equally interesting video about a different topic. In this case, the antibullying video would be the independent variable, and the amount of bullying after the children watched it would be the dependent variable. If the independent variable had the predicted effect, children who saw the anti-bullying video would show less bullying after watching it than would children who saw the other video. independent variable the experience that participants in the experimental group receive and that those in the control group do not receive dependent variable a behaviour that is measured to determine whether it is affected by exposure to the independent variable

One illustration of how experimental designs allow researchers to draw conclusions about causes and effects is a study that tested the hypothesis that having television shows running in the background while infants and toddlers play lowers the quality of that play (Schmidt et al., 2008). The independent variable was whether or not a television program was on in the room where the participants were playing; the dependent variables were a variety of measures of children’s attention to the television program and of the quality of their play. The television program being played was Jeopardy!, which presumably would have been of little interest to the 1- and 2-year-olds

in the study. Indeed, the toddlers looked at it an average of only once per minute and only for a few seconds at a time. Nonetheless, the television show disrupted the children’s play, reducing the length of play episodes and the children’s focus on them. These findings indicate that there is a causal, and negative, relation between background exposure to television shows and the quality of young children’s play.

The quality of infants’ and toddlers’ play is adversely affected by a television being on in the same room.

Experimental designs are the method of choice for establishing causal relations, a central goal of scientific research. However, as noted earlier, experimental designs cannot be applied to all issues of

interest. For example, hypotheses about why boys tend to be more physically aggressive than girls cannot be tested experimentally because gender cannot be randomly assigned to children. In addition, many experimental studies are conducted in laboratory settings; this improves experimental control but can raise doubts about the external validity of the findings—that is, whether the findings from the lab apply to the outside world. (The advantages and disadvantages of correlational and experimental designs are summarized in Table 1.5.)

TABLE 1.5 Advantages and Disadvantages of Correlational and Experimental Designs Types of

Features

Advantages

Disadvantages

Comparison of existing

Only way to compare

Direction-of-causation

groups of children or

many groups of interest

problem.

examination of relations

(boys–girls, rich–poor,

among each child’s

etc.).

Design Correlational

problem.

scores on different variables.

Third-variable

Only way to establish relations among many variables of interest (IQ and achievement, popularity and happiness, etc.).

Experimental

Random assignment of

Allows causal inferences

Need for experimental

children to groups and

because design rules out

control often leads to

experimental control of

direction-of-causation

artificial experimental

procedures presented to

and third-variable

situations.

each group.

problems.

Allows experimental

Cannot be used to

control over the exact

study many

experiences that children

differences and

encounter.

variables of interest, such as age, sex, and temperament.

Research Designs for Examining Children’s Development A great deal of research on child development focuses on how children change or remain the same as they grow older and gain experience. To study development over time, investigators use three types of research designs: cross-sectional, longitudinal, and microgenetic.

Cross-Sectional Designs The most common and easiest way to study changes and continuities with age is to use the cross-sectional approach. This method compares children of different ages on a given behaviour, ability, or characteristic by studying them at roughly the same time—for example, within the same week or month. In one cross-sectional study, Evans, Xu, and Lee (2011) examined the development of dishonesty in Chinese 3-, 4-, and 5-year-olds. The children played a game in which winning a prize required guessing the type of object

hidden under an upside-down paper cup. Before the child could guess, the experimenter said she needed to leave the room and asked the child not to peek while she was gone. The cup was so packed with candies that if the child peeked, some would spill out; putting them all back under the cup was almost impossible. cross-sectional design a research method in which participants of different ages are compared on a given behaviour or characteristic over a short period

At all ages, many children peeked and then denied doing so. However, 5-year-olds lied more often, and their lies were more ingenious, than those of the younger children. For example, many 5year-olds explained the presence of candies on the table by saying that they accidentally knocked over the cup with their elbow; others destroyed the evidence by eating it. Three-year-olds were the leastskilled fibbers, generating implausible excuses such as that the candies came out by themselves or that some other child entered the room and knocked over the cup. Cross-sectional designs are useful for revealing similarities and differences between older and younger children. However, they do not yield information about the stability of behaviour over time or about the patterns of change shown by individual children. This is where longitudinal approaches are especially valuable.

Longitudinal Designs

The longitudinal approach involves following the same children over a substantial period (usually at least a year) and observing changes and continuities in these children’s development at regular intervals during that time. The study at the beginning of this chapter on the development of children in Kauai from before birth to age 40 is one example of a longitudinal study. Another good example of what the longitudinal approach can tell us is Brendgen and colleagues’ (2001) examination of Québec children’s popularity with classmates. Each child’s popularity was examined each year from the time they were 7year-olds to the time they were 12-year-olds. The popularity of most children proved to be quite stable over this period; many were popular in the large majority of years, and many others were unpopular throughout. longitudinal design a method of study in which the same participants are studied twice or more over a substantial length of time

At the same time, some individuals showed idiosyncratic patterns of change from year to year; the same child might be popular at age 8, unpopular at age 10, and of average popularity at age 12. Such information about the stability of individual differences over time and about individual children’s patterns of change could only have been obtained in a longitudinal design, that is, in a design where the same children were examined repeatedly over time.

Being excluded is no fun for anyone. Longitudinal research has been used to determine whether the same children are unpopular year after year or whether popularity changes over time.

Although longitudinal designs are very useful for revealing stability and change over time, cross-sectional designs are far more common. The reasons for the greater prevalence of cross-sectional designs are mainly practical. Studying the same children over long periods involves the difficult task of locating the children for each reexamination. Inevitably, some children move away or stop

participating for other reasons. Such loss of participants may call into question the validity of the findings because the children who do not continue may differ from those who participate throughout. Another threat to the validity of longitudinal designs is the possible effects of repeated testing. For example, repeatedly taking IQ tests could familiarize children with the type of items on the tests, thus improving the children’s scores for reasons other than changes to their intelligence. Therefore, longitudinal designs are used primarily when the main issues are stability and change in individual children over time—issues that can only be studied longitudinally. When the central developmental issue involves age-related changes in typical performance, cross-sectional studies are more commonly used.

Microgenetic Designs An important limitation of both cross-sectional and longitudinal designs is that they provide only a broad outline of the process of change. Microgenetic designs, in contrast, are specifically designed to provide an in-depth depiction of the processes that produce change (Lavelli & Fogel, 2013; Miller & Coyle, 1999). The basic idea of this approach is to recruit children who are thought to be on the verge of an important developmental change, heighten their exposure to the type of experience that is believed to produce the change, and then intensively study the change as it is occurring. Microgenetic designs are like longitudinal ones in repeatedly testing the same children over time. They differ in that microgenetic studies typically include a

greater number of sessions presented over a shorter time than in a longitudinal study. microgenetic design a method of study in which the same participants are studied repeatedly over a short period

The excitement of discovery is evoked by an insight while this child was trying to solve a problem in the game “Magic C.”

Siegler and Jenkins (1989) used a microgenetic design to study how young children discover the counting-on strategy for adding two small numbers. This strategy involves counting up from the larger addend the number of times indicated by the smaller addend. For example, when asked the answer to 3 + 5, a child who was counting-on would start from the addend 5 and say or think “6, 7, 8” before answering “8.” Prior to discovering this strategy, children usually solve addition problems by counting from 1. Counting from the larger addend, rather than from 1, reduces the amount of counting, producing faster and more accurate solutions. To observe the discovery process, the researchers selected 4- and 5year-olds who did not yet use counting-on but who knew how to add by counting from 1. Over an 11-week period, these children received many addition problems several times per week—far more experience than U.S. children would normally have with addition before entering school—and each child’s behaviour on every problem was video-recorded. This approach allowed the researchers to identify exactly when each child discovered the counting-on strategy. Examination of the problems immediately preceding the discovery revealed a surprising fact: necessity is not always the mother of invention. Children often discovered the counting-on strategy while

solving easy problems that they previously solved correctly by counting from 1. The microgenetic method also revealed that children’s very first use of the new strategy often was accompanied by insight and excitement, like that shown by Lauren: Experimenter: How much is 6 + 3? Lauren: (long pause) 9. E: OK, how did you know that? L: I think I said … I think I said … oops, um … 7 was 1, 8 was 2, 9 was 3. E: How did you know to do that? Why didn’t you count 1, 2, 3, 4, 5, 6, 7, 8, 9? L: (with excitement) ’Cause then you have to count all those numbers. (Siegler & Jenkins, 1989, p. 66)

Despite Lauren’s insightful explanation of counting-on and her excitement over discovering it, she and most other children only gradually increased their use of the new strategy on subsequent problems, though they eventually used it quite often. Many other microgenetic studies have also shown that generalization of new strategies tends to be slow (Kuhn & Franklin, 2006). As this example illustrates, microgenetic methods provide insight into the process of change over brief periods. However, unlike standard longitudinal methods, microgenetic designs do not yield information about stability and change over long periods. They therefore are typically used when the basic pattern of age-related change has already been established and the goal becomes to

understand how the changes occur. (Table 1.6 outlines the strengths and weaknesses of the three approaches to studying changes with age and experience: cross-sectional, longitudinal, and microgenetic designs.)

TABLE 1.6 Advantages and Disadvantages of Designs for Studying Development Design

Features

Advantages

Disadvantages

Cross-

Children of different ages

Yields useful data about

Uninformative about

sectional

are studied at a single

differences among age

stability of individual

time.

groups.

differences over time.

Quick and easy to

Uninformative about

administer.

similarities and differences in individual children’s patterns of change.

Longitudinal

Children are examined

Indicates the degree of

Difficult to keep all

repeatedly over a

stability of individual

participants in study.

prolonged period.

differences over long periods.

Repeatedly testing children can threaten

Reveals individual

external validity of study.

children’s patterns of change over long periods. Microgenetic

Children are observed

Intensive observation of

Does not provide

intensively over a

changes while they are

information about typical

relatively short period

occurring can clarify

patterns of change over

while a change is

process of change.

long periods.

occurring.

Reveals individual

Does not yield data

change patterns over

regarding change

short periods in

patterns over long

considerable detail.

periods.

Ethical Issues in Child-Development Research All research with human beings raises ethical issues, and this is especially the case when the research involves children. Researchers have a vital responsibility to anticipate potential risks that children in their studies may encounter, to minimize such risks, and to ensure that the benefits of the research outweigh any potential harm. In Canada, hospital-and university-based research with humans is governed by the Tri-Council Policy Statement: Ethical Conduct for Research Involving Humans. This policy statement lays out a code of ethical conduct for investigators to follow. Some of the most important ethical principles in the policy statement are as follows: Be sure that the research does not harm children physically or psychologically. Obtain informed consent for participating in the research, preferably in writing, from parents or other responsible adults and also from children if they are old enough that the research can be explained to them. The experimenter should inform children and relevant adults of all aspects of the research that

might influence their willingness to participate and should explain that refusing to participate will not result in any adverse consequences to them. Preserve individual participants’ anonymity, and do not use information for purposes other than that for which permission was given. Discuss with parents or guardians any information yielded by the investigation that is important for the child’s welfare. Try to counteract any unforeseen negative consequences that arise during the research. Correct any inaccurate impressions that the child may develop in the course of the study. When the research has been completed, explain the main findings to participants at a level they can understand. Recognizing the importance of such ethical issues, universities and governmental agencies have established institutional review boards made up of independent scientists and sometimes others from the community. These boards evaluate the proposed research to ensure that it does not violate ethics guidelines. However, the individual investigator is in the best position to anticipate potential problems and bears the ultimate responsibility for seeing that his or her study meets high ethical standards.

REVIEW QUESTION The concept of the active child suggests that, through their actions, children

contribute to their own development. What challenges might the concept of the active child present for the various data-gathering strategies discussed in this section?

CHAPTER SUMMARY Reasons to Learn About Child Development Learning about child development is valuable for many reasons: it can help us become better parents, inform our views about social issues that affect children, and improve our understanding of human nature.

Historical Foundations of the Study of Child Development Great thinkers such as Plato, Aristotle, Locke, and Rousseau raised basic questions about child development and proposed interesting hypotheses about them, but they lacked the scientific methods to answer the questions.

Enduring Themes in Child Development The field of child development is an attempt to answer a set of fundamental questions: 1. How do nature and nurture together shape development? 2. How do children shape their own development? 3. In what ways is development continuous, and in what ways is

it discontinuous? 4. How does change occur? 5. How does the sociocultural context influence development? 6. How do children become so different from one another? 7. How can research promote children’s well-being? Every aspect of development, from the most specific behaviour to the most general trait, reflects people’s biological endowment (their nature) as well as the experiences that they have had (their nurture). Even infants and young children actively contribute to their own development through their patterns of attention, use of language, and choices of activities. Many developments can appear either continuous or discontinuous, depending on how often and how closely we look at them. The mechanisms that produce developmental changes involve a complex interplay among experiences, genes, and brain structures and activities. The contexts that shape development include the people with whom children interact directly, such as family and friends; the institutions in which they participate, such as schools and religious organizations; and societal beliefs and values, such as those related to race, ethnicity, and social class. Individual differences, even among siblings, reflect differences in children’s genes, in their treatment by other people, in their interpretations of their own experiences, and in their choices of environments. Principles, findings, and methods from child-development

research are being applied to improve the quality of children’s lives.

Methods for Studying Child Development The scientific method has made possible great advances in understanding children. It involves choosing a question, formulating a hypothesis relevant to the question, developing a method to test the hypothesis, and using data to decide whether the hypothesis is correct. For a measure to be useful, it must be directly relevant to the hypotheses being tested, reliable, and valid. Reliability means that independent observations of a given behaviour are consistent. Validity means that a measure assesses what it is intended to measure. Among the main situations used to gather data about children are interviews, naturalistic observation, and structured observation. Interviews are especially useful for revealing children’s subjective experience. Naturalistic observation is particularly useful when the primary goal is to describe how children behave in their everyday environments. Structured observation is most useful when the main goal is to describe how different children react to the identical situation. Correlation does not imply causation. The two differ in that correlations indicate the degree to which two variables are associated, whereas causation indicates that changing the value of one variable will change the value of the other. Correlational designs are especially useful when the goal is to

describe relations among variables or when the variables of interest cannot be manipulated because of technical or practical considerations. Experimental designs are especially valuable for revealing the causes of children’s behaviour. Data about development can be obtained through cross-sectional designs (examining different children of different ages), through longitudinal designs (examining the same children at different ages), or through microgenetic designs (presenting the same children repeated relevant experiences over a relatively short period and analyzing the change process in detail). It is vital for researchers to adhere to high ethical standards. Among the most important ethical principles are striving to ensure that the research does not harm children physically or psychologically; obtaining informed consent from parents and, where possible, from children; preserving participants’ anonymity; and correcting any inaccurate impressions that children form during the study.

Test Yourself 1. The “turtle shell” technique is an example of a successful intervention that helps preschoolers cope with what? a. b. c. d.

The sense of isolation Feelings of embarrassment Bullying from peers Their own anger

2. What is meta-analysis?

a. The reproduction of a past study in order to confirm or debunk the results b. A philosophical exploration of an experiment or case study c. A method for combining and analyzing the results from several independent studies d. A list of all published articles related to a specific area of research 3. Studies have shown that children’s testimony is usually accurate when which of the following conditions are met? a. b. c. d.

The interviewer does not ask leading questions. One of the child’s parents is present. The child and the interviewer are alone when the testimony is given. The child is repeatedly prompted during the interview.

4. According to developmentalists, which of the following is true? a. Development is most heavily influenced by nature. b. Development is most heavily influenced by nurture. c. Development is influenced by the joint workings of nature and nurture. d. Nature and nurture are essentially the same. 5. The concept of the “active child” refers to a. b. c. d.

.

observations of children at play whether an infant sleeps through the night the importance of physical activity to child development how children contribute to their own development

6. In recent decades, researchers have come to the conclusion that, after infancy, most developmental changes occur a. b. c. d.

.

gradually suddenly discontinuously externally

7. In the context of mechanisms of developmental change, the study of the

development of “effortful attention” provides insights into a. b. c. d.

continuous versus discontinuous development. the role of brain activity, genes, and learning experiences. the complexity of the child’s sociocultural environment. the role of the researcher in judging the validity of a study.

8. The physical, social, cultural, economic, and historical circumstances that make up a child’s environment are known as the a. b. c. d.

.

developmental foundation sociocultural context developmental stage socioeconomic status

9. The first basic step in using the scientific method involves a. b. c. d.

developing a research plan. choosing a question. formulating a hypothesis. drawing a conclusion.

10. In order to generalize her findings beyond the individuals who participated in her study, Dr. Liu needs to conduct additional research using participants from a variety of backgrounds. What quality of behavioural research is Dr. Liu addressing? a. b. c. d.

Interrater reliability Internal validity Test–retest reliability External validity

11. The experience that children in an experimental group receive—and which children in a control group do not receive—is referred to as the . a. dependent variable b. independent variable c. random assignment

d. correlational design 12. A team of researchers is studying whether stable individual differences exist in sleeping behaviour at various ages. They decide to test 3-montholds, 6-month-olds, and 9-month-olds. What type of design are they using to examine this question? a. b. c. d.

Longitudinal Cross-sectional Naturalistic observation Microgenetic

13. Which type of design is used to study developmental change as it is occurring by observing participants numerous times over a relatively short span of time? a. b. c. d.

Longitudinal Cross-sectional Structured observation Microgenetic

14. By administering the same test to the same group of participants under similar conditions two or more times, a researcher can measure reliability. a. b. c. d.

internal external test–retest interrater

15. According to the Tri-Council guidelines, which of the following is not a stated ethical principle for conducting research with children? a. Information about the child uncovered through the course of the study must not be revealed to the parent or guardian, regardless of its importance for that child’s welfare. b. Unforeseen consequences must be dealt with when they arise during research.

c. Researchers must correct any inaccurate impressions that the child may develop as a result of the study. d. The research must not harm the child, physically and psychologically.

DON’T STOP NOW! Research shows that testing yourself is a powerful learning tool. Visit LaunchPad to access the LearningCurve adaptive quizzing system, which gives you a personalized study plan to help build your mastery of the chapter material through videos, activities, and more. Go to launchpadworks.com.

Critical Thinking Questions 1. What areas of child development interest you most? Can you generate a study that would ask and perhaps answer an important question about one of those areas? What research method would your proposed experiment use? 2. What do you hope to learn from this course? Are you most interested in how to raise children, social policies to help children, or what child development tells us about human nature? 3. Have you needed to be resilient in overcoming problems that arose in your life? If so, what types of difficulties did you overcome, how did you do so, and what do you think allowed you to do so? 4. Do children have different natures, or are differences among children purely due to differences in their experiences? What personal observations, research findings, and reasoning led to your conclusion? 5. Why do you think that the children who spent less than 6 months in

orphanages in Romania were able to catch up physically, intellectually, and socially, whereas those who spent more time in the orphanages and left at older ages have not been able to catch up? Do you think they will catch up in the future? 6. In what ways is it fortunate, and in what ways unfortunate, that children shape their own development to a substantial extent? 7. Did reading about sleeping arrangements in the United States and in other cultures influence what you would like to do if you have children? Explain why or why not. 8. Given what you learned in this chapter about child-development research, can you think of practical applications of the research (other than the ones described) that seem both feasible and important to you?

Key Terms amygdala clinical interview cognitive development continuous development control group correlation correlational designs cross-sectional design cumulative risk dependent variable direction-of-causation problem

discontinuous development epigenetics experimental control experimental designs experimental group external validity genome hypotheses independent variable internal validity interrater reliability longitudinal design meta-analysis methylation microgenetic design naturalistic observation nature neurotransmitters nurture questionnaire random assignment reliability scientific method sociocultural context socioeconomic status (SES) stage theories structured interview structured observation

test–retest reliability third-variable problem validity variables

Answers to Test Yourself 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

d c a c d a b b b d b b d c a

CHAPTER 2

Prenatal Development and the Newborn Period

JOSE ORTEGA, Mother and Child

Prenatal Development Hazards to Prenatal Development The Birth Experience The Newborn Infant

THEMES NATURE AND NURTURE THE ACTIVE CHILD THE SOCIOCULTURAL CONTEXT INDIVIDUAL DIFFERENCES CONTINUITY/DISCONTINUITY RESEARCH AND CHILDREN’S WELFARE

Picture the following scenario: a developmental psychologist is investigating a very young research participant’s ability to learn. First, she plays a recording of a nonsense word for the young participant (tatata). The participant hears this word multiple times a day, for several months. The psychologist wants to use brain responses to find out whether the participant has learned the novel word. But before the psychologist can measure the participant’s brain waves, something very important has to happen: the participant has to be born! This scenario is not at all fanciful. Indeed, as you will discover later in this chapter, it describes one of many studies that has revolutionized our understanding of prenatal development (Partanen, Kujala,

Tervaniemi et al., 2013). Fetuses can detect and learn from a range of stimuli coming from both the outside world and inside the mother’s body, and they are affected by these stimuli after birth. This chapter will examine prenatal development—a time of astonishingly rapid and dramatic change. We will also consider some of the ways in which these processes can be disrupted by environmental hazards. Then, we will explore the birth process and some of the most salient aspects of neonatal behaviour. Finally, we will outline issues associated with low birth weight and premature birth. Most of the themes described in Chapter 1 play prominent roles in our discussion of the earliest periods of development. The most notable will be nature and nurture, because prenatal development relies on the continual interplay of biological and environmental factors. The active child theme will also be featured: the activity of the fetus contributes in numerous vital ways to its development. Another theme we will highlight is the sociocultural context of prenatal development and birth. There is substantial cultural variation in how the birth process unfolds. The theme of individual differences comes into play throughout prenatal development and early postnatal life. Continuity/discontinuity is also prominent: despite the dramatic contrast between prenatal and postnatal life, the behaviour of newborns shows clear connections to their experience inside the womb. Finally, the theme of research and children’s welfare is central to

our discussion of how poverty can affect prenatal development and birth outcomes, as well as to our description of intervention programs designed to foster healthy development for preterm infants.

Prenatal Development Hidden from view, the process of prenatal development has always been mysterious and fascinating, and beliefs about the origins of human life and development before birth are an important part of the lore and traditions of all societies. (Box 2.1 describes one set of cultural beliefs about the beginning of life that is quite unlike those of Western societies.)

BOX 2.1 A CLOSER LOOK Beng Beginnings Few topics have generated more intense debate and dispute in Canada in recent decades than the issue of when life begins—at the moment of conception, the moment of birth, or sometime in between. The irony is that few who engage in this debate recognize how complex the issue is or the degree to which societies throughout the world have different views on it. Consider, for example, the perspective of the Beng, a people in the Ivory Coast of West Africa. According to the Beng, every newborn is a reincarnation of an ancestor (Gottlieb, 2004). In the first weeks after birth, the ancestor’s spirit, its wru, is not fully committed to an earthly life and therefore maintains a double existence, travelling back and forth between the everyday world and wrugbe, or “spirit village.” (The term can be roughly translated as “afterlife,” but “before-life” might be just as appropriate.) It is only after the umbilical stump has dropped off that the newborn is considered to have emerged from wrugbe and become a person. If the newborn dies before this point, there is no funeral, for the infant’s passing is perceived as a return to the wrugbe.

These beliefs underlie many aspects of Beng parenting practices. One is the frequent application of an herbal mixture to the newborn’s umbilical stump to hasten its drying out and dropping off. In addition, there is the constant danger that the infant will become homesick for its life in wrugbe and decide to leave its earthly existence. To prevent this, parents try to make their babies comfortable and happy so they will want to stay in this life. Among the many recommended procedures is elaborately decorating the infant’s face and body to elicit positive attention from others. Sometimes diviners are consulted, especially if the baby seems to be unhappy; a common diagnosis for prolonged crying is that the baby wants a different name—the one from its previous life in wrugbe. So when does life begin for the Beng? Because each infant is a reincarnation of an ancestor, in one sense, an individual’s life begins well before birth. In another sense, however, life begins sometime after birth, when the wru commits to life and the individual is considered to have become a person.

The mother of this Beng baby has spent considerable time painting the baby’s face in an elaborate pattern. She does this every day in an effort to make the baby attractive so other people will help keep the baby happy in this world.

Beng Infant Caretaking Practices

In the fourth century B . C . E ., Aristotle posed a fundamental question that influenced Western thought for the next 15 centuries: Does prenatal life start with a fully formed individual, composed of a full

set of tiny parts, or do the many parts of the human body develop in succession? Aristotle argued in favour of the latter, which he termed epigenesis—the emergence of new structures and functions during development (we will revisit this idea in Chapter 3 in its more modern form, epigenetics). Seeking support for his idea, he took what was then a very unorthodox step: he opened chicken eggs to observe organs in various stages of development. epigenesis the emergence of new structures and functions in the course of development

Conception Each of us originated as a single cell that resulted from the union of two highly specialized cells—a sperm from our father and an egg from our mother. These gametes, or germ cells, are unique not only in their function but also in the fact that each one contains only half the genetic material found in other cells. Gametes are produced through meiosis, a form of cell division in which the eggs and sperm receive only one member from each of the 23 chromosome pairs contained in all other cells of the body. This reduction to 23 chromosomes in each gamete is necessary for reproduction, because the union of egg and sperm must contain the normal amount of genetic material (23 pairs of chromosomes). gametes (germ cells) reproductive cells—egg and sperm—that contain only half the genetic material of all the

other cells in the body meiosis cell division that produces gametes

The process of reproduction starts with the launching of an egg (the largest cell in the human female body) from one of the woman’s ovaries into the adjoining fallopian tube (see Figure 2.1). As the egg moves through the tube toward the uterus, it emits a chemical substance that acts as a sort of beacon, a “come-hither” signal that attracts sperm toward it. If an act of sexual intercourse takes place near the time the egg is released, conception, the union of sperm and egg, is possible. In every ejaculation, as many as 500 million sperm are pumped into the woman’s vagina. Each sperm, a streamlined vehicle for delivering the man’s genes to the woman’s egg, consists of little more than a pointed head packed full of genetic material (the 23 chromosomes) and a long tail that whips around to propel the sperm through the woman’s reproductive system. conception the union of an egg from the mother and a sperm from the father

FIGURE 2.1 Female reproductive system A simplified illustration of the female reproductive system, with a fetus developing in the uterus (womb). The umbilical cord runs from the fetus to the placenta, which is burrowed deeply into the wall of the uterus. The fetus is floating in amniotic fluid inside the amniotic sac.

Description The diagram of the female reproductive system shows the ovary and fallopian tube leading to the uterus, which has a fetus attached to its umbilical cord curled up in amniotic fluid along with the placenta. At the bottom of the uterus is the cervix which opens into the vagina.

To be a candidate for initiating conception, a sperm must travel for about 6 hours, journeying 15 to 18 centimetres from the vagina up through the uterus to the egg-bearing fallopian tube. The rate of attrition on this journey is enormous: of the millions of sperm that enter the vagina, only about 200 ever get near the egg (see Figure 2.2). Many of the sperm get tangled up with other sperm milling about in the vagina; others wind up in the fallopian tube that does not currently harbour an egg. And a substantial portion of the sperm have serious genetic or other defects that prevent them from propelling themselves vigorously enough to reach and fertilize the egg. Thus, any sperm that do get to the egg are likely to be healthy and structurally sound, revealing a Darwinian-type “survival of the fittest” process operating during conception. (Box 2.2 describes the

consequences of this selection process for the conception of males and females.)

FIGURE 2.2 (a) Sperm nearing the egg Of the millions of sperm that enter the vagina, only a few ever get near the egg. The egg is the largest human cell (the only one visible to the naked eye), but sperm are among the smallest. (b) Sperm penetrating the egg This sperm is whipping its tail around furiously to drill itself through the outer covering of the egg.

BOX 2.2 INDIVIDUAL DIFFERENCES Do Girls Outnumber Boys? Do girls outnumber boys? Because the answer to that question depends on the various forces that influence development and survival, it ultimately depends on when in the lifecycle you ask. There are slightly more male newborns (51.3%) across generations and around the world. This is the case, despite the fact that male fetuses are more susceptible to spontaneous abortion than females in both the 1st week and last several weeks of pregnancy (though it is worth noting that female fetuses are more susceptible in weeks 10–15) (Orzack et al., 2015). The apparent frailty of male fetuses, paired with the fact that males outnumber

females at birth, would seem to imply that male embryos must significantly outnumber female embryos (Austad, 2015). In fact, conception is equally likely to result in male and female embryos (Orzack et al., 2015). Researchers took advantage of the increased use of reproductive technologies and prenatal genetic tests to determine the sex of nearly 140,000 3- to 6-day-old fetuses, and they found an almost exact 50-50 split between males and females. It appears that female fetuses are actually less likely than male fetuses to survive early gestation, resulting in the slight male bias at birth. Females win the next big competition—birth. During labour and delivery, males are more likely to experience fetal distress than females, even controlling for the males’ larger size and head circumference (DiPietro, Costigan, & Voegtline, 2015). Indeed, for decades, and across many cultural contexts, infant mortality rates have been higher for boys than for girls (Drevenstedt et al., 2008). Male fetuses are more sensitive than females are to teratogens (harmful external agents), including opioids and alcohol, which affects their viability and ability to thrive after birth (e.g., DiPietro & Voegtline, 2017). Male infants’ heightened vulnerability is not limited to the immediate postnatal period. Males are also more likely than females to die from sudden infant death syndrome (SIDS, discussed in more detail in Box 2.3; Mage & Donner, 2014) and have higher rates of incidence of a wide range of developmental disabilities, including attentional disorders and autism spectrum disorders. Societal and cultural forces also play a role, sometimes to devastating effect. In many societies, both historically and currently, male offspring are more highly valued than female offspring, and parents resort to infanticide to avoid having daughters. For example, Inuit families in Canada’s North traditionally depended on male children to help in the hunt for food, and in former times, Inuit girls were often killed at birth. Until 2015, the Chinese government strictly enforced a “onechild” policy, a measure designed to reduce population growth by forbidding couples to have more than one child. This policy resulted in many parents killing or abandoning their female babies (or giving them up for adoption to Western

families) in order to make room for a male child. A more technological approach is currently practiced in some countries that place a premium on male offspring: prenatal tests are used to determine the gender of the fetus, and female fetuses are selectively aborted. These cases dramatically illustrate the sociocultural model of development described in Chapter 1: cultural values, government policy, and available technology all affect developmental outcomes. Though not addressed in the studies cited here, it is important to note that not every individual can be categorized as male or female, and that an infant’s designated sex at birth may differ from their eventual gender identity. These issues are addressed more fully in Chapter 15. It is important to remember that our understanding of the effects of environmental forces on developmental outcomes is far from complete. New research is exploring the impact of climate change on sex ratios—both in terms of higher temperatures, which may increase the ratio of boys conceived compared to girls, and stressrelated teratogens as a result of extreme weather events and subsequent environmental effects, which may negatively affect the number of male fetuses that survive through birth (Fukuda et al., 2014). Evidence at this point does not support definitive statements about the impact of climate change on birth sex ratios, but emerging research in this area reminds us of the complex network of forces at play.

As soon as one sperm’s head penetrates the outer membrane of the egg, a chemical reaction seals the membrane, preventing other sperm from entering. The tail of the sperm falls off, the contents of its head gush into the egg, and the nuclei of the two cells merge within hours. The fertilized egg, known as a zygote, now has a full complement of human genetic material, 23 chromosomes from the egg and 23 chromosomes from the sperm.

zygote a fertilized egg cell

Developmental Processes Four major developmental processes underlie the transformation of a zygote into an embryo and then a fetus. The first is cell division, known as mitosis. Within about 12 hours after conception, the zygote divides into two equal parts, each containing a full complement of genetic material. These two cells then divide into four, those four into eight, those eight into sixteen, and so on. Through continued cell division over the course of 38 weeks, the barely visible zygote becomes a newborn consisting of trillions of cells. embryo the developing organism from the 3rd to 8th week of prenatal development fetus the developing organism from the 9th week to birth mitosis cell division that results in two identical cells

A second major process is cell migration, the movement of newly formed cells away from their point of origin. Among the many cells that migrate are the neurons that originate deep inside the embryonic brain and then, like pioneers settling new territory, travel to the outer reaches of the developing brain.

The third process in prenatal development is cell differentiation. Initially, all of the embryo’s cells, referred to as embryonic stem cells, can give rise to any of the more than 200 possible cell types in the human body. (It is this unique flexibility that makes embryonic stem cells the focus of a great deal of research in regenerative medicine.) After several cell divisions, however, these cells start to specialize. Since all cells in the body share an identical set of genes, what factors determine which type of cell a given stem cell will become? While much about this process remains unknown, it is clear that the cell’s location influences its future development via chemical and cell-to-cell contact with neighbouring cells, and that gene expression—which genes in the cell are switched on—distinguishes one type of cell from another. embryonic stem cells embryonic cells, which can develop into any type of body cell

The Prenatal Period: Conception to Birth

The fourth developmental process is something you would not normally think of as developmental at all—death. The role of this genetically programmed “cell suicide,” known as apoptosis, is readily apparent in hand development: the formation of fingers depends on the death of the cells in between the ridges in the hand plate, as seen in Figure 2.3. In other words, death is preprogrammed for the cells that disappear from the hand plates. Apoptosis has been referred to as a “ticking death timer” because it follows a specific timeline, programmed into the cells themselves. apoptosis genetically programmed cell death

FIGURE 2.3 Fetal hand plate The role of apoptosis, or cell death, is clearly seen in the development of the hand, which requires the death of the cells in between the ridges of the hand plate in order for the fingers to separate.

Finally, hormones have a major influence throughout prenatal development. For example, hormones play a crucial role in sexual differentiation. All human fetuses, regardless of the genes they carry, can develop either male or female genitalia. The presence of androgens, a class of hormones that includes testosterone, leads to the development of male genitalia. If androgens are absent, female genitalia develop. The source of androgens is the male fetus itself, at around the 8th week after conception. This is just one of the many

ways in which the fetus influences its own development. Other important hormones include steroids such as glucocorticoids, which limit fetal growth and help fetal tissues mature. Toward the end of gestation, the fetus increases production of these hormones in order to facilitate maturation of key organs, such as the lungs, that are needed for life outside the womb. Later in this chapter, we will discuss the role played by glucocorticoids in the influence of maternal stress on the fetus. We now turn our attention to the general course of prenatal development.

Early Development On its journey through the fallopian tube to the womb, the zygote doubles its number of cells roughly twice a day. By the 4th day after conception, the cells arrange themselves into a hollow sphere with a bulge of cells, called the inner cell mass, on one side. This is the stage at which identical (monozygotic) twins most often originate. They result from a splitting in half of the inner cell mass, thus they have exactly the same genetic makeup. In contrast, fraternal (dizygotic) twins result when two eggs happen to be released from the ovary into the fallopian tube and both are fertilized. Because they originate from two different eggs and two different

sperm, fraternal twins are no more alike genetically than non-twin siblings with the same parents. identical (monozygotic) twins twins that result from the splitting in half of the zygote, resulting in each of the two resulting zygotes having exactly the same set of genes fraternal (dizygotic) twins twins that result when two eggs happen to be released into the fallopian tube at the same time and are fertilized by two different sperm; fraternal twins have only half their genes in common

By the end of the 1st week following conception, if all goes well (which it does for less than half the zygotes that are conceived), the zygote embeds itself in the uterine lining and becomes dependent on the mother for sustenance. The embedded ball of cells then starts to differentiate. The inner cell mass becomes the embryo, and the rest of the cells become an elaborate support system—including the amniotic sac and placenta—that enables the embryo to develop. The inner cell mass is initially a single layer thick, but during the 2nd week, it folds itself into three layers, each with a different developmental destiny. The top layer becomes the nervous system, the nails, teeth, inner ear, lens of the eyes, and the outer surface of the skin. The middle layer becomes muscles, bones, the circulatory system, the inner layers of the skin, and other internal organs. The bottom layer develops into the digestive system, lungs, urinary tract, and glands. A few days after the embryo has differentiated into these three layers, a U-shaped groove forms down the centre of the top layer. The folds at the top of the groove move together and fuse,

creating the neural tube (Figure 2.4). One end of the neural tube will swell and develop into the brain, and the rest will become the spinal cord. neural tube a groove formed in the top layer of differentiated cells in the embryo that eventually becomes the brain and spinal cord

FIGURE 2.4 Neural tube In the 4th week, the neural tube begins to develop into the brain and spinal cord. In this photo, the neural groove, which fuses together first at the centre and then outward in both directions as if two zippers were being closed, has been “zipped shut” except for one part still open at the top. Spina bifida, a congenital disorder in which the skin over the spinal cord is not fully closed, can originate at this point. After closing, the top of the neural tube will develop into the brain.

The elaborate support system that develops along with the embryo is essential to the embryo’s survival. The amniotic sac is a membrane filled with a clear, watery fluid in which the fetus floats. The amniotic fluid operates as a protective buffer for the developing fetus, providing it with a relatively even temperature and cushioning it against jolting. The placenta is a rich network of blood vessels, weighing roughly one pound, that extends into the tissues of the mother’s uterus. While we might assume that the placenta comes from the mother, 90% of the cells in the placenta come from the fetus itself. Far from just being afterbirth, the placenta is a complex organ that plays a critical role in the healthy development of the fetus. amniotic sac a transparent, fluid-filled membrane that surrounds and protects the fetus placenta a support organ for the fetus; it keeps the circulatory systems of the fetus and mother separate, but a semipermeable membrane permits the exchange of some materials between them (oxygen and nutrients from mother to fetus, and carbon dioxide and waste products from fetus to mother)

Crucially, the placenta is semipermeable: it permits the exchange of materials carried in the bloodstreams of the fetus and its mother, but it prevents the blood of the mother and fetus from mixing. Oxygen, nutrients, minerals, and some antibodies—all of which are just as vital to the fetus as they are to you—are transported to the placenta by the mother’s circulating blood. They then cross the placenta and enter the fetal blood system. Waste products (e.g., carbon dioxide and

urea) from the fetus cross the placenta in the opposite direction and are removed from the mother’s bloodstream by her normal excretory processes. The placental membrane also serves as a defensive barrier against a host of dangerous toxins and infectious agents that can inhabit the mother’s body but would be harmful or even fatal to the fetus. Unfortunately, being semipermeable, the placenta is not a perfect barrier, and, as you will see shortly, a variety of harmful elements can cross it and attack the fetus. These support system structures are illustrated in Figure 2.1. The amniotic sac is connected to the placenta via the umbilical cord, which is a tube containing the blood vessels that run to the fetus. umbilical cord a tube containing the blood vessels connecting the fetus and placenta

An Illustrated Summary of Prenatal Development The course of prenatal development from the 4th week postconception on is illustrated in Figures 2.5 through 2.11, and significant milestones are highlighted in the accompanying text. Notice that earlier development takes place at a more rapid pace than later development and that the areas nearer the head develop earlier than those farther away (e.g., head before body, hands before feet)—a general tendency known as cephalocaudal development.

cephalocaudal development the pattern of growth in which areas near the head develop earlier than areas farther from the head

Figure 2.5: At 4 weeks after conception, the embryo is curved so tightly that the head and the tail-like structure at the other end are almost touching. The round area near the top of the head is where the eyes will form, and the round gray area near the back of the “neck” is the primordial inner ear. A primitive heart is visible; it is already beating and circulating blood. An arm bud can be seen in the side of the embryo; a leg bud is also present but less distinct.

FIGURE 2.5 Embryo at 4 weeks.

Figure 2.6: (a) In this 5½-week-old fetus, the nose, mouth, and palate are beginning to differentiate into separate structures. (b) Just 3 weeks later, the nose and mouth are almost fully formed. Cleft palate, one of the most common birth defects worldwide, involves malformations of this area and originates sometime between 5½ and 8 weeks prenatally, as these structures are developing.

FIGURE 2.6 Face development from (a) 5½ to (b) 8½ weeks.

Figure 2.7: The bulging forehead of this 9-week-old fetus reflects extremely rapid brain growth. Rudimentary eyes and ears are forming. All the internal organs are present. Sexual differentiation has started. Ribs are visible, fingers and toes have emerged, and nails are growing.

FIGURE 2.7 Fetus at 9 weeks.

Figure 2.8: This image of an 11-week-old fetus clearly shows the heart, which has achieved its basic adult structure. You can also see the developing spine and ribs, as well as the major divisions of the brain.

FIGURE 2.8 Fetus at 11 weeks.

Figure 2.9: During the last 5 months of prenatal development, the growth of the lower part of the body accelerates. At this age, the external genitalia are substantially developed, and a different camera angle would have revealed the sex of this fetus.

FIGURE 2.9 Fetus at 16 weeks.

Figure 2.10: This 18-week-old fetus is covered with very fine hair, and a greasy coating protects its skin from its long immersion in liquid. The components of facial expressions are present—the fetus can raise its eyebrows, wrinkle its forehead, and move its mouth.

FIGURE 2.10 Fetus at 18 weeks.

Figure 2.11: The brain and lungs of a 28-week-old fetus are sufficiently developed that it would have a chance of surviving on its own, without medical intervention. The eyes can open, and they move, especially during periods of rapid eye movement (REM) sleep. The auditory system is functioning, and the fetus reacts to a variety of sounds.

FIGURE 2.11 Fetus at 28 weeks.

During the last 3 months of prenatal development, the fetus grows dramatically in size, essentially tripling its weight. It also develops a wide repertoire of behaviours and learns from its experiences, as described in the next section. Table 2.1 summarizes the major milestones in prenatal development.

TABLE 2.1 Milestones in Prenatal Development Trimester

Weeks

Major Milestones

1

1

Zygote travels from fallopian tube to womb and embeds in uterine lining; cells arrange into a ball and begin to form embryo and support system.

2–3

Embryo forms three layers, which will become the nervous system and skin; muscles, bones, and circulatory system; and digestive system, lungs, and glands; neural tube also develops.

4

Neural tube continues to develop into the brain and spinal cord; primitive heart is visible, as are leg and arm buds.

5–9

Facial features differentiate; rapid brain growth occurs; internal organs form; fingers and toes emerge; sexual differentiation has started.

10–12

Heart develops its basic adult structures; spine and ribs develop more fully; brain forms major divisions.

2

13–24

Lower body growth accelerates; external genitalia are fully developed; body develops hairy outer covering; fetus can make basic facial expressions; fetal movements can be felt by mother.

3

25–38

Fetus triples in size; brain and lungs are sufficiently developed at 28 weeks to allow survival outside of womb; visual and auditory systems are functional; fetus is capable of learning and behaviours begin to emerge.

Fetal Experience and Behaviour Is the womb a haven of peace and quiet? Although the uterus and the amniotic fluid buffer the fetus from much of the stimulation impinging on the mother, the fetus still experiences an abundance of sensory stimulation and is capable of learning and developing behaviours. Studies of fetal behaviour reveal many results consistent with the themes laid out in Chapter 1. Prenatal experiences shape the developing fetus (nature and nurture). The fetus participates in, and

contributes to, its own development: the formation of organs and muscles depends on fetal activity, and the fetus rehearses the behavioural repertoire it will need at birth (the active child). There is also evidence for both continuity and discontinuity. To give just one striking example, 32-week-old fetuses whose heart rates were generally slower and who moved less were more behaviourally inhibited at 10 years of age (DiPietro et al., 2018). Despite their very different environments (discontinuity), fetuses and children show surprising similarities (continuity).

Movement From 5 or 6 weeks after conception, the fetus moves spontaneously. One of the earliest distinct patterns of movement to emerge (at around 7 weeks) is, remarkably enough, hiccups. Although the reasons for prenatal hiccups are unknown, one theory posits that they are a burping reflex, preparing the fetus for eventual nursing by removing air from the stomach to make more room for milk (Howes, 2012). Swallowing is another important reflex that helps to prepare the fetus for survival outside the womb. Fetuses swallow amniotic fluid, most of which is excreted back out into the amniotic sac. The tongue movements associated with swallowing promote the normal development of the palate. In addition, the passage of amniotic fluid through the body helps the digestive system mature properly.

Another form of fetal movement anticipates breathing after birth. For breathing to occur, the respiratory system must be mature and functional. Beginning as early as 10 weeks after conception, the fetus promotes its respiratory readiness by exercising its lungs through “fetal breathing,” moving its chest wall in and out. No air is taken in, of course; rather, small amounts of amniotic fluid are pulled into the lungs and then expelled. Fetal breathing is initially infrequent and irregular but then increases in rate and stability. By the third trimester, fetuses “breathe” roughly once per second (Ulusar, Sandhal, & Mendilcioglu, 2017).

Touch The fetus experiences tactile stimulation as a result of its own activity. Fetuses have been observed not only grasping their umbilical cords but also rubbing their face and sucking their thumbs. Indeed, the majority of fetal arm movements during the second half of pregnancy result in contact between their hand and mouth (MyowaYamakoshi & Takeshita, 2006), as the fetus in Figure 2.12 demonstrates. Remarkably, fetuses’ choice of thumb to suck predicts later handedness; fetuses who suck their right thumb are more likely to be righthanded adolescents, whereas fetuses who suck their left thumb are more likely to be lefthanded adolescents (Hepper, Wells, & Lynch, 2005).

FIGURE 2.12 Fetal arm and hand movements.

As the fetus grows larger, it bumps against the walls of the uterus increasingly often. By full term, fetal heart rate responds to maternal movements, suggesting that their vestibular systems—the sensory apparatus in the inner ear that provides information about movement and balance—is also functioning before birth (Cito et al., 2005; Lecanuet & Jacquet, 2002).

Sight Although it is not totally dark inside the womb, the visual experience of the fetus is minimal. Despite minimal stimulation, fetuses can process visual information by the third trimester of pregnancy, and, much like newborn infants, fetuses have visual preferences. In a recent study, researchers used 4-D ultrasound to measure what thirdtrimester fetuses preferred to look at by projecting light patterns onto pregnant women’s abdomens (see Figure 2.13; Reid et al., 2017). Fetuses preferred light displays that are top-heavy (resembling correctly oriented faces) over those that are bottom heavy (resembling inverted faces). These data suggest that infants’ predispositions to look toward face-like stimuli may not require postnatal experience (though see Scheel et al., 2018, for an alternative view). We continue the discussion of face perception and preference in infants in Chapter 5, Box 5.1.

FIGURE 2.13 Light-pattern projection Fetuses prefer light displays that are topheavy, resembling correctly oriented faces (a, b) over bottom-heavy displays (c, d). The images on the left show the unobstructed light display, and the images on the right illustrate how this display would look to the fetus.

Description The light conveying perceptual content is projected through the uterine wall and perceived by the fetus. The results are shown in two orientations of the light pattern on the maternal abdomen. The tile (A) shows an inverted triangle, formed by the light interface through the maternal tissue. The tile (B) shows three huge, blurred red dots forming an inverted triangle. The tile (C) shows a triangle formed by the light interface through the maternal tissue. The tile (D) shows three huge, blurred red dots forming a triangle. Both the tiles (B) and

(D) shows how the fetus perceives the light.

Taste The amniotic fluid contains a variety of flavours, and fetuses like some better than others. Indeed, the fetus has a sweet tooth. The first evidence of fetal taste preferences came from a study performed

more than 60 years ago (described by Gandelman, 1992). A physician named DeSnoo (1937) devised an ingenious treatment for women with excessive amounts of amniotic fluid. He injected saccharin into their amniotic fluid, hoping that the fetus would help the mother out by ingesting increased amounts of the sweetened fluid, thereby diminishing the excess. And, in fact, tests of the mothers’ urine showed that the fetuses ingested more amniotic fluid when it had been sweetened, demonstrating that flavour preferences exist before birth.

Smell Amniotic fluid takes on odours from what the mother has eaten. Obstetricians have long reported that during birth they can smell scents like curry and coffee in the amniotic fluid of women who had recently consumed them. Smells can be transmitted through liquid, and amniotic fluid comes into contact with the fetus’s odour receptors through fetal breathing, providing fetuses with the opportunity for olfactory experience. Prenatal scent learning plays an important role in many species’ early developmental processes, demonstrating the principle of phylogenetic continuity: humans share many characteristics and developmental processes with nonhuman animals due to our shared evolutionary history. For example, during the birth process in rats, the nipples on the underside of the mother rat’s belly are smeared with amniotic fluid. The scent of the amniotic fluid is familiar to the rat pups from their

time in the womb, and it lures the pups to the mother’s nipples for nursing. When the mother rat’s nipples are washed immediately after birth, newborn rats fail to attach to her nipples (Teicher & Blass, 1977). This classic finding clearly demonstrates that nurture begins prenatally: experiences before birth play an important role in postnatal developmental processes. phylogenetic continuity the idea that because of our common evolutionary history, humans share many characteristics, behaviours, and developmental processes with non-human animals, especially mammals

Hearing The prenatal environment is surprisingly noisy. Fetuses float in a soundscape dominated by their mother’s heartbeat, blood flow, and breathing. From the fetuses’ vantage point, digestive sounds occur roughly 5 times per second (Parga et al., 2018)! The noise level in the uterus ranges from about 70–95 decibels (roughly the noise level of a vacuum to a lawnmower). The mother’s voice is particularly prominent. We know that the fetus hears its mother because its heart rate changes when the mother starts speaking (Voegtline et al., 2013). During the last trimester, external noises elicit changes in fetal movements and heart rate as well, suggesting that the fetus also perceives sounds outside the mother’s body. For instance, Canadian researchers found that fetal heart rate increases when recordings of

the mother’s or father’s voices are played near the pregnant mother’s abdomen (Lee & Kisilevsky, 2014). Similarly, changes in heart-rate patterns suggest that fetuses can distinguish between music and speech played near the mother’s abdomen (Granier-Deferre et al., 2011). The uterine auditory experience appears to be particularly well-suited to early brain development. In a study by Webb and colleagues (2015), a group of hospitalized preterm infants spent several hours each day listening to recordings of their mothers’ uterine sounds (including voices and heartbeats). At 1 month of age, their brain development was compared to another group of preterm infants who were only exposed to regular hospital sounds. The preterm infants exposed to womb sounds had larger auditory cortexes than the control group, suggesting that maternal sounds may facilitate brain development before full gestation. Because sound is such a prevalent feature of the fetal environment, it plays a major role in prenatal learning, as we discuss next.

Fetal Learning To this point, we have emphasized the impressive behavioural and sensory capabilities of the fetus. Even more impressive is the extent to which the fetus learns from its experiences in the last 3 months of

pregnancy, after the central nervous system is adequately developed to support learning. In the example of fetal learning that opened this chapter, infants remembered specific prenatal auditory experiences that were presented via audio speakers adjacent to the mother’s abdomen, such as repetitions of a single nonsense word (Partanen, Kujala, Tervaniemi et al., 2013) or a melody like Twinkle Twinkle Little Star (Partanen, Kujala, Näätänen et al., 2013). More direct evidence for fetal learning comes from studies of habituation, one of the simplest forms of learning. Much like adults and children, fetuses grow bored if a stimulus is repeated over and over again. This process is called habituation: a decrease in response to repeated or continued stimulation (see Figure 2.14). Habituation provides evidence of learning and memory: the stimulus loses its novelty (and becomes boring) only if the stimulus is remembered from one presentation to the next. When a perceptible change in the stimulus occurs, it becomes interesting again—a process known as dishabituation. Fetuses as young as 30 weeks gestation show habituation to both visual and auditory stimuli, indicating that their central nervous systems are sufficiently developed for learning and short-term memory to occur (Matuz et al., 2012; Muenssinger et al., 2013). habituation a simple form of learning that involves a decrease in response to repeated or continued stimulation dishabituation the introduction of a new stimulus rekindles interest following habituation to a

repeated stimulus

FIGURE 2.14 Habituation Habituation occurs in response to the repeated presentation of a stimulus. As the first stimulus is repeated and becomes familiar, the response to it gradually decreases. When a novel stimulus occurs, the response recovers. The decreased response to the repeated stimulus indicates the formation of memory for it; the increased response to the novel stimulus indicates discrimination of it from the familiar one, as well as a general preference for novelty.

Description The y-axis plots Response, is labelled High on the top and Low at the bottom. The x-axis shows habituation to a repeated stimulus as well as recovery to a novel stimulus, that is, dishabituation. With repetition of the first stimulus,

there is a gradual decrease in the child’s response to it. This is habituation. It indicates that a memory of the repeated stimulus has been formed in the mind of the child. There is a recovery in response of the child on the arrival of a novel stimulus. This is known as dishabituation. This indicates that the child discriminates between the novel stimulus and the familiar stimulus, and prefers the novel one.

Fetuses also learn from their extensive experience with their mother’s voice. To test this idea, Queens University’s Barbara Kisilevsky and her colleagues (2003) tested term fetuses in one of two

conditions. Half of the fetuses listened to a recording of their mother reading a poem, played through speakers placed on their mother’s abdomen. The other half listened to recordings of the same poem read by another woman. Fetal heart rate increased in response to the mother’s voice but decreased in response to the other woman’s voice. These findings suggest that the fetuses recognized (and were aroused by) the sound of their own mother’s voice relative to a stranger’s voice. For this to be the case, fetuses must be learning and remembering the sound of their mother’s voice. After birth, do newborns remember anything about their fetal experience? The answer is a resounding yes! They still prefer to listen to their own mother’s voice rather than to the voice of another woman (DeCasper & Fifer, 1980). Furthermore, newborns prefer to listen to a version of their mother’s voice that has been filtered to sound the way it did in the womb, rather than to another woman’s filtered voice (Moon & Fifer, 1990; Spence & Freeman, 1996). Newborns prefer to listen to the language they heard in the womb over another language (Mehler et al., 1988; Moon, Cooper, & Fifer, 1993). Finally, newborns remember the sounds of specific stories heard in the womb (DeCasper & Spence, 1986). Figure 2.15 describes the technique these researchers used to study prenatal learning.

FIGURE 2.15 Prenatal learning This newborn can control what he gets to listen to. His pacifier is hooked up to a computer, which is in turn connected to an audio player. If the baby sucks in one pattern (predetermined by the researchers), he will hear one recording. If he sucks in a different pattern, he will hear a different recording. Researchers have used this technique to investigate many questions about infant abilities, including the influence of fetal experience on newborn preferences.

Fetuses also learn from the tastes and smells they encounter in the womb. Like the rat pups discussed earlier, newborn humans remember the scent of amniotic fluid. They orient to their own amniotic scent and prefer scents reflecting flavours that their mother

ate while she was pregnant, like anise (licorice) or garlic (for a review, see Anzman-Frasca et al., 2018). Long-lasting taste preferences have also been observed. In one study, pregnant women drank carrot juice for three weeks near the end of their pregnancy (Mennella, Jagnow, & Beauchamp, 2001). When tested at around 5½ months of age, their babies reacted more positively to cereal prepared with carrot juice than to the same cereal prepared with water. These flavour preferences suggest a persistent effect of prenatal learning that may shed light on the origins and strength of cultural food preferences. A child whose mother ate a lot of chili peppers, ginger, and cumin during pregnancy, for example, might be more favourably disposed to Indian food than would a child whose mother’s diet lacked those flavours. Does this evidence of fetal learning suggest that there is a benefit to “prenatal education” programs, where specific music, languages, voices, or other experiences can be used to enhance cognitive abilities after birth? Probably not. In the first place, the fetal brain is unlikely to be sufficiently developed to process much about language meaning. In addition, the liquid environment in the womb filters out detailed speech and music sounds, leaving only pitch contours and rhythmic patterns. In short, the fetus learns about general sounds but not any specific content.

REVIEW QUESTION

Fetal development includes periods of rapid change, as well as periods of slower growth. Throughout the gestation process, the fetus goes through phases during which different organs and systems develop. How do the different periods of fetal development illustrate aspects of continuity and discontinuity?

Hazards to Prenatal Development Regrettably, prenatal development is not always free of error or misfortune. The most dire, and by far the most common, misfortune is spontaneous abortion—commonly referred to as miscarriage. Most miscarriages occur before the woman even knows that she is pregnant. The majority of embryos that are miscarried very early have severe defects, such as a missing chromosome or an extra one, that make further development impossible. In Canada and the United States, between 6% and 15% of clinically recognized pregnancies end in miscarriage (Arck et al., 2008; Rai & Regan, 2006). This number is similar to the rate in a very different culture, rural Kenya (18.9%), suggesting that the factors that influence miscarriage are present across a wide range of life circumstances (Dellicour et al., 2016). Across their childbearing years, at least 25% of women—and possibly as many as 50%—experience at least one miscarriage. Few women realize how common this experience is, making it all the more painful if it happens to them. Yet more agonizing is the experience of the approximately 1% of women who experience recurrent miscarriages, or the loss of three or more consecutive pregnancies. Encouragingly, though, many women who have had recurrent miscarriages successfully carry subsequent pregnancies to term (Cohain, Buxbaum, & Mankuta, 2017). For fetuses that survive the danger of miscarriage, there is still a

range of factors that can lead to unforeseen negative consequences. Here, we consider some of the many environmental risk factors. Genetic factors will be discussed in Chapter 3.

Challenges During Pregnancy

Teratogens A vast number of environmental agents, called teratogens, have the potential to harm the fetus. The effects of potential teratogens are heavily influenced by timing (one of the basic developmental principles discussed in Chapter 1). Many teratogens cause damage only if they are present during a sensitive period in prenatal

development. The major organ systems are most vulnerable to damage at the time when their basic structures are being formed. Because the timing is different for each system, the sensitive periods are different for each system, as shown in Figure 2.16. teratogen an external agent that can cause damage or death during prenatal development sensitive period the period of time during which a developing organism is most sensitive to the effects of external factors

FIGURE 2.16 Sensitive periods of prenatal development The most sensitive or critical period of prenatal development is the embryonic period. During the first 2 weeks, before implantation in the uterus, the zygote is generally not susceptible to environmental factors.

Every major organ system of the body undergoes all or a major part of its development between the 3rd and the 9th week. The dark green portions of the bars in the figure denote the times of most rapid development when major defects originate. The light green portions indicate periods of continued but less rapid development when minor defects may occur. (Information from Moore & Persaud, 1993)

Description The column headers are plotted as follows: Period of the ovum (week 1 and 2), Period of the embryo (week 3 to 8), and Period of the fetus (week 12 to 38). The row headers are: Most common site of birth defect, Severity of defect, and Most likely effect. The table presents the following information: Row 1. Most common site of birth defect: The row shows illustrations of parental development stages along the weeks and labels organs as follows: Week: 2, Heart; Week: 3, Central Nervous System; Week: 4 and 5, Eye, Heart, Arm, and Leg; Week: 6, Ear and Teeth; Week: 7, Brain, Ear, and Palate; Week: 8, Ear, Palate, and External Genitalia, Week: 12, External Genitalia; and Week: 20 to 36, Brain. Row 2. Severity of defect: Central nervous system (C N S): Highly sensitive period: From the very beginning of the third week until the first of the 6th week; less sensitive period: From the second day of the 6th week until the end of 38th week. Heart: Highly sensitive period, from the mid of the 3rd week until the fifth day of the sixth; less sensitive period, from the sixth day of the sixth week until the end of eighth week. Arms: Highly sensitive period, from the fifth day of the fourth week until the end of seventh; Less Sensitive period, entire eighth.

Eyes: Highly sensitive period, from the mid of the fourth week until the mid of the seventh; Less Sensitive period, from the mid of the seventh week till the end of the 38th. Legs: Highly sensitive period, from the beginning of the firth day of the fourth week till the end of the seventh week; Less Sensitive period, entire eighth. Teeth: Highly sensitive period, from the end of the sixth week till the end of eighth week; Less Sensitiveof period, week twelve to sixteen. Theend most dramatic illustration the importance ofweek timing comes

from the use of the drug thalidomide in the early 1960s. Thalidomide Palate: Highly sensitive period, From the end of the sixth week till the second

wasday prescribed to treat sickness things) of the twelfth; Less morning Sensitive period, the (among remainingother days of twelfth.and was considered to be so safe that it was sold over the counter in External genitalia: Highly sensitive period, From the fourth day of the seventh

numerous countries, including Canada (the last country to withdraw week until the sixth day of the twelfth; Less Sensitive period, from the end of

thalidomide the twelfth from till the the end market). of the 38th.At the time, it was believed that such medications would not cross the placental barrier. However, many Ear: Highly sensitive period, from the mid of fourth week till the mid of twelfth;

pregnant women who took this new, presumably safe drug gave birth Less Sensitive period, from the mid of the twelfth week till the end of the

to babies with major limb deformities; some babies were born with sixteenth. no arms and with flipperlike hands growing out of their shoulders. In Row 3. Most likely effect: Major structural abnormalities (week 3 to 8) and

a striking illustration of sensitive period effects, serious defects

Physiological defects and Major structural abnormalities minor structural

occurred only if the pregnant woman took the drug between the 4th abnormalities (week 12 to 38).

and 6th week after conception—the time when her fetus’s limbs were emerging and developing (look again at Figures 2.5 to 2.11). Taking thalidomide either before the limbs started to develop or after they were basically formed had no harmful effect.

This young artist exhibits the harmful prenatal effects of exposure to thalidomide. It seems likely that his mother took the drug in the 2nd month of her pregnancy, when the arm buds are developing—an unfortunate example providing clear evidence of the importance of timing in how environmental agents can affect the developing fetus.

As you can see in Figure 2.16, the sensitive periods for many organ systems occur before the woman might realize she is pregnant. Because a substantial number of pregnancies are unplanned, sexually active people of childbearing age should be aware of factors that

could compromise the health of a child they might conceive. Another crucial factor influencing the severity of teratogenic effects is the amount and duration of exposure. Most teratogens show a dose–response relation: the greater the fetus’s exposure to a potential teratogen, the more likely it is that the fetus will suffer damage and the more severe any damage is likely to be. dose–response relation a relation in which the effect of exposure to an element increases with the extent of exposure (prenatally, the more exposure a fetus has to a potential teratogen, the more severe its effect is likely to be)

Teratogens frequently occur in combination, making it difficult to separate out their effects. For families living in poverty, for example, it is hard to tease apart the effects of poor maternal nutrition, exposure to pollution, inadequate prenatal care, and psychological stress. The presence of multiple risk factors can have a cumulative impact on development, as we discuss further at the end of this chapter in the section on multiple-risk models. Negative effects of prenatal experience may not be immediately evident. Fetal programming refers to the belated emergence of effects of prenatal experience that “program the physiological set points that will govern physiology in adulthood” (Coe & Lubach, 2008). For instance, in the case of inadequate prenatal nutrition, the fetus’s metabolism adjusts to the level of nutritional deficiency experienced in the womb and does not reset itself after birth. In a postnatal

environment with abundant food, this programming sets the stage for the development of overweight and obesity issues. Evidence comes from studies of individuals who were conceived in the Netherlands in 1944, during what was known as the Dutch Hunger Winter (Schulz, 2010). At this point in World War II, the German occupying force in the Netherlands limited rations to as little as 400 to 800 calories per day. Women in the earlier stages of pregnancy during the famine had babies of normal birth weights. However, these infants grew up to have high rates of obesity. The fetuses’ metabolisms were apparently set prenatally, while they were experiencing undernutrition, and were not reset when nutrition reached normal levels. Thus, the physiology of these individuals was a poor match for the food-rich environment available later in their lives, leading to an increased risk of obesity. The effects of teratogens can also vary according to individual differences in genetic susceptibility (probably in both the mother and the fetus). Thus, a substance that is harmless to most people may trigger problems in individuals whose genes predispose them to be affected by it. Identifying teratogens is further complicated by the existence of sleeper effects, in which the impact of a given agent may not be apparent for many years. For example, between the 1940s and 1960s, the hormone diethylstilbestrol (DES) was commonly used to prevent miscarriage and had no apparent ill effects on babies born to women who had taken it. However, in adolescence and adulthood,

these offspring turned out to have elevated rates of cervical and testicular cancers. An enormous number of potential teratogens have been identified, but we will focus only on some of the most common ones.

Drugs In Canada, 6.7% of women reported using illegal drugs in the three months before becoming pregnant or before realizing that they were pregnant, while about 1% of women reported using drugs after recognizing that they were pregnant (Public Health Agency of Canada, 2009). Almost all drugs of abuse—both legal and illegal—have been shown to be, or are suspected of being, dangerous for prenatal development. And though many prescription and over-the-counter drugs are perfectly safe for pregnant women, some are not. Pregnant women (and women who have reason to think they might soon become pregnant) should take medications only under the supervision of a physician. Some prescription drugs that are in common use by women of childbearing age, such as the acne medication isotretinoin (Accutane), are known human teratogens that cause severe birth defects or fetal death. Indeed, because of the unambiguous relationship between Accutane and birth defects, physicians require women to comply with multiple contraceptive measures and ongoing pregnancy tests before prescribing the drug.

Antidepressants

Antidepressant medications raise particularly challenging issues for women contemplating pregnancy. These medications can be hugely beneficial for individuals experiencing depression. Treatment for depression during pregnancy can help reduce the risk of postpartum depression, which affects 10% to 30% of new mothers, and which is especially likely for women with previous histories of depression (Brummelte & Galea, 2016). In Canada, roughly 3% to 5% of pregnant women take antidepressant medication (Bérard & Sheehy, 2014; Smolina et al., 2015). Evidence regarding whether or not these medications are harmful to the fetus is inconclusive (Lusskin et al., 2018), raising difficult questions for pregnant women who are depressed. Should they choose a pharmaceutical intervention for their depression and risk negative outcomes from the medication? Or should they choose not to treat their mood disorder and risk negative outcomes from the depression itself? One potential solution to this issue is the use of non-pharmaceutical treatments for depression, which many pregnant women say they would prefer (Dimidjian & Goodman, 2014). Behavioural interventions, including cognitive behaviour therapy and mindfulness-based cognitive therapy, hold promise as ways to treat perinatal depression without the use of medication (e.g., Dimidjian et al., 2017).

Opioids

Another issue of increasing concern is the use of prescription opioid medications (e.g., Vicodin, Percocet, Oxycodone, Fentanyl) and the related use of illicit opioids, such as heroin. Because they are designed to mimic the effects of neurotransmitters, they have the potential to wreak havoc on the developing brain. Prescribed for pain management or used illegally, opioids can be highly damaging to fetuses, who can become addicted themselves. Neonatal abstinence syndrome (NAS) is a form of drug withdrawal seen when fetuses exposed to opioids in the womb are born. In Canada, prevalence of NAS has continued to rise (Brogly et al., 2017); for example, between 1992 and 2011, the rate of NAS increased 0.28 per 1000 live births to 4.29 per 1000 live births (Turner et al., 2015). Common effects of NAS include low birth weight, problems with breathing and feeding, and seizures. Treatment for these newborns often requires medications such as methadone or morphine to manage withdrawal symptoms. As we mentioned earlier, teratogens often occur in clusters. In the case of opioids, the co-presence of other maternal drug use (e.g., antidepressants or marijuana) increases the likelihood that the newborn will have NAS (Sanlorenzo, Stark, & Patrick, 2018).

Marijuana Marijuana is of particular interest to researchers because it is so frequently used by women of reproductive age, and its usage may

increase in Canada now that cannabis has been legalized. Even prior to legalization, which occurred in October 2018, marijuana use among pregnant women was on the rise; in Ontario, marijuana use during pregnancy grew from 1.2% in 2012 to 1.8% in 2017, with the highest rate (6.5%) among 15- to 24-year-olds (Corsi et al., 2019). Data on the effects of marijuana on fetal development are inconclusive because many users of marijuana also smoke cigarettes and/or use alcohol, and the effects of each drug are difficult to tease apart; some studies suggest that the combination of marijuana and tobacco is particularly problematic (Ryan et al., 2018). Prenatal exposure to marijuana is also associated with a range of problems involving attention, impulsivity, learning, and memory in older children (Behnke et al., 2013). The effects of opioids and marijuana on fetal development can be devastating, but the two drugs that wreak the most widespread havoc on fetal development are cigarettes (nicotine) and alcohol, which we turn to next.

Cigarette smoking When a pregnant woman smokes a cigarette, both she and her fetus get less oxygen. Indeed, the fetus makes fewer breathing movements while its mother is smoking, and the fetuses of smokers metabolize some of the cancer-causing agents contained in tobacco. Secondhand smoke has an indirect effect on fetal oxygen as well, through the

mother’s intake of cigarette gases when someone is smoking nearby. The main developmental consequences of maternal smoking are slowed fetal growth and low birth weight, both of which compromise the health of the newborn. In addition, smoking is linked to increased risk of sudden infant death syndrome (SIDS) (discussed in Box 2.3) and a variety of other problems, including lower IQ, hearing deficits, ADHD (see Box 9.3), and cancer. As with other teratogens, there is a dose–response relationship: greater smoking intensity (as measured in the number of cigarettes per day) predicts worse outcomes, including stillbirths (e.g., Marufu et al., 2015). And, as with other teratogens, timing matters: the effects of smoking are greatest early in gestation (e.g., Behnke et al., 2013). However, in spite of the welldocumented and widely advertised negative effects of maternal smoking on fetal development, approximately 12% of pregnant women in Canada continue to smoke during pregnancy (Lange et al., 2015).

BOX 2.3 APPLICATIONS Sudden Infant Death Syndrome For parents, nothing is more terrifying to contemplate than the death of their child. New parents are especially frightened by the specter of sudden infant death syndrome (SIDS). SIDS refers to the sudden, unexpected, and unexplained death of an infant younger than 1 year. The most common SIDS scenario is that an apparently healthy baby, usually between 2 and 5 months of age, is put to bed for the night and found dead in the morning. In Canada, SIDS accounts for 21.3% of

postneonatal deaths, making it the leading cause of infant mortality between 28 days and 1 year of age (Public Health Agency of Canada, 2013). Furthermore, infants from socioeconomically disadvantaged and Indigenous populations have higher incidences of SIDS than do other populations in Canada (Collins et al., 2012; Gilbert et al., 2013). sudden infant death syndrome (SIDS) the sudden, unexpected death of an infant less than 1 year of age that has no identifiable cause The causes of SIDS are not well understood, but they likely involve an interaction between an underlying biological issue that places the infant at risk and an environmental stressor—for example, limited access to oxygen due to an obstruction of the nose and mouth. Recent research suggests that at least some infants who succumbed to SIDS had altered levels of serotonin, a neurotransmitter (Haynes et al., 2017). Decreased serotonin may make it more difficult for young infants to detect and respond to a lack of oxygen by turning their head away from bedding or other soft materials, especially during sleep. A subset of cases result from a rare genetic mutation in the breathing muscles that puts infants at greater risk of respiratory challenge in situations that impair breathing (Männikkö et al., 2018). Researchers studying SIDS hope to identify biomarkers, like neurotransmitters or genetic mutations, that will help physicians flag infants at heightened risk for SIDS (Bright, Vink, & Byard, 2018). To decrease the risk of SIDS, the most important steps that parents can take entail removing any barriers to their baby’s breathing. First, putting infants to sleep on their backs reduces the possibility of breathing obstructions. Sleeping on the stomach increases the risk of SIDS more than any other single factor. A campaign encouraging parents to put their infants to sleep on their back—the “back to sleep” movement—contributed to a dramatic reduction in the number of SIDS victims. Second, parents should not smoke because it decreases the oxygen available in the infant’s environment. If they do smoke, they should not smoke

around the baby. Third, bedding should be firm; soft bedding can trap air around the infant’s face, causing the baby to inhale carbon dioxide instead of oxygen. For more recommendations, the Public Health Agency of Canada posts resources for parents and caregivers.

In Canada, death from SIDS declined by more than 71% between 1981 and 2009, likely due to Safe Sleep campaigns supported by the Public Health Agency of Canada and the

Canadian Pediatric Society.

Description The poster shows a cartoon of a baby sleeping in a crib. Text above the cartoon reads, Safe sleep for your baby: Preventing sudden infant deaths in Canada. Text below the cartoon reads, Always place your baby of his or her back to sleep, at naptime and night time. W w w dot public health dot g c dot c a forward slash safe sleep

One unanticipated consequence of the “back to sleep” movement has been that North American infants are now beginning to crawl slightly later than those in previous generations, presumably because of reduced opportunity to strengthen their muscles by pushing up off their mattress. Parents are encouraged to give their babies supervised “tummy time” to exercise their muscles during the day.

E-cigarettes (e-cigs) are becoming increasingly prevalent as an alternative to conventional cigarettes. Many pregnant women believe that vaping is healthier for their fetuses than cigarette smoking (Wagner, Camerota, & Propper, 2017). While e-cigs avoid some of the issues related to smoke exposure, the use of nicotine in any form is a risk factor for fetal development and can affect fetal cardiac, respiratory, and nervous systems. In addition, because e-cigs are largely unregulated, they range greatly in the amount of nicotine they contain, with some brands containing far more nicotine than cigarettes do (Jiang et al., 2018). Thus, the perception of the benefits of e-cigs relative to traditional cigarettes may lead pregnant women to overlook the risks.

Smoking endangers the health of the fetus.

Alcohol Maternal alcohol use is the leading cause of fetal brain injury and is generally considered to be the most preventable cause. In Canada, 1 in 10 pregnant women report using alcohol during their pregnancies (Popova et al., 2017b). This rate is similar to the worldwide estimate of the prevalence of alcohol use during pregnancy, but there are substantial cultural differences (Popova et al., 2017a). Rates are highest in European countries (25% overall, with the highest rate in Ireland at 60%), and lowest in countries in the Middle East, where Saudi Arabia, Qatar, and Oman report rates of 0% (though it is worth noting that stigma may lead women in some countries to underreport

alcohol use). These data suggest that alcohol use during pregnancy reflects broader cultural views about the use of alcohol, especially by women. When a pregnant woman drinks, the alcohol in her blood crosses the placenta into both the fetus’s bloodstream and the amniotic fluid. Thus, the fetus gets alcohol both directly—in its bloodstream—and indirectly, by drinking an amniotic-fluid cocktail. Concentrations of alcohol in the blood of mother and fetus quickly equalize, but the fetus has less ability to metabolize and remove alcohol from its blood, so it remains in the fetus’s system longer. Maternal drinking can result in fetal alcohol spectrum disorder (FASD), which comprises a continuum of alcohol-related birth defects. Babies born to alcoholic women often exhibit extreme negative outcomes, known as fetal alcohol syndrome (FAS). The most obvious symptoms of FAS are characteristic facial structures, like the eyes, nose, and lips shown in Figure 2.17. Other forms of FAS can include varying degrees of intellectual disability, attention problems, and hyperactivity. Recent analyses suggest that the rates of FAS in Canada are much greater than previously suspected, with a prevalence estimated to be between 2% and 3% based on a study of 7to 9-year-olds tested in the Greater Toronto area (Popova et al., 2018). fetal alcohol spectrum disorder (FASD) the harmful effects of maternal alcohol consumption on a developing fetus. Fetal alcohol syndrome (FAS) involves a range of effects, including facial deformities, intellectual disabilities, attention problems, hyperactivity, and other defects. Fetal

alcohol effects (FAE) is a term used for individuals who show some, but not all, of the standard effects of FAS.

FIGURE 2.17 Facial features of FAS This child displays the three primary diagnostic facial features of fetal alcohol syndrome: small eyes (as measured across); the absence of, or flattening of, the vertical groove between the nose and the upper lip (smooth philtrum); and a thin upper lip. This facial phenotype is one of the diagnostic criteria for FAS.

Even moderate drinking during pregnancy (i.e., less than one drink per day) can have both short- and long-term negative effects on development. So can occasional drinking if it involves binge drinking (four drinks or more on a single occasion). In Canada, it is estimated that 1% to 2% of pregnant women engaged in at least one incident of binge drinking during the previous month (Lange et al., 2017). The

negative effects can include low birth weight, increased risk for ADHD, and delays in cognitive development and school achievement (e.g., Behnke et al., 2013). Given the research to date, the Society of Obstetricians and Gynaecologists of Canada recommends that pregnant women avoid alcohol altogether (Carson et al., 2017).

Environmental Pollutants The bodies and bloodstreams of most Americans (including women of childbearing age) contain a noxious mix of toxic metals, synthetic hormones, and various ingredients of plastics, pesticides, and herbicides that can be teratogenic (Moore, 2003). These substances often have significant negative effects on the fetus. For instance, the infants of Inuit mothers, whose diets are high in Arctic fish, are exposed to lead, mercury, and polychlorinated biphenyls (PCBs) both prenatally and postnatally. This type of exposure has been associated with later difficulties in attention, cognition, and neuromotor development (Boucher et al., 2014; Boucher et al., 2012; Deprés et al., 2005). Air pollution from the burning of fossil fuels is associated with low birth weight and neurotoxicity and disproportionately affects low-income populations, both in North America and around the world (Perera, 2016). Often, different forms of pollution act in combination. For example, China’s rapid industrialization has led to a dramatic increase in pollution-related birth defects due to the unregulated burning of coal, water pollution, and pesticide use (e.g., Ren et al., 2011).

While progress has been made nationwide in eradicating some pollutants, the situation in Grassy Narrows and White Dog First Nations provides clear evidence that environmental hazards continue to pose risks. In the 1970s, peoples from the Grassy Narrows and White Dog First Nations, who lived near Dryden, Ontario, began experiencing symptoms consistent with methylmercury poisoning (Takaoka et al., 2014). A chemical and pulp mill was dumping mercury into the English–Wabigoon River System and poisoning the fish that were the First Nations’ main source of food and income. Four decades after the mill stopped dumping mercury into the river system, mercury levels in fish remain above safe levels, and people are still developing the symptoms of Minamata disease (named after a coastal town in Japan that suffered a similar case of factory-related methylmercury poisoning); these symptoms include numbness in the limbs, difficulty walking a straight line, vision and hearing impairments, headaches, and exhaustion. Such incidents highlight the impact that decisions by individuals, groups, and local governments can have on environmental factors, which can in turn have significant and sometimes disastrous consequences on fetal and child development. And these issues are not easily remedied; only in 2017 did the Ontario government pledge funds to remediate the river system.

Decades after the English–Wabigoon River System was originally contaminated by mercury dumping, the First Nations peoples who live and fish there are still suffering the effects.

Maternal Factors Because the mother-to-be provides the most immediate environment for her fetus, some of her characteristics can affect prenatal development. These characteristics include age, nutritional status, health, and stress level.

Age A pregnant woman’s age is related to the outcome of her pregnancy.

Infants born to girls 15 years or younger are 3 to 4 times more likely to die before their 1st birthday than are those born to mothers who are between 23 and 29 (Phipps, Blume, & DeMonner, 2002). However, the rate of teenage pregnancy in Canada is declining, and in 2014, the teen birth rate for teenagers under 17 years old fell to the lowest recorded level (5.4 births per 1000 females younger than 17; Public Health Agency of Canada, 2017). The increasing age at which many women become pregnant is also cause for concern. In recent decades, many women in industrialized countries wait until their 30s or 40s to have children. Techniques to treat infertility have continued to improve, increasing the likelihood of conception for older parents. Like many other risk factors, there is a dose–response relationship, with risk of negative outcomes for both mother and fetus increasing with maternal age. For example, children born to older mothers and/or older fathers are at heightened risk for developmental disorders such as autism spectrum disorder (ASD; Sandin et al., 2016). The causal pathways linking older mothers and fathers to their infants’ developmental outcomes are likely different, since only mothers contribute to prenatal environments and birth circumstances (Lee & McGrath, 2015). Fathers’ contributions may lie more in mutations and other chromosomal abnormalities, as we will discuss in Chapter 3.

Nutrition The fetus depends on its mother for all its nutritional requirements. If a pregnant woman has an inadequate diet, her unborn child may also be nutritionally deprived. An inadequate supply of specific nutrients can have dramatic consequences. For instance, women who get too little folic acid (a form of B vitamin) are at high risk for having an infant with a neural-tube defect such as spina bifida (see Figure 2.4). While prenatal vitamins are frequently used to address these concerns, many women do not know they are pregnant during the crucial early periods of gestation. Many processed foods, such as breakfast cereals, are fortified with folic acid to help ensure that women receive adequate nutrition during the early weeks of pregnancy. Because malnutrition is more common in impoverished families, it often coincides with the host of other risk factors associated with poverty, making it difficult to isolate its effects on prenatal development. However, one unique study of development in extreme circumstances made it possible to assess certain effects of malnutrition independent of socioeconomic status. As we discussed earlier, people of all income and education levels suffered severe famine in parts of the Netherlands during World War II. Children conceived during the Dutch Hunger Winter have been followed into adulthood. In late middle age, individuals who had experienced malnutrition as fetuses showed impaired performance on attentional

tasks and had prematurely aged brains, compared with those who had not (de Rooij et al., 2010; Franke et al., 2018).

This expectant mother, living in an evacuation camp in the Philippines, is being examined by a Doctors Without Borders medical worker. She worries about how she is going to feed her child. Whether caused by displacement due to war or natural disaster, pervasive poverty, or some other factor, concern for maternal nutrition is a situation all too common throughout the world.

Disease Although most maternal illnesses that occur during a pregnancy have no impact on the fetus, some do. For example, if contracted early in pregnancy, rubella (also called the 3-day measles) can have devastating developmental effects, including major malformations, deafness, blindness, and intellectual disabilities. The Society of Obstetricians and Gynaecologists of Canada recommends that women who do not have immunities against rubella be vaccinated before becoming pregnant (Dontigny et al., 2018). Sexually transmitted infections (STIs) are also quite hazardous to the fetus. Cytomegalovirus (CMV), a type of herpes virus that is present in 50% to 70% of women of reproductive age in North America, is the most common cause of congenital infection (affecting 1% to 5% of births; Manicklal, 2013). CMV can damage the fetus’s central nervous system and cause a variety of other serious defects, including hearing loss. Genital herpes can also be very dangerous: if the infant comes into contact with active herpes lesions in the birth canal, blindness or even death can result. HIV infection is sometimes passed to the fetus in the womb or during birth, but the majority of infants born to women who are HIV-positive or who have AIDS do not become infected themselves. HIV can also be transmitted through breast milk after birth, but research suggests that breast milk contains a carbohydrate that may actually protect infants from HIV infection (Bode et al., 2012).

Zika, a mosquito-borne viral infection, burst onto the world scene in 2016. While the illness itself is mild and often goes undetected, it can cause a serious birth defect called microcephaly, a condition in which the baby’s head is much smaller than expected. Depending on the severity of the problem, issues can range from hearing and vision loss to seizures and intellectual disability. Microcephaly occurs in roughly 6% of fetuses whose mothers were infected by Zika (Honein et al., 2017). Consistent with our earlier discussion of sensitive periods, higher rates of microcephaly are observed for women whose Zika infections occurred during the first trimester of pregnancy. The virus appears to infect fetuses’ cortical-neural progenitor cells, resulting in stunted brain growth (Tang et al., 2016). The only preventative option is to avoid mosquito bites in areas where the virus has spread. Women of reproductive age should also take heed of the fact that Zika can be transmitted sexually and through body fluids (Kim et al., 2018).

This Brazilian infant suffers from microcephaly, likely due to her mother’s Zika infection during pregnancy.

Maternal Emotional State Effects of maternal stress during pregnancy have been observed on myriad aspects of infant and child development, ranging from infant cognitive development to later psychiatric diagnoses (for review, see Van den Bergh et al., 2017). Brain-imaging studies with infants and young children reveal both structural and functional effects of prenatal maternal state on the developing brain (Van den Bergh, Dahnke, & Mennes, 2018). For example, Alberta researchers showed

that maternal prenatal depression was associated with changes in brain structure in children aged 2 to 5 years (Lebel et al., 2016). A primary mechanism for these effects is alternations in the hypothalamic–pituitary–adrenal (HPA) axis and the hormone cortisol, a glucocorticoid which helps regulate stress in both the mother and the fetus. As discussed earlier in this chapter, glucocorticoids slow the growth of the fetus. The concept of fetal programming, also discussed previously, shapes research in this area and suggests that the altered hormonal environment for the fetus may lead to long-term changes in how children and adults cope with stress via disrupted HPA axis functioning. In some wealthy countries, including the United States, pregnant women from minority ethnic groups report greater rates of prenatal stress than do women in majority ethnic groups (Liu et al., 2016). Pregnant women in less wealthy countries report even greater levels of stress (Glover et al., 2018). Their anxiety may relate to scarcity of resources, as in cases of high food insecurity, or to war or domestic violence. Women in developing countries may also have increased fears about the outcomes of their pregnancies due to high rates of infant and maternal mortality where they live. For instance, researchers in rural Nigeria found that in a group of 262 women giving birth, 5 women died and 52 experienced severe complications (Mbachu et al., 2017). These sorts of statistics, combined with their firsthand knowledge about the dangers of childbirth, likely add yet another layer of stress for many women in developing countries.

Like other types of teratogens, it is difficult to tease apart the specific effects of maternal stress from other factors that often co-occur with stress. For example, expectant mothers who are stressed during pregnancy are likely to still be stressed after giving birth. Genetic factors may also link both maternal stress and postnatal outcomes. One clever study took advantage of the increased use of assistive reproductive technology—in vitro fertilization (IVF)—to attempt to tease apart these factors (Rice et al., 2010). In this study, mothers were either genetically related or unrelated to their fetuses. The results revealed effects of maternal stress on birth weight and later antisocial behaviour, in both related and unrelated mother–fetus pairs, suggesting that the prenatal environment, not shared genetics, was the strongest predictor of later outcomes. However, for measures of child anxiety, the results suggest that postnatal maternal stress, not prenatal maternal stress, was the strongest predictor of later outcomes. This area of research reveals a complex interplay between prenatal and postnatal factors in developmental outcomes. It also points to the importance of finding ways to help minimize maternal stress both pre- and postnatally. The increased popularity of prenatal yoga and meditation classes suggests that there may be straightforward ways to reduce at least some aspects of pregnancy-related stress, with potential benefits for both mother and fetus.

Prenatal exercise classes, as well as yoga or meditation classes, may help reduce pregnancy-related stress.

REVIEW QUESTION A wide variety of environmental agents can have a negative impact on prenatal development, from drugs to pollution to maternal factors like stress, illness, or nutrition. How can research into these hazards be used to influence public policy aimed at reducing their prevalence and impact?

The Birth Experience Approximately 38 weeks after conception, contractions of the muscles of the uterus begin, initiating birth. Typically, the fetus has already contributed to the process by rotating into the normal headdown position. In addition, the maturing lungs of the fetus may release a protein that triggers the onset of labour. Uterine contractions, as well as the baby’s progress through the birth canal, are extremely painful for the mother. Is birth as painful for the newborn as for the mother? Actually, there is good reason to believe that birth is not particularly painful for the baby. Compare how much pain you feel when you pinch and pull on a piece of skin on your forearm versus when you wrap your hand around your forearm and squeeze as tightly as you can. The stretching is painful, but the squeezing is not. The mother’s pain comes from her tissues being greatly stretched, but the baby experiences squeezing.

The Birth Experience

The squeezing that the fetus experiences during birth serves several important functions. First, it temporarily reduces the overall size of the fetus’s disproportionately large head, allowing it to pass safely through the mother’s pelvic bones. This is possible because the skull is composed of separate plates that can overlap one another slightly during birth (see Figure 2.18). The squeezing of the fetus’s head during birth also stimulates the production of hormones that help the fetus withstand mild oxygen deprivation during birth and help regulate breathing after birth. The squeezing of the fetus’s body forces amniotic fluid out of the lungs, in preparation for the newborn’s first, crucial gasp of air.

FIGURE 2.18 Head plates Pressure on the head during birth can cause the separate plates of the skull to overlap, resulting in a temporarily misshapen head. Fortunately, the condition rapidly corrects itself after birth. The “soft spot,” or fontanel, is simply the temporary space between separate skull plates in the top of the baby’s head.

Diversity of Childbirth Practices Although the biological aspects of birth are pretty much the same everywhere, childbirth practices vary enormously. All cultures pursue the dual goals of (1) safeguarding the survival and health of both mother and baby and (2) ensuring the social integration of the new person. Groups differ, however, regarding the relative importance they give to these goals. An expectant mother on the South Pacific island of Bali assumes that her husband and other kin, along with any children she may already have, will all want to be

present at the joyous occasion of the birth of a new child. Her female relatives, as well as a midwife, actively help her throughout the birth, which occurs in her home. Having already been present at many births, the Balinese woman knows what to expect from childbirth, even when it is her first child (Diener, 2000). A very different scenario unfolds in twenty-first century North America, where the woman in labour usually withdraws almost totally from her everyday life. In most cases, she enters a hospital to give birth, typically attended by a small group of family or close friends. The birth is supervised by a variety of medical personnel, most of whom are strangers. Unlike her Balinese counterpart, the first-time Canadian mother has probably never witnessed a birth, so she may not have very realistic expectations about the birth process. Also, unlike her counterparts in most societies, a Canadian woman in labour has a 28% chance of having a surgical delivery by cesarean (also called C-section)—a rate that is high relative to other countries but has been in decline for the past few years (Canadian Institutes for Health Information, n.d.; Martin, Hamilton, & Osterman, 2018). C-sections are intended to assist infants and mothers facing birth complications, and indeed they have saved untold numbers of lives. However, there are other reasons for the high number of surgical deliveries in Canada, including a vastly increased rate of multiple births (discussed in the next section), scheduling convenience for the physician and/or the parents, maternal obesity, prior C-sections (which may necessitate future C-sections), and physicians’ attempts

to decrease risk of lawsuits concerning medical malpractice should problems arise from a vaginal birth (e.g., Yang et al., 2009). Indeed, one study found that among a sample of American women who had a C-section, nearly half did not appear to have any pregnancy complications (Witt et al., 2015). The Balinese approach to childbirth emphasizes the social goal of immediately integrating the newborn into the family and community —hence the presence of many kin and friends to support mother and baby. In contrast, the belief that childbirth is safer in a hospital setting outweighs the resulting social isolation of mother and baby. And indeed, while the rates of home births are increasing in North America, it is unclear whether home births are riskier than hospital births. One recent study found that in the United States, infant mortality in hospital births attended by certified midwives was significantly lower than infant mortality in home births attended by certified midwives (Grünebaum et al., 2016). It is worth noting, however, that in Ontario where home births are more common (20% of all births) and well-integrated into the healthcare system, the mortality rates for home and hospital births are equivalent, possibly because it is standard practice to transfer home-birthing mothers to the hospital when complications arise (as was the case for 25% of home births in this Canadian sample; Hutton et al., 2015).

The medical model of childbirth prevails in Canada.

The practices in both Canada and Bali have been changing to some degree. In Canada, the social dimensions of birth are increasingly recognized by doctors and hospitals, which often now employ certified midwives for expectant parents who prefer a less medicalized birth plan. As in Bali, various family members— sometimes even including the parents’ other children—are encouraged to be present to support the labouring mother and to share a family experience. Another increasingly common practice in Canada is the use of doulas, individuals trained to assist women in terms of both emotional and physical comfort during labour and delivery. This shift has been accompanied by decreased use of delivery drugs, enhancing the woman’s participation in childbirth and her ability to interact with her newborn, including engaging in activities such as skin-to-skin contact, which promotes stabilization of physiological processes in the transition from the womb to the

outside world (e.g., Rutgers & Meyers, 2015). In addition, many expectant parents attend childbirth education classes through their birth centre or educational organizations like Lamaze, where they learn some of what their Balinese counterparts pick up through routine attendance at births. Social support is a key component of these programs; the pregnant woman’s partner, or some other supportive person, is trained to assist her during the birth. Such childbirth programs are generally beneficial, and obstetricians routinely advise expectant couples to enroll in them. At the same time that these changes are occurring in Canada, Western medical practices are being increasingly adopted in societies like Bali, in an effort to improve newborn survival rates. As a final example of alternate birthing practices, let’s consider the Ju/’hoansi women of rural Botswana and Namibia, who often give birth outdoors and alone despite the dangers posed by animal predators, including lions. This practice is deeply intertwined with spiritual and cultural beliefs that have endured for centuries and reflects a specific view of individual development that sees the birth experience as a key event in a person’s maturation (Biesele, 1997). Though extreme when viewed from other cultural perspectives, and dangerous from a modern medical standpoint, the birthing traditions of the Ju/’hoansi illustrate the complex ways that childbirth, among other aspects of child development, are linked to the greater social and cultural context.

Similar to Balinese practices, this childbirth in South Sudan is quite different from the norm in Canada. The baby was born at home, with the help of a grandmother, great aunt, and a qualified birth attendant.

REVIEW QUESTIONS The diverse range of birthing practices highlights the influence of sociocultural context, and these practices can have a direct impact on the newborn. Consider the birth experiences that you have encountered: In what ways did these experiences reflect cultural practices that are beneficial to the newborn and mother? What alternate practices should have been implemented for the benefit to the newborn and mother?

The Newborn Infant Healthy newborns begin interacting with their new environment right away, exploring and learning about newfound physical and social entities. Newborns’ exploration of this uncharted territory is very much influenced by their state of arousal.

State of Arousal State refers to a continuum of arousal, ranging from deep sleep to intense activity. As you well know, your state dramatically affects your interaction with the environment—with what you notice, do, learn, and think about. It also affects the ability of others to interact with you. state level of arousal and engagement in the environment, ranging from deep sleep to intense activity

Figure 2.19 depicts the average amount of time in a 24-hour period that newborns typically spend in each of six states, ranging from quiet sleep to crying. Within this general pattern, however, there is a great deal of individual variation. To appreciate how these differences might affect parent–infant interactions, imagine yourself as the parent of a newborn who cries more than the average baby, sleeps little, and spends less time in the awake–alert state. Now

imagine yourself with a baby who cries relatively little, sleeps well, and spends an above-average amount of time quietly attending to you and the rest of his or her environment (see Figure 2.20). Clearly, you would have many more opportunities for pleasurable interactions with the second newborn.

FIGURE 2.19 Newborn states This figure shows the average proportion of time, in a 24-hour day, that Western newborns spend in each of the six states of arousal. There are substantial individual and cultural differences in how much time babies spend in the different states.

Description The data given in the pie chart are as follows:

• Quiet sleep 8 hours. • Active sleep 8 hours. • Drowsing 1 hour. • Alert awake 2.5 hours. • Active awake 2.5 hours. • Crying 2 hours.

FIGURE 2.20 Quiet-alert state The parents of this quiet-alert newborn have a good chance of having a pleasurable interaction with the baby.

The two newborn states that are of particular concern to parents— sleeping and crying—have both been studied extensively.

Sleep Two facts about sleep and its development are of particular importance. First, the average newborn sleeps twice as much as young adults do. Second, the pattern of two different sleep states —REM sleep and non-REM sleep—changes dramatically with age. Rapid eye movement (REM) sleep is an active sleep state associated with

dreaming in adults; it is characterized by quick, jerky eye movements under closed lids, a distinctive pattern of brain activity, body movements, and irregular heart rate and breathing. Non-REM sleep, in contrast, is a quiet sleep state characterized by the absence of motor activity or eye movements and more regular, slow brain waves, breathing, and heart rate. REM sleep constitutes fully 50% of a newborn’s total sleep time. The proportion of REM sleep declines quite rapidly to only 20% by 3 or 4 years of age and remains low for the rest of life. rapid eye movement (REM) sleep an active sleep state characterized by quick, jerky eye movements under closed lids and associated with dreaming in adults non-REM sleep a quiet or deep sleep state characterized by the absence of motor activity or eye movements and more regular, slow brain waves, breathing, and heart rate

Why do infants spend so much time in REM sleep? Some researchers believe that it helps develop the infant’s visual system. Because newborns spend so much time asleep, they do not have much opportunity to amass waking visual experience. The high level of internally generated brain activity that occurs during REM sleep may help to make up for the natural deprivation of visual stimulation, facilitating the early development of the visual system in both fetus and newborn. Another way in which REM sleep may be adaptive for neonates is that the natural jerking movements (called myoclonic twitching) that occur exclusively during REM sleep may give infants opportunities to build sensorimotor maps (Blumberg, 2015). These

twitching movements are most frequent during early development and may help the infant with the difficult problem of linking motor patterns with the specific sensations that they evoke.

Sleep in Infancy and Toddlerhood

Another distinctive feature of sleep in the newborn period is that neonates’ slumbering brains do not become disconnected from external stimulation to the same extent that the brains of older individuals do. This stimulation allows newborns to learn during sleep. In one study, infants were exposed to recordings of foreign vowel sounds while they slumbered in the newborn nursery. When tested in the morning, their brain activity revealed that they recognized the sounds they had heard while asleep (Cheour et al.,

2002). Although newborns are likely to be awake during part of their parents’ normal sleep time, they gradually develop the more mature pattern of sleeping through the night. Nighttime awakenings typically diminish over the course of the first postnatal year. However, there is a subset of infants who continue to wake regularly. Roughly one-third of parents of 6-month-olds in the United States report that their infants continued to wake up at least once every night (Weinraub et al., 2012). Even by 12 months of age, only about half of the infants in a Canadian study slept for at least 8 hours at a stretch (Pennestri et al., 2018).

Most Canadian parents want to avoid the 2 A . M . fate of this young father. They regard

their baby’s sleeping through the night as a developmental triumph—the sooner, the better.

A number of sleep techniques have been proposed to help parents and infants who are struggling with sleep. A recent randomizedcontrol study was designed to determine whether behavioural sleep interventions work and whether they cause undue stress for parents and infants (Gradisar et al., 2016). The results suggest that, compared with a sleep-education control group, infants in a graduatedextinction group—in which parents slowly increased their delays in responding to their crying infant—showed greater improvement in sleep behaviours, with no negative effects on infant stress (cortisol levels) or infant–mother attachment. The study also demonstrated successful effects of another behavioural method, bedtime fading, in which the infant’s bedtime is shifted later to ensure sleepiness, and then gradually moved earlier. Both groups showed large decreases in nocturnal wakefulness, with concomitant positive effects on maternal stress. In contrast with Canadian parents, Kipsigis parents in rural Kenya are relatively unconcerned about their infants’ sleep patterns. Kipsigis babies are almost always with their mothers. During the day, infants are often carried on their mother’s back as she goes about her daily activities; at night they sleep with her and are allowed to nurse whenever they awaken. As a consequence, these babies distribute their sleeping throughout the night and day for several months (Harkness & Super, 1995; Super & Harkness, 1986). Thus, cultures

vary not only in terms of where babies sleep, as you learned in Chapter 1, but also in terms of how strongly parents attempt to influence when their babies sleep.

This baby is sleeping in a baby box provided to new parents as part of a recent study funded by the Alberta government.

Crying

Infants cry for many reasons—including illness, pain, and hunger— that require the attention of caregivers. As unpleasant as it is, crying is a normal behaviour. Rather than diminishing over the first few months, as many new parents expect, it actually increases, peaking around 6 to 8 weeks of age. Crying behaviour tends to decrease in frequency around 3 to 4 months of age, potentially because infants now have somewhat more control over their environment. During this period, crying bouts tend to increase in the late afternoon and evening, a phenomenon familiar to most caregivers of young infants.

Never Shake: Preventing Shaken Baby Syndrome

Parents, especially first-timers, are often puzzled and anxious about why their baby is crying, and especially why their infants’ crying

bouts increase in frequency—and sometimes intensity—over the first 2 months. In extreme cases, caregivers may react with a form of child abuse known as shaken baby syndrome, which can result in severe head trauma or death (e.g., Barr et al., 2015). Relatively minimal parental education can play an important role in demystifying infant crying. For example, the Period of PURPLE program, developed by Ron Barr at the University of British Columbia in conjunction with the National Centre on Shaken Baby Syndrome, is provided in hospitals after birth and via public-educational outreach programs. This informational intervention can be highly effective in decreasing emergency room visits based on parental concerns about crying (Barr et al., 2015). More significantly, the intervention decreased the number of infants admitted to the hospital in British Columbia for abusive head trauma (Barr et al., 2018). Understanding that crying is a normal developmental process can significantly decrease parental stress and—in extreme cases—parent-caused injury to infants.

Soothing What are the best ways to console a crying baby? Most of the traditional standbys—rocking, singing lullabies, stroking the baby, holding the baby up to the shoulder, giving the baby a pacifier, distracting the baby—work reasonably well. Many effective soothing techniques involve moderately intense and continuous or repetitive stimulation. One very common soothing technique is swaddling, which involves wrapping a young baby tightly in cloths or a blanket,

thereby restricting limb movement. The tight wrapping provides a constant high level of tactile stimulation and warmth. This technique is practiced in cultures as diverse and widespread as those of the Navajo and Hopi in the American Southwest (Chisholm, 1983), the Quechua in Peru (Tronick, Thomas, & Daltabuit, 1994), and rural villagers in Turkey (Delaney, 2000). It is also increasing in popularity in North America; numerous popular baby-carrying devices compress the infant close to the caregiver’s body, leaving the caregiver’s hands free for daily activities. swaddling a soothing technique, used in many cultures, that involves wrapping a baby tightly in cloths or a blanket

Carrying infants close to the parent’s body results in less crying. Many North American parents are now emulating the traditional carrying methods of societies like the Quechua in Peru. Swaddling should be avoided when babies are lying on their stomachs or sides, due to increased risk for SIDS (Pease et al., 2016).

One question that often concerns parents is whether or not to respond to their infant’s signals of distress. Will quick and consistent

supportive responses reward the infant for fussing and crying and hence increase these behaviours? Or will a rapid response give the infant a sense of security that leads to less fussing and crying? The literature suggests that both perspectives are valid. In one classic study, Bell and Ainsworth (1972) found that prompt responding to infant cries predicted less crying several months later. Yet in another classic study, Hubbard & van IJzendoorn (1991) found that infants whose cries were ignored during the first 9 weeks cried less during the next 9 weeks. While most research in this area has focused on Western families, there are substantial cultural differences in parental responding that may influence these patterns. For example, mothers in the rural island communities of Fiji are more likely to rapidly respond to their infant’s negative facial displays of affect than are urban mothers in the United States (Broesch et al., 2016). As with many aspects of parenting, there is likely not one “right” answer to the question of how and when to respond to infant distress. Cultural norms and individual differences among infants jointly influence families’ preferred responses to parenting challenges.

Colic No matter how or how much their parents try to soothe them, some infants are prone to excessive, inconsolable crying for no apparent reason during the first few months of life, a condition referred to as

colic. Indeed, one of your authors was a colicky baby who resisted being held. The causes of colic are unknown and may include allergic responses to the mother’s diet (ingested via breast milk), formula intolerance, immature gut development, and/or excessive gassiness. Unfortunately, colic is not a rare condition: around 18% of young Canadian infants—and their parents—suffer from it (Wolke et al., 2017). Fortunately, it typically ends by about 3 months of age and has no long-term effects. One of the best things parents with a colicky infant can do is seek social support, which can provide relief from the stress, frustration, and sense of inadequacy they may feel because they are unable to relieve their baby’s distress. colic excessive, inconsolable crying by a young infant for no apparent reason

Coping with Colic

Negative Outcomes at Birth Neonatal caregivers worldwide use an evaluation tool called the Apgar score to quickly assess the health of newborn infants immediately following birth. A cumulative score is derived from ratings on skin tone, pulse rate, facial responses (typically grimacing), arm and leg activity, and breathing strength. Perfect scores are rare, reflecting the traumatic effect that even a normal birth can have on the newborn, but a consistently low score can indicate serious health problems. Apgar score method for evaluating the health of the newborn immediately following birth based on skin tone, pulse rate, facial response, arm and leg activity, and breathing

Parenting in Infancy and Toddlerhood

Although most clinically recognized pregnancies in an industrialized society result in the full-term birth of a healthy baby, sometimes the outcome is less positive. The worst result, obviously, is the death of an infant. A much more common negative outcome is low birth weight, which can have long-term consequences.

Infant Mortality Infant mortality—death during the first year after birth—is now relatively rare in the industrialized world, thanks to decades of improvements in public health and general economic levels. In Canada, the 2018 infant mortality rate was estimated to be 4.5 deaths per 1000 live births (Central Intelligence Agency [CIA], 2018).

infant mortality death during the first year after birth

Although the Canadian infant mortality rate is declining over time in absolute terms, it is high compared with that of other industrialized nations. The relative ranking of Canada has generally gotten worse over the past several decades, partially because the infant mortality rates in many other countries have had a higher rate of improvement and partially because of a wide variation in birth registration practices across countries. In Canada, the United States, Wales, and England, a live birth is registered if the infant shows any signs of life at birth, regardless of birth weight or gestational age. In contrast, other countries use other criteria to register a live birth, such as gestational age (e.g., >22 weeks), birth weight (e.g., >500 g), or length of survival (e.g., at least 24 hours after birth; Deb-Rinker et al., 2015). The rates of infant mortality in Canada are starkly different for different provinces and territories. For instance, infants born in Nunavut and the Northwest Territories (NWT) are two to three times more likely to die before their first birthday as infants born in British Columbia and Nova Scotia. Indeed, the infant mortality rate for Nunavut and NWT is similar to the rates observed in many developing countries. Why do so many babies die in the Canadian North, given that we are a highly developed country? There are many reasons having to do with limited access to health care, a greater prevalence of macrosomic births (births of very large babies), and higher rates of poverty (Luo et al., 2012).

In less developed countries, especially those suffering from a breakdown in social organization due to war, famine, or persistent extreme poverty, the infant mortality rates can be staggering. In Afghanistan and Somalia, for example, roughly 1 of every 10 infants dies before age 1 (CIA, 2018).

Low Birth Weight Most Canadian newborns weigh between 2500 grams and 4500 grams. Infants who weigh less than 2500 grams at birth are considered to be of low birth weight (LBW). Many LBW infants are premature, or preterm; that is, they are born at 37 weeks or earlier after conception. About 7.8% of babies born in Canada between 2015 and 2017 were premature (Statistics Canada, 2019a). Other LBW infants are referred to as small for gestational age: they may be either preterm or fullterm, but they weigh substantially less than is normal for their gestational age, which is based on weeks since conception. low birth weight (LBW) a birth weight of less than 2500 grams premature any child born at 37 weeks after conception or earlier (as opposed to the normal term of 38 weeks) small for gestational age babies who weigh substantially less than is normal for whatever their gestational age

Afghanistan has the highest infant mortality rate in the world (CIA, 2018). Among the causes are extreme poverty, poor nutrition, and poor sanitation. The great majority of the population lacks access to clean water, leading to a great many infant deaths related to dysentery, severe diarrhea, and other illnesses.

Low Birth Weight in India

In 2017, 6.5% of babies born in Canada were LBW (Statistics Canada, 2019a). As a group, LBW newborns have a heightened level of medical complications, as well as higher rates of neurosensory deficits, more frequent illness, lower IQ scores, and lower educational achievement. Very LBW babies (VLBW; those weighing less than 1500 grams) are particularly vulnerable; these infants accounted for around 1% of live births in Canada (Statistics Canada, 2019b). There are numerous causes of LBW and prematurity, including several discussed in the section on teratogens: smoking, alcohol, and

environmental pollutants such as lead and mercury. In some rapidly developing countries, such as China, high levels of airborne pollution have been linked to both LBW and preterm birth, likely due to impaired oxygen transport across the placenta (Fleischer et al., 2015). Another cause is the skyrocketing rate of twin, triplet, and other multiple births as a result of the development of increasingly successful treatments for infertility. (The use of fertility drugs typically results in multiple eggs being released during ovulation; the use of in vitro fertilization [IVF] usually involves the placement of multiple laboratory-fertilized embryos in the uterus.) Between 1991 and 2017, the rate of multiple births in Canada increased from 2% to 3.1% (Statistics Canada, 2019c). This is a concern because the rates of LBW among multiples are quite high: 53.8% of multiples weigh less than 2500 grams (Statistics Canada, 2019b). The numbers for higherorder births (triplets and up) have also increased dramatically in recent years. This is a concern because the rates of LBW among multiples are quite high: 55% for twins and higher than 95% for triplets and above (Martin, Hamilton, Osterman et al., 2018).

The Dionne quintuplets, born in 1934 in a farmhouse in Ontario, are the first known quintuplets to have survived infancy. The identical sisters were born two months prematurely. During infancy, the government removed them from their family and placed them in a specially built hospital with an observation area for tourists. In the 1930s, they were the biggest tourist attraction in Canada. In 1998, the Ontario government formally apologized to the surviving sisters.

Long-term outcomes As a group, children who were LBW infants have a higher incidence of developmental problems: the lower their birth weight, the more likely they are to have persistent difficulties. For example, 8-year-old Australian children who were born LBW showed a greater incidence of sensory impairments, poorer academic achievement, and more behaviour problems than their term-birth peers (Hutchinson et al.,

2013). Other studies suggest links between VLBW and childhood psychiatric issues, especially those involving inattention, anxiety, and social difficulties (e.g., ADHD, autism; Johnson & Marlow, 2011). The hypothesized pathways between LBW and these negative outcomes include white-matter reduction, ventricular enlargement, and other abnormal brain development outcomes. However, it is important to note that these comparisons often confound SES with birth-weight status. For example, in the aforementioned study by Hutchinson and colleagues (2013), the sample of term-birth families had higher educational attainment and employment status than the preterm sample. Indeed, a German study demonstrated that the strongest predictor of outcomes for VLBW infants is maternal education (Voss et al., 2012). The authors concluded that special services and additional support may be especially important for families of at-risk infants with less educational background. The good news is that for the majority of LBW children, the negative effects of their birth status gradually diminish, generally ending up within the normal range on most developmental measures. Figure 2.21 depicts a particularly striking example (Teoh et al., 2006). Indeed, one follow-up study of extremely LBW infants (G

Medium

Source

Size

Motor Abilities Physical strength

Childhood

Thomas & French, 1985

Adolescence

Running speed

Childhood

B>G

B>G

Very

Thomas & French,

large

1985

Medium

Thomas & French, 1985

Adolescence

B>G

Very

Thomas & French,

large

1985

G>B

Small

Voyer & Voyer, 2014

Achievement and Test Performance Overall school grades

Childhood and adolescence

Overall verbal abilityii

Childhood

G≥B

Trivial

Hyde & Linn, 1988

Reading achievementii

Childhood

G>B

Small

Nowell & Hedges,

1998; Reilly, 2012 Writing achievementii

Childhood

G>B

Medium

Nowell & Hedges, 1998

Spatial ability (mental

Childhood

rotation and spatial

and

perception)

adolescence

Math achievementii

Childhood

B>G

Small

Voyer, Voyer, & Bryden, 1995

B=G

None

Lindberg et al., 2010

B>G

Trivial

Reilly, Neumann, & Andrews, 2015

Adolescence

Life sciences achievementii

Adolescence

B>G

Small

Lindberg et al., 2010

B>G

Trivial

Reilly et al., 2015

B=G

None

Halpern et al., 2007; Lindberg et al., 2010; Reilly et al., 2015

Physical sciences achievementii

Adolescence

B>G

Small

Halpern et al., 2007; Lindberg et al., 2010; Reilly et al., 2015

Gender Stereotyping

Childhood

B>G

Small

Signorella, Bigler, & Liben, 1997

Gender-Typed Play Preference for feminine-

Childhood

G>B

Large

Todd et al., 2017

Childhood

B>G

Large

Todd et al., 2017

Childhood

B>G

Largeiii

DiPietro, 1981

stereotyped toys Preference for masculinestereotyped toys Rough-and-tumble play Ability Beliefs

Athletic self-concept

Childhood

B>G

Small

and

Wilgenbusch & Merrell, 1999

adolescence Verbal self-concept

Childhood

G>B

Small

and

Wilgenbusch & Merrell, 1999

adolescence Math self-concept

Childhood

B>G

Small

and

Wilgenbusch & Merrell, 1999;

adolescence C. Huang, 2013 Science self-concept

Childhood

B>G

and

Trivial to

Weinburgh, 1995;

small

Sikora & Pokropek,

adolescence Computing self-concept

2012

Childhood

B=G

None

Whitley, 1997

Adolescence

B>G

Medium

Whitley, 1997

Infancy

B>G

Small

Eaton & Enns, 1986

Childhood

B>G

Medium

Eaton & Enns, 1986

Childhood

G>B

Small to

Else-Quest et al.,

large

2006

Small

Byrnes, Miller, &

Personality Traits Activity level

Self-control

Risk taking

Childhood

B>G

Schafer, 1999 Interpersonal Goals Dominance and control goals

Childhood

B>G

Smalliii

and

Rose & Rudolph, 2006

adolescence Intimacy and support goals

Childhood and adolescence

G>B

Mediumiii

Rose & Rudolph, 2006

Communication with Peers Talkativeness

Childhood

G=B

None

Leaper & Smith, 2004

B>G

Small

Leaper & Smith, 2004

G>B

Small

Leaper & Smith, 2004

G>B

Smalliii

Rose & Rudolph,

and adolescence Directive speech

Childhood and adolescence

Collaborative speech

Childhood and adolescence

Self-disclosure

Childhood

2006 Adolescence

G>B

Mediumiii

Rose & Rudolph, 2006

Aggression Direct physical aggression

Childhood

B>G

and

Medium

Archer, 2004; Card et

to large

al., 2008

Small

Archer, 2004; Card et

adolescence Direct verbal aggression

Childhood

B>G

and

al., 2008

adolescence Indirect aggression

Childhood

G≥B

Trivial

Card et al., 2008

and adolescence iB indicates cisgender boys; G indicates cisgender girls. iiAchievement based on performance on standardized tests. iiiEffect size not based on a meta-analysis but refers either to magnitude of difference seen in a single study or trend from a few studies summarized in the source.

Because statistically significant gender differences in cognitive abilities and social behaviours are often in the small range of effect sizes, Janet Hyde (2005) has advocated for “the gender similarities hypothesis.” She argued that, when comparing girls and boys, it is important to appreciate that similarities far outweigh differences on most attributes. Later in the chapter, we review many of the topic areas addressed in Table 15.1. When discussing these research findings, we will note whether the effect size of any average gender difference in behaviour or cognition is trivial, small, medium, or large. Keep in mind, however, that even when there is a large average difference on any particular measure, many cisgender girls and boys are similar to one another. Also, some members of the group with the lower average exceed some members of the group with the higher average (see Figure 15.1). For example, there is a very large average gender difference in adult height: men are generally taller than women. At the same time, many women and men are the same height, and some women are taller than the average man.

REVIEW QUESTIONS How do concepts like gender nonconformity and nonbinary gender identity challenge assumptions about child development that you have learned about up to this point in the course? How could these concepts change your thinking about the study of child development?

Theoretical Approaches to Gender Development Researchers variously point to the influences of biological, cognitivemotivational, and cultural factors on gender development. First, biological differences between females and males — including the influence of sex hormones and brain structure differences — may partly account for average gender differences in some behaviours. Second, cognition and motivation — learning gender-typed roles through observation and practice — can shape children’s gender development. As highlighted in cognitive-motivational explanations, boys and girls are systematically provided different role models, opportunities, and incentives for gender-typed behaviour by parents, teachers, peers, and the media. Finally, cultural factors, including the relative status of women and men in society, may shape children’s gender development. As you will see in this section, there is empirical evidence for the role of each type of influence in certain behaviours. Indeed, it is likely that most aspects of gender development result from the complex interaction of all three sets of factors.

Biological Influences Some researchers interested in biological influences on development

emphasize possible ways that gender differences in behaviour may be based partly on sex-related genetic predispositions that emerged during the course of human evolution. Other biologically oriented researchers focus more directly on identifying hormonal factors and differences in brain functioning as possible influences on gender differences in behavioural development. Before proceeding to review some biological approaches, we want to acknowledge that trying to distinguish between biological and nonbiological influences on development is potentially misleading. Notably, all behaviour and thinking are biologically based because they depend on the functioning of your brain and other organs, and all experiences lead to changes in the brain’s organization (e.g., the connection of new synapses to create new memories). Nonetheless, when we refer to biological or physiological influences in this discussion, it usually refers to ways that sex-related variations in the physical development of the brain and the rest of the body may contribute to gender development.

Neuroscience Approaches Researchers who take a neuroscience approach focus on testing whether and how genes, hormones, and brain functioning relate to variations in gender development (Berenbaum, 2018; Hines, 2013). Some neuroscience researchers also frame their work in terms of an evolutionary psychology perspective (Geary, 2004, 2010).

Genes As explained in the previous section, biological sex is determined by whether a person has XX (genetically female) or XY (genetically male) chromosome pairs. (There are rare conditions when a person may have a missing or an extra sex chromosome; see Box 3.1.) Some psychologists argue that females and males have genetic dispositions toward different behaviours, such as men being aggressive and women being nurturing, because they helped women and men successfully mate and protect their offspring during evolution (Benenson, 2014; Buss, 2014; Geary, 2010; Kenrick, Trost, & Sundie, 2004; see Chapter 9 for more on evolutionary theories of development). Although no research with humans has provided evidence for direct genetic influences on gender-typed behaviour, research with rodents indicates some relevant effects (Hines, 2013). For instance, studies with mice indicate links between genes on the Y chromosome and later levels of some aspects of aggressive and parenting behaviours (Hines, 2013). However, to reiterate, there are no known studies documenting direct links between genes and gender-typed behaviour in humans. As described next, there is indirect evidence of possible sex-linked genetic effects mediated by the production of hormones.

Amongst the most consistent average differences seen across cultures are cisgender girls’ and boys’ preferences for gender-typed play, as well as higher average

incidences of physical aggression amongst cisgender boys than girls. However, there is variation within each gender in these trends. Also, transgender children generally show patterns of play and social behaviour that is more gender-typed for their selfidentified gender than their assigned gender.

Hormones and brain functioning In the study of gender development, much attention has been paid to the possible effects of androgens, a class of steroid hormones that includes testosterone. Androgens are produced in the bodies of genetic females and males. As discussed in Chapter 2, around the end of the first trimester of prenatal development, the testes of genetic males increase production of particular hormones, including androgens, that lead to the formation of male genitalia in genetic males; in the absence of high levels of these hormones, female genitalia are formed in genetic females. As we will discuss later in this chapter, variations in exposure or reaction to particular hormones during the prenatal period of genetic females and males can influence the development of their sexual anatomy. androgens class of steroid hormones that normally occur at slightly higher levels in males than in females and that affect physical development and functioning from the prenatal period onward

Androgens and other hormones can also have organizing or activating influences on the nervous system. Organizing influences occur when certain sex-linked hormones affect brain differentiation and

organization during prenatal development or at puberty. For example, sex-related differences in prenatal androgens may influence the organization and functioning of the nervous system; in turn, this may be related to later average gender differences in certain play preferences (see Hines, 2013). Activating influences occur when fluctuations in sex-linked hormone levels influence the contemporaneous activation of certain brain and behavioural responses (Hines, 2013). For instance, the body increases androgen production in response to perceived threats, with possible implications for gender differences in aggression. These influences are discussed later in the chapter. organizing influences potential result of certain sex-linked hormones affecting brain differentiation and organization during prenatal development or at puberty activating influences potential result of certain fluctuations in sex-linked hormone levels affecting the contemporaneous activation of the nervous system and corresponding behavioural responses

Brain structure and functioning Adult male and female brains show some small average differences in physical structure (Hines, 2004, 2013). However, these differences do not appear to result in any clear advantage to cognitive performance (Halpern, 2012). As noted in Box 15.1, there is a great deal of overlap between female and male brains, and no brain structures are unique to one sex (Hyde et al., 2019). Furthermore, an

important limitation of research documenting sex differences in brain structure is that it is mostly based on brain-imaging studies performed on adults. Given the continual interaction of genes and experience during brain development, it is unclear to what extent any average sex differences in adult brain structure or functioning are due to genetic or environmental influences. It is also unclear to what extent these small average differences in brain structure determine any average gender differences in ability and behaviour (Halpern, 2012).

The Boy Who Was a Girl

Cognitive and Motivational Influences Cognitive theories of gender development emphasize the ways that children learn gender-typed attitudes and behaviours through observation, inference, and practice. According to these explanations, children form expectations about gender that guide their behaviour. Cognitive theories stress children’s active selfsocialization: individuals use their beliefs, expectations, and preferences to guide how they perceive the world and the actions they choose (Tobin et al., 2010). Self-socialization occurs in gender development when children seek to behave in accord with their gender identity as a girl or a boy — or possibly as transgender, gender fluid, or agender. However, cognitive theories also emphasize the role of the environment — the different role models, opportunities, and incentives that girls and boys might experience. self-socialization active process during development whereby children’s cognitions lead them to perceive the world and to act in accord with their expectations and beliefs

We next discuss four pertinent cognitive theories of gender development: cognitive developmental theory, gender schema theory, social identity theory, and social cognitive theory. As you will see, these theories complement one another in many respects (see Leaper, 2011). Some researchers have proposed theoretical models that weave together some of these approaches (for some examples, see the discussion of Integrative Theoretical Approaches later in this

section).

Cognitive Developmental Theory Lawrence Kohlberg’s (1966) cognitive developmental theory of gender-role development reflects a Piagetian framework (reviewed in Chapter 4). Kohlberg proposed that children actively construct knowledge about gender in the same ways that Piaget theorized children construct knowledge about the physical world. There are two distinctive contributions of Kohlberg’s theory. First, he posited that children actively seek to understand the meaning of gender through observing and interacting with the world around them. (As described later, this feature is shared by other cognitive theories, including gender schema theory and social cognitive theory.) Second, Kohlberg proposed cognitive developmental changes in children’s understanding of gender during early childhood. Kohlberg maintained that children’s understanding of gender involves a three-stage process that occurs between approximately 2 and 6 years of age. First, by around 30 months of age, young children acquire a gender identity, categorizing themselves usually as either a girl or a boy (Fagot & Leinbach, 1989). However, they do not yet realize that gender is permanent. For example, young children may believe that a girl could grow up to be a father (Slaby & Frey, 1975). The second stage, which begins at about 3 or 4 years of age, is gender stability, wherein children come to realize that gender remains the

same over time (“I’m a girl, and I’ll always be a girl”). However, they are still not clear that gender is independent of superficial appearance and thus believe that a boy who has put on a dress and now looks like a girl has indeed become a girl. gender identity self-identifying as a boy or a girl (or possibly as both or possibly neither) gender stability awareness that gender remains the same over time

The basic understanding of gender is completed in the third stage, around 6 years of age, when children achieve gender constancy, the understanding that gender is invariant across situations (“I’m a girl, and nothing I do will change that”). Kohlberg noted that this is the same age at which children begin to succeed on Piagetian conservation problems (see Chapter 4), and he argued that both achievements reflect the same underlying thinking processes. Kohlberg maintained that children’s understanding that gender remains constant even when superficial changes occur is similar to their understanding that the amount of a substance is conserved even when its appearance is altered. For example, a ball of clay maintains the same volume after it has been mashed flat; in a similar manner, a girl remains the same gender after she gets her hair cut short and starts wearing baseball shirts. According to Kohlberg, once gender constancy is attained, children begin to seek out and attend to samegender models to learn how to behave (“Since I’m a girl, I should like to do girl things, so I need to find out what those are”).

gender constancy realization that gender is invariant despite superficial changes in a person’s appearance or behaviour

As predicted by cognitive theories, children learn a great deal about gender roles by observing other people. Television, movies, and video games provide many examples of gender stereotypes for both sexes.

Subsequent research has supported the idea that children’s understanding of gender develops in the sequence Kohlberg hypothesized and that the attainment of gender constancy occurs at more or less the same age as success on conservation problems. Some studies also indicate that acquiring gender constancy might increase the likelihood of some gender-typed behaviours (Martin et al., 2002; Halim & Ruble, 2010). That is, once most children

consolidate their understanding of gender, they tend to use their gender concepts to interpret the world. Gender schema theory, reviewed next, also addresses ways whereby attaining a concept of gender can affect children’s gender development. Kohlberg did not consider the possibility of children with transgender or nonbinary gender identities. Recent research studying 5-year-olds found that the gender identities of transgender children were equally as strong as those of cisgender children — transgender girls were similar to cisgender girls in their gender identities, while transgender boys were similar to cisgender boys (Olson & Gülgöz, 2018). This research challenges the belief that transgender children are confused in their gender identity. With regard to gender constancy, it was observed that transgender children were more likely than cisgender children to express the view that a person’s gender could sometimes change (Olson & Gülgöz, 2018). This is not surprising given transgender children’s own experience with gender identity. Interestingly, the cisgender siblings of the transgender children in this study were also more likely to believe a person’s gender could sometimes change — perhaps due to their own experience observing their transgender sibling.

Gender Schema Theory Gender schema theory is an alternative to Kohlberg’s explanation of children’s gender development (e.g., Liben & Signorella, 1980; Martin

& Halverson, 1981). In contrast to Kohlberg’s view that gender-typed interests emerge after gender constancy is achieved, gender schema theory holds that the motivation to enact gender-typed behaviour begins as soon as children can label other people’s and their own gender — in other words, usually by about 3 years of age (see Martin et al., 2002), which is younger than when gender constancy is attained. According to gender schema theory, children’s understanding of gender develops through their construction of gender schemas, which are mental representations that incorporate everything the child knows about gender. Gender schemas include memories of one’s own experiences with males and females, gender stereotypes transmitted directly by adults and peers (“boys don’t cry,” “girls play with dolls”), and messages conveyed indirectly through the media. Children use an ingroup/outgroup gender schema to classify other people as being either “the same as me” or not. The motivation for cognitive consistency leads them to prefer, pay attention to, and remember more about others of their own gender. As a consequence, an own-gender schema is formed, consisting of detailed knowledge about how to do things that are consistent with one’s own gender. Simply learning that an unfamiliar object is “for my gender” makes children like it more. Figure 15.2 illustrates how this process leads children to acquire greater knowledge and expertise with genderconsistent entities. gender schemas

organized mental representations (concepts, beliefs, memories) about gender, including gender stereotypes

FIGURE 15.2 Gender schema theory According to gender schema theory, children classify new objects and activities as “for boys” or “for girls.” They tend to investigate objects and activities that are relevant to their gender and to ignore those that are associated with the other gender.

Description The illustration starts at Girl and branches upward to Truck and downward to Doll. The arrow labeled, For whom? Points from Doll to For girls. The arrow labeled, For whom? Points from Truck to For boys. A downward dotted arrow points from For boys to Gender identity (I’m a girl). An upward arrow points from For girls to Gender identity (I’m a girl). A rightward down arrow labeled, So points from Gender identity (I’m a girl) to For me. A rightward up dotted arrow labeled, So points from Gender identity (I’m a girl) to Not for me. A rightward arrow labeled, Therefore, points from For me to a text titled, Ownsex schema, and reads, Approach; gather information; remember information. A rightward arrow labeled, Therefore, points from Not for me to Avoid; forget.

In one illustrative study that tested the impact of gender schemas on children’s information processing, researchers presented 4- to 9-yearolds with three boxes (Bradbard et al., 1986). Each box contained objects unfamiliar to the children, and each box was separately labelled as “boys,” “girls,” or “boys and girls/girls and boys.” The children spent more time exploring objects in boxes labelled for their own gender (or for both genders) than objects in the box labelled only for the other gender. One week later, not surprisingly, they remembered more details about the objects they had explored than

about the ones with which they had spent less time. Another observational study conducted in a preschool classroom demonstrated the influence of same-gender peers in determinations of gender-appropriate behaviour. Boys approached toys that were being played with primarily by boys and shunned those that seemed popular mainly with girls (Shell & Eisenberg, 1990). Gender schemas are also responsible for biased processing and remembering of information about gender. Consistent with the research described previously, studies show that children tend to remember more about what they observe from same-gender role models than from different-gender ones (see Blakemore, Berenbaum, & Liben, 2009; Martin et al., 2002). They are also more likely to accurately encode and remember information about story characters that behave in gender-consistent ways and to forget or distort information that is gender-inconsistent (Blakemore et al., 2009; Liben & Signorella, 1993; Martin et al., 2002). For example, in one study children were shown a series of pictures that included a combination of gender-typed images (e.g., a girl baking cookies) and cross-gendertyped images (e.g., a girl sawing wood) (Martin & Halverson, 1983). When they were later asked to recall the pictures, they showed a greater tendency to mistakenly recall cross-gender-typed images as gender-typed (e.g., remembering a picture of a girl sawing wood as a boy sawing wood) than the reverse (e.g., remembering a picture of a girl baking cookies as a boy baking cookies). This tendency to retain information that is schema-consistent and to ignore or distort

schema-inconsistent information helps to perpetuate gender stereotypes that have little or no basis in reality. Furthermore, this process can perpetuate thinking about gender as a dichotomous category. Liben and Bigler (2002) proposed that children use two kinds of filters when processing information about the world. One is a gender schema filter (“Is this information relevant for my gender?”) and the other is an interest filter (“Is this information interesting?”). When encountering a new toy, for example, children might decide that it is something for girls or for boys and thus explore or ignore the toy on the basis of their gender schema filter (as depicted in Figure 15.2). However, Liben and Bigler noted that children sometimes find a new toy attractive without initially evaluating its appropriateness for their gender. In these instances, they use their interest filter to evaluate information. In turn, children sometimes use their interest filter to modify their gender schemas (“If I like this toy, it must be something that is okay for my gender”). Liben and Bigler’s modification to gender schema theory helps to account for findings indicating that children are often inconsistent in their gender-typed interests (Liben & Bigler, 2002; Tobin et al., 2010). (For example, they are often more traditional in some areas than others.) It also allows for the fact that some children actively pursue certain cross-gender-typed activities simply because they enjoy them. gender schema filter initial evaluation of information as relevant for one’s own gender

interest filter initial evaluation of information as being personally interesting

Recent research finds that some (but not all) children have intense interests in particular toys, objects, or activities in early childhood. For some children, these intense interests are gender-typed, such as when a girl displays a strong interest in wearing frilly dresses and princesses or a boy demonstrates intense interest in dinosaurs or mechanical toys (DeLoache, Simcock, & Macari, 2007; Halim et al., 2014; Johnson et al., 2004). In these cases, their interests are compatible with gender-stereotyped expectations. However, some other children have intense interests in cross-gender-typed toys and activities (VanderLaan et al., 2015), such as a boy with strong interest in dress-up play or a girl with a strong preference for physical play. In these cases, the interest filter may override the gender schema filter (Leaper, 2018). That is, these children may decide to engage in the toy or activity even though they recognize it conflicts with social expectations for their assigned gender. Moreover, if the discrepancy between gender-role pressures and strong personal interests is too great, some of these children may come to identify with a more compatible gender category (see Leaper, 2018). Although gender schemas are resistant to change, they can be modified in many children through explicit instruction and encouragement. Such an approach was demonstrated by Bigler and Liben, who created a cognitive intervention program in which elementary school children learned that a person’s interests and

abilities (but not gender) are important for the kind of job that the person could have (Bigler & Liben, 1990; Liben & Bigler, 1987). (The children were encouraged to see, for instance, that if Mary was strong and liked to build things, a good job for her would be to work as a carpenter.) Children who participated in this week-long program showed decreased gender stereotyping and also had better memory for gender-inconsistent stimuli (such as a picture of a girl holding a hammer). However, a limitation of interventions aimed at reducing gender stereotyping is that their impact typically fades once the intervention ends (Bigler, 1999). That is, children gradually revert back to their old gender stereotypes. Given the pervasiveness of gender stereotyping in children’s everyday lives, cognitive interventions need to be sustained to have a longer-lasting effect.

Children’s stereotyped beliefs about gender can be changed through cognitive intervention programs. Many children who learned that a person’s interests and abilities were important for the kind of job the person could have showed significant reductions in gender stereotyping.

Social Cognitive Theory Kay Bussey and Albert Bandura (1999, 2004) proposed a theory of gender development based on Bandura’s (1986, 1997) social cognitive theory (see pages 322–323). The theory depicts a triadic model of reciprocal causation amongst personal factors, environmental factors, and behaviour patterns. Personal factors include cognitive, motivational, and biological processes. Although the theory acknowledges the potential influence of biological factors, it primarily addresses cognition and motivation. Amongst its key features are sociocognitive modes of learning and self-regulatory processes. According to social cognitive theory, learning occurs through tuition, enactive experience, and observation. Tuition refers to direct teaching during gender socialization, such as a father showing his son how to throw a baseball, or a mother teaching her daughter how to change a baby’s diaper. Enactive experience occurs when children learn to guide their behaviour by taking into account the reactions their past behaviour has evoked in others. For instance, girls and boys usually receive positive reactions for behaviours that are gender-

stereotypical and negative reactions for behaviours that are counterstereotypical (Bussey & Bandura, 1999; Harris, 1995; Witt, 2000); they tend to use this feedback to regulate their behaviour in relevant situations. Finally, observational learning — the most common form of learning — occurs through seeing and encoding the consequences other people experience as a result of children’s own actions. Thus, children learn a great deal about gender simply through observing the behaviour of their parents, siblings, teachers, and peers. They also learn about gender roles through media such as television, films, the Internet, and video games (see Box 15.2). tuition learning through direct teaching enactive experience learning to take into account the reactions one’s past behaviour has evoked in others observational learning learning through watching other people and the consequences others experience as a result of their actions

BOX 15.2 APPLICATIONS Where Are Spongesally Squarepants and Curious Jane? Differences in the gender representation of TV, movie, and video game characters have been well documented, are very large, and have changed surprisingly little over the past four decades (Geena Davis Institute on Gender in Media, 2019; Leaper et al., 2002; Scharrer, 2013; Signorielli, 2012). Fictional characters in TV, movies, and other electronic media are commonly depicted in gender-stereotypical ways in terms of behaviour, roles, and appearance (Kirsch & Murnen, 2015; Signorielli,

2012; Walsh & Leaper, in press). For example, male characters are disproportionally portrayed as heroes, powerful, aggressive, and active; in contrast, female characters are more often shown as victims needing saving, nurturing, and concerned with romance and their appearance (Kirsch & Murnen, 2015; Signorielli, 2012; Walsh & Leaper, in press). Also, one content analysis found that boys in children’s TV programs were commonly depicted as objectifying girls for their appearance, whereas girls were shown to be self-objectifying and “egostroking” of boys (Kirsch & Murnen, 2015). Another striking trend is that male characters are typically overrepresented in television programs aimed at children, teens, and adults (Geena Davis Institute on Gender in Media, 2019). For example, according to one analysis of TV and movie characters, the prevalence of female characters was 28% in family films, 39% in prime-time television programs, and 31% in children’s shows (Smith et al., 2013a; also see Leaper et al., 2002; Walsh & Leaper, in press, for similar results). Portrayals of sexual minority, transgender, nonbinary, or gender-fluid characters remain rare in television or other mass media aimed at children (Kelso, 2015). However, in recent years, there have been a few exceptions, including the cartoons Adventure Time and Steven Universe (Jane, 2015). Although television may provide limited representations of gender-nonconforming youth, the Internet offers a wide variety of sites that are supportive of LGBTQ youth as they explore their identities (Craig et al., 2015; Drabbie, Keatley, & Marcelle, 2006). However, all forms of media (including television, movies, and the Internet) also provide misleading and negative messages (Drabbie et al., 2006). From the perspectives of cognitive-motivational theories, the fact that children have so much exposure to highly stereotyped gender models matters a great deal. For example, children who watch a lot of televised and online programs have more highly stereotypic beliefs about males and females and prefer gender-typed activities to a greater extent than do children who are less avid viewers (Oppliger, 2007). Furthermore, several experimental studies have established a causal relation between TV viewing and gender stereotyping (Oppliger, 2007). For

instance, when children are randomly assigned to watch shows with either genderstereotyped or neutral content, they are more likely to endorse gender stereotypes themselves after watching the gender-stereotyped programs. Children are, of course, exposed to media other than television, but similar gender disparities have been documented in those areas as well. For example, children’s books still contain far more male than female characters, and characters of both sexes are often portrayed in gender-stereotypic ways. Males tend to be depicted as active and effective in the world at large, whereas females are frequently passive and prone to problems that require the help of males to solve (DeWitt, Cready, & Seward, 2013; Diekman & Murnen, 2004; Gooden & Gooden, 2001; Hamilton et al., 2006). Thus, although it is now possible to find more counter-stereotypical role models in children’s media, most female and male characters continue to be gender-stereotyped. Computer and online games are beginning to displace television as the primary source of children’s media entertainment. Unfortunately, like television programming, many computer games portray gender in highly stereotyped ways (Downs & Smith, 2010; Scharrer, 2013). Most characters are male, and they commonly engage in highly aggressive acts; and when female characters are present, they are commonly portrayed in highly sexualized ways (e.g., Lara Croft in Tomb Raider).

Computer and online games are beginning to displace television as the primary source of children’s media entertainment. Unfortunately, like television programming, many computer games portray the sexes in highly stereotyped ways.

Observational learning of gender-role information involves four key processes: attention, memory, production, and motivation. To learn new information, it must, of course, be attended to (noticed) and then stored in memory. As we have noted, children often notice information that is consistent with their existing gender stereotypes. (This is the main premise of gender schema theory.) Next, children need to practice the behaviour (i.e., production) they have observed (assuming that the behaviour is within their capabilities). For example, cisgender girls and boys tend to practice different behaviours in play and recreation (Todd et al., 2017; Weisgram &

Dinella, 2018). Finally, children’s motivation to repeat a gender-typed behaviour will depend on the incentives or disincentives they experience relative to the behaviour. These sanctions can be experienced either directly (as when a parent praises a daughter for helping to prepare dinner) or indirectly (as when a boy observes another boy getting teased for playing with a doll). Over time, external sanctions are usually internalized as personal standards and become self-sanctions that motivate and regulate behaviour. According to social cognitive theory, gender development becomes a process of self-regulations (or self-socialization), whereby children monitor their behaviour and evaluate how well it matches personal standards. After making this evaluation, children may feel pride or shame, depending on whether they meet their standards. When individuals experience positive self-reactions for their behaviour, they gain the sense of personal agency referred to as self-efficacy. Selfefficacy can develop gradually through practice (as when a son regularly plays catch with his father), through social modelling (as when a girl observes a female friend do well in math and thinks that maybe she could do well herself), and by social persuasion (as when a coach gives a pep talk to push the boys’ performances on the soccer field). Researchers consistently find a strong relation between feelings of self-efficacy and motivation. For example, self-efficacy in math predicts the likelihood of girls as well as boys to take advanced math courses (Stevens et al., 2007).

Social Identity Theory Henri Tajfel and John Turner’s (1979) social identity theory addresses the influence of group membership on people’s self-concepts and behaviour with others. Developmental psychologists have applied the theory to understand how group processes contribute to children’s socialization and to highlight the importance of gender as a social identity in children’s development (e.g., Bigler & Liben, 2007; Harris, 1995; Leaper, 2000; Nesdale, 2007; Powlishta, 1995). Indeed, gender may be the most central social identity in most children’s lives because it is used to organize social life in every culture (Bem, 1993). Children’s commitment to gender as a social identity is most readily apparent through their primary affiliation with same-gender peers (Leaper, 1994; Maccoby, 1998). Two influential processes that occur when a person commits to an ingroup are ingroup bias and ingroup assimilation. Ingroup bias refers to the tendency to evaluate individuals and characteristics associated with the ingroup more positively than or as superior to those associated with the outgroup. For example, Kimberly Powlishta (1995) observed that children showed same-gender favouritism when rating peers on likeability and favourable traits. Ingroup bias is related to the process of ingroup assimilation, whereby individuals are socialized to conform to the group’s norms. That is, peers expect ingroup members to demonstrate the characteristics that define the ingroup. Children anticipate ingroup approval for preferring same-

gender peers and same-gender-typed activities, as well as for avoiding other-gender peers and cross-gender-typed activities (Banerjee & Lintern, 2000; Martin et al., 1999). As a result, children tend to become more gender-typed in their preferences as they assimilate into their same-gender peer groups (Martin & Fabes, 2001). ingroup bias tendency to evaluate individuals and characteristics of the ingroup more positively than or as superior to those of the outgroup ingroup assimilation process whereby individuals are socialized to conform to the group’s norms, demonstrating the characteristics that define the ingroup

A corollary of social identity theory is that the characteristics associated with a high-status group are typically valued more than are those of a low-status group. In male-dominated societies, masculinestereotyped attributes such as assertiveness and competition tend to be valued more highly than feminine-stereotyped attributes such as affiliation and nurturance (Feinman, 1981; Wood & Eagly, 2002). Related to this pattern is the tendency of cross-gender-typed behaviour to be more common amongst girls than amongst boys. Indeed, masculine-stereotyped behaviour in a girl can sometimes enhance her status, whereas feminine-stereotyped behaviour in a boy typically tarnishes his status (see Feinman, 1981; Leaper, 1994). Social identity theory helps to explain why gender-typing pressures tend to be more rigid for boys than for girls (Leaper, 2000). Members of high-status groups, for example, are usually more invested in

maintaining group boundaries than are members of low-status groups. In most societies, males are accorded greater status and power than are females (Wood & Eagly, 2012). Consistent with social identity theory, boys are more likely than girls to initiate and maintain role and group boundaries (Fagot, 1977; Sroufe et al., 1993). Boys are also more likely to endorse gender stereotypes (Rowley et al., 2007) and to hold sexist attitudes (Brown & Bigler, 2004). Of course, gender is not the only social identity that shapes people’s lives. As discussed in Chapter 11, many people identify with social groups based on race/ethnicity, religion, sexual orientation, social class, club membership, and so forth. Moreover, developmental psychologists are increasingly trying to understand how the intersection of multiple identities affects a person’s experiences. This phenomenon is known as intersectionality (Cole, 2009; Mays & Ghavami, 2018). For instance, the expectations for a girl or a boy in a suburban upper-middle-class family may differ somewhat from the expectations in a poor or working-class family in an inner city. In the latter context, there may be more housework and childcare responsibilities assigned to girls in the home than would be seen in wealthier communities (Bornstein et al., 2016; Hilton & Haldeman, 1991). Also, in the poor inner-city environment, establishing one’s physical and emotional toughness may be more fundamental to boys’ gender identity than it would be in the suburbs; correspondingly, concerns with toughness may undermine boys’ academic motivation more often in these communities than in higher-income suburbs (Anderson, 1999; Farkas & Leaper, 2016). Furthermore, as highlighted

by the intersectionality approach, individuals can experience biases from multiple group identities (e.g., gender, ethnicity/race, sexual orientation, class, religion, and so on). When youth experience harassment and discrimination based on multiple group identities, it generally compounds the negative effects on their adjustment (Bucchianeri et al., 2014). intersectionality the interconnection of social identities such as gender, race, ethnicity, sexual orientation, and class, especially in relation to overlapping experiences of discrimination and disadvantage

Integrative Theoretical Approaches Most behaviours reflect the influences of physiological, cognitive, motivational, situational, and cultural processes over time. Hence, psychology theories tend to focus on one or a few of these processes. But there is room for increased synthesis across theories that are similar or complementary in their explanations (see Leaper, 2011). Two recent efforts in the developmental psychology of gender illustrate this theoretical synthesis: developmental intergroup theory and the gender self-socialization model. Rebecca Bigler and Lynn Liben’s developmental intergroup theory (DIT) integrates ideas from cognitive-developmental theory, gender schema theory, and social identity theory (Bigler & Liben, 2006, 2007). DIT, which was discussed in Box 15.1, highlights three key processes

that contribute to the development of stereotyping and prejudice based on a person’s gender (or other social identities): establishing the psychological salience of gender, categorizing individuals based on their gender, and developing stereotypes and prejudices based on this categorization. Bigler and Liben reviewed ways in which the psychological salience of gender is commonly established in people’s everyday lives. (Salience refers to how readily we notice something.) One way to increase the salience of gender is to make it a perceptually distinctive attribute about persons. Familiar examples include the uses of genderdifferentiated colours (pink versus blue), as well as hair and clothing styles. Another common practice is to use gender labels to categorize events in our daily lives. For example, in the English language, we are typically compelled to refer to others based on their gender through the use of gendered nouns (“girl,” “boy”) and pronouns (“he,” “she”). In other languages, such as Spanish and French, the nouns are also gendered as feminine or masculine (e.g., “ami” or “amie”). Also, many activities in children’s lives are organized by gender; these range from gender-designated bathrooms to gender-segregated sports teams to single-gender schools (Leaper, 2015a). To mitigate the psychological salience of gender, some psychologists argue for changes such as dressing children in gender-neutral clothing, using gender-neutral language, and avoiding practices that unnecessarily organize children’s activities based on gender (Bigler & Leaper, 2015;

Bigler & Liben, 2006, 2007; Leaper, 2000). Once the psychological salience of gender is established, the stage is set for stereotyping and prejudice. Bigler and Liben incorporate several cognitive processes previously addressed in cognitive developmental theory and social identity theory to explain how this occurs. For example, as articulated in social identity theory, this includes ingroup bias when people tend to favour characteristics associated with their own gender group (e.g., Powlishta, 1995). Another is known as essentialism, introduced in Chapter 7, which refers to the tendency to believe that members of a category (such as a gender group) share important qualities that make them distinct from other categories (or groups). Thus, children may view girls and boys as having inherently different traits and abilities. Another integrative theoretical model recently introduced is David Perry and his colleagues’ gender self-socialization model (GSSM), which bridges gender schema theory, social cognitive theory, social identity, and other theoretical approaches (Tobin et al., 2010). As with cognitive theories in general, the GSSM emphasizes how much of gender development is a process of self-socialization (Tobin et al., 2010). That is, children seek to discover their identities in relation to their understandings of the world around them. In turn, they often adapt their behaviour to match these understandings, as when they try to conform to expected norms for their gender.

In addition to incorporating ideas from gender schema theory and social identity theory, the GSSM builds on balanced identity theory from social psychology (Greenwald et al., 2002). The latter theory is based on the premise that individuals seek to attain cognitive consistency across their group identities (e.g., “I am a girl”), personalsocial attributes (e.g., “I like playing dolls”), and group-attribute beliefs (e.g., “Girls play with dolls”). This model is depicted in Figure 15.3.

FIGURE 15.3 Depiction of the Gender Self-Socialization Model (GSSM). The GSSM is based on the premise that children seek consistency across their group identities (e.g., “I am a girl”), self-concepts (“I like playing with dolls”), and group stereotypes (“Girls like dolls”).

(Information from Tobin et al., 2010)

Description Bidirectional arrows are in between the labels from top in clockwise direction as follows: Self; Attribute equals likes dolls, and Group equals girl. The text beside the bidirectional arrow in between Self and Attribute equals likes dolls reads, Self-concept (“I like dolls”). The text beside the bidirectional arrow in between Attribute equals likes dolls and Group equals girl reads, Stereotyped belief (“Girls like dolls”). The text beside the bidirectional arrow in between Group equals girl and Self reads, Group identity (“I am a girl”).

In their GSSM, Perry and his colleagues proposed three hypothesized ways that this balance tends to occur during gender development. First, the stereotype emulation hypothesis proposes that the more children identify with their gender ingroup, the more motivated they will be to adhere to the stereotypes for their gender ingroup. For example, if belonging to his same-gender peer group is important for a boy, then he might be especially prone to engage in the kinds of activities and behavioural styles expected amongst his peers. Second, the stereotype construction hypothesis specifies that children are apt to form generalized beliefs or stereotypes about their gender ingroup based on their own personal-social attributes. For instance, a child who likes dress-up play and identifies as a girl may assume playing dress-up is something that other girls like. Finally, the identity construction hypothesis states that children are more likely to identify with their gender ingroup when their own personal-social attributes match their stereotyped beliefs about their gender ingroup. For example, a boy may form a stronger gender identity if he likes playing sports and he also stereotypes sports as something for boys. This may strengthen a facet of gender identity known as felt gender typicality, or a sense of belonging to one’s gender ingroup. The GSSM may help us understand why some children do not identify with their assigned gender at birth (Leaper, 2018), as in the cases

noted earlier of children who have strong cross-gender-typed interests at an early age. When rejected for their gendernonconforming interests, perhaps some of these children find they do not belong in the gender group in which they were assigned. By extension, the GSSM implies that reducing cultural gender stereotypes about personal-social attributes will mean that children will not need to associate particular activities or subjects with a particular gender. Both DIT and GSSM are excellent illustrations of how different theories can be combined to provide a fuller picture of processes underlying children’s gender development. Both theories have already generated new research that is further expanding our understanding.

Cultural Influences The theoretical approaches we have discussed so far emphasize biological and cognitive-motivational processes involved in gender development. Complementing these approaches are theories that address the larger cultural and social-structural factors that can shape gender development (Best & Bush, 2016). More specifically, it is necessary to consider how gender inequalities in a society shape gender development (Leaper, 2000).

Bioecological Model As described in Chapter 9, Urie Bronfenbrenner’s bioecological model of human development differentiates amongst interconnected systems within the child (biological and cognitive processes) and in the child’s environment (see Figure 9.3). The environmental systems range from the microsystem (the immediate environment) to the macrosystem (the culture) and chronosystem (changes in the environment over the course of the child’s development) (Bronfenbrenner, 1979; Bronfenbrenner & Morris, 1998). A fundamental feature of the macrosystem is its opportunity structure, that is, the economic and social resources it offers and people’s understanding of those resources (Bussey & Bandura, 1999; Leaper, 2000; Ogbu, 1981; Wood & Eagly, 2002). Opportunities for members of a cultural community can vary depending on gender, income, and other factors, and they are reflected by the dominant adult roles within that community. According to the bioecological approach, child socialization practices in the family, peer group, classroom, and other facets of the child’s microsystem serve to prepare children for these adult roles. Thus, traditional gendertyping practices perpetuate as well as reflect the existing opportunity structures for women and men in a particular community at a particular time in history (Leaper, 2000; Whiting & Edwards, 1988; Wood & Eagly, 2002). opportunity structure

the economic and social resources offered by the macrosystem in the bioecological model, and people’s understanding of those resources

Campbell Leaper and his colleagues have highlighted how play activities provide young children with opportunities to practice particular social behaviours and cognitive abilities (Leaper, 1994, 2000; Leaper & Bigler, 2018). For example, domestic pretend play (“playing house”) provides children with contexts for practicing socioemotional skills, and playing with construction toys can help develop children’s spatial skills (Leaper & Bigler, 2018). When particular play activities are differentially encouraged in one gender more than another, however, there are corresponding differences in opportunity. In turn, this may lead to later differences in preferences, attitudes, and skills that influence the kinds of occupations they pursue or their functioning in close relationships (Leaper & Bigler, 2018). To the extent that family and occupational roles tend to be divided on the basis of gender, different behaviours are expected of women and men, as well as of girls and boys. In many countries, women have been traditionally underrepresented in politics, business, science, technology, and various other fields — a trend that continues in many societies today. In turn, girls are not expected to develop interests and skills that lead toward professions in those fields, which simply perpetuates girls’ exclusion from them. To the extent that children’s development is largely an adaptation to

their existing opportunities, changes in children’s macrosystems and microsystems can lead to greater gender equality (see Leaper, 2000). For example, increased academic and professional opportunities for girls have led to a dramatic narrowing of the gender gap in math and science within the past few decades (Halpern, 2012; Halpern et al., 2007). In summary, the bioecological model highlights how institutionalized roles impose both opportunities and constraints on people’s behaviour and beliefs in the home, schools, the labour force, and political institutions.

REVIEW QUESTION How do the various theories described in this section fit with your own concept of gender and your personal development?

Milestones in Gender Development Developmental psychologists have identified general patterns that tend to occur over the course of children’s gender development. As reviewed in this section, gender-related changes are evident in children’s physical, cognitive, and social development. Recall that these changes begin during prenatal development, when sexual differentiation occurs.

Infancy and Toddlerhood During their first year, infants’ perceptual abilities allow them to identify females and males. As we saw in Chapter 5, much research indicates that infants can detect complex regularities in perceptual information. Clothing, hairstyle, height, body shape, motion patterns, vocal pitch, and activities all tend to vary with gender, and these differences provide infants with gender cues. For example, habituation studies of infant perception and categorization indicate that by about 6 to 9 months of age, infants can distinguish males from females, usually on the basis of hairstyle (Intons-Peterson, 1988). Infants can also distinguish between male and female voices and make intermodal matches on the basis of gender (Blakemore et al., 2009; Martin et al., 2002). For instance, they expect a female voice to go with a female face rather than with a male

face. Although we cannot conclude that infants understand anything about what it means to be female or male, it does appear that older infants recognize the physical difference between females and males by using multiple perceptual cues.

Gender Development in Early Childhood

Shortly after entering toddlerhood, most children begin exhibiting distinct patterns of gender development. By the latter half of their second year, children have begun to form gender-related expectations about the kinds of objects and activities typically associated with males and females. For example, research by Diane Poulin-Dubois, Lisa Serbin, and their colleagues at Concordia

University in Montreal showed that 18-month-olds looked longer at a doll than at a toy car after viewing a series of female faces, and looked longer at a toy car than at a doll after habituating to male faces (Serbin et al., 2001). Another study with Canadian 24-month-olds found that counter-stereotypical matches of gender and action (e.g., a man putting on lipstick) led to longer looking times; it appeared that the children were surprised by the action’s gender inconsistency (Poulin-Dubois et al., 2002). These studies suggest that, at young ages, children are learning to form gender-stereotypical associations. The clearest evidence that children have acquired the concept of gender occurs around 2½ years of age, when they begin to label other people’s genders. For example, researchers might assess this ability by asking children to put pictures of children into “boys” and “girls” piles. Toddlers can also make simple gender matches, such as choosing a toy train over a doll when asked to point to the “boy’s toy” (Campbell, Shirley, & Caygill, 2002). Children typically begin to show understanding of their own gender identity within a few months after labelling other people’s gender. By age 2½ to 3 years, most children use gender terms such as “boy” and “girl” in their speech to refer to themselves and other children (Fenson et al., 1994).

In Canada, children’s play becomes differentiated by gender during the preschool period; most girls prefer to play with soft toys and to spend time in the “housekeeping” area, and most boys prefer to play with blocks and transportation toys.

Gender self-labelling is usually consistent with children’s gender assignment at birth (based on their external genitals). However, as previously noted, some children do not identify with their assigned gender as they advance into the preschool years and older; instead, these children may identify with a different gender category (transgender), with more than one gender category (gender fluid), or with neither gender category (agender). These children usually have behavioural preferences that would be cross-gender-typed for their assigned gender at birth (see Box 15.1).

Preschool Years

During the preschool years (approximately ages 3 to 5), children quickly learn gender stereotypes — the activities, traits, and roles associated with each gender. By about 3 years of age, most children begin to attribute certain toys and play activities to each gender. By about 5 years of age, they usually stereotype affiliative characteristics (e.g., nurturance, warmth) to females and assertive characteristics (e.g., directness, aggression) to males (Best & Thomas, 2004; Biernat, 1991; Liben & Bigler, 2002; Serbin, Powlishta, & Gulko, 1993). During this period, children usually lack gender constancy: they do not understand that gender remains stable across time and is consistent across situations. For example, a preschooler might think that a girl becomes a boy if she cuts her hair, or that a boy becomes a girl if he wears a dress. Indeed, as explained earlier in this chapter, most young children rigidly endorse gender stereotypes until they develop more cognitive flexibility during middle childhood.

During preschool, children begin to avoid peers who violate gender-role norms, and by age 5 to 7 years, they will actively tease peers who cross gender-role boundaries. This is especially true for boys: the one in this photo is likely to experience peer rejection if he continues to play with dolls and other toys strongly stereotyped as appropriate for girls.

Gender-Typed Behaviour Many children begin to demonstrate preferences for some gendertyped toys by about 2 years of age. These preferences become stronger for most children during the preschool years (Cherney & London, 2006; Todd et al., 2017; Weisgram & Dinella, 2018). Indeed,

during childhood, one of the largest average gender differences is in toy and play preferences, as described earlier. Although studies find large average gender differences in play preferences, there is still some variability. First, variation exists within each gender in how strongly individual children favour gender-typed over cross-gender-typed play. That is, some cisgender children are very rigid in their preferences for gender-typed toys and play activities, whereas others are more flexible (Blakemore et al., 2009; DeLoache et al., 2007). Second, some children strongly prefer cross-gender-typed play and dislike gender-typed play. This latter group includes genetic females with congenital adrenal hyperplasia (CAH), who were exposed to unusually high levels of prenatal androgens, or genetic males with androgen insensitivity syndrome (AIS), who are unable to respond to androgen during prenatal differentiation (Berenbaum, 2018; Hines, 2013; described later in this chapter). Transgender children who identify with a gender different from the one assigned to them at birth usually prefer the play activities typically associated with their self-identified gender (Boskey, 2014; Olson & Gülgöz, 2018). The preschool period is also when gender segregation emerges. Most children begin to prefer playing with same-gender peers and to avoid other-gender peers (Leaper, 1994, 2018; Maccoby, 1998). Gender segregation increases steadily between about 3 and 6 years of age, then it remains stable throughout childhood (Figure 15.4). Preference for same-gender peers is commonly seen across different cultures

(Maccoby, 1998; Munroe & Romney, 2006; Whiting & Edwards, 1988). gender segregation children’s tendency to associate with same-gender peers and to avoid other-gender peers

FIGURE 15.4 Gender segregation in play This graph reflects the increase in social playtime between preschool and 1st grade that children spent with playmates of

their own gender and the decrease in playtime with playmates of the other gender. (Data from Maccoby, 1998)

Description The key notes at the bottom of the graph read as follows: With same gender; In mixed group; and With other gender. The horizontal axis is labeled as follows: At age 4 and one-half, At age 6 and one-half. The vertical axis labeled, Percent of social playtime, ranges from 0 to 70, in increments of 10. The data are as follows: At age 4 and one-half: With same gender: 47, In mixed group: 35, With other gender: 18; At age 6 and one-half: With same gender: 68, In mixed group: 27, With other gender: 6. All values are approximate.

Gender-segregated peer groups are a laboratory for cisgender children to learn what it means to be a girl or a boy. Peers are both role models and enforcers of gender-typed behaviour. Martin and Fabes (2001) identified what they termed a “social dosage effect” of belonging to same-gender peer groups during early childhood. The amount of time that preschool or kindergarten children spent with same-gender peers predicted subsequent changes in gender-typed behaviour over 6 months. For example, boys who spent more time playing with same-gender peers showed increases over time in aggression, rough-and-tumble play, activity level, and gender-typed play. Girls who spent more time playing with same-gender peers showed increases in gender-typed play and decreases in aggression and activity level. The reasons for children’s same-gender peer preferences seem to involve a combination of temperamental, cognitive, and social forces (Leaper, 2015a, 2018; Maccoby, 1998; Martin & Ruble, 2010). Their relative influences change over time. At first, some children may prefer same-gender peers partly because they have more compatible behavioural styles and interests. For instance, girls may avoid boys because boys tend to be rough and unresponsive to girls’ attempts to influence them, whereas boys may prefer the company of other boys because they share similar activity levels. Around the time that

children begin to exhibit a same-gender peer preference, they are also establishing a gender identity; thus, they may be drawn to peers who belong to the same ingroup. As children become older, peer pressures may additionally motivate them to favour same-gender peers. Thus, behavioural compatibility may become a less important factor with age. For instance, physically active girls might frequently play with boys during early childhood; however, as these girls become older, they tend to affiliate more with girls — even though their activity preferences may be more compatible with some boys (Pellegrini et al., 2007). Therefore, ingroup identity and conformity pressures may supersede behavioural compatibility as reasons for gender segregation as children become older. For some children, assimilating into same-gender peer groups may be a challenge. As explained earlier, some children demonstrate intense cross-gender-typed interests. For example, some female children may strongly prefer physical activities and rough play while some male children may strongly prefer dress-up and doll play. Many cisgender children reject peers who do not adhere to social norms in their peer group. Similarly, many parents and other adults are disapproving of gender-nonconforming behaviours in children. As a consequence, some children with strong gender-nonconforming interests may face a conflict between social pressures and their interests. This conflict puts these children at risk for depression, anxiety, and other adjustment difficulties (Connolly et al., 2016; Olson

et al., 2016). Also, they may not feel like they belong with their gender ingroup, and perhaps this contributes to some of them adopting a different gender identity (see Leaper, 2018).

Middle Childhood By about 6 years of age, cisgender children have usually attained gender constancy, and their ideas about gender are more consolidated. Most children continue to be highly gender-stereotyped in their views. However, because they understand that gender is not necessarily tied to a person’s physical appearance, children at this age period often show a bit more flexibility in their gender stereotypes and attitudes than they did in their younger years (Katz & Ksansnak, 1994; Liben & Bigler, 2002; Serbin et al., 1993). For example, they may recognize that some boys don’t like playing hockey and that some girls don’t wear dresses. One recent study found that transgender children between 6 and 8 years old were less likely to endorse gender stereotypes than their cisgender peers and that the cisgender siblings of the transgender children were less likely to endorse gender stereotypes (Olson & Enright, 2018). At approximately 9 or 10 years of age, children start to show an even clearer understanding that gender is a social category. They typically recognize that gender roles are social conventions as opposed to biological imperatives (Carter & Patterson, 1982; Conry-Murray, 2015;

Killen, 2007; Stoddart & Turiel, 1985). As children come to appreciate the social basis of gender roles, they may recognize that some girls and boys may not want to do things that are typical for their gender. Even though children may understand the notion of individual variations in gender typing, they are typically aware that violating gender role norms would have social costs (Tobin et al., 2010). Another development in some children’s thinking in the middle childhood years is an awareness of when gender discrimination occurs, as well as the realization that it is unfair (Brown & Bigler, 2005; Killen, 2007). Killen and Stangor (2001) demonstrated this when they told children stories about a child who was excluded from a group because of the child’s gender. Examples included a boy who was kept out of a ballet club and a girl who was kept out of a baseballcards club. The researchers observed that 8- and 10-year-olds usually judged it unfair for a child to be excluded from a group solely because of gender. Yet despite their capacity to see this as wrong, children commonly exclude other children from activities based on their gender (Killen, 2007; Maccoby, 1998). Brown and Bigler (2005) identified various factors that affect whether children recognize gender discrimination. First amongst them are cognitive prerequisites, such as an understanding of cultural stereotypes, the ability to make social comparisons, and a moral understanding of fairness and equity. These abilities are typically reached by middle childhood. People’s awareness of sexism can also be influenced by individual factors such as their own self-concepts or

beliefs. For instance, girls with gender-egalitarian beliefs were more likely to recognize sexism (Brown & Bigler, 2004; Leaper & Brown, 2008). Finally, the situation can affect children’s likelihood of noticing discrimination. For instance, some children are more likely to notice discrimination directed toward someone else than toward themselves. Also, they are more apt to recognize gender discrimination from someone already known to be prejudiced (Brown & Bigler, 2005).

Gender-Typed Behaviour As previously noted, most cisgender girls and boys spend time primarily in same-gender peer groups throughout childhood. On average, boys’ and girls’ peer groups establish somewhat different norms for behaviour (Rose & Rudolph, 2006). For this reason, some researchers have suggested that girls and boys usually construct their own “culture” during childhood (Maccoby, 1998; Maltz & Borker, 1982; Thorne & Luria, 1986). The gender-role norms seen in the social interactions of many cisgender girls and boys tend to reflect differences in the balance of assertion and affiliation (see Figure 15.5 for one model of communication styles, which plots four statement categories along these two dimensions). Assertion refers to one’s attempts to exert influence over the environment (e.g., directive statements), whereas affiliation refers to making connections with others (e.g., expressing support). However, the goals of assertion and affiliation are not mutually exclusive: they are often blended together

in a style known as collaboration (Leaper, 1991; Leaper, Tenenbaum, & Shaffer, 1999). assertion tendency to take action on behalf of the self through competitive, independent, or aggressive behaviours affiliation tendency to affirm connection with others through being emotionally open, empathetic, or supportive collaboration coordination of assertion and affiliation in behaviour, such as making initiatives for joint activity

FIGURE 15.5 Communication strategies The figure illustrates a two-dimensional model of social interaction and communication. Assertion ranges from high to low along the vertical axis, and affiliation ranges from high to low along the horizontal axis. Collaborative acts are high in both affiliation and assertion. Controlling acts are high in assertion and low in affiliation. Obliging acts are high in affiliation and low in assertion. Withdrawing acts are low in both affiliation and assertion.

Description The text on top left division titled, Controlling Statements, reads, High assertion and low affiliation, Examples: Directives (“Do this.”); Negative comments. The text on top right division titled, Collaborative Statements, reads, High affiliation and high assertion, Examples: Suggestions for joint activity (“Let’s play superheroes.”); Elaborations on what the other speaker previously said. The text on bottom right division titled, Withdrawal, reads, Low assertion and low affiliation, Example: Not responding to another person’s statement. The text on bottom right division titled, Obliging Statements, reads, High affiliation and low assertion, Examples: Expressions of agreement; Going along with the other’s proposal (“Sure, that’s fine.”). A horizontal bidirectional arrow below the illustration points from Affiliation to Low at the origin and High to the right. A vertical bidirectional arrow to the left of the illustration points from Assertion to Low at the origin and High at the top.

For example, a proposal for joint action (“Let’s play a game together”) or a statement that builds positively on another’s idea are each simultaneously affiliative (connecting to the other) and self-assertive (influencing the situation). Thus, girls were more likely than boys to use collaborative communication that affirms both the self and the other (e.g., proposals for joint activity), whereas boys were more likely than girls to use power-assertive communication that primarily affirms the self (e.g., giving commands). Average gender differences in girls’ and boys’ peer cultures reflect the organization of gender in the larger society (Leaper, 2000). The traditional masculine role in most societies stresses self-assertion and downplays interpersonal affiliation. In line with this tendency, researchers observed that boys’ peer groups were more likely than girls’ peer groups to maintain norms emphasizing dominance, selfreliance, competition, and hiding vulnerability. In contrast, the traditional feminine role stresses affiliation. Accordingly, in studies, girls’ peer groups were more likely than boys’ peer groups to reinforce norms that value interpersonal sensitivity, supportiveness, and affection (Bassen & Lamb, 2006; Best & Williams, 1993; Rose & Rudolph, 2006). However, valuing affiliation is not necessarily incompatible with self-assertion. Hence, collaborative styles of social interaction have been somewhat more common amongst girls than amongst boys (Leaper, 1991; Leaper & Smith, 2004; Leaper et al., 1999). As with most average gender differences, there is also considerable

overlap between girls and boys in collaboration and other styles of social behaviour. For example, some boys are very collaborative while some girls are very directive. As we have noted, when children violate gender-role norms, their peers often react negatively (e.g., Fagot, 1977; Harris, 1995; Thorne & Luria, 1986), including mercilessly teasing someone who has crossed gender “borders.”

During the elementary school years, boys’ and girls’ groups rarely mix. Children themselves enforce gender segregation; this tendency does not seem to be due to adult influences.

Although most cisgender children typically favour same-gender peers, in certain contexts friendly mixed-gender contacts regularly occur (Sroufe et al., 1993; Strough & Covatto, 2002; Thorne, 1993; Thorne & Luria, 1986). At home and in the neighbourhood, the choice

of play companions is frequently limited. As a result, girls and boys often play cooperatively with one another. In more public settings, the implicit convention is that girls and boys can be friendly if they can attribute the reason for their cross-gender contact to an external cause. For example, this might occur when a teacher assigns them to work together on a class project or when they are waiting in line together at the cafeteria. However, beyond such exceptions, the risk of peer rejection is high when children violate the social convention to avoid cross-gender contact (Sroufe et al., 1993). Overall, gender typing during childhood tends to be more rigid amongst boys than amongst girls (Leaper, 1994; Levant, 2005). As noted earlier, amongst cisgender children, boys are more likely to endorse gender stereotypes than are girls, whereas girls are more likely than boys to endorse gender-egalitarian attitudes (Brown & Bigler, 2004). In addition, girls are less gender-typed in their behaviour. For instance, girls are more likely than boys to play with cross-gender-typed toys. Also, girls frequently pursue play activities traditionally associated with boys, such as soccer and basketball. In contrast, it is relatively rare to see cisgender boys engage in activities traditionally associated with girls, such as playing house. Furthermore, girls tend to be more flexible in coordinating interpersonal goals. For instance, as explained earlier, girls commonly coordinate both affiliative and assertive goals in their social interactions (Leaper, 1991; Leaper & Smith, 2004).

Gender segregation persists through childhood. Cross-gender teasing is used to maintain gender boundaries.

Adolescence According to some developmental psychologists, adolescence is a period when gender roles might become more rigid (gender-role intensification) or more relaxed (gender-role flexibility), depending on individual and contextual factors. As explained in Chapter 11, adolescence is a time when many youth are exploring their personal identities, including their values and beliefs regarding gender roles (e.g., Cooper & Grotevant, 1987). Many girls and boys internalize

traditional gender roles in their personal values. As a consequence, concerns with adhering to gender-role expectations may increase (Galambos, Almeida, & Petersen, 1990; Hill & Lynch, 1983). This gender-role intensification commonly occurs in the context of heterosexual dating when adolescents usually adhere to traditional heterosexual scripts. For example, it remains common for both boys and girls to expect that boys will initiate and pay for dates (see Robnett & Leaper, 2013). gender-role intensification heightened concerns with adhering to traditional gender roles that may occur during adolescence

According to psychologists Peter Glick and Susan Fiske (2001), traditional heterosexual dating scripts stem from ambivalent sexism. Ambivalent sexism refers to complementary effects of hostile sexism (whereby men are dominant and women who seek equality are disparaged) and benevolent sexism (whereby men are supposed to protect women in the context of heterosexual relationships). Although benevolent sexism may seem innocent, Glick and Fiske point out that it helps to perpetuate gender differences in status and power when women are expected to rely on their male partners for financial support and safety. Both hostile and benevolent forms of sexism tend to occur together. Thus, during adolescence, rates of sexual harassment (manifestations of hostile sexism) rise during the same period that heterosexual dating is also increasing (Leaper & Robnett, 2018). Furthermore, these patterns may set the stage for

observations that adults’ endorsement of benevolent and hostile sexism can lead to lowered relationship satisfaction between women and men in heterosexual relationships over time (Hammond & Overall, 2017). ambivalent sexism model of sexism that includes two components, hostile sexism (endorsement of men’s dominance with negative views of women seeking equality) and benevolent sexism (the belief that men need to protect women, and that women and men have complementary traits)

Gender-role intensification is also related to increases in gender discrimination during the course of adolescence (American Association of University Women [AAUW], 2011; Leaper & Brown, 2008). A national survey conducted in the United States found that most adolescent girls and boys experienced sexual harassment, and the rates increased with age — especially for girls (AAUW, 2011). A study of grade 7 and 8 students in Ontario found that 35% to 45% of students reported at least one incidence of sexual harassment during the school year (Schnoll et al., 2015). Also, instances of sexual harassment and bullying are more likely directed toward gendernonconforming children (e.g., boys who are not athletic, girls who are not viewed as pretty or feminine), as well as LGBTQ individuals (AAUW, 2011; Martin-Storey, 2016; Mitchell, Ybarra, & Korchmaros, 2014). Alternatively, some adolescents may reject traditional gender roles as social conventions. This inclination may lead to gender-role

flexibility, whereby these youths pursue a flexible range of attitudes and interests (Carter & Patterson, 1982; Katz & Ksansnak, 1994). As in childhood, greater gender-role flexibility during adolescence is more likely amongst girls than amongst boys. For instance, many girls and young women in Canada and other countries participate in sports and pursue careers in business (traditionally male-dominated domains), whereas relatively few boys and young men show similar levels of interest in childcare or homemaking (traditionally female-dominated domains). For girls and boys, gender-role flexibility will partly depend on the breadth of opportunities they experience in society for their gender ingroup (Wood & Eagly, 2012). Social support (and the absence of rejection) for gender-role flexibility from peers, family, teachers, and others is also important for gender-nonconforming youth (Olson et al., 2016). gender-role flexibility recognition of gender roles as social conventions and adoption of more flexible attitudes and interests

Parents, peers, and teachers are much more tolerant of girls who engage in masculine-stereotyped activities than they are of boys who engage in femininestereotyped activities.

When LGBTQ adolescents encounter strong heteronormative (and cisgender) expectations in their community, they may face stigmatization and corresponding challenges in embracing their sexual identities (Toomey et al., 2010). However, in many schools in Canada, there are Straight–LGBTQ alliances that foster acceptance and support for sexual-minority and other gender-nonconforming youth (e.g., Saewyc et al., 2019).

Gender-Typed Behaviour

During early adolescence, peer contacts for most youth remain primarily with members of the same gender. However, in many cultural communities, mixed-gender interactions and friendships become more common during adolescence (see Figure 15.6) (Poulin & Pedersen, 2007). These interactions can open the way to romantic relationships amongst heterosexual youth. In some cultural settings, however, there are strict rules regarding mixed-gender contacts, especially as youth enter adolescence. For example, in Orthodox Jewish, Islamic, and Amish societies, girls and boys are separated outside the home, and any mixed-gender contact must be supervised by family.

FIGURE 15.6 Friends by gender and grade The data shown in this figure demonstrate that younger children tend to be friends with children who are the same gender as they are. As children move into adolescence, the number of cross-gender friends tends to increase for both boys and girls.

(Data from Poulin & Pedersen, 2007)

Description The key notes at the bottom of the graph read as follows: Girls, same-gender friends; Boys, same-gender friends; Girls, mixed-gender friends; Boys, mixedgender friends. The horizontal axis is labeled as follows: Grade 6, Grade 7, Grade 8, Grade 9, and Grade 10. The vertical axis labeled, Mean number of friends, ranges from 0 to 8, in increments of 1. The data are as follows: Grade 6: Girls, same-gender friends: 7.4, Boys, same-gender friends: 6.6, Girls, mixed-gender friends: 1.8, Boys, mixed-gender friends: 1.3; Grade 7: Girls, same-gender friends: 6.8, Boys, same-gender friends: 6, Girls, mixed-gender friends: 1.9, Boys, mixed-gender friends: 1.1; Grade 8: Girls, same-gender friends: 6.8, Boys, same-gender friends: 6.9, Girls, mixed-gender friends: 2.3, Boys, mixed-gender friends: 1.3; Grade 9: Girls, same-gender friends: 6.2, Boys, same-gender friends: 6.4, Girls, mixed-gender friends: 2.7, Boys, mixed-gender friends: 1.6; Grade 10: Girls, same-gender friends: 6, Boys, same-gender friends: 6.1, Girls, mixed-gender friends: 2.5, Boys, mixedgender friends: 1.8. All values are approximate.

Adolescence is also a period of increased intimacy in same-gender friendships. For many girls and boys, increased emotional closeness is often attained through sharing personal feelings and thoughts, although there appears to be more variability amongst boys in the ways they experience and express closeness in friendships (Camarena, Sarigiani, & Petersen, 1990). While some boys attain intimacy through shared disclosures with same-gender friends, other boys tend to avoid self-disclosure with same-gender friends because they wish to appear strong. Instead, they usually attain a feeling of emotional closeness with friends through shared activities, such as playing sports. At the same time, many boys who avoid expressing feelings with male friends may seek emotional support with their female friends or girlfriends (Youniss & Smollar, 1985). Self-disclosure and supportive listening are generally associated with relationship satisfaction and emotional adjustment (Rubin, Bukowski, & Parker, 2006; see Chapter 13). However, it is possible to have too much of a good thing. This occurs when friends dwell too long on upsetting events by talking to one another about them over and over. As discussed in Chapter 10, this process of co-rumination is more common amongst girls than amongst boys (Rose, Carlson, & Waller, 2007). To be clear, self-disclosure is generally positive for emotional adjustment, but it can be a problem when friends persistently focus on upset feelings without exploring proactive ways

to cope with the distress.

REVIEW QUESTION What role does gender stereotyping play at the various stages of child development?

Patterns of Gender Development In the following sections, we consider patterns of gender development in four areas that receive particular attention in the study of gender development: physical growth, cognitive abilities and academic achievement, interpersonal goals and communication, and aggression.

Physical Growth: Prenatal Development Through Adolescence Sex differences in physical development appear early in prenatal development. The most dramatic of these, of course, is the emergence of male or female internal and external genitalia. Thereafter, the differences that occur between males and females are relatively subtle prior to the onset of puberty.

Prenatal Development As noted in our earlier discussions, a key prenatal factor in sexual development is the presence or absence of androgens. Research suggests that prenatal exposure to androgens may influence the organization of the nervous system, and these effects may be partly related to some average gender differences in behaviour seen at later

ages (Berenbaum, 2018; Hines, 2013). During prenatal development, a gene on the Y chromosome of genetic males normally triggers the increased production of androgen hormones around 6 to 8 weeks after conception. This leads to a series of processes leading to the formation of male internal reproductive structures and male external genitalia. Rarely occurring recessive genes may result in a person of one genetic sex who develops the sexual structures associated with the other genetic sex or undergoes only partial development of sexual structures associated with their genetic sex. These are known as intersex conditions (Preves, 2003). Two intersex conditions, congenital adrenal hyperplasia and androgen insensitivity syndrome, have been of particular interest to gender development researchers. intersex conditions rare conditions in which an individual of one genetic sex can develop genitalia associated with the other genetic sex, both genetic sexes, or undergo only partial development of genitalia associated with their genetic sex

Congenital adrenal hyperplasia (CAH) is associated with a recessive gene that leads to the production of high levels of androgen hormones during prenatal development. Although CAH can occur in genetic females and males, it primarily affects the development of genetic females. These high levels of androgens can lead to the formation of male (or partly masculinized) external genitalia in females, such as a clitoris that is enlarged and may resemble a penis,

although the internal reproductive structures are usually female. Researchers studying the possible influence of androgens on later gender development have found that girls with CAH were more likely than girls without CAH to choose physically active forms of play, such as rough-and-tumble play, and to avoid sedentary forms of play, such as playing with dolls (Berenbaum, 2018; Hines, 2013; Nordenström et al., 2002). However, CAH does not have a strong impact on gender identity, as most females with CAH self-identify as girls (Hines, 2013). Research indicates that these behavioural tendencies do not appear to be caused by parents’ treating these girls differently because of their masculinized genitalia (Hines, 2013). congenital adrenal hyperplasia (CAH) condition during prenatal development in which the adrenal glands produce high levels of androgens; sometimes associated with masculinization of external genitalia in genetic females and sometimes associated with higher rates of masculine-stereotyped play in genetic females

In cases of androgen insensitivity syndrome (AIS), a recessive gene causes androgen receptors to malfunction in genetic males. Although increased androgen production may occur during prenatal development, the hormones do not trigger the typical physical changes in sexual differentiation. In these cases, genetic males may be born with female external genitalia (but not with female internal reproductive structures). Boys with AIS commonly self-identify as girls (and later as women). In addition, they typically show preferences for stereotypically feminine interests (Hines, 2013).

androgen insensitivity syndrome (AIS) condition during prenatal development in which androgen receptors malfunction in genetic males, impeding the formation of male external genitalia; in these cases, the child may be born with female external genitalia

Cases of children with CAH and AIS offer evidence to support the premise that prenatal androgens may partly contribute to boys’ and girls’ gender identities and to gender-typed play preferences. In addition, this kind of evidence is sometimes used to support evolutionary accounts of gender development (Alexander, 2003). However, it is important to reiterate that there are normal variations within each genetic sex in their exposure to prenatal androgens, as well as in their later preferences for different kinds of activities and interests. Hence, there are multiple influences on children’s gender development.

Childhood and Adolescence At birth, males, on average, weigh only about half a pound more than females do. Also, during infancy and into childhood, girls and boys grow at roughly the same rate and are essentially equal in height and weight (see Chapter 3). But during childhood, boys become notably stronger, on average, compared to girls. During adolescence, a series of dramatic bodily transformations is associated with puberty, the developmental period marked by the ability to reproduce — that is, the ability of males to inseminate, and the ability of females to menstruate, gestate, and lactate (Gaddis & Brooks-Gunn, 1985;

Jorgensen, Keiding, & Skakkebaek, 1991). In females, puberty typically begins with enlargement of the breasts and the general growth spurt in height and weight, followed by the appearance of pubic hair and then menarche (the onset of menstruation). Menarche is triggered in part by the increase in body fat that typically occurs in adolescence. In males, puberty generally starts with the growth of the testes, followed by the appearance of pubic hair, the general growth spurt, growth of the penis, and spermarche (the capacity for ejaculation). puberty developmental period marked by the ability to reproduce and other dramatic bodily changes menarche onset of menstruation spermarche onset of capacity for ejaculation

Puberty

For both females and males, there is considerable variability in physical maturation due to both genetic and environmental factors. Genes affect growth and sexual maturation in large part by influencing the production of hormones, especially growth hormone (secreted by the pituitary gland) and thyroxin (released by the thyroid gland). The influence of environmental factors is particularly evident in the changes in physical development that have occurred over generations (see Chapter 3). In many industrialized countries, females begin menstruating several years earlier than their ancestors did 200 years ago. This change is thought to reflect improvement in nutrition over the generations. With the changes in body composition that occur in early adolescence, particularly the substantial increase in muscle mass in

boys, the gender gap in physical and motor skills greatly increases. After puberty, average gender differences are very large in strength, speed, and size: few adolescent females can run as fast or throw a ball as far as most males can (Malina & Bouchard, 1991; Thomas & French, 1985). These are amongst the largest average differences in abilities seen between females and males (see Table 15.1). Physical differences in strength, speed, and size, as well as women’s childbearing capacity, may be amongst the most significant sex differences that shape the organization of gender relations in a society. Psychologists Wendy Wood and Alice Eagly (2002) argued that greater gender inequalities have occurred in societies when economic subsistence favoured physical strength and disadvantaged nursing and childcare. In industrial-technological societies, physical strength is no longer an advantage for most jobs and resources such as birth control, family leave, and childcare make it possible for women (and men) to maintain engagement in the workforce.

In early puberty, females are typically taller than males because of females’ earlier physical maturation. By the end of adolescence, males catch up and surpass females in average height and weight.

The physical changes that males and females experience during puberty are accompanied by psychological and behavioural changes. For example, in some cultures, the increase in body fat that adolescent females undergo may be related to gender differences in body image — how an individual perceives and feels about his or her physical appearance. On average, girls tend to have more negative attitudes toward their bodies than boys do, and teenage girls typically want to lose several pounds regardless of how much they actually weigh (Tyrka, Graber, & Brooks-Gunn, 2000). A survey of more than 1500 Canadian preadolescents found that roughly half of both the girls and boys were dissatisfied with their bodies, but that the type of dissatisfaction varied across genders: Girls were mostly concerned about losing weight; boys, with being more muscular (Dion et al., 2016). Dissatisfaction with body image has long been associated with a host of difficulties, ranging from low self-esteem and depression to eating disorders. Surveys across different cultures indicate similar patterns of body image and eating disorders (Levine & Smolak, 2010). body image an individual’s perception of, and feelings about, her or his own body

Another change that accompanies physical maturation is the onset of sexual attraction, which usually begins before the physical process of puberty is complete. According to the recollections of a sample of adults in the United States, sexual attraction is first experienced at about 10 years of age — regardless of whether the attraction was for individuals of the other sex or the same sex (McClintock & Herdt,

1996). The onset of sexual attraction correlates with the maturation of the adrenal glands, which are the major source of sex steroids other than the testes and ovaries. This stage has been termed adrenarche, although the child’s body does not yet show any outside signs of maturation. (Sexual identity and romantic relationships are reviewed in Chapters 11 and 13.) adrenarche period prior to the emergence of visible signs of puberty during which the adrenal glands mature, providing a major source of sex steroid hormones; correlates with the onset of sexual attraction

Cognitive Abilities and Academic Achievement The following sections summarize the evidence comparing cisgender boys’ and girls’ cognitive abilities and academic achievement. When average gender-differences in cognitive ability or performance have been observed, the effect sizes have usually been small (Halpern, 2012; Halpern et al., 2007; see Table 15.1). Somewhat greater differences appear when it comes to motivation for particular subjects. After summarizing these comparisons, we consider biological, cognitive-motivational, and cultural influences that might account for these findings. The relation between gender and academic achievement during childhood and adolescence has important implications for adult gender roles and equality. To the

extent that cisgender girls and boys develop different cognitive abilities, academic interests, and achievement, gender differences in their future occupations and income may follow. Thus, reducing gender differences in academic motivation and achievement are critical steps toward increasing gender equality in society (Dasgupta & Stout, 2014). To our knowledge, no research has examined the extent that children’s academic interests might differ on average between cisgender children and transgender or gender-nonbinary children. However, because of the discrimination and bullying that gendernonconforming youth often encounter in school, many transgender and nonbinary children suffer academically (Day, Perez-Brumer, & Russell, 2018).

General Intelligence and Overall Academic Achievement Despite widespread belief to the contrary, boys and girls are equivalent in most aspects of intelligence and cognitive functioning. The average IQ scores of girls and boys are virtually identical (Halpern, 2012). However, proportionally more boys than girls have scored at both the lowest and the highest extremes. That is, somewhat more boys than girls have been diagnosed with intellectual disabilities or are classified as intellectually gifted (Halpern, 2012).

Although girls and boys are similar in general intelligence, some average differences in academic achievement were seen from elementary school through university. Recent statistics indicate that girls tend to show higher levels of school adjustment and achievement than do boys across a number of different countries (Child Trends Data Bank, 2015; Snyder & Dillow, 2010; Lam, Jimerson et al., 2012; Voyer & Voyer, 2014). In one meta-analysis carried out by researchers at the University of New Brunswick, data showed a small average difference indicating that girls tended to attain higher overall school grades than did boys (Voyer & Voyer, 2014). Also, the high school dropout rate in Canada tends to be higher for boys than for girls: in 2016, 8% of 25- to 34-year-old men had not completed high school compared to 5% of women of the same age (Uppal, 2017). Furthermore, in 2016, 57% of Canadian university graduates were women (Statistics Canada, 2018). The magnitude of gender difference in academic achievement varies somewhat across different cultural and ethnic groups and socioeconomic levels.

Verbal Skills Compared with boys, girls have tended to be slightly advanced in early language development, including fluency and clarity of articulation and vocabulary development (Gleason & Ely, 2002). On standardized tests of children’s overall verbal ability, there has been a negligible average gender difference favouring girls (Hyde & Linn, 1988). Larger average differences were seen when specific verbal

skills were examined. Girls tended to achieve higher average performance in reading and writing from elementary school to high school; the effect sizes of the average differences were small for reading and medium for writing (Hedges & Nowell, 1995; Nowell & Hedges, 1998; Reilly, 2012; Voyer & Voyer, 2014; see Table 15.1). Boys were more likely to suffer speech-related difficulties, such as poor articulation and stuttering, as well as more reading-related problems such as dyslexia (Halpern, 2012).

Spatial Skills On average, boys have tended to perform somewhat better than girls in some aspects of visual-spatial processing (see Table 15.1). This difference has typically emerged between 3 and 4 years of age and became more substantial during adolescence and adulthood (Halpern, 2012). Gender differences are most pronounced on tasks that involve mental rotation of a complex geometric figure in order to decide whether it matches another figure presented in a different orientation; on average, boys have tended to perform somewhat better than girls in that area. However, other spatial tasks — such as finding a hidden figure embedded within a larger image — have shown much smaller gender differences. Thus, the conclusion that more boys than girls have superior spatial ability depends on the particular type of spatial ability.

STEM-Related Skills Policymakers, educators, and researchers have been concerned with gender disparities in many science, technology, engineering, and mathematics (STEM) fields (Halpern, 2012; National Science Foundation, 2017). These are amongst the fastest-growing and highest-paying occupations, and therefore women’s underrepresentation in many of these fields contributes to overall gender inequities in pay and status in society (Cheryan et al., 2017). Moreover, because these fields are considered important for progress and innovation, societies should foster the talents of all interested persons starting at a young age (Cheryan et al., 2017). Until recent decades in Canada and many other countries, boys tended to perform somewhat better on standardized tests of mathematical ability than did girls. As we have noted, however, the gender gap in mathematics achievement has closed dramatically as a result of efforts made by schools and parents to improve girls’ performance. According to the most recent studies, no average gender differences in standardized test performance or basic numerical skills were seen in the elementary or middle school levels (Hutchison, Lyons, Ansari, 2019; Lindberg et al., 2010), and only a small average difference (favouring boys) was indicated at the high school level (Halpern et al., 2007; Lindberg et al., 2010; see Table 15.1). However, cross-national comparisons revealed some countries in which girls exceeded boys in average mathematics performance

(Else-Quest, Hyde, & Linn, 2010).

Encouragement of girls’ interest in STEM-related fields on the part of parents and schools has led to the dramatic closing of the achievement gap in these areas.

Girls and women are also underrepresented in the engineering, computer science, and other technological fields. In Canada as of 2016, for example, 23% of postsecondary degrees and diplomas in engineering, 13.5% of postsecondary degrees and diplomas in engineering technology and related fields, and 24% of postsecondary degrees and diplomas in computer and information sciences were held by women between the ages of 25 and 34 years (Statistics Canada, 2017). Following the attention paid to the gender gap in math achievement a few decades ago, educators and researchers are increasingly addressing the gender gap in the physical sciences and

engineering and technology (see Cheryan et al., 2017), and progress has been made in some of these areas — for example, 46% of degrees and diplomas in math and statistics and 39% of degrees and diplomas in the physical sciences were held by women aged 25 to 34 years, as of 2016. In contrast to engineering and computer sciences, girls and women are attaining gender equity in the biological and health sciences. At the high school level, there is no average gender difference in achievement. At the postsecondary level as of 2016, 63% of postsecondary degrees and diplomas in biological and biomedical sciences went to women between 25 and 34 years.

Explanations for Gender Differences in Cognitive Abilities and Achievement Researchers have variously pointed to physiological, cognitivemotivational, and cultural factors in relation to gender-related variations in cognitive abilities and achievement. We now examine each possible area of influence.

Brain and hormonal influences Some researchers have proposed that sex differences in brain structure and function may underlie some differences in how male

and female brains process different types of information. However, because the research supporting this interpretation has largely been based on studies of adults, it is impossible to determine whether any differences in brain structure and function seen in adults are due to genetic or environmental influences. Also, a slight biological tendency can get exaggerated through differential experience (Halpern, 2012). For example, boys may initially have a slight average advantage over girls in some types of spatial processing. Yet, when boys spend more time playing video games and sports than girls do, they practice their spatial skills more (Moreau et al., 2012; Spence & Feng, 2010). As a consequence, the magnitude of the gender difference in spatial ability may widen. However, several studies indicate that spatial skills can be substantially improved in girls as well as boys through training (Uttal et al., 2013). Stronger evidence for possible physiological influences is suggested by research showing that some sex differences in brain structure may be partly due to the influence of sex-related hormones on the developing fetal brain (Berenbaum, 2018; Hines, 2013). For instance, androgens may affect parts of the brain associated with spatial skills (Grön et al., 2000; Hines, 2013). Because males are exposed to higher levels of androgens than are females during typical prenatal development, this difference may lead to greater specialization in parts of the brain related to spatial ability, which contributes to more proficiency in spatial ability later in life. Support for this hypothesis comes from studies that have linked very high levels of prenatal

androgens in girls with above-average spatial ability (Grimshaw, Sitarenios, & Finegan, 1995; Hines et al., 2003; Mueller et al., 2008). Conversely, it has been found that males with androgen insensitivity syndrome tend to score lower than average in spatial ability (Imperato-McGinley et al., 1991/2007). Keep in mind there is considerable variability within each gender group in their spatial abilities.

Cognitive and motivational influences The process of self-socialization emphasized in cognitive motivational theories plays a role in children’s academic achievement. According to Eccles’s expectancy-value model of achievement (Eccles & Wigfield, 2002), children are most motivated to achieve in areas in which they expect to succeed (i.e., self-efficacy or ability belief in a subject) and that they value (i.e., intrinsic interest and perceived importance of a subject). Gender stereotypes can shape the kinds of subjects that girls and boys tend to value (see Table 15.1). For instance, many children internalize gender stereotypes that science, technology, and math are for boys and that reading, writing, and the arts are for girls (Kessels, 2015; Papastergiou, 2008; Plante, Théorêt, & Favreau, 2009). However, some evidence suggests that these stereotypes are possibly becoming less common (Plante et al., 2009), perhaps due to the efforts of many educators, policymakers, and parents over the years.

To the extent that gender stereotyping about academic subjects does persist, perhaps it is not surprising, then, that average gender differences in interest and ability beliefs exist in these academic areas (Eccles & Wigfield, 2002; Else-Quest, Hyde, & Linn, 2010; Simpkins, Fredricks, & Eccles, 2015; Wilgenbusch & Merrell, 1999) and that these self-concepts predict academic achievement and occupational aspirations (Guo et al., 2015; Halpern, 2012; Watt, 2010; Wigfield, Cambria, & Eccles, 2012). As discussed next, social and cultural factors also influence the development of gender-related variations in academic self-concepts and achievement. That is, the role models, opportunities, and incentives that children experience in their environments affect their motivation and achievement.

Parental influences As noted in Chapter 6, parents’ talking to their children is a strong predictor of children’s language learning. A meta-analysis of studies conducted with mostly Western middle-class families found that mothers tended to have average higher rates of verbal interaction with daughters than with sons (Leaper, Anderson, & Sanders, 1998). Thus, one possibility is that young girls learn language at a slightly faster rate than do boys partly because mothers may spend more time talking with daughters than with sons. Alternatively, because many girls tend to acquire language earlier than some boys, perhaps girls are more likely to elicit talk from their mothers (Leaper & Smith, 2004). Finally, both patterns may tend to occur — a possible

bidirectional influence whereby both mothers and daughters tend to be talkative and reinforce this behaviour in one another.

Some studies find that mothers are more talkative with daughters than with sons. Studies also find that, on average, girls acquire language at a faster rate than do boys. Does mothers’ greater talkativeness with girls contribute to girls’ faster language acquisition? Or does girls’ faster language acquisition influence mothers’ talkativeness with them?

Parents’ gender stereotyping is also related to children’s academic achievement. Many parents accept the prevailing stereotypes about boys’ and girls’ relative interests and aptitudes regarding various academic subjects (Eccles, 2015; Eccles et al., 2000; Leaper, 2015a), and these gender-typed expectations can affect children’s achievement motivation (Eccles, 2015; Eccles et al., 2000). Observational research suggests that some parents may communicate gender-stereotyped expectations to their children through differential

encouragement (Bhanot & Jovanovic, 2005; Crowley et al., 2001; Tenenbaum & Leaper, 2003). You might think that parents’ beliefs about their children’s academic potential would be based primarily on their children’s own self-concepts and achievement, but researchers have found that parents often hold gender-typed beliefs before any average gender differences in academic interest or performance occur. In fact, longitudinal research suggests that parents’ expectations can sometimes have a stronger impact on children’s later achievement than the children’s earlier performance in particular subject areas (Bleeker & Jacobs, 2004).

Teacher influences Teachers can influence gender differences in children’s academic motivation and achievement. Some teachers may hold genderstereotyped beliefs about girls’ and boys’ abilities. When this occurs, they may expect higher school achievement in girls than in boys (Jones & Myhill, 2004), or they may stereotype boys as being better at math and science (Cimpian et al., 2016; Riegle-Crumb & Humphries, 2012; Tiedemann, 2000). When teachers hold gender-typed expectations, they may differentially assess, encourage, and pay attention to students according to their gender. In this manner, teachers can lay the groundwork for self-fulfilling prophecies that affect children’s later academic achievement (see Cimpian et al., 2016; Halpern, 2012; Halpern et al., 2007). However, many educators have become more aware of gender bias over the years, as in the case

of proactive efforts to promote girls’ participation in math, science, and technology programs (e.g., Fredricks et al., 2018; Stake & Mares, 2005).

Some teachers hold gender-stereotyped expectations about girls’ and boys’ abilities that may affect their interactions with students.

Peer influences As described earlier in this chapter, children are usually concerned with gaining acceptance from their peers, and their interests often are shaped by the activities and values they associate with their classmates and friends. Consequently, peers can shape children’s academic achievement (Wentzel, 2009). This influence begins with the kinds of play activities children practice with their peers. Many activities commonly favoured amongst boys — including construction

play, sports, and video games — provide them with opportunities to develop their spatial abilities as well as math- and science-related skills. In contrast, the types of play more common amongst girls — such as domestic role-play — are talk-oriented and build verbal skills (Leaper, 2015a; Leaper & Bigler, 2018). Girls and boys may be more likely to strive in particular school subjects when they are viewed as compatible with peer norms (Robnett & Leaper, 2013). In some schools, girls may experience negative comments if they express interest in subjects such as science or computers; and boys may experience teasing if they show interest in reading or doing well in school (Dasgupta & Stout, 2014; Leaper & Brown, 2014; Schwartz, Kelly, & Duong, 2013). Thus, peer norms regarding particular academic subjects may be related to how likely girls or boys are apt to value those subjects (Leaper, 2015b; Leaper & Brown, 2014; Schwartz et al., 2013). Traditional masculinity norms emphasizing dominance and selfreliance may undermine some boys’ academic achievement in Western industrialized countries (Farkas & Leaper, 2016; Levant, 2005; Steinmayr & Spinath, 2009; Van Houtte, 2004). That is, some boys may not consider it masculine to do well in certain subjects, such as reading and writing, or possibly in school overall (Kessels & Steinmayr, 2013; Leaper, Farkas, & Starr, 2018; Martinot, Bagès, & Désert, 2012; Santos et al., 2013; Van de Gaer et al., 2006; Van Houtte, 2004). At the same time, some U.S. research suggests that gender-role flexibility may be related to stronger interest in nontraditional majors

amongst male undergraduates (Jome & Tokar, 1998; Leaper & Van, 2008).

Peer norms can have a strong impact on girls’ and boys’ achievement motivation. For example, research indicates that girls are more likely to maintain their interest in science and computers when their friends support achievement in these subjects.

Cultural influences The bioecological model maintains that socialization practices prepare children for their adult roles in society. If women and men tend to hold different occupations, then different abilities and preferences are apt to be encouraged in girls and boys. Therefore,

where there are cultural variations in girls’ and boys’ academic achievement, there should be corresponding differences in socialization.

Educating Girls of the World

A meta-analysis conducted by Else-Quest, Hyde, and Linn (2010) pointed to cultural influences on gender-related variations in mathematics achievement. To assess possible cultural influences, the researchers considered the representation of women in higher education in the given country. They found that average gender differences in several math-related outcomes were less likely in nations with higher percentages of women in higher levels of

education. This was seen for adolescents’ test performance, selfconfidence, and intrinsic motivation regarding math. One might expect the gender gap in fields such as physics, computer science, and engineering to be smaller in countries with greater gender equality. However, a recent cross-national analysis indicated the opposite (Stoet & Geary, 2018). Although the researcher noted girls performing similarly or even better than boys in most countries, there was a gender gap favouring men in attaining STEM degrees. The authors noted that the countries that were less gender-egalitarian also tended to have poorer economic conditions; additional analyses suggested that women in these countries tended to pursue STEM occupations for their economic value. In contrast, women in more egalitarian (and wealthier) countries may find they have more career options for attaining an adequate income. Furthermore, as others have argued, when women have career alternatives, they may be more likely to leave STEM majors when they experience gender bias (Cheryan et al., 2017; Leaper & Starr, 2019). Other cultural factors have also been found to predict gender-related variations in academic achievement within Western industrialized societies. Average gender differences in overall academic success and verbal achievement tend to be less common amongst children from higher-income neighbourhoods, amongst children of highly educated parents, and amongst children of egalitarian parents (Burkam, Lee, & Smerdon, 1997; Croft et al., 2014; Ferry, Fouad, & Smith, 2000; Melby et al., 2008; Updegraff, McHale, & Crouter, 1996). Furthermore, the

local community in which children are raised may have an impact. In one study, a comparison of different communities in the United States found the gender gap in physics achievement (usually favouring boys) was smaller in high schools in which more women were employed in science and technology occupations within the community (Riegle-Crumb & Moore, 2014).

Interpersonal Goals and Communication Although average differences between cisgender (and mostly heterosexual) women’s and men’s speech have been documented, the magnitude of the differences has usually been in the small-tomedium range (Leaper & Ayres, 2007). The average gender differences in communication and interpersonal goals during childhood and adolescence have likewise been found to be modest (see Table 15.1). In terms of interpersonal goals during childhood and adolescence, researchers have found average gender differences that are consistent with traditional gender roles amongst cisgender youth (Rose & Rudolph, 2006). More boys than girls tended to emphasize dominance and power as goals in their social relationships. In contrast, more girls than boys tended to favour intimacy and support as goals in their relationships. The effect sizes for these differences,

however, were small to medium. Researchers have also observed some average gender differences amongst cisgender children’s communication styles with peers. Contrary to the stereotypes of talkative girls and taciturn boys, studies generally do not find average differences in talkativeness after early childhood (Leaper & Smith, 2004). However, with regard to selfdisclosures about personal thoughts and feelings, there has been a small-to-medium gender difference, with higher average rates amongst girls than boys (Rose & Rudolph, 2006). Girls also tend to be somewhat more likely than boys to use collaborative statements, which reflect high affiliation and high assertion. Examples include suggestions for joint activity (“Let’s play superheroes”) or elaborations on what the other speaker previously said. In contrast, boys tend to be more likely than girls to use controlling statements (e.g., “Do this”), which reflect high assertion and low affiliation. As with most average differences, there is considerable overlap between cisgender girls and boys in communication style. Although some children act in gender-stereotypical ways, many girls use controlling speech and many boys use high levels of collaborative speech. Indeed, as we have seen throughout this chapter, girls and boys are quite similar to one another in a wide variety of behaviours. As with many social behaviours, some children are more gendertyped than others. Future research could examine the interpersonal goals and communication styles of children and adolescents with transgender or gender-fluid identities, as well as cisgender youth with

more gender-egalitarian attitudes. Because transgender children preferred play activities that were consistent more with their selfidentified gender (Olson & Gülgöz, 2018), one might expect a similar pattern would be seen in their interpersonal goals and communication styles.

Explanations for Gender Differences in Interpersonal Goals and Communication Researchers have identified a variety of cognitive-motivational, social-interactional, and cultural factors that are related to the likelihood of average gender differences in interpersonal goals and communication.

Cognitive and motivational influences Average gender differences in interpersonal goals and communication style are related. To the extent that some cisgender girls and boys differ in their primary goals for social relationships, they are apt to use different language styles to attain those goals (Crosby, Fireman, & Clopton, 2011; Miller, Danaher, & Forbes, 1986; Strough & Berg, 2000). For example, if a boy is especially interested in establishing dominance, using directive statements may help him attain that goal; and if a girl wants to establish intimacy, then talking about personal feelings or elaborating on the other person’s thoughts

would help realize that goal. Individual differences in interpersonal goals within any gender group may partly account for corresponding variations in whether particular children exhibit highly gender-typed behaviours.

Parental influences Many children observe their parents modelling gender-typed communication patterns. One meta-analysis summarized trends across studies (most of which were conducted with Western middleclass families with heterosexual parents) comparing mothers’ and fathers’ speech to their children (Leaper et al., 1998). The results indicated small average effect sizes: first, mothers were more likely than fathers to use affiliative speech; in contrast, fathers were more likely than mothers to use controlling (high in assertion and low in affiliation) speech. Additional research is needed to explore variations in parents’ gender-typed communication depending on their gender attitudes, sexual orientation, and cultural background. Moreover, a larger question to address in longitudinal research is whether and how parental modelling shapes the kinds of communication strategies their children will favour as they get older.

Peer influences The social norms and activities traditionally practiced within children’s gender-segregated peer groups foster different

interpersonal goals in cisgender girls and boys. For example, in their peer interactions, many girls commonly engage in domestic scenarios (“playing house”) that are structured around collaborative and affectionate interchanges. Boys’ play is more likely to involve competitive contexts (“playing war” or sports) that are structured around dominance and power. The impact of same-gender peer norms was implicated in Leaper and Smith’s (2004) meta-analysis, which found that gender differences in communication were more likely to be detected in studies of same-gender interactions than in mixed-gender interactions.

Cultural influences Cross-cultural comparisons generally find a similar pattern of average gender difference in social behaviour. That is, affiliative social behaviour tends to be more common amongst girls and women than amongst boys and men, whereas directive social behaviour tends to be more common amongst boys and men than amongst girls and women (Best, 2010). However, there are cultural variations in the degree to which these behaviours might be seen. For instance, in many Asian cultures, such as Japan, it is generally considered important for boys as well as girls to show high levels of affiliation in social interaction. Yet, within these cultures, boys and men tend to be more direct in their speech than do girls and women (Smith, 1992). Also, there are cultural variations within diverse nations, such as the United States. For example, some researchers have observed highly

direct social interactions amongst African American girls from working-class and low-income neighbourhoods in contrast to European American girls from middle-class communities (Kyratzis, 2004).

Aggressive Behaviour The conventional wisdom is that boys are more aggressive than girls. In support of this expectation, research studies indicate a reliable average gender difference in aggression. But the magnitude of the gender difference is not as great as many people expect. Also, this difference depends partly on the type of aggression being considered (see Table 15.1). As noted in Chapter 13, researchers distinguish between direct and indirect forms of aggression (Archer & Coyne, 2005; Björkqvist, Österman, & Kaukiainen, 1992). Direct aggression involves overt physical or verbal acts openly intended to cause harm, whereas indirect aggression (also known as relational or social aggression) involves attempts to damage a person’s social standing or group acceptance through covert means such as negative gossip and social exclusion. Average gender differences in the incidence of physical aggression emerge gradually during the preschool years (Hay, 2007). In two comprehensive meta-analyses of studies comparing boys’ and girls’ aggressive behaviour, both physical and verbal forms of direct

aggression occurred more often amongst boys than amongst girls (Archer, 2004; Card et al., 2008). The average difference was small during childhood and medium to large during adolescence. Although direct aggression generally declined for both boys and girls with age, the drop was more pronounced for girls than for boys (Archer, 2004). There appears to be no average gender difference during childhood in the use of indirect aggression. In a meta-analysis of studies testing for such gender differences (Card et al., 2008), only a negligible effect size during adolescence was indicated, with girls slightly more likely than boys to use indirect aggression. The trivial effect size may seem surprising given the popular notion of “mean girls” who use indirect strategies such as negative gossip and social exclusion. However, because direct aggression is less likely amongst girls than boys, girls tend to use proportionally more indirect than direct aggression than boys, on average. Thus, when most girls do express aggression, they may be more apt to use indirect rather than direct physical or verbal aggression (Leaper, 2013). Many boys may use a similar amount of indirect aggression as girls and additionally use more direct aggression. Average gender differences in aggression have been found primarily in research on same-gender interactions. Research conducted with mostly European American children suggests that different rules may apply when some girls and boys have conflicts with one another. Beginning in early childhood, boys are more likely than girls to ignore the other gender’s attempts to exert influence (Maccoby,

1998). Thus, when they are more assertive and less affiliative, boys may be more apt to get their way in unsupervised mixed-gender groups.

Indirect aggression includes behaviours such as criticizing and spreading rumors about a peer or excluding a peer from the friendship group. Contrary to the “mean girl” stereotype in popular media, average rates of indirect aggression appear similar for girls and boys. However, boys use higher average rates of direct physical and

verbal aggression. Therefore, when acting aggressively, girls may tend to use proportionally more indirect than direct aggression than boys do.

Studies in the United States comparing children’s behaviour in samegender versus cross-gender conflicts revealed another interesting pattern. In same-gender conflicts, boys were more likely to use power-assertive strategies (e.g., threats, demands) and girls were more likely to use conflict-mitigation strategies (e.g., compromise, change the topic). Yet in cross-gender conflicts, girls’ use of powerassertive strategies increased, while boys’ use of conflict-mitigation strategies did not change (Miller et al., 1986; Sims, Hutchins, & Taylor, 1998). These studies suggest that cisgender girls often may find it necessary to play by the boys’ rules to gain influence in mixedgender settings.

Explanations for Gender Differences in Aggression Possible explanations for gender differences in aggression range from the effects of physiological factors to the socializing influences of family, peers, the media, and the culture at large. Each factor likely has a contributing role.

Brain and hormonal influences

It is well known that, on average, males have higher baseline levels of testosterone than do females. Many people assume that this accounts for gender differences in aggression. Contrary to this popular belief, there does not appear to be a direct association between aggression and baseline testosterone levels (Archer, Graham-Kevan, & Davies, 2005). However, there is an indirect one: the body increases its production of testosterone in response to perceived threats and challenges, and this increase can lead to more aggressive behaviour (Archer, 2006). Furthermore, people who are impulsive and less inhibited are more likely to perceive the behaviour of others as threatening. Thus, because boys, on average, have more difficulty regulating emotional arousal (Else-Quest et al., 2006), they may be more prone to engage in direct aggression (Hay, 2007). Conversely, greater average emotion regulation amongst girls (compared to boys) may contribute to higher rates of prosocial behaviour and lower rates of direct aggressive behaviour.

Cognitive and motivational influences Average gender differences in empathy and prosocial behaviour may be related to differences in boys’ and girls’ rates of aggression (Knight, Fabes, & Higgins, 1996; Lemerise & Arsenio, 2000; Levant, 2005; Mayberry & Espelage, 2007). On average, girls are somewhat more likely than boys to report feelings of empathy and sympathy in response to people’s distress (Eisenberg & Fabes, 1998), and they also tend to display more concern in their behavioural reactions (e.g.,

looks of concern and attempts to help). Direct aggression may be more likely amongst children who are less empathetic and have fewer prosocial skills. In support of this explanation, one study found average gender differences, with boys demonstrating higher rates of direct aggression and lower rates of empathy than girls, but both aggressive girls and aggressive boys were rated lower on empathy than were nonaggressive girls and boys (Mayberry & Espelage, 2007). The gender-typed social norms and goals regarding assertion and affiliation may further contribute to the average gender difference in conflict and aggression (Chang, 2004; Miller et al., 1986; Rose & Rudolph, 2006; see Table 15.1). More boys than girls tend to favour assertive over affiliative goals (e.g., being dominant), whereas more girls than boys tend to endorse affiliative goals or a combination of affiliative and assertive goals (e.g., maintaining intimacy). When some boys focus on dominance goals, they may be more likely to appraise conflicts as competitions that require the use of direct aggression. In addition, some boys may initiate direct aggression as a way to enhance their status. In contrast, by emphasizing intimacy and nurturance goals, many girls may be more likely to view relationship conflicts as threats to interpersonal harmony that need to be resolved through compromise (Miller et al., 1986). The normative social pressures amongst many girls to act “nice” may also lead them to avoid direct confrontation. However, when girls who adhere to these norms are unable to resolve a conflict, they may try to hurt one another through indirect

strategies such as criticizing or excluding the offender or sharing secret information about the offender with other girls (Murray-Close, Ostrov, & Crick, 2007; Underwood, 2003).

Parental and other adult influences In general, most parents and other adults disapprove of physical aggression in both boys and girls. After the preschool years, however, adults tend to be more tolerant of aggression in boys and often adopt a “boys will be boys” attitude toward it (Martin & Ross, 2005). In a classic experiment demonstrating this effect, researchers asked people to watch a short film of two children engaged in rough-andtumble play in the snow and to rate the level of the play’s aggressiveness (Condry & Ross, 1985). The children were dressed in gender-neutral snowsuits and filmed at a distance that made their gender undeterminable. Some viewers were told that both children were boys; others were told that the children were both girls; still others were told that the children were a boy and girl. Viewers who thought that both children were boys rated their play as much less aggressive than did viewers who thought that both children were girls. A subsequent Canadian study showed that this “boys will be boys” bias may vary somewhat with observer gender: male early childhood educators were less concerned about boys’ physical aggression than were female early childhood educators (Bosacki et al., 2015).

Children also appear aware of this “boys will be boys” bias. They believe that physical aggression is more acceptable, and less likely to be punished, when enacted by boys than when enacted by girls (Giles & Heyman, 2005; Perry, Perry, & Weiss, 1989). Thus, girls’ average reliance on primarily indirect strategies of aggression — that are covert and easily denied if detected — may reflect their recognition that displays of physical aggression on their part will attract adult attention and punishment. Parenting style may also factor into children’s manifestations of aggression. Harsh, inconsistent parenting and poor monitoring increase the likelihood of physical aggression in childhood (Leve, Pears, & Fisher, 2002; Vitaro et al., 2006). Children who experience such parenting may learn to mistrust others and make hostile attributions about other people’s intentions (Crick & Dodge, 1996). The association between harsh parenting and later physical aggression is stronger for boys than for girls. Also, as noted in Chapter 14, poor parental monitoring increases children’s susceptibility to negative peer influences and is correlated with higher rates of aggression and delinquency (Jacobson & Crockett, 2000). Thus, the fact that parents monitor daughters more closely than sons may contribute to gender differences in aggression.

Peer influences Gender differences in aggression are consistent with the gender-

typed social norms of girls’ and boys’ same-gender peer groups. For example, a study conducted in China of 82 junior high school classrooms (with 50–60 students each) found that average gender differences in rates of aggression varied across classrooms, depending on whether there were gender differences in classroom norms for accepting aggression (Chang, 2004). However, it is worth noting that children who are high in aggression and low in prosocial behaviour are typically rejected in both male and female peer groups (Hawley, Little, & Card, 2008). These children tend to seek out marginal peer groups of other similarly rejected peers; these contacts strengthen the likelihood of physical aggression over time (Werner & Crick, 2004). Another peer influence on aggression may be boys’ regular participation in aggressive contact sports, which sanction the use of physical force and may contribute to higher rates of direct aggression amongst boys (Kidd, 2013; Messner, 2002). Support for this proposal is the finding that participation in aggressive sports, such as football, in high school is correlated with a higher likelihood of sexual aggression in university (Forbes et al., 2006). As explained in Box 15.3, aggressive behaviours may also involve sexual harassment.

BOX 15.3 APPLICATIONS Sexual Harassment and Dating Violence Sexual harassment commonly affects children and adolescents, and it can involve

direct (physical or verbal) or indirect (relational) aggression. Physical sexual harassment involves inappropriate touching or forced sexual activity. Verbal sexual harassment involves unwanted, demeaning, or homophobic sexual comments, whether spoken directly to the target or indirectly, behind her or his back. Also, verbal harassment commonly spreads via electronic media (Ybarra & Mitchell, 2007). Surveys in the United States and Canada indicate that the vast majority of youth of all genders have experienced sexual harassment during adolescence (AAUW, 2011; Leaper & Brown, 2008; McMaster et al., 2002; Mitchell et al., 2014). Most teen sexual harassment occurs in school hallways and classrooms, and the perpetrators are more likely to be peers rather than teachers or other adults. In a large-scale study of Canadian students, 41% of girls and 30% of boys in grade 10 reported having experienced sexual harassment at least once during the prior two months (Craig, Lambe, & McIver, 2016). A more recent online survey of adolescent Internet users in the United States (Mitchell et al., 2014) examined rates of reported sexual harassment separately for youth based on their gender and self-identified sexual orientation. Across ages (13 to 18 years), the percent reporting sexual harassment was 43% for heterosexual girls, 72% for lesbian girls, 66% for bisexual girls, 23% for heterosexual boys, 82% for transgender youth, 66% for gay boys, and 50% for bisexual boys. The findings from Mitchell and colleagues’ survey are consistent with other reports, including data from Canadian adolescents, that rates of sexual harassment may be higher for sexual-minority (lesbian, gay, bisexual), transgender, and other gendernonconforming youths (AAUW, 2011; Williams et al., 2005). When the adolescents in a U.S. national survey were asked to indicate whether and how sexual harassment affected them, girls were more likely than boys to report negative effects (AAUW, 2011; also found in Mitchell et al., 2014). The most common responses to sexual harassment in this survey included not wanting to go to school (37% of girls, 25% of boys) and finding it difficult to study (34% of girls, 24% of boys). Boys were more likely than girls to report that experiences with

sexual harassment had no effect on them (17% of boys, 10% of girls). Amongst cisgender heterosexual youth, girls appear to have more negative reactions to sexual harassment on average than do boys — perhaps partly because girls are somewhat more likely than boys to experience repeated sexual harassment (AAUW, 2011). Also, because of traditional masculine socialization, boys may be more reluctant to admit vulnerability (Farkas & Leaper, 2016). For any individual, repeated experiences with sexual harassment can have long-term negative consequences on self-esteem and adjustment (Bucchianeri et al., 2014; Leaper & Brown, 2008; Olson et al., 2016). Sexual harassment and violence also occur in dating relationships. Physical aggression occurs in an estimated one-fourth of adolescent heterosexual dating relationships in the United States (Hickman, Jaycox, & Aronoff, 2004; O’Leary et al., 2008), with boys the more likely perpetrators (Swahn et al., 2008; Wolitzky-Taylor et al., 2008). A recent study in British Columbia suggests that physical aggression in adolescent dating relationships has declined slightly over the past 10 years, perhaps due to programming that emphasizes healthy relationships (Shaffer et al., 2018). In a recent nationwide survey of 9th- to 12th-grade students in the United States (Kann et al., 2016), the reported incidence of having been forced to have unwanted sexual intercourse was 18% for gay, lesbian, and bisexual respondents compared to 5% for heterosexual respondents. In addition, 18% of gay, lesbian, and bisexual students reported being victims of dating violence in the past year compared with 8% of heterosexual students (Kann et al., 2016). The surveys described above were primarily conducted in the United States but generally align with Canadian data. Other studies indicate that sexual harassment and sexual violence are also problems for teens in many parts of the world (see Leaper & Robnett, 2018). A cross-national comparison indicated that rates of sexual violence against women were higher in countries with greater societal gender inequality (Yodanis, 2004).

Media influences A common question raised by parents and researchers is whether frequently watching violent TV shows and movies or playing violent video games has a negative impact on children. As you might expect, boys are more likely than girls to devote time to these activities (Cherney & London, 2006). One possible inference is that consuming more violent media may contribute to average gender differences in physical aggression. Our discussion of media violence in Chapter 9 makes clear that viewing aggression in movies, TV programming, and video games is associated with children’s aggressive behaviour and that this holds true for girls as well as boys. As also noted in that chapter, the degree and nature of this relationship remains a topic of debate. Whereas boys are more likely than girls to favour TV shows and movies with violent content, one study found that adolescent girls were more likely than boys to prefer shows depicting indirect aggression (Coyne & Archer, 2005). Furthermore, an experimental study demonstrated that observing indirect aggression on TV increased the subsequent likelihood of indirect aggressive behaviour but had no impact on direct aggression (Coyne, Archer, & Eslea, 2004).

Other cultural influences Although gender differences in aggression have been observed in all cultures, cultural norms also play an important role in determining the levels of aggression that are observed in boys and girls. Douglas Fry (1988) studied rural communities in the mountains of Mexico and found that the levels of childhood aggression that were considered normal varied widely from one area to another. Boys in each community showed more aggression than girls did. However, girls in the high-aggression communities were more aggressive than boys in the low-aggression communities. The community context must also be considered in relation to the emergence of differential rates of aggression. More than 60% of children (under 18 years) in the United States are estimated to have experienced or witnessed violence in their community within the past year (Child Trends Data Bank, 2016; Finkelhor et al., 2009). Moreover, these experiences are more common for children living in lowincome, inner-city environments than those in wealthier suburbs. When children are exposed to violence in their homes and communities, boys and girls both experience an increased risk of emotional and behavioural problems and show an increase in aggressive behaviours. However, boys are more likely than girls to be exposed to the highest levels of violence, and the average impact of exposure is also greater for boys than for girls (Guerra, Huesmann, & Spindler, 2003).

Boys are more likely to witness violent events, and these experiences may contribute to higher average rates of aggression for boys compared with girls.

REVIEW QUESTION How do social cultural norms influence the various patterns of gender development discussed in this section?

CHAPTER SUMMARY Sex and Gender Sex describes distinctions between genetic females (XX) and genetic males (XY), as well as other genetic sex compositions; gender indicates social assignment or self-categorization as female or male (or neither). A variety of terms are used to distinguish between different gender identities, including cisgender, transgender, nonbinary (genderqueer), gender-fluid, bigender, and agender. Terms are also used to describe how gender is socialized: gender typing refers to the process of gender socialization during development, and terms such as cross-gender-typed and gender nonconforming describe behaviours contrary to those stereotyped for a given person’s assigned gender. Research has shown gender differences in some areas, including cognitive abilities, personality traits, and social behaviours, but these differences tend to be small and there is often considerable overlap between genders. Hyde’s gender similarities hypothesis argues that similarities between genders far outweigh differences on most attributes.

Theoretical Approaches to Gender

Development Biosocial theory focuses on the impact of evolved physical differences between females (childbearing and nursing capacities) and males (greater strength, speed, and size) in relation to the social ecology. Other biological researchers take a neuroscience approach to gender development by focusing on sex differences in brain organization and the influences of sex hormones (such as androgens) both before birth and after. Another approach, which addresses cognitive and motivational influences on gender development, includes cognitive developmental theory, gender schema theory, social cognitive theory, and social identity theory. All emphasize children’s active participation in learning gender roles and adopting the preferences and behaviours considered appropriate for their gender, thereby highlighting how gender development is largely a process of self-socialization. According to cognitive developmental theory, once children realize that their gender is consistent across situations (gender constancy), they pay close attention to same-gender models to learn how to behave. Gender schema theory maintains that children construct mental representations of gender based on their own experience and the gender-related ideas they are exposed to. Children begin to acquire same-gender interests and values as soon as they can identify their own gender. Subsequently, children pay greater attention to, and learn more about, those things that they regard

as relevant for their own gender. Social cognitive theory addresses many processes involved in learning gender-typed values and behaviours, including observing others’ behaviour and determining the consequences of particular behaviours in relation to one’s own or other people’s gender. Children internalize gender-typed norms, standards that they use to monitor their own behaviour. Social identity theory also stresses the importance of adopting a gender identity and proposes that children tend to form an ingroup bias favouring attributes associated with their own gender and also to enforce conformity to gender-role norms. Two recent theoretical approaches have attempted to integrate aspects of physiological, cognitive, motivational, situation, and cultural influences on gender development. Developmental intergroup theory (DIT) describes how diverse processes contribute to the development of stereotyping and prejudice based on a person’s gender. The gender self-socialization model (GSSM) emphasizes the degree to which children’s efforts to form an identity and understand the world around them contributes to their gender development. The bioecological model characterizes children’s development as embedded in nested systems ranging from the microsystem (immediate environment) to the macrosystem (society). A key feature of the macrosystem is its opportunity structure and the corresponding roles available to women and men that shape the ways in which girls and boys are socialized.

Milestones in Gender Development

Between 6 and 8 weeks of prenatal development, sexual differentiation begins. External and internal genitalia are normally completed by the end of the first trimester. During their first year, infants learn to distinguish male from female faces. Between ages 2 and 3, children learn to identify their own gender, start to acquire stereotypes about males and females, and begin to prefer gender-typed toys and play activities. During preschool, children begin to gravitate toward samegender peers, and a strong tendency for children to selfsegregate by gender persists until adolescence. Preschool children also stereotype certain traits and activities for each gender. Preferences for gender-typed play become stronger from early to middle childhood. At about 6 years of age, children develop gender constancy. In addition, during middle childhood, they come to understand that gender roles are social conventions. They also may understand that gender discrimination is unfair and notice when it occurs. Average gender differences in social behaviour begin to emerge, with boys more likely than girls to stress assertion over affiliation, and girls more apt to emphasize affiliation or a combination of affiliation and assertion. During adolescence, gender roles sometimes become more flexible (due to increased cognitive flexibility) or more rigid (due to concerns with heterosexual roles and adoption of conventional gender attitudes).

Patterns of Gender Development

Boys and girls are quite similar in physical development until puberty, which begins earlier for girls than for boys. Amongst the largest average gender differences are physical strength, speed, and size after puberty, and a moderate difference exists in physical activity level. Girls and boys score similarly on tests of general intelligence. Slight-to-small average gender differences have been reported in specific cognitive abilities: boys show higher proficiency with certain types of spatial reasoning and mathematic ability, and girls show a small advantage in verbal ability. In academic achievement, girls have tended to do better than boys in reading and writing, whereas boys have tended to do better than girls in the physical sciences. Girls also tend to do better in overall school performance. Biological, cognitive-motivational, and cultural factors may contribute to gender-related variations in academic achievement. Researchers find academic achievement in particular domains is related to the expectations of parents, peers, and teachers. The gender gap in U.S. achievement in STEM fields has dramatically closed in recent decades, and such differences are less likely in societies characterized by greater overall gender equality. Average gender differences in communication and interpersonal goals during childhood and adolescence have been found to be modest. More boys than girls tended to emphasize dominance and power as goals in their social relationships, and more girls than boys tended to favour intimacy and support as goals in their relationships.

Direct (physical and verbal) aggression is associated with an average gender difference of moderate effect size, with higher rates amongst boys than amongst girls. No meaningful average gender difference appears in indirect aggression (such as social exclusion or negative gossip). However, indirect aggression constitutes a larger proportion of all aggressive behaviours amongst girls than amongst boys. Lower average levels of selfregulation may be partly related to the higher incidence of direct aggression amongst boys. Some cultural variations in the magnitude of gender difference in direct aggression are related to the degree that behaviours such as sexual harassment are tolerated in a particular culture.

Test Yourself 1. The gender similarities hypothesis emphasizes that in areas of cognitive behaviours and social abilities a. b. c. d.

all measurable differences between the sexes are trivial. boys and girls develop on parallel but unequal tracks. similarities between boys and girls far outweigh differences. differences between boys and girls outweigh similarities.

2. Rose is a 9-year-old girl. She strongly prefers wearing T-shirts and jeans to dresses and other “girly” clothes. She loves sports and hates playing with dolls. Rose’s preferences are an example of a. b. c. d.

gender-role intensification cross-gender-typed behaviour cisgender modelling gender segregation

3. Gender typing refers to

.

a. b. c. d.

the identification of an individual based on sex chromosomes. an individual’s personal identification as male, female, or neither. the process of gender socialization that occurs during development. the genetic forces that determine an individual’s sex during prenatal development.

4. The use of gendered nouns and pronouns, the association of certain hairstyles with specific genders, and the gender differentiation of specific colours are all examples of which of the following? a. b. c. d.

The psychological salience of gender Gender identity Organizational influences Gender-role intensification

5. Finnegan, a 5-year-old boy, is given a choice between playing with a toy truck or a ballerina doll. He chooses the truck because he has learned that boys play with trucks and girls play with dolls. This episode illustrates the child’s a. b. c. d.

.

interest filter intersectionality gender schema filter gender segregation

6. Exposure to high levels of prenatal androgens in genetic females may influence the development of their nervous system in such a way that results in certain cross-gender-typed behaviours. This example demonstrates the effect of a. b. c. d.

.

activating influences cisgender disposition organizing influences self-socialization

7. Which of the following statements is most representative of Kohlberg’s conception of the gender constancy stage?

a. b. c. d.

“Girls can have babies, boys cannot.” “I am a boy today, but could be a girl tomorrow.” “Even if I cut my hair and dress like a boy, I am a girl.” “I will always be a girl.”

8. The complex web of influences—including gender, sexual orientation, race, social class, and other group affiliations—that shape an individual’s social identity and experiences is known as a. b. c. d.

.

gender schema in-group assimilation intersectionality collaboration

9. Alex is a 6-year-old boy. His father disapproves when Alex plays with his sister’s dolls but happily engages with him when Alex plays with trucks. This scenario is an example of the influence of

in shaping

Alex’s gender identity. a. b. c. d.

observational learning collaboration enactive experience intersectionality

10. Gender segregation refers to a. the tendency of young children to associate with same-gender peers and avoid other-gender peers. b. the difference between the sexes in cognitive and behavioural tendencies. c. the tendency for an individual to engage in gender-typed behaviours. d. the tendency of an individual to retain information that is gender schema-consistent. 11. An individual who is high in both assertion and affiliation is likely to display which of the following communication styles? a. Collaboration b. Withdrawal

c. Obliging statements d. Controlling statements 12. The tendency of adolescents to integrate elements of traditional gender roles into their personal values, which can lead to increased gender discrimination, is known as a. b. c. d.

.

gender-role flexibility gender-role intensification assimilation collaboration

13. Some people believe that men are supposed to protect women. They may also believe that men and women possess complementary traits, such as men are leaders and protectors and women are submissive and nurturing. These attitudes reflect a. b. c. d.

.

gender constancy the interest filter benevolent sexism hostile sexism

14. Children tend to be motivated to achieve in those areas that they find personally valuable and in which they expect to succeed. This tendency is described by which of the following models? a. b. c. d.

Gender self-socialization model Developmental intergroup model Expectancy-value model of achievement Affiliation-assertion model

15. Small but consistent gender differences have been found in all of the following domains except a. b. c. d.

self-concept general intelligence communication skills mental spatial rotation tasks

.

DON’T STOP NOW! Research shows that testing yourself is a powerful learning tool. Visit LaunchPad to access the LearningCurve adaptive quizzing system, which gives you a personalized study plan to help build your mastery of the chapter material through videos, activities, and more. Go to launchpadworks.com.

Critical Thinking Questions 1. The four children described at the start of the chapter were portrayed to highlight variations in gender-typed behaviour and interests both between gender and within genders. How would the different theories outlined in this chapter attempt to explain these differences and similarities? How would different theories account for other children who have more flexible gender-typed behaviours and interests? 2. Think about how females and males were portrayed in shows, movies, and video games as you were growing up. How might these depictions have affected your gender development? 3. Imagine that you wanted to raise your own children to be as minimally gender-typed as possible. Which of the theoretical perspectives outlined in the chapter would you rely on most? Do you think you would be more likely to achieve your goal with a daughter or a son? 4. Historically, men have held dominant status in society, but over the course of the last several decades, women have significantly increased their status and power in Canada and in many other countries. Women now occupy top ranks in many occupations, and it is no longer uncommon to see men engaged in childcare and housework. How do

you think this trend toward gender equality amongst adults will affect the kinds of play activities and behaviours in which girls and boys engage in the future? 5. Research on gender development has tended to focus on cisgender children. How might the inclusion of a wider range of gender identities affect our understanding of gender differences and gender development in the future?

Key Terms activating influences adrenarche affiliation agender ambivalent sexism androgen insensitivity syndrome (AIS) androgens assertion bigender body image cisgender collaboration congenital adrenal hyperplasia (CAH) cross-gender-typed effect size enactive experience gender

gender constancy gender-fluid gender identity gender nonconforming gender schema filter gender schemas gender segregation gender stability gender-typed gender typing gender-role flexibility gender-role intensification ingroup assimilation ingroup bias interest filter intersectionality intersex condition menarche meta-analysis nonbinary (genderqueer) observational learning opportunity structure organizing influences puberty self-socialization sex spermarche transgender

tuition

Answers to Test Yourself 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

c b c a c c c c c a a b c c b

CHAPTER 16

Conclusions

LINCOLN SELIGMAN, Kite Flying (watercolour on paper, 2000)

Theme 1: Nature and Nurture: All Interactions, All the Time Theme 2: Children Play Active Roles in Their Own Development

Theme 3: Development Is Both Continuous and Discontinuous Theme 4: Mechanisms of Developmental Change Theme 5: The Sociocultural Context Shapes Development Theme 6: Individual Differences Theme 7: Child-Development Research Can Improve Children’s Lives

THEMES NATURE AND NURTURE THE ACTIVE CHILD CONTINUITY/DISCONTINUITY MECHANISMS OF CHANGE THE SOCIOCULTURAL CONTEXT INDIVIDUAL DIFFERENCES RESEARCH AND CHILDREN’S WELFARE

In the preceding 15 chapters, you have encountered a great deal of information about how children develop. You learned about the development of perception, attachment, conceptual understanding, language, intelligence, emotional regulation, peer relations, aggression, morality, gender, and a host of other vital human characteristics. Although these are all important parts of child development, the sheer amount of information may seem daunting: getting lost in the trees and losing a sense of the forest is a real risk. We therefore devote this final chapter to providing an overview of the forest by organizing many of the specifics that you have learned into an integrative framework. A likely side benefit of reading this chapter

is that you will probably discover that you understand much more about child development than you realized. The integrative framework that organizes this chapter consists of the seven themes that were introduced in Chapter 1 and highlighted throughout the book. As we have noted, most child-development research is ultimately aimed at understanding fundamental issues related to these themes. This is true regardless of the type of development that the research addresses and regardless of whether the research focuses on fetuses, infants, toddlers, preschoolers, school-age children, or adolescents. Beneath the myriad details, the seven themes emerge again and again.

Theme 1: Nature and Nurture: All Interactions, All the Time When people think about a child’s nature, they typically focus on the biological characteristics with which the child enters the world. When they think of the child’s nurture, they focus on the childrearing experiences provided by parents, caregivers, and other adults. Within this view, nurture is like a sculptor, shaping the raw material provided by the child’s nature into ever closer approximations of its final form. Although this metaphor is appealing, the reality is much more complex. Unlike the sculptor’s passive media of marble and clay, children are active participants in their own development. They seek out experiences based on their inclinations and interests. They also influence other people’s behaviour toward them: from birth onward, their nature influences the nurture they receive. In addition, rather than nature doing its work before birth and nurture doing its work after, nurture influences development even before birth, and nature is just as influential in adolescence and adulthood as earlier. In this section, we review how nature and nurture interact to produce development.

Nature and Nurture Begin Interacting

Before Birth When prenatal development proceeds normally, it is easy to think of it as a simple unfolding of innate potential, one in which the environment matters little. When things go wrong, however, the interaction of nature and nurture is all too apparent. Consider the effects of teratogens. Prenatal exposure to these potentially harmful substances — which include toxins in the general environment, such as mercury, radiation, lead, insects (e.g., mosquitoes carrying the Zika virus), and air pollution, as well as toxins that depend on parental behaviour (e.g., cigarettes, alcohol, and illegal drugs) — can cause a wide variety of physical and cognitive impairments. Nevertheless, whether and how much a given baby will actually be affected depends on innumerable interactions amongst the genetics of the mother, the genetics of the fetus, and a host of environmental factors such as the particular teratogen and the timing and amount of exposure. The interaction of nature and nurture during the prenatal period is also evident in fetal learning. The experience of hearing the mother’s voice while in the womb leads a newborn to prefer her voice to that of other women. The influence of prenatal experience can be longlasting; for example, prenatal exposure to garlic-flavoured food influences liking of such flavours amongst 8- and 9-year-olds. Thus, preferences that are often thought of as being determined purely by nature reflect nurture as well.

Infants’ Nature Elicits Nurture Nature equips babies with a host of qualities that elicit appropriate nurture from parents and other caregivers. One big factor in babies’ favour is that they are cute; most people enjoy watching and interacting with them. By looking and smiling at other people, babies motivate others to feel warmly toward them and to care for them. Their emotional expressions — cries, coos, and smiles — guide caregivers’ efforts to figure out what to do to make them happy and comfortable. In addition, their attentiveness to sights and sounds that they find interesting encourages others to talk to them and to provide the stimulation necessary for learning. One simple example of this interactive relationship is the fact that parents everywhere sing to their infants; infants throughout the world find singing soothing, bounce in response to rhythm, and respond positively to melodies.

Timing Matters The effects of an experience on development depend on the state of the organism at the time of the experience. Timing of exposure to teratogens greatly influences their effects on prenatal development. For example, if a pregnant woman comes down with rubella early in pregnancy, when the developing visual and auditory systems are at a particularly sensitive point, her baby may be born deaf or blind; if she comes down with rubella late in pregnancy, the risk that damage

will occur is considerably lower. Timing also influences many aspects of development in the months and years following birth. The development of perceptual capabilities presents numerous illustrations of the importance of appropriate experience at the appropriate time. The general rule in such cases is “use it or lose it”: for normal development to occur, children must encounter the relevant experiences during a certain window of time. Auditory development provides a good example. Until 8 months of age, infants can discriminate between phonemes regardless of whether they occur in the language the infants hear daily. By age 12 months, however, infants lose the ability to hear the difference between similar sounds that they do not ordinarily encounter or that are not meaningfully different in their native language. Similar sensitive periods occur in grammatical development. Children from East Asia who move to the United States and begin to learn English as a second language before age 7 acquire grammatical competence in English that eventually matches that of native-born American children. Those who arrive between ages 7 and 11 learn almost as well. However, individuals who arrive at later ages rarely master English grammar, even after many years of hearing and speaking the language of their adopted land. Deaf children’s learning of sign language shows a similar pattern: early exposure results in more complete grammatical mastery.

The importance of normal early experience is also evident in social, emotional, and intellectual development. Infants and toddlers who do not have an emotional connection with any caregiver, such as the children who spent their first years in the infamous orphanages of Romania in the 1980s or in concentration camps during World War II, often continue to interact atypically with other people long after being placed in loving homes. Those who spent their first 2 years or more in the Romanian orphanages also had unusually high rates of low IQ for many years after they were adopted into the loving families. Thus, in many aspects of the development of perception, language, intelligence, emotions, and social behaviour, the timing of experience is crucial.

Infants’ expressions of contentment and happiness when engaging in certain activities motivate their parents and other adults to engage in the activities with them.

Nature Does Not Reveal Itself All at Once Many genetically influenced properties do not become evident until middle childhood, adolescence, or adulthood. One obvious example is the physical changes that occur at puberty. A less obvious example involves nearsightedness. Many children are born with genes that predispose them to become nearsighted, but most do not become so until late childhood or early adolescence. A third example involves the steep rise during adolescence in the incidence of depression. Depression has a genetic component, but the increased rate of depression in adolescence, especially in girls, is also attributable to the many challenges of dealing with the world of adolescence, such as encountering cruel comments on social media.

Differences in running speeds are partially attributable to genetic differences that are present at birth, but nature takes time to reveal itself. Who could have looked at these children when they were newborns and predicted who would be the best runners?

The development of schizophrenia follows a similar path. Schizophrenia is highly influenced by genes inherited at conception, but most people who become schizophrenic do not do so until late adolescence or early adulthood. As with other aspects of development, the emergence of schizophrenia reflects a complex interplay between nature and nurture. Children with a schizophrenic biological parent who are raised by nonschizophrenic parents are more likely to become schizophrenic themselves than are the biological children of the nonschizophrenic parents. Children who are raised in troubled homes are also more likely than others to become schizophrenic. However, the only children with a substantial likelihood of becoming schizophrenic are those who grow up in a troubled family and have a biological parent who is schizophrenic. As in other contexts, the interaction between the children’s nature and the nurture they receive is crucial. Perhaps the most surprising and compelling evidence for the interaction of nature and nurture comes from the emerging field of epigenetics. Although people often think of the genotype as being “fixed” at birth, experience can enhance or silence gene expression. Early stressful environments, such as those imposed by poverty, seem to especially influence later gene expression. Thus, adults who grew up in low-income families exhibit different patterns of gene expression decades later than do adults who grew up in high-income homes, regardless of their incomes as adults. Even more remarkably, some of these effects of the early environment on the genome are

passed down to the next generation, perhaps through the mechanism of early adversity influencing methylation of sperm cells. Thus, not only does nature not reveal itself all at once, but nature itself changes as a result of nurture.

Everything Influences Everything One common reaction to learning about the complex interactions between nature and nurture is “It sounds like everything influences everything else.” Although it sounds glib, this conclusion is basically accurate. Consider some of the factors that influence children’s and adolescents’ self-esteem. Genes matter; the closer the biological relation between two children or adolescents, the more similar their degree of self-esteem is likely to be. A large part of the reason for this genetic influence on self-esteem is that genes influence a wide range of other characteristics that themselves influence self-esteem. For example, genes strongly affect attractiveness, athletic talent, and academic success, all of which contribute to self-esteem. Factors other than genes also play large roles in the development of self-esteem. Support from one’s family and peers contribute in positive ways; poverty and unpopularity contribute in negative ways. Unrelated adults also can have positive or negative influences on selfesteem. For example, having a supportive teacher can promote a child’s self-esteem, and having a hostile or demeaning teacher can

reduce it. Values of the broader society are also influential. East Asian societies tend to emphasize the importance of self-criticism, and children and adolescents in those societies report lower levels of selfesteem than do peers in Western societies. Complex interactions are not limited to the development of selfesteem or to social development; they are characteristic of development in all areas. For example, in the development of intelligence, the influence of genetics seems to be greater than that of shared environment for children from middle- and upper-income backgrounds, but the opposite seems to be true for children from impoverished backgrounds. Similarly, parental involvement in school is more closely related to academic achievement in lowincome families than in more affluent families. Thus, children’s nature — their genes, personal characteristics, and behavioural tendencies — interact with the nurture they receive from parents, teachers, peers, the broader society, and the physical environment to shape their self-esteem, intellect, and other qualities.

Theme 2: Children Play Active Roles in Their Own Development Physical activity begins even before the fetus leaves the womb; the kicking that thrills prospective parents is perhaps the most obvious example. Less obviously, fetuses are also mentally active. While still in the womb, they can learn enough about the sounds in a story their mother repeatedly reads aloud that, as newborns, they react differently to that story than to ones their mother did not read aloud. Moreover, from their first minutes outside the womb, infants selectively focus on objects and events that interest them rather than passively gazing at whatever appears before their eyes. Infants’ and older children’s actions also produce reactions in other people, which further shape the children’s development. In this section, we examine four ways in which children contribute to their own development: through physically interacting with the environment, interpreting their experience, regulating their behaviour, and eliciting reactions from other people.

As this infant’s eager gaze suggests, children’s choices of where to look are amongst the ways in which they shape their own development.

Self-Initiated Activity Even in the womb, typical development depends on the activity of the fetus. Fetuses make breathing movements that strengthen their lungs, and they swallow amniotic fluid that prepares their digestive system to function properly after birth. They also “work out” various muscles by tugging on their umbilical cord, sucking their thumb, kicking, and turning somersaults.

From the day they are born, infants display looking preferences that guide their attention to the most informative aspects of the environment that their processing abilities can handle. They like looking at objects rather than at blank fields. They like looking at moving objects rather than at stationary ones and at the edges of objects rather than at their interiors. And they particularly like looking at faces, especially their mother’s. Infants’ ability to interact with the environment expands greatly during the first year. At about 3 months, most infants become able to fairly smoothly follow moving objects with their eyes, which improves their ability to learn about the actions occurring around them. At 6 or 7 months, many become able to crawl on their bellies and, soon after, on their hands and knees; as a result, they no longer have to wait for the world to come to them. By 8 or 9 months, most can hold up their heads, which allows them to reach accurately for objects even when they are not being supported. And by 13 or 14 months, most begin to walk independently, which opens new frontiers for exploration. As development proceeds, children’s self-initiated activity extends to additional domains such as language. Toddlers delight in telling their parents the names of objects — for no reason beyond the joy of doing so. They practice talking in their cribs, even when nobody else is present to hear them. They and older children, both deaf and hearing, invent gestures and words to represent objects and events. As their language proficiency develops, children become skilled at

initiating conversations that bring them information, allow them to express their feelings and desires, and help them regulate their emotions.

Children’s choices of activities shape their development. This child’s interest in print led him to learn to read and write at age 3; the fact that he is one of the authors’ children also probably had something to do with his early interest in these skills. (He also is now the father of the baby in the preceding photo.)

The effects of self-initiated activities are also seen at older ages in other areas, such as self-socialization and antisocial behaviour. Throughout the world, boys and girls choose to play predominantly with members of their own gender, especially between the ages of 6 and 10 years. The play patterns reflect the children’s own choices.

Gender segregation is rarely imposed by adults; rather, it arises from differences in the kinds of play that boys and girls tend to prefer. Beginning in the school years, these preferences tend to be reinforced by unkind comments and ridicule from peers when a child crosses the “gender border.” In later childhood and adolescence, children’s choices of friends and peer groups become important influences on their own behaviour, in that children tend to increasingly act like their friends and others in their social group in both positive and negative ways. Thus, from the prenatal period through adolescence, children’s self-initiated activities contribute to their development.

Active Interpretation of Experience Children also contribute to their development by trying to understand the world around them. Even in the first year, infants gain a sense of what is possible in the physical world. Thus, they look longer at an “impossible” event — such as when one solid object appears to move through the space occupied by another object, or when an object seems to be suspended in midair without support — than they do at an event that is similar but physically possible. Toddlers’ and preschoolers’ continuous “why” questions, and school-age children’s searching for the explanations of magic tricks, provide other compelling examples of children’s eagerness to understand the

world. This desire to understand also motivates young children to construct informal theories concerning inanimate objects, living things, and people. These theories allow children to go beyond the data provided by their senses to infer underlying causes. For example, preschoolers reason that there must be something inside animals that causes them to grow, breathe, have babies, get sick, and so on, even though they do not know what that something is. They also reason that inanimate objects must have different material inside them than living things do. Children’s and adolescents’ interpretations of their experiences extend to inferences about themselves as well as about the external world. When some children fail to solve a problem, for example, they feel sad and question their ability. Other children who fail on the same task take the failure as a challenge and an opportunity to learn. Similarly, in ambiguous social situations, aggressive children tend to attribute hostile intent to others even when the others’ motives are unclear; this interpretation sometimes leads aggressive children to lash out before the other person can hurt them. Thus, subjective interpretations of experiences, as well as objective reality, shape development.

Self-Regulation

Another way in which children contribute to their own development is by regulating their behaviour. Consider how they regulate their emotions. In the first months after they are born, infants rely almost entirely on parents and other caregivers to help them cope with fright and frustration. By age 6 months, they learn to cope with some upsetting situations by rubbing their bodies to soothe themselves. During the toddler and preschool periods, children become increasingly adept at using physical strategies, such as looking away, when faced with stressors or temptation. During elementary school, they increasingly use cognitive strategies, such as reminding themselves that an unpleasant experience will soon be over, to cope with negative situations. Across a wide range of ages, children who successfully regulate their emotions tend to be more popular and more socially competent than those who are less skilled at emotional regulation. These early self-regulation skills are related to long-term developmental outcomes. For example, boys who exhibit strong selfregulation abilities in the preschool and early elementary school periods are less likely as adults to use cocaine and other drugs. Children’s early self-control also has been found to be a strong predictor of their later grades in school and of occupational and economic success in adulthood. Over the course of childhood and adolescence, children increasingly regulate their development through their choice of activities. Whether young children go to sports events, movies, libraries, or

religious services depends mainly on whether their parents take them there. Whether adolescents engage in the same activities depends mainly on their own preferences. Selecting moral values, choosing a romantic partner, pursuing an occupation, and deciding whether to have children are just a few of the major decisions that adolescents and young adults face. The wisdom of their choices strongly influences their subsequent lives.

Eliciting Reactions from Other People Because children of all ages differ from one another in behaviour and appearance, they evoke different reactions from other people. For example, babies with easy temperaments elicit more positive reactions from their parents than do cranky or fussy babies. Similarly, attractive babies elicit more affectionate and playful mothering than do less attractive ones. And in trying times, attractive children are less likely to suffer parental rejection and punishment than are less attractive ones. Other adults also are influenced by children’s actions. For example, when children encounter difficulty learning particular material, teachers act in more encouraging ways if the child has generally been well behaved than if the child has been badly behaved in the past. The effects that children’s initial inclinations have on their parents’ behaviour toward them multiply over time. Most parents of children

who are disobedient, angry, and challenging try to be supportive but firm with them. However, if the negative behaviour and defiance continue, many parents become hostile and punitive. Other parents, faced with belligerence and aggression, back down from confrontations and increasingly give in to their children’s demands. Once such negative cycles are established, they are difficult to stop. If teenagers act disruptively, and parents respond with hostility, problems generally worsen over the course of adolescence.

It is all too easy for relations between parents and children to spiral downward, with disobedience and anger from children eliciting anger and hostility from parents, which then elicits more disobedience and anger from children, and so on.

Description The daughter is facing away from her mother, at the edge of a park bench, with earphones in her ears and looking displeased. The mother, seated

beside her, talks to her animatedly and looking distressed.

Children’s characteristics and behaviour influence not just their parents’ and teachers’ reactions but also those of their peers. At all

ages, children who are cooperative, friendly, sociable, and sensitive to others tend to be popular with their peers, whereas those who are aggressive or disruptive tend to be disliked and rejected. In some cases, peers’ reactions to one another’s behaviour change with age; for example, kindergartners tend to neither like nor dislike withdrawn peers, but older elementary and middle school students tend to dislike such children. Peer reactions to children’s behaviour often have long-term consequences; children who were rejected by peers when younger are more likely than children who were popular to have difficulty later in school and to engage in criminal activity. In many ways, then, children influence their own development not only by initiating actions, interpreting their experiences, and regulating their emotions, but also by eliciting reactions from other people that then shape their subsequent behaviour.

Theme 3: Development Is Both Continuous and Discontinuous Long before there was a scientific discipline of child development, philosophers and others interested in human nature argued about whether development is continuous or discontinuous. Current disputes between those who believe that development is continuous, such as social-learning theorists, and those who believe it is discontinuous, such as stage theorists, thus have a long history. Both positions have endured so long for good reason: each captures important truths about development, yet neither captures the whole truth. Two particularly important issues in this long-standing debate involve continuity/discontinuity of individual differences and continuity/discontinuity of the standard course of development with age.

Continuity/Discontinuity of Individual Differences One sense of continuity/discontinuity involves stability of individual differences over time. The basic question is whether children who initially are higher or lower than most peers in some quality continue to be higher or lower in that quality years later. It turns out that many individual differences in psychological properties are moderately

stable over the course of development, but the stability is always far from 100%. Consider the development of intelligence. Some stability is present from infancy onward. For instance, the faster that infants habituate to repeated presentation of the same display, the higher their IQ scores tend to be 10 or more years later. Infants’ patterns of electrical brain activity also are related to their speed of processing and attention regulation more than 10 years later. The amount of stability increases with age. IQ scores show some stability from age 3 to age 13, considerable stability from age 5 to age 15, and substantial stability from age 8 to age 18. Even in later childhood, however, IQ scores vary from occasion to occasion. For example, when the same children take IQ tests at ages 8 and 17, the two scores differ on average by 9 points. Part of this variability reflects random fluctuations in how sharp the person is on the day of testing and in the person’s knowledge about the particular questions on each test. Another part of the variability reflects the fact that even if two children start out with equal intelligence, one may show greater intellectual growth over time. Individual differences in social and personality characteristics also show some continuity over time. Shy toddlers tend to grow into shy children, fearful toddlers into fearful children, aggressive children into aggressive adolescents, generous children into generous adults, and so on. The continuity also carries over into situations quite

different from any that the children faced at the earlier time; for example, secure attachments in infancy predict positive romantic relationships in adolescence. Although there is some continuity of individual differences in social, emotional, and personality development, the degree of continuity is generally lower than in intellectual development. For example, whereas children who are high in reading and math achievement in 5th grade generally remain so in 7th grade, children who are popular in 5th grade may or may not be popular in 7th grade. In addition, aspects of temperament such as fearfulness and shyness often change considerably over the course of early and middle childhood. Regardless of whether the focus is on intellectual, social, or emotional development, the stability of individual differences is influenced by the stability of the environment. For instance, an infant’s attachment to his or her mother correlates positively with the infant’s long-term security, but the correlation is higher if the home environment is consistent than if serious disruptions occur. Similarly, IQ scores are more stable if the home environment remains stable. Thus, continuities in individual differences reflect continuities in children’s environments as well as in their genes.

Continuity/Discontinuity of Overall Development: The Question of Stages

Many of the most prominent theories of development divide childhood and adolescence into a small number of discrete stages. Piaget’s theory of cognitive development, Freud’s theory of psychosexual development, Erikson’s theory of psychosocial development, and Kohlberg’s theory of moral development all describe development in this way. The enduring popularity of these stage approaches is easy to understand: they simplify the enormously complicated process of development by dividing it into a few distinct periods; they point to important characteristics of behaviour during each period; and they impart an overall sense of coherence to the developmental process. Although stage theories differ in their particulars, they share four key assumptions: (1) development progresses through a series of qualitatively distinct stages; (2) when children are in a given stage, a fairly broad range of their thinking and behaviour exhibits the features characteristic of that stage; (3) the stages occur in the same order for all children; and (4) transitions between stages occur quickly. Development turns out to be considerably less tidy than stage approaches imply, however. For example, children who exhibit preoperational reasoning on some tasks often exhibit concrete operational reasoning on others; children who reason in a preconventional way about some moral dilemmas often reason in a conventional way about others; and so on. Rarely is a sudden change evident across a broad range of tasks.

In addition, developmental processes often show a great deal of continuity. Throughout childhood and adolescence, there are gradual, continuous increases in the ability to regulate emotions, make friends, take other people’s perspectives, remember events, solve problems, and engage in many other activities. This does not mean that there are no sudden jumps. When we consider specific tasks and processes, rather than broad domains, we see many discontinuities. Typically, 3-month-olds move from having almost no binocular depth perception to having adultlike levels within 1 or 2 weeks. Fear of strangers is rare at 4 months but very common by 8 months. Many toddlers move in a single day from being unable to walk without support to walking unsupported for a number of steps. After acquiring about one word per week between ages 12 and 18 months, many toddlers undergo a vocabulary explosion, in which the number of words they know and use expands rapidly for years thereafter. Thus, although broad domains, such as intelligence and personality, rarely show discontinuous changes, specific aspects of development fairly often do. Whether development appears to be continuous or discontinuous often depends on whether the focus is on behaviour or on underlying processes. Behaviours that emerge or disappear quite suddenly may reflect continuous underlying processes. Recall the case of infants’ stepping reflex. For the first 2 months after birth, if infants are supported in an upright position with their feet touching the ground, they will first lift one leg and then the other in a pattern similar to

walking. At around age 2 months, this reflex suddenly disappears. Underlying the abrupt change in behaviour, however, are gradual changes in two dimensions — the infant’s weight and leg strength. As babies grow, their gain in weight temporarily outstrips their gain in leg strength, and they become unable to lift their legs without help. When babies who have stopped exhibiting the stepping reflex are supported in a tank of water, making it easier for them to lift their legs, the stepping reflex reappears. Whether development appears continuous or discontinuous also depends on the timescale being considered. Recall that when a child’s height was measured every 6 months from birth to 18 years, the growth looked continuous (see Figure 1.3). When height was measured daily, however, development looked discontinuous, with occasional “growth days” sprinkled amongst numerous days without growth. One useful framework for thinking about developmental continuities and discontinuities is to envision development as a road trip across Canada, from St. John’s to Victoria. In one sense, the drive is a continuous progression westward along the Trans-Canada Highway (with a few ferry rides along the way!). In another sense, the drive starts in the East and then proceeds (in an invariant order, without the possibility of skipping a region) through the Atlantic provinces, central Canada, the Prairies, and the Rocky Mountains before reaching its end point in British Columbia. The East includes the Atlantic provinces, and they tend to be hilly, cloudy, and green;

central Canada is made up of lowlands, lakes, and rivers; the Prairies tend to be flatter, drier, and sunnier; and the West has extensive mountainous areas where heavy snow falls. The differences between regions in climate, colour, and topography are large and real, but the boundaries between them are arbitrary. For example, is Quebec the westernmost Atlantic province (given its extensive Atlantic coast) or the eastern part of Central Canada?

A trip along the Trans-Canada Highway (and on a few ferries) from St. John’s to Victoria takes a driver through six time zones in which the main features of the land change dramatically. The changes in topography, like those in development, however, are not discontinuous. Adjacent areas tend to be highly similar, and classification of a border area as being in one zone or another is often quite arbitrary. In all of these ways, the journey resembles psychological development.

Description The map has the northern portion of Canada in the north, the eastern portion of Canada and the north eastern portion of the United States in the east, the central portions of the United States in the south, and Alaska in the west. The data from the map are as follows: British Columbia in the south western portion of Canada and Yukon to the north of it, have one time zone. Alberta to the east of British Columbia, the Northwest Territories to the north of Alberta, and the north west portions of Nunavut all come under the same time zone. The south and the north central portions of Nunavut, Saskatchewan to the east of Alberta, Manitoba to the east of Saskatchewan, and the western portions of Ontario all come under the same time zone. The eastern portions of Nunavut, much of Ontario, and most of Quebec, all come under the same time zone. The south eastern portion of Quebec, New Brunswick, Nova Scotia, and Prince Edward Island, all come under one time zone. Newfoundland and Labrador have one time zone. The Trans-Canada Highway extends from the south western tip of Canada, moves through the southern regions of British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick, the northern portion of Nova Scotia, and the southern portion of Prince Edward Island and ends at the south eastern tip of Newfoundland and Labrador.

The continuities and discontinuities in development are a lot like those on the road trip. Consider children’s conceptions of the self. At one level of analysis, the development of the self is continuous. Over the course of development, children (and adults) understand more and more about themselves. At another level of analysis, milestones characterize each period of development. During infancy, children come to distinguish between themselves and other people, but they rarely if ever see themselves from another person’s perspective. During the toddler period, children increasingly view themselves as others might, which allows them to feel such emotions as shame and guilt. During the preschool period, children realize that certain of their personal characteristics are permanent, and they use this knowledge to guide their behaviour. During the elementary school years, children increasingly think of themselves in terms of their competencies relative to other children’s (intelligence, athletic skill, popularity, and so forth). During adolescence, they come to recognize how differently they themselves act in different situations. Thus, any statement about when a given competency emerges is somewhat arbitrary, much like a statement about where a geographic region begins. Nonetheless, identifying the milestones helps us understand roughly where we are on the map.

Theme 4: Mechanisms of Developmental Change As with so many other issues, contemporary thinking about developmental change owes a large debt to the ideas of Jean Piaget. Within Piaget’s theory, change occurs through the interaction of assimilation and accommodation. Through assimilation, children interpret new experiences in terms of their existing mental structures; through accommodation, they revise their existing mental structures in accordance with the new experiences. Thus, when we hear a truly unfamiliar type of music (for most of us, Javanese 12-tone music would fit this description), we assimilate the sounds to more familiar musical patterns to the extent we can. At the same time, our understanding accommodates to the experience so that when we next encounter the unfamiliar music, it will be a little easier to grasp and will feel a little less strange. A great deal has been learned about developmental mechanisms since Piaget formulated his theory. Some of the advances have come in understanding change at the biological level, others in understanding it at the behavioural level, and still others in understanding it at the level of cognitive processes.

Biological Change Mechanisms

Biological change mechanisms come into play from the moment a sperm unites with an egg. The sperm and egg each contain half of the DNA that will constitute the child’s genotype throughout life. The genotype contains instructions that specify the rough outline of development, but all particulars are filled in by subsequent interactions between the genotype and the environment. The way in which the brain forms after conception illustrates the complexity of change at the biological level. The first key process in brain development is neurogenesis, which by the 3rd or 4th week after conception is producing roughly 10,000 brain cells per minute. About 100 days later, the brain contains almost all the neurons it ever will have. As neurons form, a process of cell migration causes many of them to travel from where they were produced to their long-term location. Once neurons reach their destination, they undergo a process of differentiation, in which dendrites and axons grow out from the original cell body. Later in the prenatal period, the process of myelination adds an insulating sheath over certain axons, which speeds up the rate of transmission of electrical signals along them. Myelination continues through childhood and into adolescence. Yet another process, synaptogenesis, involves formation of synapses between the ends of axons and the beginnings of dendrites that allow neurotransmitters to transmit signals from neuron to neuron. The

number of synapses increases rapidly from the prenatal period to early or middle childhood (depending on the particular brain area). By the end of this period of explosive growth, the number of synapses in a given area far exceeds the number in the brains of adults. A process of pruning then reduces the number of synapses. The greatest pruning occurs at different times in different brain areas; in some areas, notably the prefrontal cortex, the pruning process occurs throughout adolescence and beyond. Those synapses that are frequently used are maintained; those that are not are eliminated (reflecting “use it or lose it” at the biological level). The pruning of unused synapses increases the efficiency of information processing. The brain includes a number of areas that are specialized for specific functions. This specialization makes possible rapid and universal development of these functions and thus enhances learning of the relevant type of information. Some of the functions are closely linked to sensory and motor systems. The visual cortex is particularly active in processing sights; the auditory cortex is particularly active in processing sounds; the motor cortex is particularly active in making movements; and so on.

The scans show the group average pattern of brain activation for each of three increasingly difficult items (from left to right) on a problem-solving task that requires both executive functioning and spatial processing. As shown, with increasing problem difficulty, the amount of neural activity increases in the prefrontal cortex (toward the front of the brain, often involved in executive functioning) and in the superior parietal cortex (toward the back of the brain, often involved in spatial processing).

Description The first scan has the Dorsolateral prefrontal cortex labeled at the top right portion of the brain, and shows an increase in executive functioning, with the neural activity increasing in the prefrontal cortext, that is, in the front portion of the brain. R is labeled at the top left portion of the scan and L is labeled at the top right portion of the scan. The next scan shows an increase both in executive functioning and spatial processing, meaning increase in neural activity along the front and the back portion of the brain. The final scan has

the Superior parietal cortex labeled at the bottom left portion of the brain scan, and shows an increase in spatial processing, referring to significant increase in neural activity in the back portion of the brain.

Other brain areas are specialized for functions that are not specific to any one sensory or motor system. The limbic system, located in the lower part of the brain, is particularly prominent in producing emotions. The prefrontal cortex is particularly involved in executive functioning. Some areas in the parietal lobe are particularly active in processing space, time, and number. All of these areas are involved

in numerous other types of processing, and all types of processing involve numerous brain areas, but each of the areas is especially active in processing the type of information associated with it. Thus, biological mechanisms underlie both specific and broad changes.

Behavioural Change Mechanisms Behavioural change mechanisms describe responses to environmental contingencies that contribute to development. These learning mechanisms shape behaviour from the prenatal period onward.

Habituation, Conditioning, Statistical Learning, and Rational Learning The capacity to habituate to familiar stimuli begins before fetuses leave the womb. By 30 weeks after conception (8 to 10 weeks before the typical time of birth), the central nervous system is sufficiently developed for habituation to occur, as reflected in a fetus’s heart rate initially slowing down (a sign of interest) when a bell is rung next to the mother’s belly and then the heart rate returning toward the typical rate as the bell is rung repeatedly. Habituation continues after birth as well, and it is seen in changes in looking patterns as well as in heart-rate patterns. For example, when a picture of a face is shown

repeatedly, infants reduce the time they spend looking at it, but they show renewed interest when a different face appears. Habituation motivates babies to seek new stimulation when they have already learned from an experience and thus helps them learn more. From their first days in the outside world, infants also can learn through classical conditioning. If an initially neutral stimulus is repeatedly presented just before an unconditioned stimulus, it comes to elicit a similar response to that elicited by the unconditioned stimulus. For example, when a tone is presented simultaneously with a puff of air to a newborn’s eye, the infant learns to blink when the tone is sounded, even without the air puff. Like older children, infants also learn through instrumental conditioning; behaviours that are rewarded become more frequent, and behaviours that do not lead to rewards become less frequent. Even young infants appear highly motivated to learn in this way: 2month-olds express joy and interest when they see a behaviour produce a desired outcome, and they cry and express anger when a learned response no longer produces the desired results. Infants in their first year generalize their instrumental learning to somewhat novel situations, as well as learning about the specific earlier situation. Thus, after learning to kick in order to make a particular mobile jiggle, 6-month-olds (though not 3-month-olds) generalize the kicking to other mobiles. As this example illustrates, instrumental learning is narrower early in infancy than it will be later.

Yet another mechanism that allows infants to acquire information rapidly is statistical learning. From birth onward, infants quickly learn the likelihood that one sight or sound will follow another. Because many events, including the sounds within words and certain daily routines, occur in predictable orders, statistical learning helps infants anticipate other people’s actions and generate similar sequences of behaviour themselves. Closely related to statistical learning is rational learning, which involves integrating the learner’s prior beliefs and biases with what actually occurs in the environment. When, for example, infants observe an adult pulling balls of two different colours out of a transparent box, seemingly at random, and the ratio of the colours of those balls deviates greatly from that of the total set of balls in the box, the infants’ looking times suggest that they are surprised. Together with habituation, classical conditioning, generalization, and instrumental and statistical learning, such rational learning allows infants to acquire knowledge of the world from the first days following birth.

Social Learning Children (and adults) learn a great deal from observing and interacting with other people. This social learning pervades our lives to such an extent that it is difficult to think of it as a specific learning capability. However, when we compare humans with other animals

— even close relatives such as chimpanzees and other apes — the centrality of social learning in people’s lives becomes apparent. Humans are far more skillful than any other animal in learning what others are trying to teach us; we also are far more inclined to teach others what we know. Amongst the crucial contributors to this social learning are imitation, social referencing, language, and guided participation. The first discernible form of social learning is imitation. At first, the imitation is limited to behaviours that infants sometimes spontaneously produce on their own, such as sticking out the tongue, and even that is inconsistent. However, by the second half of the first year, infants imitate novel behaviours that they never make spontaneously. By 15 months, toddlers not only learn novel behaviours but can also remember and continue to produce them for at least a week. This imitation is not just “monkey see, monkey do.” When children of this age see a model unsuccessfully try to do something, they imitate what the model was trying to do rather than what the model actually did and use alternative means to reach what they see as the intended goal. Social learning influences socioemotional development as well as knowledge acquisition. When an unfamiliar person enters the room, 12-month-olds look to their mother for guidance. If the mother’s face or voice shows fear, the baby tends to stay close to her; if the mother smiles, the baby is more likely to approach the stranger. Similarly, in the laboratory, a baby of this age will often cross the visual cliff — in

which a transparent plexiglass floor is placed over what looks like a steep drop off — but only if the mother smiles; they rarely will cross if she looks worried.

Imitation starts in infancy.

Social learning also shapes children’s standards and values. From the second year of life, toddlers internalize their parents’ values and standards and use them to guide and evaluate their own conduct. Later in development, peers, teachers, and other adults also influence children’s standards and values through the process of social learning. Peers, in particular, play a steadily increasing role over the course of childhood and adolescence. Imitation is not the only mechanism of social learning. Another is social scaffolding. In this change mechanism, a more knowledgeable

person may provide the learner with an overview of a given task, demonstrate how to do the most difficult parts, provide help with the most difficult parts, and offer suggestions to the learner on how to proceed. Such scaffolding allows a beginner to do more than he or she could do without help. Then, as the learner masters the basics of the task, the more expert person transfers more and more responsibility to the learner until the learner is doing the entire task. Thus, children and other people collaborate to produce social learning.

Using tools to build and repair things is a common context for social scaffolding, in which the more experienced person helps the younger and less experienced person to operate at a higher level than would otherwise be possible.

Cognitive Change Mechanisms Many of the most compelling analyses of developmental change are at the level of cognitive processes. Both general and specific information-processing mechanisms play important roles.

General Information-Processing Mechanisms Four types of information-processing mechanisms are especially general and pervasive: basic processes, strategies, metacognition, and content knowledge. Basic processes are the simplest, most broadly applicable, and earliest-developing general information-processing mechanisms. They overlap considerably with behavioural learning processes and include associating events with each other, recognizing objects as familiar, recalling facts and procedures, encoding key features of events, and generalizing from one instance to another. Changes with age occur in the speed and efficiency of these basic processes, but all

of the basic processes are present from early infancy onward. These basic processes provide a foundation that allows infants to learn about the world from their very first days. Strategies also contribute to many types of development. Toddlers, for example, form strategies for achieving goals such as obtaining a toy that is out of reach or descending a steep ramp; preschoolers form strategies for counting and solving arithmetic problems; schoolage children form strategies for playing games and getting along with others; and so on. Often, children acquire multiple strategies for solving a single kind of problem — for example, strategies for approaching unfamiliar children on a playground or for solving arithmetic problems. Knowing multiple strategies allows children to adapt to the demands of different problems and situations. Metacognition is a third type of cognitive process that contributes to development in large ways. For instance, increasing use of memory strategies stems in large part from children’s increasing realization that they are unlikely to remember large amounts of material verbatim without such strategies. Amongst the most important applications of metacognition is adaptive choice amongst alternative strategies, such as whether to reread to understand text, whether to count or state a retrieved answer to solve an arithmetic problem, and whether to write an outline before beginning an essay. The cognitive control involved in executive functioning — for example, inhibiting tempting but counterproductive actions, being cognitively flexible, and considering other people’s perspectives — is another crucial type

of metacognition. Content knowledge is a fourth pervasive contributor to cognitive change. The more children know about any topic — whether it be chess, soccer, dinosaurs, or language — the better able they are to learn and remember new information about it. Knowledge also facilitates learning of unfamiliar content by allowing children to draw analogies between the new content and previously acquired information.

Exceptional content knowledge can outweigh all of adults’ usual intellectual advantages over children. On the day this photograph was taken, this 8-year-old boy became the youngest person ever to defeat a chess grandmaster (the ranking awarded to the greatest chess players in the world).

Domain-Specific Learning Mechanisms Infants acquire some complex competencies surprisingly rapidly, including basic perception, understanding of the physical world, language comprehension and production, interpretation of emotions, and attachment to caregivers. What seems to unite the varied capabilities that children acquire especially rapidly is their importance for further learning and survival. A number of theorists have posited that the nearly universal, rapid learning in these domains is produced by domain-specific learning mechanisms that operate on everyday experience to produce accurate conclusions about the world. For example, even infants in their first year seem to expect stationary objects to be more strongly affected by collisions with bigger moving objects than with smaller moving objects. Similarly, toddlers’ word learning seems to be aided by the whole-object assumption (the idea that words used to label objects refer to the whole object rather than to a part of it) and the mutual exclusivity assumption (the idea that each object has a single name). These assumptions are usually correct for the words that toddlers hear, thus helping them learn what the words mean. Children’s informal theories about the main types of entities in the world — inanimate objects, people, and other living things — also facilitate their learning about them. The value of learning rapidly about the properties of people, other living things, and inanimate

objects is clear; saying “More juice” to another person, for example, is considerably more likely to yield the desired outcome than is saying the same words to a dog, no matter how intelligent the dog is. Crucial in children’s informal theories, as in scientists’ formal ones, are causal relations that explain a large number of observations in terms of a few basic unobservable processes. Possessing basic understanding of key concepts — such as inertia and solidity for inanimate objects; goal-directed movement and growth for living things; and intentions, beliefs, and desires for people — helps children act appropriately in new situations. For example, a preschooler who meets an unfamiliar peer assumes that the other child will have intentions, beliefs, and desires — an assumption that helps the preschooler understand the other child’s actions and react appropriately to them. These assumptions about other people’s minds aid the social understanding of children in all societies. Thus, both general and domain-specific cognitive learning mechanisms help children understand the world around them.

Change Mechanisms Work Together Although it is often easiest to discuss different change mechanisms separately, it is crucial to remember that biological, cognitive, and behavioural mechanisms all reflect interactions between the person and the environment and that all types of mechanisms work together

to produce change. For instance, consider effortful attention. The development of this capability reflects a combination of biological and environmental factors. On the biological side, genes influence the production of neurotransmitters that affect children’s ability to focus and ignore distractions. Effortful attention also relies on the development of connections between two parts of the brain — the anterior cingulate, which is active in attention to goals, and the limbic area, which is active in emotional reactions. On the environmental side, the development of effortful attention is influenced by the quality of parenting a child receives — though this is true primarily for children with a particular genotype. For children with one form of a relevant gene, quality of parenting substantially influences the development of effortful attention, whereas for children with another form of the gene, quality of parenting has little effect on its development. Specific experiences can also be influential; for example, playing specially designed computer games increases the activity of the anterior cingulate and thus may aid the ability to sustain attention on both experimental tasks and intelligence tests. In short, varied types of mechanisms work together to produce development of even a single capability.

Theme 5: The Sociocultural Context Shapes Development Children develop within a personal context of other people: families, friends, neighbours, teachers, and classmates. They also develop within an impersonal context of historical, economic, technological, and political forces, as well as societal beliefs, attitudes, and values. The impersonal context is important in shaping development, just as the personal one is. There is little reason to think that parents in economically advanced societies in the twenty-first century love their children more than parents of the past did. Yet children today die less often, get sick less often, eat a more nutritious diet, and receive more formal education than did children from even the wealthiest families of 100 or 200 years ago. Thus, when and where children grow up profoundly influences their lives.

Growing Up in Societies with Different Practices and Values Values and practices that people within a society take for granted as “natural” often vary substantially amongst societies. These variations influence the rate and form of development. Throughout the book, you have encountered examples of this in every aspect of development, including in domains that are commonly thought of as

being governed entirely by maturation. For example, people often assume that the timing of walking and other motor skills in infancy is determined solely by biology, but babies who grow up in African tribes that strongly encourage infants’ motor development tend to walk and reach other motor milestones earlier than do infants in Canada and the United States. Similarly, infants in societies where babies sleep with their mothers for several years exhibit less fear at bedtime than do children in Canada and the United States, where babies rarely sleep in the same bed or even the same room as their mothers past the first 6 months of their lives. Emotional reactions provide another example of how cultural practices and values influence behaviour, even when we might not expect them to do so. Infants in all societies that have been studied show the same attachment patterns, but the frequency of occurrence of each pattern varies with the values of the society. Relative to babies in Canada and the United States, for instance, Japanese and Korean babies who are placed in the Strange Situation more often become very upset, showing the insecure/resistant attachment pattern (see Chapter 11). These differences in attachment patterns appear to be due to differing cultural values and practices. Japanese and Korean mothers traditionally encourage dependence in children and rarely leave their babies alone, which may lead the babies to become especially upset when they are left alone in the Strange Situation. In contrast, Canadian and U.S. parents emphasize independence to a greater degree and more often leave babies alone in a room or with other people.

Cultural influences such as these continue well beyond infancy. Japanese culture, for instance, places a higher value on hiding negative emotions, especially anger, than does American culture, and Japanese mothers discourage their children from expressing negative emotions. Quite likely because of these cultural influences, Japanese preschoolers and school-age children less often express anger and other negative emotions than do U.S. peers. Similarly, child rearing in rural Mexican villages emphasizes cooperation and caring about others, and children raised in these villages are more likely to share their possessions than are children from Mexican cities.

The culture of Mexican villages successfully encourages cooperation and helping amongst children and others.

Culture influences not only parents’ actions but also children’s interpretations of those actions. For example, harsh parenting is

associated with more aggressive behaviour at school for children from European-Canadian families, but it is associated with less aggressive behaviour in children from South-Asian Canadian families (C. Ho et al., 2008). The differing effectiveness of the disciplinary approaches may reflect children’s interpretations of their parents’ behaviour. If children believe that scolding and inducing shame and guilt are in their best interest, those behaviours can be effective. However, if children see such disciplinary approaches as reflecting negative parental feelings toward them, the discipline tends to be ineffective or harmful. Sociocultural differences exert a similar influence on cognitive development. They help determine which skills and knowledge children acquire — for instance, whether children learn to operate abacuses, iPads, or both. They also influence how well children learn skills that everyone acquires to some degree; for example, Australian aboriginal children, whose adult lives will depend on their ability to trek through the desert to distant oases, develop spatial skills superior to those of urban Australian children. Finally, cultural values influence the educational system, which in turn influences what and how deeply children learn. For instance, students in community-oflearners classrooms learn about fewer scientific topics than do children in traditional classrooms, but they learn about them in greater depth.

Growing Up in Different Times and Places When and where children grow up profoundly influences their development. As noted earlier, in modern societies, children’s lives are greatly improved over what they were in the past, in terms of health, nutrition, shelter, and other material factors. Modern life also enhances some types of opportunities for learning; for example, watching the children’s television program Sesame Street appears to have enhanced children’s learning in countries around the world. Not all of the changes in modern societies have promoted children’s wellbeing, however. For example, in North America and Europe, far more children grow up with divorced parents than in the past, and these children are at risk for many problems. On average, they are more prone to sadness and depression, have lower self-esteem, do less well in school, and are less socially competent than peers who live in intact families. Although most children from divorced families do not have serious problems, a minority do: engaging in delinquent activities, dropping out of school, and having children out of wedlock all are more common amongst children whose parents are divorced. Other historical changes result in children’s lives being different but not necessarily better or worse. The great expansion of childcare outside the home is one such case. In Canada, about 60% of children under 5 currently receive childcare outside their homes — a figure that has grown significantly since the 1960s. As this change was

occurring, many people feared that such care would weaken attachment between babies and mothers. Others expressed hopes that such care would greatly stimulate cognitive development, especially of children from impoverished backgrounds, because of the greater opportunities for interaction with other children and adults. In fact, the data indicate that neither the fears nor the hopes were justified. In almost all respects, children who receive care outside the home tend to develop similarly, both emotionally and cognitively, to those who do not. More generally, the same cultural or technological change can bring either positive or negative effects, depending on who the child is and how the innovation is used. For instance, the Internet can be used to communicate with friends, which tends to strengthen friendships, but it can also be used for cyberbullying. Playing certain electronic games stimulates development of attention, but very high frequency of playing such games can harm the quality of friendships. Similarly, moderate amounts of digital screen time do not appear to affect adolescents’ mental health, but high amounts are associated with greater risk of adolescents’ developing mental health problems. Thus, in terms of health, comfort, intellectual stimulation, and material well-being, children growing up today in modern societies are, on the whole, better off than those who grew up in the past, but in other ways, the picture is more mixed.

Growing Up in Different Circumstances Within a Society Even amongst children growing up at the same time in the same society, differences in economic circumstances, family relationships, and peer groups lead to large differences in children’s lives.

Economic Influences In every society, the economic circumstances of a child’s family considerably influence the child’s life. However, the degree of economic inequality within each society influences how large a difference the economic circumstances make. In societies with large income inequalities, such as the United States, poor children’s academic achievement is far lower than that of children from wealthier families. In societies with smaller inequalities, such as Canada, Japan, and Sweden, children from affluent families also do better academically than children from poorer families, but the differences are smaller. It is not just academic achievement that is influenced by economic circumstances; all aspects of development are. Infants from impoverished families more often are insecurely attached to their mothers. Children and adolescents from impoverished families more often are rejected as friends and more often report being lonely.

Illegal substance use, crime, and depression also are more common amongst poor adolescents than amongst peers from wealthier backgrounds. These negative outcomes are unsurprising, given the many disadvantages that children from impoverished families face. Relative to children who grow up in more affluent environments, poor children more often live in dangerous neighbourhoods; grow up in homes with one or no biological parents; attend inferior childcare centres and schools; less often are read to and spoken to by their parents; and have fewer books, magazines, and other intellectually stimulating material in their homes. The cumulative burden of these disadvantages, rather than any one of them, poses the greatest obstacle to successful development.

The Great Depression of the 1930s greatly increased the number of children in the United States, Canada, and other countries growing up in extreme poverty. How might the extreme poverty and instability faced by these children have affected their development, compared to that of their more affluent peers?

Influences of Family and Peers Families and peer groups vary considerably in ways other than income, and many of these differences also have a substantial

influence on development. In some families, regardless of income, parents are sensitive to babies’ needs and form close attachments with them; in others, this does not occur. In some families, again regardless of income, parents read to their children each night, thus helping the children learn to read; in others, this practice does not occur. The influence of friends, other peers, teachers, and other adults varies in as many ways as that of families. Friends, for example, can provide companionship and feedback, contribute to self-esteem, and serve as a buffer against stress; during adolescence, they can be particularly important sources of sympathy and support. On the other hand, friends can also have negative influences, drawing children and adolescents into reckless and aggressive behaviour, including crime, drinking, and drug use. Thus, personal relationships, like economic circumstances, culture, and technology, influence development, but the effects of these influences vary with the particulars.

Theme 6: Individual Differences Children differ on a huge number of dimensions — demographic characteristics (gender, race, ethnicity, socioeconomic status), psychological characteristics (intellect, personality, artistic ability), experiences (where they grow up; whether their parents are divorced; whether they participate in plays, bands, or organized sports), and so on. How can we tell which individual differences are the crucial ones for understanding children and predicting their futures? As illustrated in Figure 16.1, three variables — breadth of related characteristics, stability over time, and predictive value — are crucial in determining the importance of any dimension of individual differences. First, as shown by the red arrows in Figure 16.1, children’s status on the most important dimensions is associated with their status at that time on other important dimensions. Thus, one reason intelligence is considered a central individual difference is that the higher a child’s IQ at a given age, the higher the child’s grades, achievement test scores, and general knowledge tend to be at the same time. A second key characteristic is stability over time (the blue arrows in Figure 16.1). A dimension of individual differences is of greater interest if the higher or lower that children score on it early in development, the higher or lower they are likely to score on it later. Thus, another reason for interest in IQ is that children with high (or low) IQs usually grow into adults with high (or low) IQs. A

third characteristic of major dimensions of individual differences is that a child’s status on a dimension predicts outcomes on other important characteristics in the future (the green arrows in Figure 16.1). Thus, a third reason for interest in IQ scores is that a person’s IQ during middle childhood and adolescence predicts that person’s later earnings, occupational status, and years of education.

FIGURE 16.1 Intelligence and individual differences Intelligence is considered a crucial dimension of individual differences because IQ scores (1) correlate with other conceptually related dimensions such as general knowledge and grades at any one age (red arrows extending from IQ to other outcomes at age 7); (2) show considerable continuity over age (blue arrows); and (3) predict future outcomes, such as years of education and income in adulthood (green arrows connecting IQ score at age 7 to other later outcomes).

Description The flowchart is divided into three categories namely: Age: 7-year-olds, 15year-olds, and Adults. In the 7-year-olds category, two downward arrows from

the component with text reading, I Q score points to two components with the text reading, Grades, and Achievement test scores respectively. An upward arrow from the I Q score component points to a component with text reading, General knowledge. Arrows from the I Q score component point to a component with text reading, Achievement test scores under the 15-year-olds category; to the component with text reading, Years of education under the Adults category; to another I Q score component under the 15-year-olds category; to the Grades component under the 15-year-olds category; the Earnings, and Income components under the Adults category. An arrow from the I Q score component under the 15-year-olds category points to the I Q score component under the Adults category.

This analysis makes clear why demographic variables such as gender, race, ethnicity, and SES are studied so often. Consider gender, for

example. Gender differences are related to a wide variety of other differences. On average, cisgender boys tend to be larger, stronger, more physically active, and more physically aggressive; to play in larger groups; to be better at some forms of spatial thinking; and more often to have ADHD and math or reading disabilities. On average, cisgender girls tend to be more verbal, quicker to perceive emotions, better at writing, and more likely to express sympathy and empathy for people in distress. Gender identity as male or female also is generally stable over time. Finally, being male or female predicts future individual differences. If a newborn is female, it is likely that, compared with males, she will be more self-revealing with friends, more vulnerable to depression, more inclined to prosocial behaviour, and more disposed to using indirect aggression. However, keep in mind a few points. First, the correlation between a person’s gender and future individual differences reflects complex interactions amongst social and biological influences. Neither biological nor social factors in isolation cause these characteristics — they both do. For example, one reason that a person’s gender may predict their later behaviour is because girls and boys tend to be treated differently. Second, there is much variability within each gender. For example, not all boys are physically active and not all girls are good at perceiving emotions. Finally, there is much overlap between females and males in each of these behaviours, as can be seen in Table 15.1. For example, many girls and boys are good at spatial skills or verbal skills, and many girls and boys score poorly in these domains.

We next consider the extent to which several other variables show these three key features of individual differences.

Breadth of Individual Differences at a Given Time Individual differences are not randomly distributed. Children who are high on one dimension also tend to be high on other, conceptually related dimensions. Thus, children who do well on one measure of intellect — language, memory, conceptual understanding, problem solving, reading, or mathematics — tend to do well on others. Similarly, children who do well on one measure of social or emotional functioning — relations with parents, relations with peers, relations with teachers, self-esteem, prosocial behaviour, and lack of aggression and lying — also tend to do well on others. Sometimes, as with the relation between intelligence and school achievement, the connections are very strong. More often, the relations are moderate. Thus, although children who get along well with their parents also tend to get along well with peers, there are many exceptions. Beyond intelligence and gender, two other crucial dimensions of individual differences are attachment and self-esteem. Compared with their insecurely attached peers, a toddler who is securely attached to his or her mother tends to be more enthusiastic and positive about solving problems with her, to comply more often with

her directives, and to obey her requests even when she isn’t present. Such children also tend to get along better with other toddlers and to be more sociable and more socially competent. Similarly, children and adolescents who are high in self-esteem also tend to be strong on many other dimensions of social and emotional functioning. They tend to be generally hopeful and popular, to have many friends, and to have good academic and self-regulation skills. In contrast, those with low self-esteem tend to feel hopeless and to be prone to problems such as depression, aggression, and social withdrawal.

Stability Over Time Many individual differences show moderate stability over time. For instance, people who have easy temperaments during infancy tend to continue to have easy temperaments in middle and later childhood. Similarly, elementary school children with ADHD, reading disabilities, or mathematics disabilities usually have lifelong difficulties in those areas. The reasons for such stability of psychological characteristics are to be found in the stability of both genes and environment. A child’s genotype remains identical over the course of development (though particular genes switch on and off at different times). Most children’s environments remain fairly stable as well. Families that are middle class when a child is born tend to remain middle class; families that

value education when the child is born usually continue to value education; parents who are sensitive and supportive generally remain that way; and so on. Major changes, such as divorce and job loss, do occur, and they affect children’s happiness, self-esteem, and other characteristics. Nonetheless, the stability of children’s environments, like the stability of their genes, contributes to the stability of their psychological functioning over time.

Predicting Future Individual Differences on Other Dimensions Individual differences on some dimensions are related not only to future status on that dimension but also to future status on other dimensions. For instance, children who are securely attached as infants tend as toddlers and preschoolers to have more social ties to their peers than do children who were insecurely attached as infants. When they reach school age, these securely attached children tend to understand other children’s emotions relatively well and to be relatively skilled in resolving conflicts. When they reach adolescence and adulthood, they tend to form close attachments with romantic partners. All of these outcomes are consistent with the view that secure early attachment provides a working model that influences subsequent relationships with other people. As with stability over time of a single dimension, the relative stability

of most children’s environments contributes to these long-term continuities of psychological functioning. If children’s environments change in important ways, the typical continuities may be disrupted. Thus, stressful events such as divorce reduce the likelihood that children who were securely attached during infancy will continue to show the positive relations with peers usually associated with secure attachment.

Determinants of Individual Differences Individual differences, like all other aspects of development, are ultimately attributable to the interaction of children’s genes and the environments they encounter.

Genetics For a number of important characteristics — including IQ, prosocial behaviour, and empathy — about 50% of the differences amongst individuals in a given population are attributable to differences in genetic inheritance. The degree of genetic influence on individual differences tends to increase over the course of development. For example, correlations between the IQs of adopted children and their biological parents steadily increase over the course of childhood and adolescence, even if the children never meet or have any contact with their biological parents. One reason is that many genes related to

intellectual functioning do not exercise their effects until late childhood or adolescence. Another reason is that over the course of development, children become increasingly free to choose environments that are in accord with their genetic predispositions.

Genetic similarities sometimes produce a striking physical resemblance between parent and child. We can only wonder whether this baby, as she develops, will come to resemble her father in other ways as well.

Experience

Individual differences reflect children’s experiences as well as their genes. Consider just one major environmental influence: the parents who raise the children. The more that parents address speech to their toddlers, the more rapidly the toddlers recognize familiar words and learn new ones. The more that parents aim their scaffolding at, but not beyond, the upper end of their children’s capabilities, the greater the improvement in their children’s problem solving. The more stimulating and responsive the home intellectual environment, the higher children’s IQ tends to be. Parents exert at least as large an influence on their children’s social and emotional development as on their intellectual development. For example, the likelihood that children will adopt their parents’ standards and values appears to be influenced by the type of discipline their parents use with them. Similarly, parents influence their children’s willingness to share, especially if they discuss the reasons for sharing with their children and have good relationships with them. The effects of different types of parenting, like the effects of children’s other experiences, depends on the child. One example of this involves the development of conscience. For fearful children, the key factor determining whether the child internalizes the parents’ moral values is gentle discipline. Fearful children may become so anxious in the face of rigorous discipline that they cannot focus on the moral values that the parents are trying to instill. For fearless children, on the other hand, the key factor is a positive relationship

with one’s parents. Such fearless children often do not respond to gentle discipline; they tend to internalize their parents’ values only if they feel close to them. As an old adage states, “It’s a wise parent who knows his child.”

Theme 7: Child-Development Research Can Improve Children’s Lives One of the few goals shared by virtually everyone is for children to be as happy and healthy as possible. Understanding how children develop can contribute to this goal. Theories of development provide general principles for interpreting children’s behaviour and for analyzing their problems. Many empirical studies yield specific lessons regarding how to promote children’s physical well-being, positive relationships with other people, and learning. In this section, we review practical implications of child-development research for raising children, educating them, and helping them overcome problems.

Implications for Parenting Several principles of good parenting are so obvious that noting them might seem unnecessary. However, the number of children who are disadvantaged each year by poor parenting makes it clear that these principles cannot be stated too often.

Pick a Good Partner

The first principle of good parenting comes into play before parenthood even begins: pick a good partner. Given the importance of the environment, if you think you might want to have children, pick a partner whose intellectual and emotional characteristics seem likely to lead to their becoming a good mother or father. In terms of your child’s development, no decision is more important than your choice of partner.

Ensure a Healthy Pregnancy An expectant mother should maintain a healthy diet, have regular checkups, and keep stress levels as low as possible to increase the likelihood of a successful pregnancy. Equally important is avoiding teratogens such as tobacco, alcohol, and harmful drugs.

Know Which Decisions Are Likely to Have a Long-Term Impact In addition to the joy they feel when their baby is born, new parents face a daunting number of decisions. Fortunately, babies are quite resilient. In the context of a loving and supportive home, a wide range of choices work out about equally well. Some decisions that seem minor, however, can have important effects. One such decision involves the baby’s sleeping position: having a baby sleep on his or her back, rather than on his or her stomach, reduces the possibility of

SIDS. Another decision with important long-term impact is vaccinating children against German measles and other diseases that are common in childhood or can negatively affect children’s development; this is important not only for the health of one’s own child but also for the health of other children in the community. In other cases, the lesson of child-development research is that early problems are often transitory, so there is no reason to worry about them. Colic, which affects about 10% of babies, is one such problem. A colicky baby’s frequent, high-pitched, grating, sick-sounding cries are difficult for parents to bear, but they have no long-term implications for the baby’s development. In the short run, the best approach is to soothe the baby to the extent possible and not feel at fault if the effort fails. In the longer run, the best path for parents is to relax, seek social support, and obtain help to allow some time off from caregiving — and to remember that colic usually ends by the time babies are 3 months old.

Form a Secure Attachment Most parents have no difficulty forming a secure attachment with their baby, but some parents and babies do not form such bonds. One reason is genetics: variant forms of certain genes can influence the likelihood of a child’s forming a secure parental attachment in at least some circumstances. Of course, no one can control the genes that babies inherit, but parents and other caretakers can maximize the

likelihood of a baby’s becoming securely attached by maintaining a positive approach in their caregiving and by being responsive to the baby’s needs. This is easier said than done, of course, and other dimensions of a baby’s temperament, as well as the parents’ attitude and responsiveness, influence the quality of attachment. However, even when babies are initially irritable and difficult, programs that teach parents how to be responsive and positive with them can lead to more secure attachments.

Provide a Stimulating Environment The home environment has a great deal to do with children’s learning. One good example involves reading acquisition. Reading to young children positively influences their later reading achievement. One reason is that such activities promote phonological awareness (the ability to identify the component sounds within words). Nursery rhymes seem to be particularly effective in this regard; children who repeatedly hear Green Eggs and Ham, for instance, generally learn to appreciate the similarities and differences in Sam, ham, am, and related words. Phonological awareness helps children learn to sound out words, which, in turn, helps them learn to retrieve the words’ identities quickly and effortlessly. Successful early reading leads children to read more, which helps them improve their reading further over the course of schooling. More generally, the more stimulating the intellectual environment, the more eager children are to learn.

Family activities, such as looking at photo albums and reminiscing about the people and settings they depict, provide both stimulation and warm, positive feelings for many children.

Implications for Education Theories and research on child development hold a number of further lessons for how to educate children most effectively. Consider the instructional implications of several major theories of cognitive development. Piaget’s theory emphasizes the importance of the child’s active involvement, both mental and physical, in the learning process. This active involvement is especially important in helping children master

counterintuitive ideas. For example, the physical experience of walking around a pivot while holding a long metal rod at points close to and far from the pivot allowed children to overcome a widely held misconception that previous paper-and-pencil physics lessons had failed to correct — the misconception that all parts of an object must move at the same speed. Information-processing theories suggest that analyzing the types of information available to children in everyday activities can improve learning. One such analysis indicated that the simple board game Snakes and Ladders provides visual, auditory, kinesthetic, and temporal information that can help children learn the sizes of numbers. Consistent with this analysis, having children from lowincome families play a game based on Snakes and Ladders improved the children’s understanding of the sizes of numbers, as well as their counting, recognition of numbers, and arithmetic learning. Sociocultural theories emphasize the need to turn classrooms into communities of learners, in which children cooperate with one another in their pursuit of knowledge. Rather than following the traditional model of instruction in which teachers lecture and children take notes, community-of-learners classrooms follow an approach in which teachers provide the minimum guidance needed for children to learn and gradually decrease their directive role as children’s competence increases. Such programs also encourage children to make use of the resources of the broader community — children and teachers at other schools, outside experts, reference

books, websites, and so on. The approach can be effective not only in building intellectual skills but also in promoting desirable values, such as personal responsibility and mutual respect.

Implications for Helping Children at Risk Several principles that have emerged from empirical research offer valuable guidance for helping children at risk for serious developmental problems.

The Importance of Timing Providing interventions at the optimal time is crucial in a variety of developmental contexts. One important example involves efforts to help children at risk for learning difficulties. All theories of cognitive development indicate that such difficulties should be addressed early, before children lose confidence in their ability to learn and before they become resentful toward schools and teachers. This realization, together with research documenting that many children from impoverished backgrounds have difficulty in school, laid the groundwork for various early intervention and prevention programs. Evaluations of the programs’ effects indicate that these programs increase children’s IQs and achievement test scores by the end of the

programs and briefly thereafter. Subsequently, the positive effects on IQ and academic achievement usually fade, but other positive effects continue. At-risk children who participate in such programs are less likely to ever be held back in school or assigned to special-education classes than are those who do not participate, and they are more likely to graduate from high school and go to university. These are important gains. Even greater positive effects of early educational programs are possible, as illustrated by the Better Beginnings, Better Futures (BBBF) project and the Carolina Abecedarian Project. BBBF offered a variety of child-, parent-, and family- and community-focused programming to families with children between the ages of 4 and 8 years living in four Ontario communities considered “at risk.” Similarly, the Carolina Abecedarian Project was designed to show what could be achieved through an optimally staffed, highly funded, and carefully designed program that started during infancy and lasted through age 5. The Abecedarian Project produced large gains in both academic achievement and social skills that continued throughout childhood and adolescence. Its results demonstrate that it is possible for intensive programs that start early to have substantial, lasting benefits on poor children’s academic achievement.

Experiences such as this one in classrooms with early intervention programs lead to a variety of lasting benefits.

Early detection of child maltreatment and rapid intervention to end it are also crucial. Neglect, physical abuse, and sexual abuse are the three most common forms of child maltreatment. Parents who are stressed economically, have few friends, use alcohol and illegal drugs, or are being abused by their partner are the most likely to mistreat their children. Knowing the characteristics of abused and neglected children can help teachers and others who come into contact with children recognize potential problems early and alert social service agencies so that they can investigate and remedy the problems. Children who are maltreated tend to have difficult temperaments, to have few

friends, to be in poor physical and mental health, to do poorly in school, and to show atypical aggression or passivity. Adolescents who are maltreated may be depressed or hyperactive, use drugs or alcohol, and have sexual problems such as promiscuity or atypical fearfulness. Early recognition of such signs of abuse can literally save children’s lives.

Biology and Environment Work Together Another principle with important practical implications is that biology and environment work together to produce all behaviour. This principle has proved important in designing treatments for ADHD. Although stimulant drugs such as Ritalin are the best-known treatment for this problem, research has shown that when medications are used alone, their benefits usually end as soon as children stop taking them. Longer-lasting benefits require behavioural therapy as well as medication. One effective treatment is to teach children cognitive strategies for screening out distractions. The medications calm children with ADHD sufficiently that they can benefit from the therapy; the therapy helps them learn effective ways for coping with their problems and for interacting with other people.

Every Problem Has Many Causes An additional principle that has proved useful for helping children is

that trying to identify the cause of any particular problem is futile; problems almost always have multiple causes. The greater the number of risks, the more likely a child is to have low IQ, poor socioemotional skills, and psychiatric disorders. Accordingly, providing effective treatment often requires addressing many particular difficulties. This principle has provided useful guidance for intervening with children who are rejected by other children. Helping these children gain better social skills requires increasing their understanding of other people. It also requires helping them learn new strategies, such as how to enter an ongoing group interaction unobtrusively and how to resolve conflicts without resorting to aggression. It also requires helping them learn from their own experience — for example, by monitoring the success of the different strategies they try and, when necessary, analyzing what went wrong. Together, these approaches can help rejected children make friends and become better accepted.

Improving Social Policy Even if you do not have children of your own and do not interact with children in your own work, your actions as a citizen can influence the lives of the children in your community. Votes in elections and referenda, opinions expressed in informal discussions, and participation in advocacy organizations all can make a difference. Knowledge of child-development research can inform your

perspectives on many issues relevant to children. The conclusions that you reach will, and should, reflect your values as well as the evidence. For example, reductions in class size in kindergarten through 3rd-grade classrooms have had variable effects on student achievement. A large-scale, well-implemented study in Tennessee indicated positive effects on student achievement (Krueger, 1999), whereas a large-scale, well-implemented study in California did not show any effect on achievement (Stecher, McCaffrey, & Bugliari, 2003). Teachers and parents appeared to be pleased with the class-size reductions in both cases and believed that the smaller classes helped their children. Are these outcomes worth the many billions of dollars that hiring the number of teachers needed to implement such a reform throughout a large country would cost? Research cannot answer this question because the answer depends on values as well as data. How expensive is too expensive? Nonetheless, as the example illustrates, knowing the scientific evidence can help us, as citizens, make better-informed decisions.

Parental Leave Should society require employers to grant paid parental leave in the months after a baby is born, and if so, for how long? Canada is amongst the many countries in the world that have a national

parental leave policy, but the duration of leave varies significantly across these countries, and there are some countries, including the United States, with no such policy in place. Long hours of lower quality childcare before an infant is 9 months old can have negative effects on early social development; therefore, we could say that society should make it easier for parents to take leave for that period of time. However, other considerations, such as economic costs, are also important: Should governments require all employers to provide paid leave, or should small or very small businesses be exempted from the requirement? For how long should paid leave be required? Should the amount of paid leave be equal to the employee’s usual salary or a reduced amount? Should the length of paid leave be identical for both parents, longer for the primary caretaker, or only provided for the primary caretaker? As noted earlier, scientific evidence can never answer such questions, which inevitably reflect values and priorities.

Childcare Should the general society subsidize childcare payments for parents of young children? One argument against such a policy has been the claim that children develop more successfully if they stay at home with one of their parents or another relative than if they attend day care. This argument has turned out to be incorrect, however. Children who attend good-quality day care develop similarly to children who receive care at home from their parents.

Eyewitness Testimony Understanding child development is also vital for deciding whether children should be allowed to testify in court cases and for obtaining the most accurate testimony possible from them. Each year, tens of thousands of children in Canada testify in legal cases, either about crimes they experienced or witnessed. Often, the child and the accused are the only ones who witnessed the events. Research indicates that, in general, the accuracy of testimony increases with age; 8-year-olds recall more than do 6-year-olds, and 6-year-olds recall more than do 4-year-olds. However, when children are shielded from misleading and repeated questioning, even 4- and 5year-olds usually provide accurate testimony about the types of issues that are central in court cases. Given the high stakes in such cases, using the lessons of research to elicit the most accurate possible testimony from children is essential for just verdicts. Child-development research holds lessons for numerous other social problems as well. Research on the causes of aggression has led to programs such as Fast Track, which are designed to teach aggressive children to manage their anger and avoid violence. Research on the development of helping and sharing behaviour has led to programs such as Roots of Empathy, designed to promote children’s prosocial behaviours and decrease their aggressive behaviours. Research on the effects of poverty has provided the basis for the Better Beginnings, Better Futures project, the Carolina Abecedarian Project,

and other early education efforts. There is no end of social problems; understanding child development can help address the ones that affect children’s futures.

Children are naturally curious about the world; encouraging this curiosity and channeling it in fruitful directions are amongst the most vital goals facing both parents and society.

CHAPTER SUMMARY Test Yourself 1. Which of the following statements accurately describes the interaction of nature and nurture? a. Nature does its work before birth, and nurture takes over only after birth. b. Nature’s influence continues through infancy before giving way to the influence of nurture. c. Nature and nurture begin interacting on the fetus in the womb, and both continue to shape the individual’s development throughout life. d. The role that both nature and nurture play in development is often overstated. 2. Which of the following is an example of the crucial role that timing plays in the potential impact of a teratogen? a. The diet of a pregnant mother will influence taste preferences that the fetus will exhibit after birth. b. By age 12 months, infants lose the ability to hear the difference between similar sounds that they do not encounter on a regular basis. c. A virus will cause damage to the development of a fetus if contracted by the pregnant mother at specific sensitive times during pregnancy. d. It is more difficult for children older than 11 or 12 years of age to gain competence in a new language than it is for younger children. 3. The emerging field of epigenetics has helped to explain the ways in which a child’s environment can influence gene expression. Which of

the following is an example of this interaction? a. Children with certain types of brain damage will perform on par with other children on IQ tests up to a certain age but will fall behind after that point. b. It is more difficult for children older than 11 or 12 years of age to gain competence in a new language than it is for younger children. c. A child who loses capability in one sense, such as sight, will often compensate with enhanced ability in another sense. d. The amount of stress that a mother experiences during her child’s infancy can affect that child’s ability to regulate reaction to stress later in life. 4. Looking preferences, self-initiated activities, self-socialization, and even the manner in which infants react to their parents are all examples of a. the active role children play in their development. b. the greater influence that nurture plays compared with nature in child development. c. the ways in which development is discontinuous. d. the ways in which the sociocultural context shapes development. 5. Which of the following is an example of the theme of the active child? a. The stability of IQ scores on average tends to increase with age. b. Stressful maternal experiences, such as a periodic shortage of food at certain points during pregnancy, will influence the future physical development of the child. c. Children who exhibit preoperational reasoning in some contexts may also exhibit concrete operational reasoning in others. d. Children who are better able to regulate their emotions tend to be more socially competent and, therefore, elicit more positive reactions from other people than those who are less skilled at emotion regulation. 6. Piaget’s theory of cognitive development, Freud’s theory of psychosexual development, and Erikson’s theory of psychosocial development are all examples of

a. b. c. d.

social learning theory. the stage approach to development. theories based on an empiricist perspective of development. theories based on the nativist approach to child development.

7. An infant’s attachment to his or her mother will more reliably predict that child’s long-term security if there are no significant disruptions in the home environment. This example illustrates a. the degree to which genetic influence on individual differences tends to decrease over time. b. how continuity in individual differences is influenced by continuity in the environment. c. the manner in which sociocultural differences exert influence on cognitive development. d. the role of domain-specific learning mechanisms in child development. 8. Which of the following statements accurately expresses a key understanding regarding the continuity and discontinuity of development? a. Child psychologists today generally believe that, for the vast majority of traits, development occurs in a discontinuous manner. b. Very few individual differences in psychological properties show stability over time. c. Contrary to the theories by early behavioural psychologists like Piaget and Erikson, developmental processes rarely show a great deal of continuity. d. The apparent continuity or discontinuity of a given developmental trait depends on the timescale on which it is considered. 9. Before writing an essay, a child first considers what readers already know about the topic. Which of the four general information-processing mechanisms is illustrated by this example? a. Strategy formation

b. Basic processes c. Metacognition d. Content knowledge 10. Which of the following statements is not true of the development of a child’s cognitive abilities? a. A child’s content knowledge in a given area can outweigh an adult’s general intellectual ability. b. Statistical learning emerges in middle childhood, after the child has begun to understand basic mathematical properties. c. Understanding basic causal relationships allows children to infer explanations for a wide variety of observations. d. Knowing multiple strategies for achieving goals helps children adapt to different problems and situations they will face. 11. Babies who grow up in African tribes that strongly encourage infants’ motor development tend to walk and reach other motor milestones earlier than do infants in Canada. This is an example of the effect of on development. a. b. c. d.

change mechanisms historical change discontinuity the sociocultural context

12. Which of the following is not a reason why demographic variables such as gender, race, ethnicity, and socioeconomic status are particularly useful to child-development researchers? a. Each of these variables relates directly to a wide variety of other individual differences. b. These variables tend to remain stable over time. c. These variables have been shown to reliably predict some future outcomes. d. These variables tend to be unaffected by environmental factors. 13. Which of the following is an important contribution that Piaget’s theory

has made to children’s education? a. Piaget helped to delineate the interactions between a child’s genes and his or her environment. b. Piaget’s theory emphasizes the importance of the child’s active involvement in the learning process. c. Piaget brought attention to the role that cultural influences play in a child’s learning. d. Piaget explained cognitive development as a continuous process rather than as a series of stages. 14. Habituation is a learning process in which a child becomes familiar with a repeated stimulus. This process can motivate the child to seek out new stimulation. Besides illustrating the role of behavioural mechanisms in a child’s development, this example also demonstrates which other theme of child development? a. b. c. d.

The sociocultural context of an individual’s development The role of the active child The discontinuity of change over time The influence of nature over nurture

15. Consider the statement “Individual differences are not randomly distributed.” What is meant by this observation? a. A child’s performance in one area of development will predict the child’s achievement in another, related area. b. A child’s genotype will always exert a stronger influence on the child’s outcomes than will any environmental factors. c. Each individual child is different from all other children. d. A child’s performance on one measure of intelligence will not predict the child’s performance in another.

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Critical Thinking Questions 1. What qualities of children influence the way that other people act toward them, and how do these actions influence their development? 2. Individual differences show some stability over time. How do genes and environment contribute to this stability? 3. How would growing up in one modern society rather than another — for example, Canada rather than Japan — be expected to influence a child’s development? 4. How have the changes that have taken place in Canada over the past century influenced children’s development? Has the overall effect of the changes on children been predominantly beneficial or predominantly harmful? 5. What findings that you read about in this book surprised you the most? Were there any findings or conclusions that you just don’t believe? 6. What practical lessons have you learned from this course that will influence how you might raise your children if you have them?

Answers to Test Yourself 1. c 2. c

3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

d a d b b d c b d d b b a

Glossary accommodation the process by which people adapt current knowledge structures in response to new experiences. acculturation the process of adjusting to a new culture while retaining some aspects of one’s culture of origin. achievement motivation refers to whether children are motivated by mastery or by others’ views of their success. activating influences potential result of certain fluctuations in sex-linked hormone levels affecting the contemporaneous activation of the nervous system and corresponding behavioural responses. active learning learning by engaging with the world, rather than passively observing objects and events. adrenarche period prior to the emergence of visible signs of puberty during which the adrenal glands mature, providing a major source of sex steroid hormones; correlates with the onset of sexual attraction. adverse childhood experiences (ACEs) traumatic childhood experiences, such as abuse, neglect, violence exposure, or death of a parent, that are linked to mental and physical health problems later in life. affiliation tendency to affirm connection with others through being emotionally open, empathetic, or supportive. affordances the possibilities for action offered, or afforded, by objects and situations.

agender individuals who do not identify with any gender category. aggression behaviour aimed at physically or emotionally harming or injuring others. aggressive-rejected (peer status) children who are viewed by their peers as especially prone to physical aggression, disruptive behaviour, delinquency, and negative behaviour such as hostility and threatening others. alleles two or more different forms of a gene. ambivalent sexism model of sexism that includes two components, hostile sexism (endorsement of men’s dominance with negative views of women seeking equality) and benevolent sexism (the belief that men need to protect women, and that women and men have complementary traits). amniotic sac a transparent, fluid-filled membrane that surrounds and protects the fetus. amygdala an area of the brain that is involved in emotional reactions. anal stage the second stage in Freud’s theory, lasting from the second year through the third year, in which the primary source of pleasure comes from defecation. androgen insensitivity syndrome (AIS) condition during prenatal development in which androgen receptors malfunction in genetic males, impeding the formation of male external genitalia; in these cases, the child may be born with female external genitalia. androgens class of steroid hormones that normally occur at slightly higher levels in males than in females and that affect physical development and functioning from the prenatal period onward. A-not-B error the tendency to reach for a hidden object where it was last found rather than in the new location where it was last hidden. antisocial behaviour

disruptive, hostile, or aggressive behaviour that violates social norms or rules and that harms or takes advantage of others. anxiety disorders a set of mental disorders that involve the inability to regulate fear and worry. Apgar score method for evaluating the health of the newborn immediately following birth based on skin tone, pulse rate, facial response, arm and leg activity, and breathing. apoptosis genetically programmed cell death. arborization formation of new dendritic trees and branches. assertion tendency to take action on behalf of the self through competitive, independent, or aggressive behaviours. assimilation the process by which people translate incoming information into a form that fits concepts they already understand. association areas parts of the brain that lie between the major sensory and motor areas and that process and integrate input from those areas. attachment an emotional bond with a specific person that is enduring across space and time. attachment theory theory based on John Bowlby’s work that posits that children are biologically predisposed to develop attachments to caregivers as a means of increasing the chances of their own survival. attention-deficit hyperactivity disorder (ADHD) a syndrome that involves difficulty in sustaining attention. auditory localization perception of the location in space of a sound source. authoritarian parenting a parenting style that is high in demandingness and low in responsiveness. Authoritarian parents are nonresponsive to their children’s needs and tend to enforce their demands through the exercise of parental power and the use of threats and

punishment. They are oriented toward obedience and authority and expect their children to comply with their demands without question or explanation. authoritative parenting a parenting style that is high in demandingness and supportiveness. Authoritative parents set clear standards and limits for their children and are firm about enforcing them; at the same time, they allow their children considerable autonomy within those limits, are attentive and responsive to their children’s concerns and needs, and respect and consider their children’s perspective. axons neural fibres that conduct electrical signals away from the cell body to connections with other neurons. babbling repetitive consonant–vowel sequences (“bababa …”) or hand movements (for learners of sign languages). basic level the middle level, and often the first level learned, within a category hierarchy, such as “dog” in the animal/dog/poodle example. basic processes the simplest and most frequently used mental activities. behaviour genetics the science concerned with how variation in behaviour and development results from the combination of genetic and environmental factors. behaviour modification a form of therapy based on principles of operant conditioning in which reinforcement contingencies are changed to encourage more adaptive behaviour. Better Beginnings, Better Futures (BBBF) Ontario-based prevention project designed for young children who have multiple risks for poorer child development. bidirectionality of parent–child interactions the idea that parents and their children are mutually affected by one another’s characteristics and behaviours. bigender individuals who identify with two genders.

bilingualism fluency in two languages. binocular disparity the difference between the retinal image of an object in each eye that results in two slightly different signals being sent to the brain. body image an individual’s perception of, and feelings about, her or his own body. Carolina Abecedarian Project comprehensive and successful enrichment program in the United States for children from low-income families. carrier genetic testing genetic testing used to determine whether prospective parents are carriers of specific disorders. categorical perception the perception of phonemes as belonging to discrete categories. category hierarchy a category that is organized by set–subset relations, such as animal/dog/poodle. cell body a component of the neuron that contains the basic biological material that keeps the neuron functioning. centration the tendency to focus on a single, perceptually striking feature of an object or event. cephalocaudal development the pattern of growth in which areas near the head develop earlier than areas farther from the head. cerebral cortex the “grey matter” of the brain, consisting of four distinct lobes. cerebral hemispheres the two halves of the cortex. cerebral lateralization the specialization of the hemispheres of the brain for different modes of processing. child maltreatment action or failure to act on the part of a parent or caretaker that results in physical or

emotional harm to a child or a risk of serious harm. chromosomes molecules of DNA that transmit genetic information; chromosomes are made up of DNA. chronosystem historical changes that influence the other systems. cisgender individuals who identify with their gender assigned at birth (or their biological sex). classical conditioning a form of learning that consists of associating an initially neutral stimulus with a stimulus that always evokes a particular reflexive response. clinical interview a procedure in which questions are adjusted in accord with the answers the interviewee provides. cognitive development the development of thinking and reasoning. colic excessive, inconsolable crying by a young infant for no apparent reason. collaboration coordination of assertion and affiliation in behaviour, such as making initiatives for joint activity. collective monologue conversation between children that involves a series of non sequiturs. comprehension monitoring process of keeping track of one’s understanding of a verbal description or text. computer simulation a type of mathematical model that expresses ideas about mental processes in precise ways. conception the union of an egg from the mother and a sperm from the father. concepts general ideas or understandings that can be used to group together objects, events, qualities, or abstractions that are similar in some way. concrete operational stage the period (7 to 12 years) within Piaget’s theory in which children become able to

reason logically about concrete objects and events. conditioned response (CR) the originally reflexive response that comes to be elicited by the conditioned stimulus. conditioned stimulus (CS) the neutral stimulus that is repeatedly paired with the unconditioned stimulus. conduct disorder (CD) a disorder that involves severe antisocial and aggressive behaviours that inflict pain on others or involve destruction of property or denial of the rights of others. cone cells light-sensitive neurons that are highly concentrated in the fovea (the central region of the retina). congenital adrenal hyperplasia (CAH) condition during prenatal development in which the adrenal glands produce high levels of androgens; sometimes associated with masculinization of external genitalia in genetic females and sometimes associated with higher rates of masculine-stereotyped play in genetic females. connectionism a computational modelling approach that emphasizes the simultaneous activity of numerous interconnected processing units. conscience an internal regulatory mechanism that increases an individual’s ability to conform to standards of conduct accepted in their culture. conservation concept the idea that merely changing the appearance of objects does not necessarily change the objects’ other key properties. constructivism the theory that infants build increasingly advanced understanding by combining rudimentary innate knowledge with subsequent experiences. continuous development the idea that changes with age occur gradually, in small increments, like that of a pine tree growing taller and taller. contrast sensitivity the ability to detect differences in light and dark areas in a visual pattern. control group

the group of participants in an experimental design who are not presented the experience of interest but in other ways are treated similarly. controversial (peer status) children or adolescents who are liked by quite a few peers and are disliked by quite a few others. core-knowledge theories approaches that view children as having some innate knowledge in domains of special evolutionary importance and domain-specific learning mechanisms for rapidly and effortlessly acquiring additional information in those domains. co-regulation the process by which a caregiver provides the needed comfort or distraction to help a child reduce his or her distress. corpus callosum a dense tract of nerve fibres that enable the two hemispheres of the brain to communicate. correlation the association between two variables. correlational designs studies intended to indicate how two variables are related to each other. co-rumination extensively discussing and self-disclosing emotional problems with another person. cross-gender-typed behaviours stereotyped or expected for the gender other than that of a given person. crossing over the process by which sections of DNA switch from one chromosome to the other; crossing over promotes variability among individuals. cross-sectional design a research method in which participants of different ages are compared on a given behaviour or characteristic over a short period. cross-situational word learning determining word meanings by tracking the correlations between labels and meanings across scenes and contexts. crystallized intelligence factual knowledge about the world.

cultural tools the innumerable products of human ingenuity that enhance thinking. cumulative risk the accumulation of disadvantages over years of development. cyberbullying repeated and intentional harassment or mistreatment of an individual via digital devices such as cell phones, computers, and tablets. deferred imitation the repetition of other people’s behaviour a substantial time after it originally occurred. dendrites neural fibres that receive input from other cells and conduct it toward the cell body in the form of electrical impulses. dependent variable a behaviour that is measured to determine whether it is affected by exposure to the independent variable. depression a mental disorder that involves a sad or irritable mood along with physical and cognitive changes that interfere with daily life. developmental resilience successful development in spite of multiple and seemingly overwhelming developmental hazards. differential susceptibility a circumstance in which the same temperament characteristic that puts some children at high risk for negative outcomes when exposed to a harsh home environment also causes them to blossom when their home environment is positive. direction-of-causation problem the concept that a correlation between two variables does not indicate which, if either, variable is the cause of the other. discipline the set of strategies and behaviours parents use to teach children how to behave appropriately. discontinuous development the idea that changes with age include occasional large shifts, like the transition from

caterpillar to cocoon to butterfly. discrete emotions theory a theory in which emotions are viewed as innate, and each emotion has a specific and distinctive set of bodily and facial reactions. dishabituation the introduction of a new stimulus rekindles interest following habituation to a repeated stimulus. disorganized/disoriented attachment a type of insecure attachment in which infants or young children have no consistent way of coping with the stress of the Strange Situation. Their behaviour is confused or even contradictory, and they often appear dazed or disoriented. display rules a social group’s informal norms about when, where, and how much one should show emotions and when and where displays of emotion should be suppressed or masked by displays of other emotions. distributional properties of speech in any language, certain sounds are more likely to occur together than are others. DNA (deoxyribonucleic acid) molecules that carry all the biochemical instructions involved in the formation and functioning of an organism. domain specific information about a particular content area. dominant allele the allele that, if present, gets expressed. dose–response relation a relation in which the effect of exposure to an element increases with the extent of exposure (prenatally, the more exposure a fetus has to a potential teratogen, the more severe its effect is likely to be). dual representation treating a symbolic artefact both as a real object and as a symbol for something other than itself. dynamic-systems theories a class of theories that focus on how change occurs over time in complex systems. dyslexia

inability to read and spell well despite having normal intelligence. effect size magnitude of difference between two group’s averages and the amount of overlap in their distributions. ego in psychoanalytic theory, the second personality structure to develop. It is the rational, logical, problem-solving component of personality. egocentric spatial representations coding of spatial locations relative to one’s own body, without regard to the surroundings. egocentrism the tendency to perceive the world solely from one’s own point of view. embryo the developing organism from the 3rd to 8th week of prenatal development. embryonic stem cells embryonic cells, which can develop into any type of body cell. emotion coaching the use of discussion and other forms of instruction to teach children how to cope with and properly express emotions. emotion regulation a set of both conscious and unconscious processes used to both monitor and modulate emotional experiences and expressions. emotion socialization the process through which children acquire the values, standards, skills, knowledge, and behaviours that are regarded as appropriate for their present and future roles in their particular culture. emotional intelligence the ability to cognitively process information about emotions and to use that information to guide both thought and behaviour. emotions neural and physiological responses to the environment, subjective feelings, cognitions related to those feelings, and the desire to take action. enactive experience

learning to take into account the reactions one’s past behaviour has evoked in others. encoding the process of representing in memory information that draws attention or is considered important. endophenotypes intermediate phenotypes, including the brain and nervous systems, that do not involve overt behaviour. entity theory a theory that a person’s level of intelligence is fixed and unchangeable. entity/helpless orientation a tendency to attribute success and failure to enduring aspects of the self and to give up in the face of failure. environment every aspect of individuals and their surroundings other than genes. epigenesis the emergence of new structures and functions in the course of development. epigenetics the study of stable changes in gene expression that are mediated by the environment. equifinality the concept that various causes can lead to the same mental disorder. equilibration the process by which children (or other people) balance assimilation and accommodation to create stable understanding. erogenous zones in Freud’s theory, areas of the body that become erotically sensitive in successive stages of development. essentialism the view that living things have an essence inside them that makes them what they are. ethnic and racial identity the beliefs and attitudes an individual has about the ethnic or racial groups to which they belong. ethology the study of the evolutionary bases of behaviour. exosystem

environmental settings that a child does not directly experience but that can affect the child indirectly. experience-dependent plasticity the process through which neural connections are created and reorganized throughout life as a function of an individual’s experiences. experience-expectant plasticity the process through which the normal wiring of the brain occurs in part as a result of species-typical experiences. experimental control the ability of researchers to determine the specific experiences of participants during the course of an experiment. experimental designs a group of approaches that allow inferences about causes and effects to be drawn. experimental group the group of participants in an experimental design who are presented the experience of interest. external validity the degree to which results can be generalized beyond the particulars of the research. false-belief problems tasks that test a child’s understanding that other people will act in accord with their own beliefs even when the child knows that those beliefs are incorrect. family a group that involves at least one adult who is related to the child by birth, marriage, adoption, or foster status and who is responsible for providing basic necessities as well as love, support, safety, stability, and opportunities for learning. family dynamics the way in which family members interact through various relationships: mother with each child, father with each child, mother with father, and siblings with one another. family structure the number of and relationships amongst the people living in a household. fetal alcohol spectrum disorder (FASD) the harmful effects of maternal alcohol consumption on a developing fetus. Fetal alcohol syndrome (FAS) involves a range of effects, including facial deformities,

intellectual disabilities, attention problems, hyperactivity, and other defects. Fetal alcohol effects (FAE) is a term used for individuals who show some, but not all, of the standard effects of FAS. fetus the developing organism from the 9th week to birth. fluid intelligence ability to think on the spot to solve novel problems. Flynn effect consistent rise in average IQ scores that has occurred over the past 80 years in many countries. formal operational stage the period (12 years and beyond) within Piaget’s theory in which people become able to think about abstractions and hypothetical situations. fraternal (dizygotic) twins twins that result when two eggs happen to be released into the fallopian tube at the same time and are fertilized by two different sperm; fraternal twins have only half their genes in common. friend a person with whom an individual has an intimate, reciprocated, positive relationship. frontal lobe major area of the cortex that is associated with working memory and cognitive control. functionalist perspective a theory which argues that the basic function of emotions is to promote action toward achieving a goal. In this view, emotions are not discrete from one another and vary somewhat based on the social environment. g (general intelligence) cognitive processes that influence the ability to think and learn on all intellectual tasks. gametes (germ cells) reproductive cells—egg and sperm—that contain only half the genetic material of all the other cells in the body. gender social assignment or self-categorization as “a girl” or “a boy” (or possibly both, neither, or a different category).

gender constancy realization that gender is invariant despite superficial changes in a person’s appearance or behaviour. gender-fluid individuals who self-identify with different gender categories depending on the context. gender identity self-identifying as a boy or a girl (or possibly as both or possibly neither). gender nonconforming individuals who are highly cross-gender-typed in relation to their assigned gender. gender-role flexibility recognition of gender roles as social conventions and adoption of more flexible attitudes and interests. gender-role intensification heightened concerns with adhering to traditional gender roles that may occur during adolescence. gender schema filter initial evaluation of information as relevant for one’s own gender. gender schemas organized mental representations (concepts, beliefs, memories) about gender, including gender stereotypes. gender segregation children’s tendency to associate with same-gender peers and to avoid other-gender peers. gender stability awareness that gender remains the same over time. gender-typed behaviours stereotyped or expected for a given person’s assigned gender. gender typing the process of gender socialization. generative a system in which a finite set of words can be combined to generate an infinite number of sentences. genes sections of chromosomes that are the basic unit of heredity in all living things.

genital stage the final stage in Freud’s theory, beginning in adolescence, in which sexual maturation is complete. genome each person’s complete set of hereditary information; the complete set of DNA of any organism, including all of its genes. genotype the genetic material an individual inherits. gesture–speech mismatches phenomenon in which hand movements and verbal statements convey different ideas. glial cells cells in the brain that provide a variety of critical supportive functions. goodness of fit the degree to which an individual’s temperament is compatible with the demands and expectations of his or her social environment. guided participation a process in which more knowledgeable individuals organize activities in ways that allow less knowledgeable people to learn. habituation a simple form of learning that involves a decrease in response to repeated or continued stimulation. heritability a statistical estimate of the proportion of the measured variance on a trait among individuals in a given population that is attributable to genetic differences among those individuals. heritable refers to characteristics or traits that are genetically transmitted. heterozygous having two different alleles for a trait. homozygous having two of the same allele for a trait. hostile attributional bias in Dodge’s theory, the tendency to assume that other people’s ambiguous actions stem

from hostile intent. hypotheses testable predictions of the presence or absence of phenomena or relations. id in psychoanalytic theory, the earliest and most primitive personality structure. It is unconscious and operates with the goal of seeking pleasure. identical (monozygotic) twins twins that result from the splitting in half of the zygote, resulting in each of the two resulting zygotes having exactly the same set of genes. identity a description of the self that is often externally imposed, such as through membership in a group. identity achievement an integration of various aspects of the self into a coherent whole that is stable over time and across events. identity diffusion period in which the individual does not have firm commitments regarding the issues in question and is not making progress toward developing them. identity foreclosure period in which the individual has not engaged in any identity experimentation and has established a vocational or ideological identity based on the choices or values of others. imaginary audience the belief, stemming from adolescent egocentrism, that everyone else is focused on the adolescent’s appearance and behaviour. imprinting a form of learning in which the newborns of some species become attached to and follow adult members of the species. incremental theory a theory that a person’s intelligence can grow as a function of experience. incremental/mastery orientation a general tendency to attribute success and failure to the amount of effort expended and to persist in the face of failure. independent variable

the experience that participants in the experimental group receive and that those in the control group do not receive. infant-directed speech (IDS) the distinctive mode of speech used when speaking to infants and toddlers. infant mortality death during the first year after birth. information-processing theories a class of theories that focus on the structure of the cognitive system and the mental activities used to deploy attention and memory to solve problems. ingroup assimilation process whereby individuals are socialized to conform to the group’s norms, demonstrating the characteristics that define the ingroup. ingroup bias tendency to evaluate individuals and characteristics of the ingroup more positively than or as superior to those of the outgroup. insecure/avoidant attachment a type of insecure attachment in which infants or young children seem somewhat indifferent toward their caregiver and may even avoid the caregiver. If the infant gets upset when left alone, he or she is as easily comforted by a stranger as by a parent. insecure/resistant attachment a type of insecure attachment in which infants or young children are clingy and stay close to their caregiver rather than exploring their environment. In the Strange Situation, insecure/resistant infants tend to become very upset when the caregiver leaves them alone in the room. When their caregiver returns, they are not easily comforted and both seek comfort and resist efforts by the caregiver to comfort them. instrumental aggression aggression motivated by the desire to obtain a concrete goal. instrumental (operant) conditioning learning the relation between one’s own behaviour and the consequences that result from it. interest filter initial evaluation of information as being personally interesting. intermittent reinforcement inconsistent response to a behaviour; for example, sometimes punishing unacceptable

behaviours, and other times ignoring it. intermodal perception the combining of information from two or more sensory systems. internal validity the degree to which effects observed within experiments can be attributed to the factor that the researcher is testing. internal working model of attachment the child’s mental representation of the self, of attachment figure(s), and of relationships in general that is constructed as a result of experiences with caregivers. The working model guides children’s interactions with caregivers and other people in infancy and at older ages. internalization the process by which children learn and accept the reasons for desired behaviour. interrater reliability the amount of agreement in the observations of different raters who witness the same behaviour. intersectionality the interconnection of social identities such as gender, race, ethnicity, sexual orientation, and class, especially in relation to overlapping experiences of discrimination and disadvantage. intersex condition rare conditions in which an individual of one genetic sex can develop genitalia associated with the other genetic sex, both genetic sexes, or undergo only partial development of genitalia associated with their genetic sex. intersubjectivity the mutual understanding that people share during communication. IQ (intelligence quotient) a quantitative measure of a child’s intelligence relative to that of other children of the same age. joint attention a process in which social partners intentionally focus on a common referent in the external environment.

language comprehension understanding what others say (or sign or write). language production the process of speaking (or signing or writing). latency period the fourth stage in Freud’s theory, lasting from age 6 to age 12, in which sexual energy gets channelled into socially acceptable activities. longitudinal design a method of study in which the same participants are studied twice or more over a substantial length of time. long-term memory information retained on an enduring basis. low birth weight (LBW) a birth weight of less than 2500 grams. macrosystem the larger cultural and social context within which the other systems are embedded. mathematical equality concept that the values on each side of the equal sign must be equivalent. meiosis cell division that produces gametes. menarche onset of menstruation. mental disorder a state of having problems with emotional reactions to the environment and with social relationships in ways that affect daily life. mental health children’s sense of well-being both internally, such as in their emotions and stress levels, and externally, such as in their relationships with family members and peers. mesosystem the interconnections among immediate, or microsystem, settings. meta-analysis a statistical method for combining the results from independent studies to reach conclusions based on all of them; used to summarize average effect size and statistical

significance across several research studies. methylation a biochemical process that influences behaviour by suppressing gene activity and expression. microgenetic design a method of study in which the same participants are studied repeatedly over a short period. microsystem the immediate environment that an individual child personally experiences and participates in. mitosis cell division that results in two identical cells. monocular depth (pictorial) cues the perceptual cues of depth (such as relative size and interposition) that can be perceived by one eye alone. moral domain an area of social knowledge based on concepts of right and wrong, fairness, justice, and individual rights; these concepts apply across contexts and supersede rules or authority. moratorium period in which the individual is exploring various occupational and ideological choices and has not yet made a clear commitment to them. morphemes the smallest units of meaning in a language. multifinality the concept that certain risk factors do not always lead to a mental disorder. multiple intelligences theory Gardner’s theory of intellect, based on the view that people possess at least eight types of intelligence. mutation a change in a section of DNA. myelin sheath a fatty sheath that forms around certain axons in the body and increases the speed and efficiency of information transmission.

myelination the formation of myelin (a fatty sheath) around the axons of neurons that speeds and increases information-processing abilities. naïve psychology a commonsense level of understanding of other people and oneself. narratives story-like structured descriptions of past events. nativism the theory that infants have substantial innate knowledge of evolutionarily important domains. naturalistic observation examination of ongoing behaviour in an environment not controlled by the researcher. nature our biological endowment; the genes we receive from our parents. neglected (peer status) children or adolescents who are infrequently mentioned as either liked or disliked; they simply are not noticed much by peers. neural tube a groove formed in the top layer of differentiated cells in the embryo that eventually becomes the brain and spinal cord. neurogenesis the proliferation of neurons through cell division. neurons cells that are specialized for sending and receiving messages between the brain and all parts of the body, as well as within the brain itself. neurotransmitters chemicals involved in communication among brain cells. newborn screening tests used to screen newborn infants for a range of genetic and non-genetic disorders. nonbinary individuals who do not identify exclusively as one gender; also referred to as genderqueer. non-REM sleep

a quiet or deep sleep state characterized by the absence of motor activity or eye movements and more regular, slow brain waves, breathing, and heart rate. normal distribution pattern of data in which scores fall symmetrically around a mean value, with most scores falling close to the mean and fewer and fewer scores farther from it. numerical equality the realization that all sets of N objects have something in common. numerical magnitude representations mental models of the sizes of numbers, ordered along a less-to-more dimension. nurture the environments, both physical and social, that influence our development. object permanence the knowledge that objects continue to exist even when they are out of view. object segregation the identification of separate objects in a visual array. object substitution a form of pretense in which an object is used as something other than itself, for example, using a broom to represent a horse. observational learning learning through watching other people and the consequences others experience as a result of their actions. occipital lobe major area of the cortex that is primarily involved in processing visual information. opportunity structure the economic and social resources offered by the macrosystem in the bioecological model, and people’s understanding of those resources. oppositional defiant disorder (ODD) a disorder characterized by age-inappropriate and persistent displays of angry, defiant, and irritable behaviours. optical expansion a depth cue in which an object occludes increasingly more of the background, indicating that the object is approaching. oral stage

the first stage in Freud’s theory, occurring in the first year, in which the primary source of satisfaction and pleasure is oral activity. organizing influences potential result of certain sex-linked hormones affecting brain differentiation and organization during prenatal development or at puberty. overextension an overly broad interpretation of the meaning of a word. overlapping waves theory an information-processing approach that emphasizes the variability of children’s thinking. overregularization speech errors in which children treat irregular forms of words as if they were regular. parental-investment theory a theory that stresses the evolutionary basis of many aspects of parental behaviour that benefit their offspring. parental sensitivity caregiving behaviour that involves the expression of warmth and contingent responsiveness to children, such as when they require assistance or are in distress. parenting style parenting behaviours and attitudes that set the emotional climate in regard to parent– child interactions, such as parental responsiveness and demandingness. parietal lobe major area of the cortex that is associated with spatial processing and sensory information integration. peers people of approximately the same age and status who are unrelated to one another. perception the process of organizing and interpreting sensory information. perceptual categorization the grouping together of objects that have similar appearances. perceptual constancy the perception of objects as being of constant size, shape, colour, and so on, in spite of physical differences in the retinal image of the object.

perceptual narrowing developmental changes in which experience fine-tunes the perceptual system. permissive parenting a parenting style that is high in responsiveness but low in demandingness. Permissive parents are responsive to their children’s needs and do not require their children to regulate themselves or act in appropriate or mature ways. personal domain an area of social knowledge that pertains to actions in which individual preferences are the main consideration; there are no right or wrong choices. personal fable a form of adolescent egocentrism that involves beliefs in the uniqueness of one’s own feelings and thoughts. phallic stage the third stage in Freud’s theory, lasting from age 3 to age 6, in which sexual pleasure is focused on the genitalia. phenotype the observable expression of the genotype, including both body characteristics and behaviour. phenylketonuria (PKU) a disorder related to a defective recessive gene on chromosome 12 that prevents metabolism of the amino acid phenylalanine. phonemes the smallest units of meaningful sound. phonemic awareness ability to identify component sounds within words. phonological recoding skills ability to translate letters into sounds and to blend sounds into words; informally called sounding out. phylogenetic continuity the idea that because of our common evolutionary history, humans share many characteristics, behaviours, and developmental processes with non-human animals, especially mammals. Piaget’s theory the theory of Swiss psychologist Jean Piaget, which posits that cognitive development

involves a sequence of four stages—the sensorimotor, preoperational, concrete operational, and formal operational stages—that are constructed through the processes of assimilation, accommodation, and equilibration. placenta a support organ for the fetus; it keeps the circulatory systems of the fetus and mother separate, but a semipermeable membrane permits the exchange of some materials between them (oxygen and nutrients from mother to fetus, and carbon dioxide and waste products from fetus to mother). plasticity the capacity of the brain to be affected by experience. play voluntary activities, particularly those of children, with no specific motivation beyond their inherent enjoyment. polygenic inheritance inheritance pattern in which traits are governed by more than one gene. polyvictimization the co-occurrence of multiple forms of maltreatment. popular (peer status) children or adolescents who are viewed positively (liked) by many peers and are viewed negatively (disliked) by few peers. positive reinforcement a reward that reliably follows a behaviour and increases the likelihood that the behaviour will be repeated. positive youth development an approach to youth intervention that focuses on developing and nurturing strengths and assets rather than on correcting weaknesses and deficits. pragmatic cues aspects of the social context used for word learning. pragmatics knowledge about how language is used. preferential-looking technique a method for studying visual attention in infants that involves showing infants two images simultaneously to see if the infants prefer one over the other (indexed by longer looking).

premature any child born at 37 weeks after conception or earlier (as opposed to the normal term of 38 weeks). prenatal testing genetic testing used to assess the fetus’s risk for genetic disorders. preoperational stage the period (2 to 7 years) within Piaget’s theory in which children become able to represent their experiences in language, mental imagery, and symbolic thought. pre-reaching movements clumsy swiping movements by young infants toward objects they see. pretend play make-believe activities in which children create new symbolic relations, acting as if they were in a situation different from their actual one. primary mental abilities seven abilities proposed by Thurstone as crucial to intelligence. primary prevention a program targeting all individuals in a particular setting (e.g., a school) in order to prevent the occurrence of a problematic behaviour or condition. private speech the second phase of Vygotsky’s internalization-of-thought process, in which children develop self-regulation and problem-solving abilities by telling themselves aloud what to do, much as their parents did in the first stage. proactive aggression unemotional aggression aimed at fulfilling a need or desire. problem solving the process of attaining a goal by using a strategy to overcome an obstacle. prosocial behaviour voluntary behaviour intended to benefit another, such as helping, sharing with, and comforting others. prosody the characteristic rhythm and intonational patterns with which a language is spoken. puberty developmental period marked by the ability to reproduce and other dramatic bodily changes.

punishment a negative stimulus that follows a behaviour to reduce the likelihood that the behaviour will occur again. questionnaire a method that allows researchers to gather information from a large number of participants simultaneously by presenting them a uniform set of printed questions. random assignment a procedure in which each participant has an equal chance of being assigned to each group within an experiment. rapid eye movement (REM) sleep an active sleep state characterized by quick, jerky eye movements under closed lids and associated with dreaming in adults. rational learning the ability to use prior experiences to predict what will occur in the future. reactive aggression emotionally driven, antagonistic aggression sparked by one’s perception that other people’s motives are hostile. recessive allele the allele that is not expressed if a dominant allele is present. reciprocal determinism child–environment influences operate in both directions; children are both affected by and influence aspects of their environment. reflexes fixed patterns of action that occur in response to particular stimulation. regulator genes genes that control the activity of other genes. rehearsal the process of repeating information multiple times to aid memory of it. rejected (peer status) children or adolescents who are liked by few peers and disliked by many peers. relational aggression a kind of aggression that involves excluding others from the social group and

attempting to do harm to other people’s relationships; it includes spreading rumors about peers, withholding friendship to inflict harm, and ignoring peers when angry or frustrated or trying to get one’s own way. reliability the degree to which independent measurements of a given behaviour are consistent. role taking being aware of the perspective of another person. rumination the act of focusing on one’s own negative emotions and negative self-appraisals and on their causes and consequences, without engaging in efforts to improve one’s situation. scale error the attempt by a young child to perform an action on a miniature object that is impossible due to the large discrepancy in the relative sizes of the child and the object. scientific method an approach to testing beliefs that involves choosing a question, formulating a hypothesis, testing the hypothesis, and drawing a conclusion. script typical sequence of actions used to organize and interpret repeated events, such as eating at restaurants, going to doctors’ appointments, and writing reports. secondary prevention a program designed to help individuals at risk for developing a problem or condition, with the goal of preventing the problem or condition. secular trends marked changes in physical development that have occurred over generations. secure attachment a pattern of attachment in which infants or young children have a positive and trusting relationship with their attachment figure. In the Strange Situation, a securely attached infant may be upset when the caregiver leaves but may be happy to see the caregiver return, recovering quickly from any distress. When children are securely attached, they can use caregivers as a secure base for exploration. secure base refers to the idea that the presence of a trusted caregiver provides an infant or toddler with a sense of security that makes it possible for the child to explore the environment.

selective attention the process of intentionally focusing on the information that is most relevant to the current goal. self-comforting behaviours repetitive actions that regulate arousal by providing a mildly positive physical sensation. self-concept a conceptual system made up of one’s thoughts and attitudes about oneself. self-conscious emotions emotions such as guilt, shame, embarrassment, and pride that relate to our sense of self and our consciousness of others’ reactions to us. self-discipline ability to inhibit actions, follow rules, and avoid impulsive reactions. self-distraction looking away from an upsetting stimulus in order to regulate one’s level of arousal. self-esteem an individual’s overall subjective evaluation of his or her worth and the feelings he or she has about that evaluation. self-locomotion the ability to move oneself around in the environment. self-socialization active process during development whereby children’s cognitions lead them to perceive the world and to act in accord with their expectations and beliefs, through their activity preferences, friendship choices, and so on. sensation the processing of basic information from the external world via receptors in the sense organs (eyes, ears, skin, etc.) and brain. sensitive period the period of time during which a developing organism is most sensitive to the effects of external factors. sensorimotor stage the period (birth to 2 years) within Piaget’s theory in which intelligence is expressed through sensory and motor abilities. separation anxiety

feelings of distress that children, especially infants and toddlers, experience when they are separated, or expect to be separated, from individuals to whom they are emotionally attached. service learning a strategy for promoting positive youth development that integrates school-based instruction with community involvement in order to promote civic responsibility and enhance learning. sex distinction between genetic females (XX) and genetic males (XY) as well as other genetic sex compositions (e.g., XO, XXY, XYY). sex chromosomes the chromosomes (X and Y) that determine an individual’s designated sex at birth. sexual identity one’s sense of oneself as a sexual being. sexual-minority youth young people who experience same-sex attractions. sexual orientation a person’s preference in regard to males or females as objects of erotic feelings. simple view of reading perspective that comprehension depends solely on decoding skill and comprehension of oral language. situation model cognitive processes used to represent a situation or sequence of events. small for gestational age babies who weigh substantially less than is normal for whatever their gestational age. smooth pursuit eye movements visual behaviour in which the viewer’s gaze shifts at the same rate and angle as a moving object. social comparison the process of comparing aspects of one’s own psychological, behavioural, or physical functioning to that of others in order to evaluate oneself. social competence the ability to achieve personal goals in social interactions while simultaneously maintaining positive relationships with others.

social referencing the use of a parent’s or another adult’s facial expression or vocal cues to decide how to deal with novel, ambiguous, or possibly threatening situations. social scaffolding a process in which more competent people provide a temporary framework that supports children’s thinking at a higher level than children could manage on their own. social smiles smiles that are directed at people; they first emerge around the third month of life. socialization the process through which children acquire the values, standards, skills, knowledge, and behaviours that are regarded as appropriate for their present and future roles in their particular culture. societal domain an area of social knowledge that encompasses concepts regarding the rules and conventions through which societies maintain order. sociocultural context the physical, social, cultural, economic, and historical circumstances that make up any child’s environment. sociocultural theories approaches that emphasize that other people and the surrounding culture contribute greatly to children’s development. sociodramatic play activities in which children enact miniature dramas with other children or adults, such as “mother comforting baby.” socioeconomic status (SES) a measure of social class based on income and education. sociometric status a measurement that reflects the degree to which children are liked or disliked by their peers as a group. spermarche onset of capacity for ejaculation. spines formations on the dendrites of neurons that increase the dendrites’ capacity to form connections with other neurons.

stage theories approaches proposing that development involves a series of large, discontinuous, agerelated phases. standard deviation (SD) measure of the variability of scores in a distribution; in a normal distribution, 68% of scores fall within 1 SD of the mean, and 95% of scores fall within 2 SDs of the mean. state level of arousal and engagement in the environment, ranging from deep sleep to intense activity. stepping reflex a neonatal reflex in which an infant lifts first one leg and then the other in a coordinated pattern like walking. stereopsis the process by which the visual cortex combines the differing neural signals caused by binocular disparity, resulting in the perception of depth. Strange Situation a procedure developed by Mary Ainsworth to assess infants’ attachment to their primary caregiver. strategy–choice process procedure for selecting among alternative ways to solve a problem. stress a physiological reaction to some change or threat in the environment. structured interview a research procedure in which all participants are asked to answer the same questions. structured observation a method that involves presenting an identical situation to each participant and recording the participant’s behaviour. subordinate level the most specific level within a category hierarchy, such as “poodle” in the animal/dog/poodle example. sudden infant death syndrome (SIDS) the sudden, unexpected death of an infant less than 1 year of age that has no identifiable cause. superego

in psychoanalytic theory, the third personality structure, consisting of internalized moral standards. superordinate level the general level within a category hierarchy, such as “animal” in the animal/dog/poodle example. swaddling a soothing technique, used in many cultures, that involves wrapping a baby tightly in cloths or a blanket. symbolic representation the use of one object to stand for another. symbols systems for representing our thoughts, feelings, and knowledge, and for communicating them to other people. synapses microscopic junctions between the axon terminal of one neuron and the dendritic branches or cell body of another. synaptic pruning the normal developmental process through which synapses that are rarely activated are eliminated. synaptogenesis the process by which neurons form synapses with other neurons, resulting in trillions of connections. syntactic bootstrapping the strategy of using grammatical structure to infer the meaning of a new word. syntax rules specifying how words from different categories (nouns, verbs, adjectives, etc.) can be combined. task analysis the research technique of specifying the goals, obstacles to their realization, and potential solution strategies involved in problem solving. telegraphic speech short utterances that leave out non-essential words. temperament

individual differences in emotion, activity level, and attention that are exhibited across contexts and that are present from infancy and thus thought to be genetically based. temporal lobe major area of the cortex that is associated with speech and language, music, and emotional information. teratogen an external agent that can cause damage or death during prenatal development. tertiary intervention a program designed to help individuals who already exhibit a problem or condition. test–retest reliability the degree of similarity of a participant’s performance on two or more occasions. theory of mind an organized understanding of how mental processes such as intentions, desires, beliefs, perceptions, and emotions influence behaviour. theory of mind module (TOMM) a hypothesized brain mechanism devoted to understanding other human beings. theory of successful intelligence Sternberg’s theory of intellect, based on the view that intelligence is the ability to achieve success in life. third-variable problem the concept that a correlation between two variables may stem from both being influenced by some third variable. three-stratum theory of intelligence Carroll’s model that places g at the top of the intelligence hierarchy, eight moderately general abilities in the middle, and many specific processes at the bottom. toxic stress the experience of overwhelming levels of stress without support from adults to help mitigate the effects of that stress. transgender individuals who do not identify with the gender assigned at birth (which is typically based on their external genitalia). tuition learning through direct teaching.

umbilical cord a tube containing the blood vessels connecting the fetus and placenta. unconditioned response (UCR) a reflexive response that is elicited by the unconditioned stimulus. unconditioned stimulus (UCS) a stimulus that evokes a reflexive response. underextension an overly narrow interpretation of the meaning of a word. uninvolved parenting a parenting style that is low in both demandingness and responsiveness to their children; in other words, this style describes parents who are generally disengaged. Universal Grammar a proposed set of highly abstract structures that are common to all languages. validity the degree to which a test measures what it is intended to measure. variables attributes that vary across individuals and situations, such as age, sex, and popularity. vicarious reinforcement observing someone else receive a reward or punishment. violation-of-expectancy a procedure used to study infant cognition in which infants are shown an event that should evoke surprise or interest if it goes against something the infant knows. visual acuity the sharpness and clarity of vision. visually based retrieval proceeding directly from the visual form of a word to its meaning. voice onset time (VOT) the length of time between when air passes through the lips and when the vocal cords start vibrating. Wechsler Intelligence Scale for Children (WISC) widely used test designed to measure the intelligence of children 6 years and older. withdrawn-rejected (peer status)

rejected children who are socially withdrawn, wary, and often timid. word segmentation discovering where words begin and end in fluent speech. working memory memory system that involves actively attending to, maintaining, and processing information. zygote a fertilized egg cell.

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