Origins of Aggression 9783110800494, 9789027976734

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O R I G I N S OF A G G R E S S I O N

PSYCHOLOGICAL STUDIES

Editorial

Committee

JOHAN T. BARENDREGT HANS C. BRENGELMANN/GOSTA EKMAN + SIPKE D. FOKKEMA/NICO H. FRIJDA JOHN P. VAN DE GEER/ ADRIAAN D. DE GROOT MAUK MULDER/RONALD WILLIAM RAMSAY SIES WIEGERSMA

MOUTON

THE H A G U E • PARIS • NEW YORK

Origins of Aggression Edited by

W I L L A R D W. H A R T U P and JAN DE WIT

MOUTON

THE H A G U E

PARIS

NEW YORK

ISBN: 90-279-7673-2 © 1978, Mouton Publishers, The Hague, The Netherlands Printed in the Netherlands

Preface

Science has produced an immense and diverse literature concerning the problem of aggression. A vast number of scientific works catalog the varieties of human harm-doing, the role of aggression in phylogenetic adaptation, the motivational bases of aggression, ecological constraints on hostile behavior, and ethical and legal problems in aggression control. One issue - the functioning of aggression in the growth and development of the individual - has been relatively neglected. Although hundreds of studies have been devoted to aggression in children, few deal with such behavior from a developmental perspective. What constitutes such a perspective? In part, to be concerned with development suggests a concern for continuities and discontinuities in harmdoing activity during the years before maturity. A developmental view, however, requires more than an examination of individual differences in the frequency of harm-doing at various points in the lives of infants, children, and adolescents. Attention must be paid to changes across the life-span in the morphology and functioning of aggressive behavior, the reorganization of various neural and psychic structures as these involve aggression, and the role of violence in the development of attitudes toward oneself and toward others. This book is a compendium of articles dealing with aggression and developmental process. Each chapter is based on a contribution to an international conference that was organized and held under the auspices of the Scientific Affairs Division (Human Factors), North Atlantic Treaty Organization. The collection includes biological orientations, evolutionary views, psychophysiological analyses, cross-cultural perspectives, historical

vi

Preface

and legal comparisons, as well as sociological and psychological studies. The diversity of these contributions matches the diversity of the developmental sciences in general. The first 'set' of chapters in the volume deals with the biological determinants and functions of aggression. Here, developmental issues receive attention within contrasting evolutionary perspectives (Hinde, EiblEibesfeldt) and within a framework furnished by field studies of both human and non-human primates (Hamburg and Goodall). Recent work in behavior genetics, as applied to criminality, is represented (Christiansen) and one chapter is devoted to brain mechanisms involved in aggressive behavior (Karli). In this instance, the role of the central nervous system, and its development, is elucidated with respect to a specific form of aggression - the rat's mouse-killing behavior. Next, a series of papers is included dealing with conceptual issues in the psychological study of aggression. Here, too, the work is not explicitly focused on ontogeny, but on problems of viewpoint which are fundamental to a developmental analysis. Rule, in her paper, argues that the prosocial functions of aggression must be considered separately from the personal or hostile functions of aggression; Berkowitz deals with situational determinants of impulsive aggression; and Feshbach discusses cognitive factors involved in aggressive motivation. Three papers are included that deal with social/contextual issues in the aggression of human children. Lambert presents new data from the Six Cultures Study, in which peer and family contexts were studied across six different societies. Eron and his associates consider a broad range of field and experimental possibilities for studying the socialization of aggression and provide follow-up data from their well-known longitudinal study of a large group of American children and adolescents. Olweus, in a paper that has been cited for excellence by the International Society for Research on Aggression, deals with bullying displayed in peer groups of elementary school boys. The final paper in the volume (Hartup and De Wit) concerns problems and research gaps in plotting adequate 'growth functions' for various kinds of aggressive behavior. The editors would like to acknowledge the contributions of each author, the interest of B. A. Bayraktar and J. Bremond in this volume, and the technical assistance of Freeke Bruijn and Melynda Mason. Financial support for this publication was furnished by the North Atlantic Treaty Organization, the Institute of Child Development (University of Minnesota), the Paedologisch Instituut (Free University, Amsterdam), and the

Preface

VII

Netherlands Organization for the Advancement of Pure Research. The editors are especially indebted to Douglas Sawin and Linda Sawin for their comprehensive bibliography. Prepared early in 1976, through the utilization of a computerized retrieval system, this bibliography contains approximately 1,000 selected titles from the entire range of scientific literatures that bear on aggression and its development. Minneapolis/Amsterdam December, 1976

Willard W. Hartup Jan de Wit

Contents

Preface 1. The study of aggression: Determinants, consequences, goals and functions, by Robert A. Hinde (University of Cambridge, Madingley) 2. Phylogenetic adaptation as determinants of aggressive behavior in man, by Irenaus Eibl-Eibesfeldt (Max Planck Institute, Percha/ Starnberg) 3. Factors facilitating development of aggressive behavior in chimpanzees and humans, by David A. Hamburg and Jane van Lawick-Goodall (Stanford University) 4. Aggressive behavior and its brain mechanisms (as exemplified by an experimental analysis of the rat's mouse-killing behavior), by Pierre Karli (Université Louis Pasteur, Strasbourg) 5. The genesis of aggressive criminality: Implications of a study of crime in a Danish twin study, by Karl O. Christiansen (University of Copenhagen) 6. The hostile and instrumental functions of human aggression, by Brendan Gail Rule (University of Alberta, Edmonton) 7. External determinants of impulsive aggression, by Leonard Berkowitz (University of Wisconsin, Madison) 8. The development and regulation of aggression: Some research

x

Contents

9.

10.

11.

12.

13.

gaps and a proposed cognitive approach, by Seymour Feshbach (University of California, Los Angeles) Promise and problems of cross-cultural exploration of children's aggressive strategies, by William W. Lambert (Cornell University, Ithaca) The convergence of laboratory and field studies of the development of aggression, by Leonard D. Eron (University of Illinois at Chicago Circle), Leopold O. Walder (Organization for Research in Behavioral Sciences), L. Rowell Huesmann (Yale University), Monroe M. Lefkowitz (New York Department of Mental Hygiene) Personality factors and aggression: With special reference to violence within the peer group, by Dan Olweus (University of Bergen) The development of aggression: Problems and perspectives, by Willard W. Hartup (University of Minnesota) and Jan de Wit (Free University, Amsterdam) Origins of aggressive behavior: A selected bibliography, by Douglas B. Sawin and Linda Sawin (University of Texas, Austin)

163

189

213

247

279

305

Author index

355

Subject index

363

The study of aggression: Determinants, consequences, goals and functions R O B E R T A. H I N D E University

of Cambridge,

Madingley

The purpose of this paper is to open the conference with a discussion of some of the more basic problems that arise in studying the origins and determinants of aggressive behavior. Since the program includes studies of aggression in both animals and man, perhaps the first thing that should be mentioned is the problem of the relations between them. It is all too easy to argue from one to the other, neglecting the enormous differences in complexity of behavior between man and other species. These differences include the level of cognitive functioning of which man is capable, his value systems, the diversity of weapons at his command, the deviousness with which he can operate and, perhaps especially, the time span over which his behavior is organized. There is no evidence to suggest that aggressive behavior in nonhuman primates is ever directed towards goals as distant as those that sometimes determine our own. So there is no need to say that we must argue from one to the other only with the greatest caution. Nevertheless studies of aggression in animals can be of help in three ways: 1. Some forms of aggression in animals can be legitimately compared with some relatively simple forms of aggression in man - for example, some of the aggressive behavior to be seen in children, and perhaps impulsive aggression in adults. There are also likely to be similarities in some of the basic mechanisms underlying aggression. 2. If we are sufficiently sophisticated about the level of analysis at which we operate, we can perhaps abstract from the animal data principles whose validity at the human level is worth testing. For

2

Robert A. Hinde

example, the animal data suggest that we should be constantly aware that aggressive encounters often involve a delicate interplay between attack and withdrawal; that the independent variables affecting aggression operate in diverse ways; that contextual factors may be crucial in its elicitation; that the development of aggressive behavior may involve the integration of previously independent elements; and that the manner in which an individual's aggressive behavior is affected by experience is constrained by his nature. These principles may also be applicable to man. To these and other issues I shall return later. 3. An issue too often overlooked is that studies of animal aggression are important not only because animals and men are in some ways similar, but also precisely because they are different. This is of practical importance, since some issues can be studied in animals unclouded by the complexity of the human case. It is also of theoretical importance in placing limits on the complexity of the explanations needed for some examples of aggressive behavior. A second general issue that has to be mentioned is the matter of definition. Many definitions of aggressive behavior have been coined, but none is wholly satisfactory. Aggressive behavior is not peculiar in this respect but resembles practically every category used in the study of behavior: Man-made pigeon-holes almost inevitably constrain nature. There is of course a hard nugget: We all agree that behavior directed towards causing harm to others is properly labelled as aggressive. But we must accept that the category is shady at the edges, and that where each of us places the limits will depend on the problems in which he is interested. And, as Dr. Feshbach (1964, 1970) and others have pointed out, if the primary feature by which we define aggression is related to a consequence (namely, harm to others), the items included may have almost unlimited causal heterogeneity. If however we try to find a definition in terms of process, state or predisposition, we find that the ways it may be expressed in action are almost infinitely diverse. The issue is of importance only because the range of validity of any generalizations we make is inversely related to their precision. As more diverse phenomena are included within our category of aggressive behavior, our generalizations inevitably become less precise. However, there is one source of disagreement that must be mentioned. Behavior directed towards causing harm to others often leads to the establishment of status, precedence or access to some object or

The study of aggression

3

space. Is all behavior with such consequences to be classed as aggressive? On the whole psychiatrists and social psychologists tend to say yes, while ethologists and experimental psychologists say no. The difference is important not only when we are seeking generalizations about the causes of aggression but also, as we shall see, in the value judgments we make about it. So much for two very general matters. Now to turn to some more specific issues in which the study of aggressive behavior seems to pose special problems. Like any item of behavior, each aggressive act lies in a nexus of events that precede and follow it. The preceding events that affect the probability of aggressive acts can be divided into (a) eliciting factors, responsible for the aggressive episode, (b) predisposing factors, determining the effectiveness of the eliciting factors and (c) ontogenetic factors, giving rise to a potentiality for behaving aggressively. It is immediately obvious that these categories overlap extensively, but they will serve the present purpose. First, one point with regard to the eliciting factors. Nearly every aggressive act carries with it some risk of injury to the attacker, and many of the stimulus situations that elicit aggressive behavior often also elicit self-protective responses. It is for this reason that many writers (e.g., Scott & Fredericson, 1951) prefer the category of 'agonistic behavior', embracing the continuum that includes attack, threat, submission and withdrawal, to aggressive behavior. Many encounters involve complex sequences of threat and counter-threat, attack and withdrawal, or submission. And many threat postures themselves involve elements of attack and fleeing. A classic example comes from Tinbergen's (1959) analysis of the threat posture of the herring gull (Larus argentatus) which varies between two extremes - one involves elements of attack (downward pointing beak, wings slightly raised preparatory to striking), and the other elements of withdrawal (neck upright and withdrawn). A more complex example, which reveals the nature of aggressive encounters, is provided by Stokes' (1962) careful analysis of the agonistic behavior of the blue tit (Parus caeruleus). Studying birds at a winter feeding station, Stokes recorded nine behavioral components (e.g., crest up or down, wings raised or down, etc.), and the subsequent action of the displaying bird, which he classified as attacking, staying or fleeing. The associations between particular components and subsequent behavior were usually not large: Although birds which raised the crest or body

4

Robert A. Hinde

feathers subsequently fled on 90 % of the occasions, for other individual components the probability of subsequently attacking, fleeing or staying was 5 2 % or less (Table 1). This was due in part to interaction between the components. For instance, when the nape feathers were raised in an otherwise nonaggressive posture, there was an increased probability that the bird would attack (Table 2). But when the nape feathers were raised in combination with aggressive elements, the probability of subsequent aggression was little affected or reduced, and that of staying was increased. Table 1. Blue tit agonistic display. Single components which provided the best indication of the outcome of an encounter, and the subsequent action as a percent of total occurrences (From Stokes, 1962) Best single indicator of outcome Attack Body horizontal Crest erect Crest normal

Subsequent action (% of total occurrences) Escape Stay

40 90

52

Table 2. Blue tit agonistic display. The relation of nape position, when combined with various other types of behavior, to subsequent action (From Stokes, 1962) First element Nape erect Second element

+ —

+ —

+ —

+

—

+ —

Body horizontal (aggressive) Wings raised (aggressive) Body normal (nonaggressive) Wings normal (nonaggressive) Body feathers normal (nonaggressive)

** p < .01 ns = Not significant at .05 level.

Resultant behavior (Percent of total occurrences) Attack Escape Stay Probability 39 39 27 35 32 6 43 12 41 17

15 26 13 21 16 47 15 45 34 34

46 35 60 44 52 47 42 43 47 49

ns ns **

**

**

The study of aggression 5 The combinations of components showed more reliable relationships with subsequent behavior. One combination led to escape on 97 % of the occasions, another to staying on 7 9 % and another to attack on 48 % (Table 3).

Table 3. Blue tit agonistic display. The use of five behavior elements to predict the outcome of an encounter (From Stokes, 1962) Initial behavior elements Crest erect

+ +

Nape erect

Facing rival

—

+

—

—

Body horizontal

—

—

—

—

—

—

—

—

—

+ +

+ + + +

+ + + +

— — —

—

—

—

Wings raised

—

+ —

+ —

+ —

Subsequent action (percent of total occurrences) Stay Attack Escape

0 0 7 0 28 48 44 43

94 89 14 35 16 10 20 21

6 11 79 66 56 42 37 36

Stokes emphasizes that no combination gave a precise prediction of what the bird would do next. This could have been because the observations were not sufficiently acute, but there is also a more interesting possibility. If an individual is going either to attack or to flee, then he would do best to do so quickly, without giving notice of his intentions. Thus, threat postures are likely to be used only when he is uncertain what to do, and what he does do depends in part on the behavior of the rival. Threat postures are, in fact, a means of sounding out the opposition. This view receives further support from Simpson's (1968) study of the threat display of the Siamese fighting fish (Betta splendens; Figure 1). In this species, display between two individuals may continue for many minutes before there is any actual biting. The display behavior of each individual increases in parallel with that of the other, so that it is not at all apparent to an observer who will win, until finally one of them 'gives up'. In Figure 2 each diagram refers to one skirmish, and the ordinates show the seconds (per two minutes) spent with the gill covers erect by winners (solid lines) and losers (discontinuous lines); the asterisk shows the first period in which there was a rapid exchange

6

Robert A. Hinde

Figure 1. Threat 1968)

display

of Siamese

fighting

fish

(From Simpson,

(a), (b) Non-displaying fish; (c), (d) displaying fish; o, operculum; bs, branchiostegal membrane. In (c) the fish is broadside with pelvic fin nearest rival raised. In (d) it is facing the rival, with gill-covers raised.

of bites. Simpson's analysis shows that each encounter is much more than a show of strength, for each fish varies its behavior in response to the timing of the rival's display relative to its own in such a manner that the fight gradually escalates. Thus the display is related not merely to the internal state of the displaying individual or even to its ultimate potential to attack or flee, but also to its immediate assessment of the probabilities of the rival's action. Simpson's work was concerned with a fish, but in the manner in which the conflict escalates there are parallels to conflicts between human children as described by Patterson and Cobb (1971). In studying the bases of aggression we must be concerned not only with how en-

The study of aggression

7

Figure 2. Skirmishes between pairs of individuals of the Siamese fighting fish (From Simpson, 1968) 80 -

134.14

1&2

60 40

20 /

0

80

344

i

l

l

155« 16

60 40

20 0

100

J

I

I

L 9 S. 10

80 60 40

20 0

J

I

I

L

Each figure refers to one skirmish and shows the seconds per 2-min period spent with gill covers erect by winners (solid points and continuous lines) and losers (open points and broken lines) in successive 2-min periods. * * , the first 2-min period with a rapid exchange of bites; !, the 2-min period was incomplete, but the time spent was corrected to a proportion.

8

Robert A. Hinde

counters are initiated, but with why and how they escalate. For this, the facts that the situations that elicit aggression may elicit withdrawal also, and that tendencies to attack and flee may be delicately balanced, may be crucial to our understanding. A related issue concerns the use of punishment to control aggression. Since pain can act both as a stimulant and a deterrent for aggression, attempts to reduce aggressive behavior by punishment can have complex consequences (Ulrich & Symmanek, 1969). Turning to predisposing factors for aggression, there are two issues that need to be taken up. The first concerns the use of energy models of motivation. Although these are much less in vogue than they were, from time to time they still rear their ugly heads. Their influence is apt to be especially pernicious in the study of aggressive behavior, as shown for instance by the recent books of Lorenz (1966), Ardrey (1967), and Storr (1968). Their use would imply that a potentiality for aggression can only be discharged by action - probably, though not necessarily, action of an aggressive type. Such models have major implications for the control of aggression, so it may be well to mention some of their major shortcomings. 1. Such models imply a unitary basis for aggression, whereas all the evidence suggests that the causal bases of aggression are much more complex. 2. Energy models imply that a tendency to behave aggressively can be lowered only if the energy is discharged in action. There is no hard evidence for this view. Although an aggressive episode is sometimes followed by reduced aggressivenesss, in other circumstances aggressive behavior enhances the subsequent tendency to aggression (e.g., Berkowitz, 1962; Lagerspetz, 1964; Kuo, 1967; Hokanson, 1970). Indeed, quite apart from any reinforcing consequence or punishment that ensues, we should expect, by analogy with other forms of behavior, that the performance of a series of aggressive acts would be followed by interacting positive and negative effects on subsequent aggression, decaying with varied time courses. For example, the mobbing response of chaffinches (Fringilla coelebs) to predators, a type of behavior involving conflicting elements of aggression, curiosity and withdrawal, first increases in intensity and then gradually wanes when a model predator is presented. It was possible to classify the effects of responding on subsequent responding according to whether they decayed with a half-period measurable in seconds,

The study of aggression

9

minutes or days, and according to whether subsequent responding increased or decreased. Changes of all these types occurred even though the stimulus was a static, stuffed predator. Whether the resultant effect was positive or negative depended on the strength of the stimulus, the length of the initial period of exposure of the stimulus and the time interval between exposure and test (Hinde, 1960). 3. Energy models imply that aggressiveness is necessarily enhanced by isolation. This is true in some cases - for instance, with mice (e.g., Valzelli, 1969, Figure 3) - but not in others, such as the Cichlid fish studied by Heiligenberg (in press, Figure 4). Figure 3. Rise in intensity of aggression between mice previously isolated for the periods shown on the abscissa (From Valzelli, 1969)

AGGRESSIVENESS SCORE

Where it is true, alternative types of explanation supported by hard data render hypothetical energy models unnecessary. An example comes from the careful analysis by Cairns (1972) of isolation-induced aggression in mice. Isolation induces a greater tendency to initiate exploratory interactions with another individual. It also produces a greater reactivity to stimulation received in the course of such an

10 Robert A. Hinde Figure 4. Rise in attack rate of Haplochromis on small individuals living in its aquarium during ten days (bar underlining abscissa) of repeated presentation of a fish model with a naturally oriented black eye bar (From Heiligenberg, in press)

attacks / min 0.5

0

days

interaction, so that the encounter more readily escalates into an aggressive episode. The latter effect Cairns relates to a lowered threshold to stimulation which is found also in nonsocial situations and probably results from the lack of close body contact with other individuals during the isolation period. Cairns' elegant study provides clear evidence of the mechanism whereby isolation affects aggression in one case. Of course other mechanisms may operate in other cases, but as they are identified energy models will prove unnecessary. 4. Energy models imply that increased responsiveness to aggressioneliciting stimuli is necessarily accompanied by an increased tendency to seek out such stimuli. For this there is as yet no evidence, and Cairns' data, amongst others, suggest the opposite. In the light of this kind of evidence, and much further data could be cited, it is clear that energy models are unnecessary. They are also dangerous because they imply that an individual deprived of aggression-eliciting stimuli will show a gradually increasing tendency to

The study of aggression 11 behave aggressively until he seeks avidly for an object to attack or dissipates the 'energy' in some other way. Such a view is not a conclusion from data but from an outdated model of motivation. Now for the second issue concerning factors predisposing an individual to behave aggressively. It is important to remember that these do not necessarily operate directly to enhance aggression, for their effects may be quite indirect. For example: 1. and 2. Effects on general activity, suppression of fear responses. Certain passerine birds, kept in caged flocks, fight more if fooddeprived. This might seem to be a direct effect of hunger on aggression. In fact, the probability that two individuals, perched a given distance apart, will behave aggressively is unaffected by hunger. However, hunger does affect activity and also the readiness of a subordinate to approach a dominant near the food supply. It thus affects aggression by affecting the frequency of encounters (Marler, 1956; Andrew, 1957). 3. Changes in effectors. The dominance order in bachelor groups of red deer (Cervus elephas) is largely determined by antler size, the immediate hormone level being of minor importance. The shedding and growth of antlers is, however, under hormonal control, which thus affects aggression indirectly (Lincoln, Youngson & Short, 1970). 4. Changes in the effectiveness of eliciting factors. One example has already been mentioned - the responsiveness of mice to tactile contact with another individual is affected by a period of isolation, so that exploratory contacts then escalate more readily into an aggressive episode (Cairns, 1972). Another example is provided by the work of MacDonnell and Flynn (1966) on cats. Electrical stimulation of the attack areas in the hypothalamus increases the sensitivity of the reflexogenous zones around the mouth which mediate the head-orienting and jaw-opening responses preparatory to biting. 5. Changes in context. In yet other cases predisposing factors affect the context in which eliciting factors are effective. For example, in the weaver bird Quelea dominance rank in nonbreeding birds is affected by LH, while testosterone affects social rank in encounters over a sexually valent commodity such as nest material (Crook & Butterfield, 1970). These five examples are enough to show that we must determine not only which factors affect aggressive behavior but also how they act. Now to turn to some points about ontogenetic studies. Basically

12 Robert A. Hinde these must follow the same course as studies of more immediate causation. First, the influence of a given factor is assessed by determining the extent of the aggressive behavior shown when it has and has not been present, other factors being kept constant. Then the means by which aggression is affected must be determined. Considering first genetic differences, these may influence aggression by diverse routes such as the production of changes in effectors or in the stimuli presented to another individual, or changes in the ability to profit by experience, or in diverse other mechanisms as well as in those specifically associated with aggression. But there is also a special difficulty in studying genetic influences on aggression in mammals which arises from the facts that (a) aggressiveness is also affected by the early social environment, and especially by the type of maternal care received; (b) the early social environment provided by the social companions is influenced by their genetic constitution, and this (especially in the case of the mother) is likely to be closely linked to that of the subject; and (c) the early social experience depends on interactive relationships, so that, for instance, the maternal care received depends on the behavior of the subject as well as on that of the mother. The possible complexities are considerable (Figure 5). Turning now to studies of the influence of experiential factors on aggression, it seems important that the factors manipulated in experimental studies should be relatively small. For example, the usefulness of assessing the effects of rearing animals in isolation

Figure 5. Diagrammatic representation of the complexities arising in studies of the genetic bases of aggression in mammals. The discontinuous lines indicate the effects of unspecified causal factors Genetic constitution of social companions

>I

Social behavior of companions

Genetic constitution of subject

Interactional T relationship

N

Social behavior of subject Aggressive behavior of subject

The study of aggression

13

seems rather doubtful. Rearing in isolation is such an extreme condition and could affect aggression in diverse ways. A further issue is that the environment does not mold an individual as a potter molds passive clay; rather the individual determines what aspects of the environment affect him, and how. The consequences of experience depend on the nature of the experiencing individual. In the first place, this is a further reason to be wary of cross-species generalizations in studies of ontogeny. An experimental factor that enhances aggression in one species may have the reverse effect, or be merely irrelevant, in another. Furthermore, how the individual comes to behave in a given situation may be determined to a considerable extent by response tendencies independent of that situation. I am referring here to studies of the operant conditioning of fighting behavior of pigeons for food (Reynolds, Catania & Skinner, 1963; Azrin & Hutchinson, 1967) or rats for water (Ulrich, Johnston, Richardson & Wolff, 1963). Although the requirements for reinforcement were only a minimal form of attack, the subjects often came to show much aggressive behavior other than that originally reinforced. Furthermore, factors that affect aggression at one stage in development may not do so at another (Seligman & Hager, 1972; Hinde & Stevenson-Hinde, 1973). This influence of nature on the effects of experience operates also in the area of sex differences in aggression-related behavior. For example, while prenatal androgens may affect the extent to which a young rhesus monkey takes the initiative in rough-and-tumble social play, the influence of those androgens becomes apparent only as a result of social experience. Differences in prenatal hormones predispose young males and young females to respond in a statistically different fashion to a similar environment (Goy & Phoenix, 1971). A third point about ontogenetic studies concerns the need for more descriptive studies. In no species has the course of development from its earliest beginnings yet been traced in any detail. One of the most interesting studies here - that by Kruijt (1964) of the Burmese jungle-fowl (Gallus gallus) - shows that the precursors of aggression occur in the context of locomotion. When hopping about the chicks sometimes bump into each other, and after a while the hopping becomes oriented to other individuals so that clashes become more frequent, the birds bumping their breasts against each other. Frontal threatening, leaping, aggressive pecking and kicking appear successively

14 Robert A. Hinde between 8 and 21 days after hatching. At this stage the factors controlling fighting seem to be similar to those controlling locomotion; fighting is more common in active chicks, and both fighting and locomotion are increased by a period of confinement. There is also evidence that factors controlling feeding affect aggression: Not only does the motor pattern of aggressive pecking resemble that of feeding, but aggressive pecking is more common in the fighting of hungry chicks than in that of satiated ones, even though the fights themselves are no more frequent. The early development of aggression thus involves integration of and interaction between causal factors and movement patterns initially unrelated to each other. In birds many movement patterns appear initially in the absence of the motivational factors that will later control them. For instance, food-pecking by chaffinches appears initially when the young bird is well fed. The same appears to be true of aggression in monkeys; many of the motor patterns first appear in rough-and-tumble play. Indeed in a study of young baboons Owens (1973) found it impossible to say when play-fighting ceased and 'real' fighting began. Rough-andtumble play may also be one of the precursors of aggression in human children. Although it is motivationally distinct from aggression in young children (Blurton Jones, 1972), it may not remain so. Certainly the motivational bases of aggression change in ontogeny. Blurton Jones (1972) has strong evidence that in nursery school children the taking of objects is independent of aggression, though it may provide the context in which aggression occurs. Later, of course, instrumental goals become a potent cause of aggression. At an older stage, observational studies emphasize the great importance of contextual factors in the control of aggression. In many birds reproductive fighting at first decreases in intensity with distance from certain song posts, and subsequently becomes confined to a certain area. Fighting with particular neighbors comes to have particular properties. It is easy to forget the importance of context in laboratory studies, in which we are preoccupied with the variables we are manipulating; in the study of the mobbing response of chaffinches referred to earlier context turned out to be paramount. Finally, so far as ontogenetic studies are concerned, students of animal behavior must not forget that different kinds of processes come into operation at the primate level. Observational learning may be important in the development of aggression in primates; imitation

The study of aggression 15 and identification certainly become so in man. The difference is especially pertinent in the inhibition of aggression. In animals this is primarily the result of simultaneous fear; only in man and perhaps other higher primates do other processes of socialization intervene. So far we have proceeded backwards in time from the aggressive episode, considering successively eliciting, predisposing and ontogenetic factors. Now working the other way, we shall consider subsequent events whose probability is affected by the aggressive act - that is, its consequences. These can be classified in a number of ways: 1. The consequences may be classified according to whether they are beneficial, neutral or harmful to the individual concerned or to the group or species to which he belongs. The only point that needs to be made here is an obvious one, but often overlooked: Consequences beneficial to the individual may not be so to his group, and vice versa. We shall return to this later. 2. They may be classified according to whether or not they form the goal of the aggressive act. 'Goal', although clearly a necessary concept for the description of human behavior, has been in disrepute among students of animal behavior. This was partly because terms like 'goal', 'goal-directed', or 'purposive' often carry meaning in addition to that necessary for them to fill their explanatory role. It required recognition that machines with negative feedback can be regarded as teleological mechanisms (Rosenblueth, Weiner, & Bigelow, 1943), before it became respectable to interpret animal behavior as goalseeking. This does not mean that it is easy to draw a line between behavior that is and is not goal-directed; rather it is possible to recognize a dimension of goal-directedness (Hinde & Stevenson, 1969; Hinde, in press). A necessary criterion is that the behavior is influenced by discrepancy between the present situation and the goal situation; thus potential consequences are also causes. Aggressive behavior is in fact often divided into that which is and is not instrumental in character. The criterion concerns whether or not the fighting behavior is influenced by a goal other than the vanquishing of the opponent. Positive evidence might, for example, come from the observation that fighting does not occur if the goal is reached in some other way. The difficulty is that it is sometimes impossible to prove the absence of such a goal. If aggressive behavior occurs whenever two individuals approach within a certain distance, it could be argued that the goal is to maintain an area clear of other individuals.

16 Robert A. Hinde Another difficulty is that goals may shift. An attack directed towards obtaining an object may grade into fighting 'for its own sake', in which the object becomes irrelevant. In the human case, goals are often other than they appear at first sight. For instance, one reason why violence often escalates in mobs is that one of the goals of the individuals concerned is communication - both by the leaders to the followers within the group, and by the mob to outsiders. Testing out the enemy, like that we saw in the fighting fish, becomes an end in itself. 3. The consequences of aggression may be classified according to whether or not they are reinforcing - that is, according to whether or not their occurrence enhances the probability of the aggressive act. That food, access to a mate or escape from a painful stimulus and other conventional reinforcers can act also as reinforcers for aggressive behavior has been proven abundantly in both man and animals (e.g., Kuo, 1967). There is also evidence that fighting per se can be reinforcing (e.g., Thompson, 1969). It is probable that most consequences of aggressive acts classified as goals would also act as reinforcers, but not all reinforcers need have been goals - for instance, when fighting is reinforced adventitiously. 4. Finally, the consequences of aggressive acts may be classified according to whether or not they are to be regarded as functions in a biological sense. The biological use of function, referring forward in time, is of course to be distinguished from the more mathematical usage implying merely a relationship between two events. The biological concept is concerned ultimately with the extent to which the genes of the individual concerned are maintained in the population. This formulation could imply that all characters have the same function - that of contributing to eventual reproductive success. The effect of a given act on reproductive success may, however, be mediated by a nexus of intervening events. The term 'function' is often applied to items on such chains following fairly soon after the behavior itself, and preceding the subsequent enhancement of reproductive success. For instance, territorial aggression may space out a breeding population; spacing out may reduce predation and thus improve reproductive success (Tinbergen, 1956); either spacing out or the reduction in predation may be called the function of the territorial behavior. In a weak sense, biologists use function to refer to any beneficial consequence. In a strong sense, it refers only to functions through which

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17

natural selection acts to maintain the behavior in the repertoire of the species. For example, the preservation of biological necessities, such as food and a nest-site and the prevention of epidemic diseases have both been suggested as consequences of the territorial behavior of birds. If the variability of territory size were sufficient to affect the availability of necessities, but not the spread of disease, then natural selection could operate only through the former, and it alone would be a function in a strong sense. This difficulty disappears if we remember that the term function must ultimately refer to the consequence of a difference. The prevention of epidemic disease, although a beneficial consequence of territorial behavior, would also be a function in a strong sense only if the differences between territorial and nonterritorial populations were being considered but would not with differences between individuals in a population in which territories differed in size too little to affect disease. Since natural selection operates through the survival and spread of genes within a population, it is possible for behavior to have a biological function in the strong sense, and yet be detrimental to the individual concerned. Aggressive behavior of parents in defense of their young is an example: Its overall fitness is to be assessed from the effects on the parents' genes in the population. This fitness depends not only on its (detrimental) effects on the probability that the parent will breed again but also on its (incremental) effects on the probability that the young, who share some genes with that parent, will breed (Hamilton, 1964; Trivers, in press). It is, of course, difficult to prove that natural selection operates through a given consequence of aggressive behavior. In practice a variety of lines of evidence must be used, and it would not be relevant to discuss them here. It is, however, worth emphasizing that superficial evidence can be misleading. For example, it is often said that the function of threat displays is to reduce actual physical combat, and it is in fact the case that physical contact does not occur while animals are displaying. Insofar as combat is potentially harmful to both parties, this is a beneficial consequence of displaying. However, we have seen that the display may have a more immediate function - that of testing out the rival. Two points about these last three systems of classifying the consequences of an aggressive act must be made. First, in each system one category has causal relevance, but in different ways. Goals are also

18 Robert A. Hinde Figure 6. Relations between goals, reinjorcers and functions

1

Beneficial consequences

- Goals Reinforcers Aggressive act

> Functions Beneficial consequences

predisposing or eliciting factors for the act that leads to them; reinforcers increase the probability of the repetition of that act; and functions increase the probability that later members of the species will behave similarly. Second, these categories are not coextensive (Figure 6). Most goals are reinforcing, but not all reinforcers are goals. Neither reinforcing consequences nor goals are necessarily functions (as with pathological aggression), and functions are not necessarily reinforcing (though the closer in time to the aggressive act that the consequence labelled as function is, the more likely is it to be so). Functions are not necessarily beneficial to the individual concerned (though they enhance the spread of his genes), and beneficial consequences are not necessarily functions (in the strong sense). Now to turn to a slightly different matter. It is a matter to do not with hard science, but with its bogus application in the making of value judgments about aggression in human society. Although the topic has been considered elsewhere (Hinde, 1972; in press), so many false arguments have been used in this field that I consider it appropriate to discuss it again here. It is partly because aggression is sometimes used in a broad sense to include all ways in which man asserts himself over his environment and expresses his individuality (Hinde, 1972; in press) that it is sometimes regarded as a praisewdrthy human characteristic. If 'aggressive behavior' is taken to embrace all man's influence over his environment, the world would certainly be a different place without it. But of

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course judgments about the value of aggression in that broad sense need have no relevance to aggression in the sense of causing harm to others. Even in this narrow sense, however, some authors imply that aggression is not so unpleasant and useless for mankind as it might appear. Their arguments all rest on loose thinking. Some argue that since aggression arose through natural selection, it must be valuable to the species. Several points must be made here. Natural selection operates primarily through individuals. A trait is selected because those individuals that possess it are most likely to survive and reproduce. The question of whether a trait is valuable to the individuals that possess it is an entirely different one from that of whether the possession of the trait by some individuals is valuable to the group to which they belong. In our own society those who are prepared to use physical violence may be able to achieve their own ends more readily than others, but that is not the same as saying that their behavior is beneficial for society. This sort of confusion forms the basis of the interpretations put on many forms of aggressive behavior by Wynne-Edwards (e.g. 1962, 1972). Holding the view that animals have evolved means to keep their population levels below that at which food shortages become a problem, he believes that aggressive behavior is one means to that end. For example, red grouse show territorial aggression which results in some individuals claiming territories while others are forced to retire to live in flocks in less suitable areas. Wynne-Edwards sees this as a means for ensuring that the breeding habitat is not over-populated and even regards the behavior of the losers as 'altruistic'. But it would be more in keeping with what we know about the way in which natural selection acts to assume that the behavior of both territorial winners and territorial losers is in their own best interests. The territorial winners secure for themselves an adequate space for the rearing of their young. The chances for the losers of reproducing successfully are small, but they may do better to withdraw from a hopeless fight while there is at least some chance of another opportunity later on, than to expend their energies in attempting to carve out an inadequate territory against insuperable odds (see Lack, 1966, p. 299 ff, for a critique of Wynne-Edwards' views). Another point about the argument that aggression must be beneficial because it arose through natural selection is that, when applied to man, it neglects his rapid cultural evolution. This has placed him in cir-

20 Robert A. Hinde cumstances quite different from those in which natural selection operated, so that traits that were selected for in protohominids may be maladaptive now. It is also suggested that aggression is beneficial to the species because it ensures that the fitter individuals get priority of access to food, mates and other valuable commodities (e.g., McDougall, 1923; Ulrich & Symannek, 1969). In that fitter is equated with more aggressive, the argument is circular and also implies that the more aggressive individuals are the ones that society wishes to perpetuate. Not all would agree with this view. If fitter is not to be equated with more aggressive, the argument fails through lack of evidence for a correlation between aggressiveness and fitness in other respects. Even where there is a correlation (Lagerspetz, 1964; Karczmar & Scudder, 1969), the nature of the causal link still has to be investigated; for instance, both could be consequences of more efficient metabolism. As applied to animals (e.g., by Boelkins & Heiser, 1970) the view that aggression is beneficial to the species in this way involves the false view of natural selection discussed in the preceding paragraphs. As applied to man, it also overlooks the fact that there are other ways of reducing competition. Yet another argument is that a hierarchical structure in society ensures peace and order within the community and that the aggression involved in its maintenance is therefore, in the end, beneficial (e.g., Stokes & Cox, 1969). Clearly this would be unnecessary if aggression were not potentially present. The argument thus has a modicum of circularity. Presumably what is meant is that societies with a hierarchical structure imposed from above are often stable. But the stability, far from being a beneficial consequence of the aggressiveness of individuals, occurs in spite of it. The ordered dominance system gains stability only when the subordinate individuals cease to challenge the more aggressive ones - presumably because it is better for them to accept a subordinate position than struggle against hopeless odds (Stokes & Cox, 1969). And whether it is beneficial for the society as a whole depends on the values of those at the top. Now of course law and order must be maintained, but a social order based on a hierarchical system maintained by force may not be so desirable as it seems. It may conceal untold tensions. And support for such an imposed hierarchy because it ensures government by those fittest to govern implies a positive correlation between strength and

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21

wisdom not always borne out by common experience. Such support becomes even more positively objectionable when it is further implied (e.g., by Storr, 1968) that pariah castes, such as the Untouchables of India 'serve a valuable function in human communities for the discharge of aggressive tensions'. The Untouchables would be unlikely to share this view. It is also often said that aggression forms part of many normal and pleasurable human activities. Some, for example, have argued that aggressive male dominance is essential to the relations between the sexes. Not many would nowadays agree with this view as applied to man. Among animals, while aggressive and fleeing responses are often closely interwoven with sexual ones, they interfere with mating rather than promote it. In fish and birds courtship displays are usually given during a period in which male dominance is reduced to a point at which mating is possible (Tinbergen, 1959; Hinde, 1970); and in fish, birds and mammals a high tendency to aggression may interfere with mating (King, 1956; Sevenster, 1961; Lagerspetz, 1969). Under certain circumstances the occurrence of aggressive behavior, in addition to having a short-term negative effect on sexual behavior, may also be correlated with a longer-term positive one (Sevenster, 1961). However, there is no evidence that the long-term effect is specific to aggression, and it may be mediated by a change in general arousal affecting many different activities (Wilz, 1972). Many psychoanalysts hold the view that sex and aggression are closely related, but the fact that words like 'screw' and 'fuck' are used in both contexts, adduced in support of their view (Solomon, 1970), is an example of the risks entailed in basing scientific conclusions on colloquial speech. One other argument must be mentioned. Pointing to evidence that only species that show interindividual aggressiveness show interindividual bonds, Lorenz (1966) and others have argued that some of the best aspects of social life exist only because of their antitheses. But the evolutionary correlation, insofar as it exists, between aggressiveness and social bonds is of dubious relevance to the quite different question of whether a causal relation exists, that is, of whether aggression contributes to affectional bonds within the lifetime of any one individual or society. And the height of absurdity is reached when Storr argues 'that it is only when intense aggressiveness exists between two individuals that love can arise' (Storr, 1968, p. 36). Some time has been spent on these views because they are so dan-

22

Robert A. Hinde

gerous if accepted uncritically. There is of course no dispute that aggressive behavior has been selected as an adaptive characteristic in the great majority of species of higher animals, and that individuals who show it to a reasonable degree are more likely to survive and leave offspring than individuals who do not. But this is a completely different matter from the implication that aggressiveness in man may be a characteristic valuable for human society. There is no need to emphasize that aggressiveness can be a vice, and our concern must be with means to reduce it. It is sometimes argued that we do not know what repercussions a reduction in individual aggressiveness might have on the structure of human personality, but it seems unlikely that a reduced tendency to injure others could have deleterious effects. In any case, the question can justifiably be postponed in the face of the urgency of the present situation. This brings us back to the point at which we began — the relevance of studies of animal aggression to the human problem. There is one form of human aggression with no valid parallel in other species - war. Living in the shadow of the bomb for twenty-five years has made us acutely conscious of the dangers of war, but this must not distract us from the equally important problem of individual aggression. In terms of the total sum of human misery caused, individual aggression is at least as potent as war, and problems of its control are equally pressing.

REFERENCES Andrew, R. J., 1957, Influence of hunger on aggressive behavior in certain buntings of the genus Emberiza. Physiological Zoology, 30:177-185. Ardrey, R., 1967, The territorial imperative. New York, Atheneum. Azrin, N. H., & Hutchinson, R. R., 1967, Conditioning of the aggressive behavior of pigeons by a fixed-interval schedule of reinforcement. Journal of the Experimental Analysis of Behavior, 10:395-402. Berkowitz, L., 1962, Aggression. New York, McGraw-Hill. Blurton Jones, N. (Ed.), 1972, Ethological studies of child behavior. Cambridge, Cambridge University Press. Boelkins, R. C., & Heiser, J. F., 1970, Biological bases of aggression. In D. N . Daniels, M. F. Gilula & F. M. Ochberg (Eds.), Violence and the struggle for existence. Boston, Little Brown. Cairns, R. B., 1972, Fighting and punishment from a developmental perspective. In J. K . Cole & D. D. Jensen (Eds.), Nebraska symposium on motivation. Lincoln, University of Nebraska Press. Crook, J. H., & Butterfield, P. A., 1970, Gender role in the social system of Quelea. In J. H. Crook (Ed.), Social behavior in birds and mammals. London, Academic Press.

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Feshbach, S., 1964, The function of aggression and the regulation of aggressive drive. Psychological Review, 71:257-272. Feshbach, S., 1970, Aggression. In P. H. Müssen (Ed.), Carmichael's manual of child psychology. 2nd ed. New York, Wiley. Goy, R. H., & Phoenix, C. H., 1971, The effects of testosterone propionate administered before birth on the development of behavior in genetic female rhesus monkeys. In C. H. Sawyer & R. A. Gorski (Eds.), Steroid hormones and brain function. Berkeley, University of Calif. Press. Hamilton, W. D., 1964, The genetical evolution of social behavior. Journal of Theoretical Biology, 7:1-52. Heiligenberg, W., in press, In Advances in the study of behavior. Vol. 5. Hinde, R. A., 1960, Energy models of motivation. Symposia of the Society for Research in Experimental Biology, 14:199-213. Hinde, R. A., 1970, Animal behavior: A synthesis of ethology and comparative psychology. New York, McGraw-Hill. Hinde, R. A., 1972, Aggression. In J. W. S. Pringle (Ed.), Biology and the human sciences. Oxford, Oxford University Press. Hinde, R. A., in press, The bases of social behavior. New York, McGraw-Hill. Hinde, R. A., & Stevenson, J. G., 1969, Goals and response control. In L. R. Aronson, E. Tobach, J. S. Rosenblatt, & D. S. Lehrman (Eds.), Development and evolution of behavior, 1. New York, Freeman. Hinde, R. A., & Stevenson-Hinde, J. (Eds.), 1973, Constraints on learning: Limitations and predispositions. London, Academic Press. Hokanson, J. E., 1970, Psychophysiological evaluation of the catharsis hypothesis. In E. I. Megargee & J. E. Hokanson (Eds.), The dynamics of aggression. New York, Harper and Row. Karczmar, A. G., & Scudder, C. L., 1969, Aggression and neurochemical changes in different strains and genera of mice. In S. Garattini & E. B. Sigg (Eds.), Aggressive behavior. Amsterdam, Excerpta Medica. King, J. A., 1956, Sexual behavior of C^BL/IO mice and its relation to early social experience. Journal of Genetic Psychology, 88:223-229. Kruijt, J. P., 1964, Ontogeny of social behavior in Burmese red junglefowl. Behavior, Supplement, 12. Kuo, Z. Y., 1967, The dynamics of behavior development. New York, Random House. Lack, D., 1966, Population studies of birds. Oxford, University Press. Lagerspetz, K. M. J., 1964, Studies on the aggressive behavior of mice. Suomalaisen Tiedeakatemian Toimituksia Annates Acad. Sei. Fennicae. B. 131:1-131. Lagerspetz, K. M. J., 1969, Aggression and aggressiveness in laboratory mice. In S. Garattini & E. B. Sigg (Eds.), Aggressive behavior. Amsterdam, Excerpta Medica. Lincoln, G. A., Youngson, R. W., & Short, R. V., 1970, The social and sexual behavior of the red deer stag. Journal of Reproduction and Fertility, Supplement, 77:71-103. Lorenz, K., 1966, On aggression. London, Methuen. Macdonnell, M. F., & Flynn, J. P., 1966, Sensory control of hypothalamic attack. Animal Behavior, 74:399-405. McDougall, W., 1923, An outline of psychology. London, Methuen. Marler, P., 1956, Studies of fighting in chaffinches. 3. Proximity as a cause of aggression. British Journal of Animal Behavior, 4:23-30.

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Owens, N. W., 1973, The development of behavior in free-living baboons. Unpublished doctoral dissertation, University of Cambridge. Patterson, G. R., & Cobb, J. A., 1971, A dyadic analysis of 'aggressive' behaviors. In J. P. Hill (Ed.), Minnesota symposia on child psychology. Vol. 5. Minneapolis, University of Minnesota. Reynolds, G. S., Catania, A. C., & Skinner, B. F., 1963, Conditioned and unconditioned aggression in pigeons. Journal of the Experimental Analysis of Behavior, 1:73-75. Rosenblueth, A., Wiener, N., & Bigelow, J., 1943, Behavior, purpose and teleology. Philosophy of Science, 10:18-24. Scott, J. P., & Fredericson, E., 1951, The causes of fighting in mice and rats. Physiological Zoology, 24:273-309. Seligman, M. E. P., & Hager, J. L. (Eds.), 1972, Biological boundaries of learning. New York, Appleton-Century-Crofts. Sevenster, P., 1961, A causal analysis of a displacement activity (fanning in Gasterosteus aculeatus). Behavior Supplement, 9:1-170. Simpson, M. J. A., 1968, The display of the Siamese fighting fish, Betta splendens. Animal Behavior Monographs, 1:1. Solomon, G. F., 1970, Psychodynamic aspects of aggression, hostility, and violence. In D. N. Daniels, M. F. Gilula, & F. M. Ochberg (Eds.), Violence and the struggle for existence. Boston, Little Brown. Stokes, A. W., 1962, Agonistic behavior among blue tits at a winter feeding station. Behavior, 19:208-218. Stokes, A. W., & Cox, L. M., 1969, Aggressive man and aggressive beast. Bioscience, 20:1092-1093. Storr, A., 1968, Human aggression. Allen Lane, Penguin Press. Thompson, T. I., 1969, Aggressive behavior of Siamese fighting fish: Analysis and synthesis of conditioned and unconditioned components. In S. Garattini & E. B. Sigg (Eds.), Aggressive behavior. Amsterdam, Excerpta Medica. Tinbergen, N., 1956, On the functions of territory in gulls. Ibis, 95:401-411. Tinbergen, N., 1959, Comparative studies of the behavior of gulls (Laridae): A progress report. Behavior, 15:1-70. Trivers, R. L., in press, Parent-offspring conflict. American Zoologist. Ulrich, R. E., Johnston, M., Richardson, J., & Wolff, P. C., 1963, The operant conditioning of fighting behavior in rats. Psychological Record, 13:465. Ulrich, R. E., & Symannek, B., 1969, Pain as a stimulus for aggression. In S. Garattini & E. B. Sigg (Eds.), Aggressive behavior. Amsterdam, Excerpta Medica. Valzelli, L., 1969, Aggressive behavior induced by isolation. In S. Garattini & E. B. Sigg (Eds.), Aggressive behavior. Amsterdam, Excerpta Medica. Wilz, K. J., 1972, Causal relationships between aggression and the sexual and nest behaviors in the three-spined stickleback (Gasterosteus aculeatus). Animal Behavior,20:335-340. Wynne-Edwards, V. C., 1962, Animal dispersion in relation to social behavior. Edinburgh, Oliver and Boyd. Wynne-Edwards, V. C., 1972, Ecology and the evolution of social ethics. In J. W. S. Pringle (Ed.), Biology and the human sciences. Oxford, Oxford University Press.

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ABSTRACT To understand and control human aggression, we must use all available tools, including comparative studies of other species. There is no generally agreed upon definition of aggression. The complexity of aggressive episodes is due in part to the simultaneous arousal of tendencies to attack and escape, to the use of threat to test out the rival, and to the propensity of encounters to escalate. Energy models of aggressive motivation are misleading. Factors predisposing an individual to aggression may act indirectly. Developmental studies must involve first the identification of relevant variables, and then the study of how they act. The effectiveness of experimental factors depends on the nature of the individual. Development may involve the integration of previously independent elements. The relations between the consequences, goals, reinforcers and functions of aggressive acts are considered. Arguments that individual aggressiveness is valuable to the community rest on loose thinking.

RÉSUMÉ Pour comprendre et contrôler l'agression humaine, nous devons utiliser tous les outils disponibles, y compris les études comparatives d'autres espèces. Il n'existe pas de définition de l'agression généralement admise. La complexité des épisodes agressifs est due en partie à l'éveil simultané de tendances à l'attaque et à la fuite, à l'utilisation de la menace pour mettre le rival à l'épreuve, et à la propension à l'escalade des antagonistes. Les modèles énergétiques de la motivation agressive sont fallacieux. Des facteurs prédisposants et individuels peuvent agir indirectement. Les études développementales doivent inclure d'abord l'identification des variables adéquates, ensuite l'étude de leur mode d'action. L'efficacité des facteurs expérimentaux dépend de l'individu. Le développement peut comprendre l'intégration d'éléments antérieurement indépendants. Les relations entre les conséquences, les buts, les éléments renforçateurs et les fonctions des actes agressifs sont examinées dans cet article. L'idée que l'agressivité individuelle présente une valeur pour la communauté demeure non fondée.

Phylogenetic adaptation as determinants of aggressive behavior in man IRENAUS

EIBL-EIBESFELDT

Max Planck Institute,

Percha/Starnberg

The last few years have witnessed lively discussions on the determinants of aggression. Attempts at understanding this phenomenon and at subsequently finding ways to control it have led to a variety of explanatory models: 1. The proponents of learning theory assume that aggressive behavior is learned; its roots lie in early childhood, where the individual's attempts to satisfy his demands by aggressive means are successful and are thus reinforced. In addition, social learning from a model plays an important part in the acquisition of aggressive behavior patterns (Bandura & Walters, 1963). 2. According to the frustration-aggression hypothesis, aggressive behavior is the result of deprivation experiences in early childhood. Since, in practice, such experiences never can be totally avoided, the development of aggressive behavior is just about inevitable (Dollard, Doob, Miller, Mowrer, & Sears, 1939). 3. The drive model of Lorenz and Freud assumes an innate drive for aggression. This theory is also referred to as an instinct theory of aggression (Lorenz, 1963). In its wider version, the instinct theory of aggression assumes that phylogenetic adaptations preprogram aggressive behavior in various ways, the aggressive drive being just one possibility. Preprogramming occurs, for example, also on the receptor and motor levels. Since all these paradigms are built on observations and experiments, it seems strange indeed that some proponents of learning theory models insist upon their exclusive validity with such monistic vehemence.

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Eibl-Eibesfeldt

Must we regard the different interpretational models as incompatible? It seems more plausible to take into consideration all evidence and to construct an interactional model which does justice to various theoretical frameworks. In the following pages, we shall attempt to do just that. First, however, we shall clarify a few ethological concepts and present an outline of our basic strategy.

The concept of phylogenetic

adaptations

There has been considerable confusion regarding the concepts of instinct and instinctive. A more precise definition of those terms has been effected only recently. Lorenz (1961) pointed out that animals are equipped at birth with particular movement patterns and develop further skills during their ontogeny. Much is learned in this process; nevertheless, deprivation experiments show that certain movements mature independently of experience. In such cases, no practice and no models for imitation are necessary. Thus, certain birds develop their species-specific calls and songs even under conditions of auditory deprivation (Sauer, 1954; Konishi, 1963, 1964, 1965). The movement patterns of these animals are, to use the common, short-hand terminology, 'innate'. The German word Erbkoordinationen, often poorly translated into English as 'fixed action patterns', supplies a good description of this phenomenon. Innate, or inborn, means that the neuromotoric structures on which the movement patterns are based develop in a process of self-differentiation, guided by chemical instructions laid down in the genome. Furthermore, animals are innately capable of 'recognizing', so to speak, certain stimulus situations and to respond with certain behavior patterns. Thus we can say that animals are equipped with data processing mechanisms, or detectors. Those mechanisms which mediate the release of a particular behavior are termed 'innate releasing mechanisms'. Important also is the fact that animals do not simply respond passively to external stimuli. In themselves they are active, impelled by physiological machineries which drive the animal to search out stimulus situations, e.g., in states of hunger, thirst or sexual arousal - situations which will allow the satisfaction of its present drive through the sequences of consummatory activity. The processes of learning finally are structured in such a way as to guarantee, as a rule, the adaptiveness of resulting behavior

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modifications. In other words, the behavior modified through learning must contribute to the survival of the individual. In this context it is plausible that the various animal species evolved species-specific learning dispositions. (For details on the concept of phylogenetic adaptations see Eibl-Eibesfeldt, 1972a.) Any individual who wishes to delve into the framework of ethology must, of course, first gain an understanding of ethological concepts. Most critics of this approach are attacking a concept of 'instinct' which has been obsolete for a good thirty years, a fact which makes objective and fruitful discussion rather difficult. Further misunderstandings revolve around the meaning and purpose of comparisons between man and other animals. Thus, in Schmidt-Mummendey (1971) we find: 'All expositions on aggressive behavior in man are based by Lorenz and Eibl-Eibesfeldt on analogies between fish, goose, or wolf and man. Such comparisons when untouched by evidence coming from human psychology, are of little value in the analysis, control, and prediction of human behavior' (p. 13). And on the same page: 'It is unacceptable to generalize the results of observations on a few animal species, with Lorenz mainly on fish and geese, to all other species including man.' Such critical remarks are all the more incomprehensible since ethologists have emphasized specifically and repeatedly the unacceptability of drawing conclusions from one species to another. All that is gained, as a first step, are working hypotheses, whose validity for another species (such as man) can be tested only by direct examination. One good example of such a research approach can be found in physiology, and indeed, much has thus been gained in the knowledge of functional relationships. Pure analogies, that is, similarities not based on a common phylogenetic stem, are helpful in understanding functionally based structural traits (Wickler, 1971). Should a researcher, for example, wish to examine the laws governing sexual pair-bonding, he would be ill-advised to look at our nearest primate relatives, who in adaptation to different environmental conditions did not develop this particular social trait. In this case, we would be more enlightened by the examination of various monogamous insects or birds. If, on the other hand, we are interested in the discovery of homologies - similarities based on a common genetic background then our nearest primate relatives are indeed better objects for study. If we wish to gain insight into general construction principles, we should start by examining structures displaying the same functions in

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organisms of the greatest possible diversity. Thus, all kinds of wings, whether they consist of a cuticular fold or of modified forelegs in birds or mammals, are subject to the same functional laws. If, by contrast, we wish to discover the evolutionary potential of one group sharing a common genetic base, then we would study closely related species living within the greatest possible range of environmental conditions. In this way, study of adaptive radiation enables us to make basic discoveries about the potentialities of such a genetically related group. Intraspecific

aggression

Patterns of aggressive behavior and biological control of aggression At this point we shall begin to examine whether aggressive behavior of animals and man is 'preprogrammed' by phylogenetic adaptations in the manner discussed above. The author defines aggressive behaviors as those which serve the function of spacing. Often we find in the literature of psychology a determination of aggressive behavior according to the individual's intention of damaging a conspecific. A biologist, however, finds little use for such an indication. We are limiting ourselves here to a discussion of intraspecific aggression. All too often, the interand intraspecific kinds of aggression are confused, as for example in discussions by Ardrey (1966) and Kuo (1960, 1961). Such broadening of concepts is truly unacceptable, for often we are dealing with essentially different behavior patterns, controlled by different neuronal mechanisms. A cat stalking its prey displays a totally different behavior from one fighting with a conspecific. Very frequently, animals fight with members of their own species. We need only observe the meeting of two male dogs which do not know one another; in all probability they will soon engage in a fight. Such aggressiveness is not confined to predatory animals; herbivorous creatures display very similar tendencies; so, for example, do bulls and barnyard roosters. A biologist detecting such a common characteristic will surely not assume that he is dealing with a mere epiphenomenon, or a degeneration of some other adaptive process. Rather, he will speculate that a behavior recurring with such regularity must have evolved in the service of a particular function. In a less finalistic sense, the assumption will be made that the behavior in question developed to specific pressures of natural selection. This assumption has been verified by studies on a wide range of

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animal species. We can touch upon several advantages for aggressive behavior. Frequently, animals fight their rivals only within certain territorial boundaries. This geographical intolerance leads to the establishment of individual territories. In most cases, however, it is not one solitary animal which defends a territory. Birds of song often do this in pairs, many mammals even in groups. But the effect remains the same: Pressure is placed on the individuals of a species to disperse. The animals spread out over a greater region and will exploit even peripheral areas less well suited to their needs. Also, overpopulation in any particular area is avoided; the advantage of such a condition is obvious. Suppose that robins would not fight each other: All too easily, then, several pairs could make use of a desirable brooding spot under the same barn roof. The first spell of bad weather would limit the activity radius of the whole group, and the next generation would be greatly endangered because the supply of insects in the neighborhood would quickly be depleted. In many cases, intraspecific intolerance is confined to the period of reproduction. For most of the year, the marine iguanas of the Galapagos Islands populate the coastal cliffs in a peaceful manner, and often we can observe hundreds of them lying tightly packed together. But at reproduction time the males become intolerant of each other, individuals demarcating small coastal territories and driving off approaching rivals (Eibl-Eibesfeldt, 1955). Resulting intraspecific disputes lead to a selection of the stronger and most capable, thus healthiest, males for reproduction. This represents one mechanism for the prevention of any possible biological degeneration. Another advantage of this kind of territorial defense is that in brood-caring or parenting species strong males are better able to defend their young. In higher vertebrates where grouping occurs, fights also come about between members of the same group. This results in the establishment of a dominance hierarchy. The highest-ranking position then brings with it privileges but duties as well that are connected with the function of leadership. This latter point applies especially to higher monkeys. Again we can see the biological advantage of this system, since the healthiest and strongest will best fulfill the leading role. These and other advantages of natural selection help to explain the widespread occurrence of aggressive behavior patterns. Aggression of this kind, far from constituting an epiphenomenon or a mere bad habit, fulfills a whole series of functions serving the survival of the species.

32 Irenaus Eibl-Eibesfeldt The demands of natural selection, however, did not produce creatures of unrestrained aggressiveness. Despite the occasional claim that Cain rules the world (Szondi, 1969), careful observation quickly makes us conclude that, in general, the killing of conspecifics is avoided. The goal of aggressive behavior is not physical destruction of the opponent. Quite the contrary: Those species in which individuals are equipped with dangerous weapons, and who could easily kill their rivals in a fight, have evolved special inhibitory mechanisms; in most cases, then, the partner is not seriously damaged. Two dogs in an encounter may begin by exchanging bites, but as soon as one realizes he is the weaker, he can submit. Submission in this case can be expressed in two ways: The loser can expose the side of his neck to the other, or he can drop on his back like a puppy. In both cases he demonstrates defenselessness, and the victor, showing a marked inhibition to continue his attack, ceases to bite. The loser's puppy-like behavior may even release acts of nurturance in the opponent, who may lick the other, especially in the genital region. An amiable relationship may result. Occasionally, disputes are enacted as 'tournaments'. Marine iguanas, for example, indulge in such bloodless matches of strength. At reproduction time, as we have mentioned, males fight others of their kind. If a rival comes too close, the occupant of a particular spot threatens by opening his mouth as though ready to bite, nods the head, and struts with stiffened back in front of the opponent. During this ritual he displays the length of his side, enlarging the silhouette by raising the crest on neck and back. If the other remains unimpressed, a fight ensues. The antagonists rush upon each other. Their mouths are open and threatening, and they lead any observer to expect an exchange of vicious bites, but this does not happen. Instead, the animals lower their heads and clash together with their skulls. Each attempts to push the other from his place, and the fight may last for some time. Frequently there are pauses during which the animals face each other threateningly. At last, one of the disputants, feeling the weaker, ends the fight by lying flat on the ground. The other respects this submissive posture, stops attacking and waits quietly for the loser to go away (Eibl-Eibesfeldt, 1955). This exemplifies a bloodless tournament with a strict set of rules. The stronger wins without damaging the weaker, a condition obviously favorable to the survival of the species. A marine iguana biting the other with his razor-sharp

Phylogenetic adaptation as determinants of aggression 33 teeth would greatly injure him, and the species as a whole would be endangered by such a depletion of male reserves. Tournaments, or ritualized fights, have evolved in numerous vertebrates. Well-known examples are the mouth fights of the Cichlid fishes, the wrestling matches of poisonous snakes and the diversity of tournament fights among antelopes. In this last example, every species has its own rules of battle, best suited to its particular kind of horns. The horns are always employed so as to avoid damage to the opponent. Thus, an Oryx-antelope will never stab her partner in the unprotected flanks. Rather, she will hook her horns into those of her opponent, aiming to push the other away. Oryx-antelopes use their pointed horns as weapons only against predatory enemies (Walther, 1966). In some animal species, individuals are inhibited only against killing members of their group. Appeasement signals here serve their function only when the partners know each other. Signals from 'strangers' are ineffective. The lion, who lives in a group, or 'pride', attempts to kill every approaching outsider (Schenkel, 1966). Finally, inhibitions against killing are absent in those animals who either lack dangerous weapons or who can flee from each other quickly after no more than a short exchange of bites. In such cases, the rival is usually spared injury. Although accidents occasionally happen, these do not exert a selection pressure great enough to necessitate the development of killing inhibitions. How it may be with humans we shall discuss later. To summarize briefly: Behavior patterns of intraspecific aggression evolve in the course of phylogenetic development to serve various functions. Selection pressures favoring aggressivity are counteracted by pressures to avoid serious injury to conspecifics. The result of these, at first glance contradictory, selection pressures was the evolution of tournament fights and killing inhibitions. Phylogenetic adaptations in aggressive behavior of animals Motor patterns. Based on the above discussions, we may expect, first, that animals are equipped with species-specific, physical 'weapons' and, second, that their fighting behavior is largely preprogrammed by phylogenetic adaptations. The development of such genetically based behavior was demonstrated through experiments in which animals were raised in isolation. Marine iguanas thus deprived of all social experience perform the head-butting combat exercises in the same way as conspecifies raised under 'normal' conditions. Lava lizards (Tropidu-

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rus) growing up in social isolation fight by lashing with their tails in the species-specific manner. Cichlid fishes raised in isolation display the species-specific behavior patterns of threat and mouth fighting. Fighting cocks, as well as rats, without social experience combat in the species-specific way (Eibl-Eibesfeldt, 1972a). These and many other experiments have yielded strong evidence that a large number of animals are born with the particular movement patterns used for fighting. But not only in the realm of motor patterns do we observe the results of phylogenetic adaptations. Releasing stimuli (releasers). Aggressive behavior in numerous vertebrates is released by particular stimuli characterizing the conspecific. These stimuli can easily be reconstructed in a model. Robins, for instance, respond to the red patch on the chest of a rival by attacking him. If we mount the plumage of a robin in the territory of a male, the latter will attack. If the red feathers are removed, the robin will ignore the rest. But a simple bundle of red feathers tied to a branch will draw the attack of the territory holder (Lack, 1943). Males of the Fence lizard (Sceloporus) sport blue stripes at the side; females of the species are gray. If we reverse the situation and paint blue stripes onto the female, she will be attacked. If we cover the blue stripes of the male, he will not be attacked by other males (Noble & Bradley, 1934). Stickleback males attack upon seeing the red belly of their rival. A bloated silvery belly, on the other hand, releases courtship behavior. Even males raised in isolation react immediately with attack or courtship behavior to the appropriate models (Tinbergen, 1951; Cullen, 1960). Learning dispositions. Experimenters have found that the opportunity to threaten or fight a rival can be used as inducement for learning. Fighting fish master a maze if as a reward they may threaten the model of a conspecific through a glass pane. Similar results were obtained with roosters (Thompson, 1963, 1964). Mice learn a task when reinforced with the opportunity to fight another mouse (Tellegen & Horn, 1972). Thus, the acts of fighting and threatening seem to hold some element of pleasure. Drive jor aggression. Experiments have shown that animals do not respond to the same releasing stimuli with unvarying intensity. Fluctuations in the readiness to attack are influenced, among other things, by hormonal factors. In many male birds and mammals, the male sex hormone is linked to an increase in aggression at the time of reproduc-

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tion. Animals thus aroused exhibit so-called appetitive behavior, seeking out releasing stimuli. In some animal species the endogenous fighting impulse or drive is so intense that, in the absence of an appropriate rival, individuals will satisfy their drive on some substitute object. They may even perform part of the motions without any object at all, akin to behavior in vacuo. Male Cichlid fish (Etroplus maculatus) become more aggressive the longer they are kept in isolation. After a certain length of time, females added to the tank are not courted but attacked and killed. But if another male is quickly added, he will be attacked and the female courted. Upon removal of this 'scapegoat', the female once again becomes the victim of built-up aggression (Rasa, 1969, 1971). Wickler (1971) objects that these results are not conclusive since quite possibly the female, which resembles the male, stimulates and gradually intensifies the male's preparedness to fight. In the spaciousness of his natural surroundings, the male has sufficient opportunity to fight other males. In captivity, however, the female becomes the object of the male's aggression which she herself has stimulated. This alternative explanation is plausible, but as yet no evidence backs it up. Of interest, however, are Rasa's experiments with the damselfish (Microspathodon chrysurus). The fish learn a simple L-maze when exposed to a conspecific which they can 'fight' through the glass pane of a goal box. Subjects may choose their length of stay, which varies with the strength of aggressive drive which again depends on length of isolation. We must emphasize, however, that the physiology of aggression differs from one species to another and, in fact, even changes within the group of Cichlids. Fighting cocks raised in isolation fight their own shadow if no rival is available. They also attempt to peck at their tail and kick it with their claws, which results in a seemingly senseless circular movement (Kruijt, 1964, 1971). These roosters certainly have not acquired their urge to fight by social experience. Although not all vertebrates are motivated in the same way by physiological drive mechanisms, in many cases we can demonstrate the influence of an endogenetic component. We do not know the role of central nervous factors in the build-up of fight motivation. Their part may be played in the term of self-arousing neural circuits. But already it has become possible to release fighting appetence by electrical stimulation of the brain (v. Hoist & Saint Paul, 1960). In this context we can cite several noteworthy experiments by

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Jouvet (1972) on cats. During 'paradoxical sleep', cats are in an atonic state, their eyes move rapidly, there is a twitching of the ears, vibrissae and paws, and breathing is irregular. At the same time there is an increase in electrical activity in certain areas of the brain. Lesioning of a certain spot in the cat's posterior cortex will produce 'rage behavior' during paradoxical sleep. Normally, motor discharges are inhibited by centers in the posterior cortex. When this inhibitory mechanism is eliminated, however, the spontaneity lying at the base of motoric aggression leads to spontaneous outbursts of movement. Some critics of the aggressive drive hypothesis claim that rather absurd consequences should result if there were a spontaneous motivation for aggression, 'for example, that an animal which after many battles has finally secured its territory and has driven off all rivals, will now go forth like a knight on horseback seeking new enemies . . . ' (Schmidbauer, 1972, p. 29). Such behavior is certainly not the inevitable consequence of an aggressive drive. A lowering of threshold must lead neither to a behavior discharge in vacuo nor to abandonment of a territory. The organism's system could easily be constructed so that the territorial tie suppresses any motivation to leave. For species often engaged in fights, it must be advantageous to experience an increase in aggressive motivation by means of the appropriate drives. Furthermore, the motivation to attack surely differs from one species to another, depending on ecological demands. And, lastly, Wickler has rightly pointed out that aggression probably evolved repeatedly and independently in various animal groups, just like the flight wings of birds, bats and insects. Genetics. We may assume that the hypothesis of a genetic base for aggressive dispositions now rests on a solid foundation. Among others, Lagerspetz (1969) has experimented with aggressive and nonaggressive strains of mice. The young of nonaggressive mothers were put in with aggressive mothers, whose young again were given to the 'peaceful' mothers. Yet, in the maturing young, no behavioral influence was observed: Those born of aggressive mothers became themselves aggressive, whereas those of nonaggressive mothers remained peaceful. We do not mean to say, of course, that social experience is of little or no importance. Scott (1960), for instance, has shown that with training he could significantly increase or decrease the aggressivity of house mice. Nevertheless, we may assume that aggressive behavior of animals is largely determined by phylogenetic adaptation.

Phylogenetic adaptation as determinants of aggression 37 Aggression and control of aggression in man Innate movement patterns The subject of human aggression is fraught with controversy. Much of this stems from the fact that discussants do not fully grasp the meaning of each others' concepts and claims. So it happens, for example, that the instinct theory of aggression and the hypothesis of an aggressive drive are often treated as one and the same, and the concept of phylogenetic adaptation is then rejected along with that of the dynamic instinct concept of aggression. In light of our preceding discussion, it must have become clear that we should ask questions more discriminately. In modern terminology, 'instinct' has come to mean 'phylogenetically adapted', and such adaptations have been demonstrated in the realms of motor behavior, receptive phenomena, drive systems and learning dispositions. While examining human aggressive behavior, we should therefore ask: Are there universal patterns of threat and aggression, in other words, patterns which can be observed in all cultures? Can we uncover universally releasing stimulus situations? Does man possess drive mechanisms and innate learning dispositions? Answers must be derived from various sources of information. Of great theoretical interest are observations on human beings who grew up under defined conditions of deprivation. Children born deaf and blind, for example, develop attitudes of intolerance, provided they are not severely brain-damaged. Such tendencies appear despite educational efforts to the contrary. At a certain age these children begin to reject the advances of those they do not know. At first, this tendency takes the form of a classical fear of strangers. Once the children have determined a person's odor to be unfamiliar, they turn away and seek contact with a reference person. Such negative reactions consistently develop, although everyone concerned takes the utmost care to provide these children with security. Certainly our subjects never had an experience with strangers bad enough to justify their reaction. Therefore, we must be dealing with a normal maturation of social attitudes. In the course of further development, rejection of strangers becomes coupled with elements of aggression. The deaf-blind child not only evades the stranger but may even hit at him, should he persist in his efforts at contact. Reactions according to the formula strange = enemy, familiar = friend develop even without negative experiences. Some children develop habits of place. They insist upon their place

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at the table and defend it against others. I have also observed the defense of 'property' (small gift parcels). Aggressive behavior patterns of the congenitally deaf and blind are quite similar to those of 'normal' children. In a dispute they bite, hit at the other with open hand and push him away with palm or back of hand. Arrogance is expressed by vertical folds on the forehead and a gritting of the teeth, which are sometimes exposed by pulling back the lips. The head is often thrown right back, which demonstrates rejection of contact. When angry, the children may bite their own hand and kick about with their feet. When turning away abruptly, they may stamp on the floor with one foot. Fists are often clenched. Crying and pouting are submissive behaviors: The head is lowered, and seated subjects may shrink into themselves (Eibl-Eibesfeldt, in press). In principle, these behavior patterns are very much like those of normal children, except that the latter's repertoire is more varied. Cross-cultural comparisons, to be discussed further on, show that behavior patterns of threat and fighting are universal (see Eibl-Eibesfeldt, 1972b). Kortlandt (1972) has described numerous similarities in threat and combat behavior of chimpanzee, gorilla and man. In all three species, individuals threatening, for example, beat with flat hand against some base, stamp with their foot on or against a resounding object, shake branches with both hands (human beings will also do this with an opponent), tear out plants and branches, wave branches and sticks in their raised hand, throw objects, beat with objects, and more. Recently, A. Jolly (1972) has drawn attention to many primate similarities in the expression of threat and submission. Thus we may speculate that even human motor behavior contains not a few elements of phylogenetic adaptation serving the function of agonistic behavior (aggression, defense, submission). The tendency to create territorial boundaries and to keep a distance Individual distances vary across cultures (Hall, 1966) but within a culture are generally maintained. There will always be situations in which body contact with a stranger is permitted - for example, in a crowded elevator or bus, or around a campfire. But these are exceptions, and, in general, people will insist on their privacy or personal space. Those who first occupy a particular space acquire certain rights, and so the next comer will politely ask permission before taking the remaining seat at a restaurant table. Felipe and Sommer (1966) con-

Phylogenetic adaptation as determinants of aggression 39 ducted an experiment in various libraries. They overstepped individual distances by sitting, as if by chance, very close to a person working at a table. The victim first tried to move away; if that was not possible, he would create artificial boundaries with books, rulers, and other objects. If these attempts at disengagement failed, the subject would leave the table. Esser (1970) and Paluck and Esser (1971a, 1971b) have made observations on boys with severe mental retardation and learning difficulties. In an experimental room with many opportunities for drawing boundary lines, each of these 21 boys exhibited marked territorial behavior in the sense of place-bound intolerance. Each occupied a certain part of the room and defended his spot against others. After an initial period of fighting, mere threat behavior proved sufficient to maintain territories. Territorial behavior of these children, whose IQs were below 50, was more pronounced than in 'normal' children. Quite possibly we are dealing with a more 'primitive' social behavioral trait which would normally be under cortical control. Negative reinforcement, or punishment, quite effective with these boys in other circumstances, had little influence. Paluck and Esser (1971a, 1971b) feel that territorial division was of primary importance to the boys in creating social order and organization, in particular because each is left in peace within the space he has fought for and established for himself. On the basis of more general observations, as well, we may conclude that territoriality is a universal human trait. Examples have been quoted to prove the contrary but, on closer examination, such 'exceptional' cases have repeatedly proven invalid. We shall cite further examples on this topic. Contributions of cross-cultural research It is claimed frequently that aggressive behavior must result from education alone, since cultures have been found which do not seem to manifest such behavioral tendencies at all (Hellmuth, 1967; Schmidbauer, 1970). But after critical examination, these assertions prove to be unfounded (Weidkuhn, 1969; Eibl-Eibesfeldt, 1972b). Hopi Indians, supposedly devoid of aggression, have brutal initiation rites; Eskimos, said to be peaceful, carry out their disputes as face-slapping rituals or song duels, the form changing from one tribe to another. In Schjelderup's Einführung in die Psychologie, we are told: 'The Kwakiutl Indians seem to have no conception of our so-called fighting instinct' (p. 38). Yet in any anthropological text we may read about

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the Kwakiutl potlatch rituals, competitions in which the host chiefs waste and destroy property to gain prestige and discredit the others. Translations of accompanying songs make their intentions perfectly clear. So, for example, one chief said as he burned one of his valuable copper plates: 'Furthermore, such is my pride, that I will kill on this fire my copper Dandalayu, which is groaning in my house. You all know how much I paid for it. I bought it for four thousand blankets. Now I will break it in order to vanquish my rival. I will make my house a fighting place for you, my tribe. Be happy, chiefs, this is the first time that so great a potlatch has been given' (Benedict, 1955, p. 195). Boas (1895) described several examples. How does one derive from the behavior of these people no less than a lack of fighting instinct? Recently, it has been claimed that the Bushmen of the Kalahari Desert live in open groups, without aggression. These people are classified as stone-age hunters and gatherers, representing a level of cultural and technological development which has characterized man for 99 % of his evolutionary time-span. If man were biologically (genetically) adapted to a particular way of life, we may assume that it is life in a hunting and gathering society because it has been predominant for most of his existence. Should it be found, therefore, that Bushmen are devoid of aggressive tendencies, then this would be a strong argument indeed that man is not genetically preprogrammed for aggressive behavior. Now, in the last few years we have conducted an intensive study of the Bushmen, visiting them repeatedly in the scope of our cross-cultural documentation of unstaged social behavior. Detailed observations of their social interactions have convinced us that, indeed, there can be no mention of a society without aggression. Early writings support our observations (see references in Eibl-Eibesfeldt, 1972b, and Heinz, 1972). Among other reports, there are several descriptions of territorial aggression among Bushmen tribes which are assiduously ignored by proponents of neo-Rousseauean conceptions. We have filmed and listed the number of aggressive interactions in several play groups of Bushmen children. In one observation period of 191 minutes focussing on a group of nine children, we counted 166 aggressive acts, such as hitting with the fist, throwing objects at another, spitting at others, showing the tongue, jostling, biting, kicking with the feet, and more (Eibl-Eibesfeldt, 1972b). In their facial expressions and gestures of threat these Bushmen children easily compare

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with European children. Not all disputes would escalate into physical fighting - confrontations could be limited to insults and mutual gaze fixation. Such a threat stare duel often terminated with one partner giving in, lowering the head and pouting. The other seemed appeased. In our culture, we observe very similar behavior, and indeed we have recorded it in several diverse societies. Patterns such as these must surely represent universals in the realm of motor behavior, evolved in adaptation to aggressive alterations. We have found the ritualization of threat stare and submission especially noteworthy. Of further interest is the fact that Bushmen children generally socialize their aggressive impulses within the play group. Adults rarely interfere. Children gain experience with aggressive manifestations and learn to control them so that they do not intrude upon group life. In this context, older children provide guidance; they instruct, comfort and often play the referee. Aggressive behavior is not considered a virtue in Bushmen society, whereas much emphasis is placed on many kinds of binding behavior. Important are the rituals of sharing and giving (Eibl-Eibesfeldt, 1970, 1972b). Peaceability and a harmonious group life is the Bushmen's cultural ideal, a goal which is certainly achieved. But we must keep in mind that the process of socialization involves confrontation with aggressive tendencies and other behaviors. Observation teaches us that aggressive tendencies first appear during ontogeny and must then be dealt with in the process of education (Eibl-Eibesfeldt, 1972b). Releasing stimulus situations To our great misfortune, demagogues seem better informed than scientists about those stimulus situations which release aggressive behavior. How easy it must be to direct aggressiveness between groups by manipulating prejudices or oversimplified clichés about the 'enemy'. They are created or encouraged by every demagogue, and some clichés seem to be universally effective. Any ficticious threat of danger, for example, will strengthen the group bond by means of collective group aggression. In all cultures visited, we have observed defense of territorial space and objects (property), at least with children - for example, among the Bushmen, Waika Indians, Papuans, and Balinese. In all these cultures, children at an age of one to one-and-one-half years already fight for objects. Male babies, in particular, attack when they perceive

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another baby with an object that they desire. Often it is one of their toys the playmate has taken, but not necessarily so. Children rob each other, and this is a universal and quite basic pattern, easily observed in our culture as well. Furthermore, at a very early age, small children defend the spot where they play, as well as the place at the mothers' breast. As another universal, we can state the fact that group members behaving contrary to the respective cultural norms may be taunted, mocked or even abused. Group conformity appeases aggression while deviation releases it; taking offense at someone stepping out of line is a manifestation which has been observed everywhere. We have also seen that children new to a group are exposed at least to some light form of aggression. The extent to which a conspecific generally releases aggressive responses in man remains, however, to be tested. We have mentioned that the response formula strange = enemy, familiar = friend develops in deaf-blind children although they may have had no negative experience with strangers. We assume this to be in concordance with an innate disposition. Fear of strangers is a maturational trait which also develops in children of so-called 'primitive' societies. Of interest is the observation that we must constantly appease even those closest to us by performing friendly rituals. Aggressive reactions would quickly meet those who fail to greet another under prescribed circumstances. The essential role of appeasing and bonding rituals (see Eibl-Eibesfeldt, 1970) not only bears witness to our strong readiness for aggression but also indicates that everyone of our fellow humans is a bearer of aggression-releasing signals. Personal acquaintance, it seems, does not suffice to neutralize provocative characteristics. Finally, we have noted that, in man and apes alike, aggressive behavior appears mainly in the following situations: (a) Competition for food, (b) defending a young animal, (c) in a fight for hegemony between two individuals of approximately equal rank, (d) passing down received aggressive abuse to lower-ranking animals, (e) perceiving a group member whose behavior deviates from the norm,1 (f) in a change of dominance, (g) in formation of a pair bond, (h) intrusion of a stranger into a group and (i) fighting for objects (robbing) is a characteristic of man, evident already in small children. 1. Jane van Lawick-Goodall describes how polio-stricken chimpanzees were severely attacked by their group fellows.

Phylogenetic adaptation as determinants of aggression 43 Inhibition to kill In our discussion of animal aggression, we suggested that fighting individuals do not generally aim at harming each other. The conspecific is expediently spared from any significant injury. At first glance, human behavior seems to be an exception. We throw bombs on our opponents' cities, greet the enemy with machine gun bullets, in short, destroy our fellows in such frightening numbers that some writers have marked man as a murderous Cain (Szondi, 1969). Fortunately, more careful observation proves the contrary. Inhibition to harm another seems already evident in children: We can observe that a child in an aggressive mood does not simply launch an unrestrained attack. Fear alone is not the reason. He seems rather to possess a real inhibition to attack another who has done him no harm. By means of small aggressive acts, the bellicose individual will provoke his victim into a reaction which then seemingly justifies a massive counter-attack. The aggressor challenges by hitting lightly, teasing and mocking. (Similar behavior will occur in larger human groups.) Next, in disputes between children we can observe a whole series of appeasing behavior patterns. As we have mentioned, a child's pouting will immediately dampen the other's aggression. The same applies to crying and lamenting. A person submitting to another acts like a child in many ways. Such infantilisms have universal meaning as appeals of appeasement. Similarly, a child puts others into an amiable mood by its friendly signals. Universally effective as well are certain gestures of submission, from bowing the head to lying prone. Not only do such patterns inhibit aggression, they may even change the partner's attitude and cause him to solicit his former opponent with friendly behaviors. We may say that the aggressor feels pity, a sentiment which has been activated by rather simple signals (certain expressive movements) coming from the partner. Pity, in turn, may be expressed by universal patterns of comfort behavior. On the one hand, then, we are equipped with aggressive behavior patterns, on the other, with the means to appease aggression when it occurs. Now we may ask: Are appeasement signals effective only within a particular group, as with our example of the lions, or do they inhibit attack in a more general way? Certainly, our aggression is less inhibited towards strangers than it is towards fellow members of a group, with whom we have a bond of personal acquaintance. This

44 Irenaus Eibl-Eibesfeldt phenomenon was described in greater detail in a previous discussion (Eibl-Eibesfeldt, 1970). Without doubt even strangers may appease and release responses of pity. One such pacifier is the smile. Everywhere, human beings seeking contact use the same appeals, such as the presence of children. Australian aborigines who sought contact with the feared Europeans used to push a child in front of them, in the assumption that it would afford protection. Similar behavior mechanisms have been recorded in many cultures. Yet how frighteningly unrestrained are many warlike conflicts! Even women and children may fall victim in an altercation between groups. How can this be? One of the causes for such indiscrimination, as Lorenz (1963) had pointed out, is surely the invention of weapons. In the course of our evolution, we had developed an inhibition to kill which became adapted to our bodily capacities. Seldom would humans kill each other with their fists or strangle with their hands. But the hand that swings a club can knock down the opponent so quickly that the other has little chance to give in, to submit by means of the appropriate behavior patterns. From anthropologists we learn that the first skulls to bear the marks of violence concur with the invention of weapons (Roper, 1969). Our viewpoint is further supported by the fact that, under natural circumstances, adult apes rarely kill each other, though they possess a far more powerful jaw than does man.2 Furthermore, man the creature of imagination is capable of creating 'realities' in his mind. He can, for example, convince himself that members of certain other groups aren't 'really' human. If he indoctrinates himself long enough, he will truly come to believe it. In very gross neurological terms, he will create structures in his brain, connections of ganglion cells or molecular structures, on the basis of which he will perceive reality in a subjectively distorted way. His thoughts pressed into a particular mold, a person thus indoctrinated no longer receives the sympathy-releasing appeals of the other. It is quite interesting that every human group in conflict with another acts according to this principle. Indians living in the jungles of Brazil speak of their neighbors as of hunting prey; and 2. Chimpanzees do occasionally capture and eat infants of mothers not belonging to their group. Not infrequently, this observation is seen as proof that chimps do not have an inhibition to kill. This conclusion is not necessarily correct. Perhaps chimp infants cannot yet transmit the signals of appeasement, in contrast to sub-adults and adults, and thus are the occasional victims of attack.

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how well do we know the dehumanization tactics of so-called civilized nations against their 'enemies'. Incredibly large sums are spent on war propaganda; barriers of communications must be erected at all cost (nonfraternization laws, etc.). These very facts, however, indicate that our inhibition to kill, even towards strangers, must be strong indeed. In this context, it is also interesting to note that in many cultures a victorious killer is considered 'impure'. He is then subject to various taboos which often have the character of expiation. Freud (1950) himself saw in this an expression of bad conscience: 'All these regulations give us reason to conclude that in the behavior towards enemies sentiments other than hostility come to the fore. We see therein expression of remorse, of bad conscience in having killed another human being. It would seem that even these savages acknowledge the commandment: "Thou shall not kill!" ' (p. 52). Humans must be forced to fight others; the enemy must be slaughtered at great expense. This fact seems to allow for a greater optimism. Surely at some stage in man's history, he profited from this aggressive segregation. Intense competition encouraged selection for intelligence and a cultural differentiation. Yet as a result, we have reached a level of mental development which now permits us to break out of this mechanism of violence, to continue our evolution in a more rational way. Emotionally, through our capacity for sympathy and altruism, we are equipped to coexist in harmony even with those strange to us. As one of the first steps, we must tear down the barriers to communication and ban all demagoguery by which other groups are dehumanized. Aggressive drives Thus far, we have been concerned with the motor patterns of aggressive behavior and with releasing stimulus situations. Much evidence points to the fact that phylogenetic adaptations play a significant role. Before continuing along this line of argument, we must emphasize that no reasonable ethologist would doubt that, as well, aggressive tendencies can be encouraged or suppressed by educative processes. But we shall now turn to a discussion of the dynamics of aggression - for some time the focus of rather vehement debates. Adults can be driven by a real urge for aggressive acts. Tyrolian farm boys often seek to quarrel; they find obvious pleasure in fights. Such observations can be made all over the world. Where actual fight-

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ing is prohibited, one finds, instead, ritualized altercations such as combat games, song duels and other customs, which probably function as safety valves for pent-up aggressive impulses. Certain experiments have also demonstrated and measured the phenomena of aggression build-up and discharge. In one situation, the experimenter deliberately aroused anger in student subjects, who subsequently showed a rise in blood pressure. Next, the experimenter stated he would try to solve a series of problems, and the subjects could indicate errors to him by pressing a button. One-half of the aroused students were told that the experimenter would receive an electric shock, the other half that a blue light would flash on. Blood pressure fell in those subjects who thought they were giving the experimenter an electric shock. In the others, blood pressure remained at a high level for some time, and these subjects also reported a feeling of angry arousal which continued for quite a while (Hokanson & Shetler, 1961). Further experiments showed that aroused subjects could release their aggression when allowed to watch films with aggressive content. Here, they seemed to identify with an aggressive role and could 'live out' their aggression. In this particular situation, then, aggressive films had a tension-releasing effect (Feshbach, 1961). By no means do we now suggest that films with aggressive content are in general to be approved. Individuals who are not aggressively aroused would surely experience a change of mood, in the sense that such films would heighten their aggressivity. Furthermore, repeated vicarious release of aggressive tension results in a reinforcement and learning of aggressive behavior (Berkowitz, Corwin, & Heironimus, 1963; Feshbach & Singer, 1971). 3 We might add, however, that the enormous number of films with aggressive content constantly thrown on the movie market gives a valid indication of man's need to satisfy his aggressive drive. Violence has a greater market value than sex. Although we are left with little doubt as to the dynamics of aggressive behavior, we are still faced with the question: Are the basic physiological drive systems acquired by learning in the course of ontogeny, or are they innate? Many organisms undergo endogenous fluctuations in their aggressive motivation or preparedness. In lower 3. Bandura and Walters (1963) also found that films with aggressive content could place subjects in an aggressive mood. They concluded that these results served to disprove the cathartic hypothesis. But we feel that such a claim cannot be made simply on the basis of these experiments.

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vertebrates, changes in the level of male hormones effect an increase in aggressive tension. Beyond that, are there any primary central nervous drive mechanisms which also influence aggressivity? Proponents of the secondary drive hypothesis hold that aggression cannot claim its own primary drive but, instead, serves other primary drives which it helps to gratify. According to this theory, aggression is aroused only by the suppression of other drives. In other words, if these primary drives were completely satisfied, there would be no aggression. Thus Arno Plack (1968) attributes all aggression to suppression of the sex drive. The same basic premise is contained in the frustration-aggression hypothesis of Dollard and his co-workers (Dollard et al., 1939). These researchers proposed that every privation, defined as the obstruction of a goal-directed behavior, results in aggressivity, especially those frustrations experienced in early childhood. Again, this means that aggression should be viewed merely as a vehicle designed to serve other motivations, i.e., there is no separate aggression drive. Aggressive motivation is further viewed as secondary by proponents of the social-learning hypothesis: Aggressive behavior is learned from social models. Kunz (1946) went so far as to say that aggression is a 'degeneration of the organism's natural activity', i.e., a pathological condition. We quite agree that, as yet, there is no actual proof of an innate aggressive drive in man. Neither do claims to the contrary, however (e.g., Rattner, 1970), rest on a better empirical foundation. We remain largely dependent on circumstantial evidence. Here, in our opinion, the scales are tipped in favor of an innate drive for aggression. A strong indication is the fact that some manifestation of aggression can be observed even in basically peaceful societies. Next, a close look at the ontogenesis of social behavior reveals that aggressive behavior first develops in every individual and is secondarily socialized. One may well object that no culture provides for a childhood completely devoid of frustrating experiences. If we define the concept of frustration broadly enough, this proves to be true. Still, this does not constitute proof that experiences of frustration are the sole cause of aggressive behavior. A further argument against the aggressive drive hypothesis is that a child is reinforced for aggression when such behavior, in the form of demands for food, nurturance, and so on, frequently leads to success. Again this is a valid objection but still does not exclude the possibility

48 Irenaus Eibl-Eibesfeldt of a primary drive for aggression. For reasons of economy, we might well accept the above alternative explanation as the most simple one were it not for discoveries in the field of neurophysiology which strongly suggest a different interpretation. One of the observations made in the course of certain experiments is that human beings are subject to neurogenetic fits of rage, produced by spontaneous firings of cells in the brain siem and temporal lobes (Gibbs, 1951; Moyer, 1969; 1971; Sweet, Ervin & Mark, 1969). These spontaneous paroxysms are accompanied by a characteristic electrical activity in the above-mentioned regions of the brain. Conversely, rage fits can be generated by electrical stimulation of these same areas. A healthy individual has the same structures as the patients on whom experiments were performed and will also exhibit aggressivity if the same brain regions are stimulated (Moyer, 1971a, 1971b). It is known that every ganglion cell exhibits spontaneity (Roeder, 1955; Bullock & Horridge, 1965).4 Thus, the hypothesis that human aggression has its origin in these automatic structures should not be pushed aside as carelessly as occasionally happens. We must wait, of course, for further neurophysiological experiments to shed light on these questions. Our next concern is the not uncommon query: Just how 'useful', in a biological sense, is such a spontaneous aggression drive? Would it not have been more expedient to develop a reactive mechanism for aggression? Possibly, though not certainly, this would be so. But how simple is the construction of such a mechanism? The building blocks of the system in question, as we have seen, are spontaneously active neurons. Perhaps it is a characteristic of neural construction that complex systems so frequently display spontaneity. Even the escape behavior in many birds and mammals seems subject to an 'escape drive', or 'flight instinct', although such a drive would at first glance seem rather pointless.5 Researchers with training in neurophysiology regard Lorenz's drive model as well founded. Moyer (1971a, 1971b) states, for example: 4. Again we make mention of Jouvet's (1972) discovery of spontaneous aggressive discharge during dreaming. 5. The human brain also contains neural systems whose activation leads to blockage of aggressive behavior. On this basis, violent patients were calmed by stimulation applied to the ventro-medial frontal lobe and in the central region of the temporal lobe (Moyer, 1971a, 1971b).

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'The hydraulic model for aggressive behavior tendencies postulated by Lorenz (1966) draws validity from physiological facts. Possibly a number of the "pressures" towards aggressive behavior increase when the respective neural systems are sensitized by means of chemical changes in the blood. As a result, the individual would be increasingly more inclined to behave in a hostile manner. On the other hand, we should not over-simplify the issue by assuming that this "pressure" can only be reduced by an overt display of aggression' (p. 50). Mark and Ervin (1970) point out that those mechanisms forming the basis of aggressive behavior are localized in the oldest parts of the brain. They feel that this discovery is hardly surprising, since aggressive behavior is a very old evolutionary trait: 'Violent behavior as one aspect of self-preservation has existed on this earth for hundreds of years. It is not surprising, therefore, to find that the mechanisms that initiate it are in the deepest, most primitive centers of the vertebrate brain, the brainstem. Nor is it surprising to find that mechanisms for controlling violence and other brainstem functions are situated in the deepest and oldest part of the vertebrate "large brain" or cerebrum' (P- 14). Misinterpreting ethological arguments We have suggested that human aggression is preprogrammed through phylogenetic adaptations at the motor and receptor levels of behavior and quite probably influenced this way by drive mechanisms as well. Much criticism has come our way. What are the objections to our claim and what, on the other hand, really stands written in the works of ethological researchers? We shall make a final summary of this discussion and let each reader draw his own conclusions. The accusations are all of a more or less similar content: Ethologists, it is claimed, are aiming to make aggressive behavior and tendencies seem innocuous, justifiable, excusable and ultimately inevitable. As an example of this kind of reasoning, Rattner states: 'In a political context, we cannot ignore that a grandiose disparagement of the dangers of aggression must provide a great comfort to those who had taken part in the mass crimes of the last decades . . . The doctrine of an "aggression instinct" lends support to a method of social windowdressing well in accord with the conservative mentality of our bourgeoisie. The observer's eye is . . . detracted from shortcomings within society, henceforth to perceive no more than the hypothetical instinct

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basis of man which is beyond the reach of human influence' (1970, p. 35). Similarly, Denker speculates on the consequences of Lorenz's book: 'According to many readers, aggression as a natural urge or manifestation is endowed with the sanctity of a causal explanation which, to a large extent, frees man from self-responsibility' (1966, p. 95). Lumsden states: 'The danger with the instinct of aggression theory is that, far from emancipating man, it may enslave him to a reactionary ideology by apparently demonstrating the biological necessity of an authoritarian social system organized for internal and external repression' (1970, p. 408). And again, we hear from Lepenius and Nolte (1971): 'Taking recourse to the archaic (aggressive) biological heritage of man in no way serves to encourage mental reflection or to provide the conditions of emancipation. Rather, this tendency is one of anti-enlightenment.' The latter author also draws the remarkable conclusion that whoever regards man as naturally aggressive will also provide him with aggressive goals! Would a psychiatrist fatefully accept his patient's illness and set goals accordingly? These accusations are repeated with a rubber-stamp monotony, and in their framework we may include Selg (1971), Hollitscher (1973) and also Montagu's (1968) collection of polemics. In addition, we are faced with the reproach that 'behind the interpretations of Lorenz always stands the hypothesis of man as a beast of prey' (Rattner, 1970, p. 30). Livingstone (1971) similarly claims that Lorenz has attributed a 'killer instinct' to man. Did Lorenz really make this claim? Even the cursory reader will note that Lorenz in no way defined aggressive drive as a killer instinct, i.e., one aimed at the destruction of a conspecific. Quite the contrary, he emphasized that aggression never aims at killing the opponent. Instead, we may observe that in those cases where fatality would result from aggression, special forms of ritualization (tournament fights, inhibition to kill) serve to prevent the murder of a conspecific. Secondly, is it true that ethologists accept and exculpate aggressive behavior as 'natural' and drive-determined (Schmidt-Mummendey, 1971, p. 19)? Such an interpretation, if aimed at Lorenz, is highly inappropriate. In his book, Lorenz is primarily concerned with the possibilities and necessity of aggression control. Thus he writes: We have good reason to say that intraspecific aggression is the greatest of all dangers in man's present cultural-historical and

Phylogenetic adaptation as determinants of aggression 51 technological stage of development. But our chance of meeting this challenge is surely not improved by accepting aggression as something metaphysical or inevitable. More likely, the problem of aggression can be countered by research into the chain of its natural causation. Wherever man has found the means to consciously direct a natural phenomenon, it has been gaining insight into the chain of causal events lying at its base. The study of a normal life process fulfilling its function of maintaining the species - the science of physiology - provides an indispensible prerequisite for the study of its disorder, the science of pathology (Lorenz, 1963, p. 47). These words should leave no doubt that ethologists do not intend to accept aggression as inevitable. Far from it! Often enough we have stated that phylogenetic adaptations could lose their adaptedness under the changed conditions of our time. Do we not carry the evolutionary burden of various morphological relics, such as the oftencited vermiform appendix, which are no longer adaptive? We do not, after all, accept the appendix as an unavoidable cause simply because each of us is born with it. Few people today die of appendicitis. In a similar sense, there is no reason to accept behavioral dispositions as inevitable or uncontrollable. As 'cultural creatures by nature', we can and must harness our drives within a cultural framework. To achieve this control, of course, we must gain knowledge of the relevant facts and causal relationships (Eibl-Eibesfeldt, 1970, 1972a). We cannot achieve rational solutions by purely emotional discussions, which would rather serve to create new barriers to communication. We must learn to speak about aggression without undue aggressivity. We also wish to point briefly to the dangers of an exclusively behavioristic approach, of an extreme emphasis on the importance of cultural and educational conditioning. Recent prominent illustrations of this trend are Skinner's publications. The Skinnerian ethics of absolute behavioral control are, to say the least, precarious, and are doubtlessly the products of a kind of learning theory which takes no consideration of any biologically determined ethical norms. Finally, in a great many discussions about human aggression we have been forced to note an alarming one-sidedness. Those taking part display a strange fascination for this behavioral trait, as if aggression were the single motivating impulse of man. They completely ignore the

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fact that even enemy troops exchange cigarettes when opponents get to know one another, although in such phenomena we find some of the most fruitful possibilities for the control of aggressivity. Do we not see here the evidence that man is by nature a social creature, impelled by a drive to establish social bonds? We are equipped with natural antagonism to aggression (which cannot be discussed here), and we need not be fatalistic about the problem. Of central importance remains our ability to see others as fellow human beings. It is the phenomenon of enemy clichés which may actually offer possibilities for solving human conflict. Facilitating personal acquaintance often automatically leads to social bonding. In the destruction of communication barriers we should find one of the first steps in education for peace. Ethologists, as well, regard appropriate education as the key to the elimination of obstructions to peaceful coexistence. The emphasis in our efforts to develop proper educational strategies, however, rests not on ideology, but on gaining knowledge of the nature of man.

REFERENCES Ardrey, R., 1966, The territorial imperative. New York, Atheneum. developBandura, A., & Walters, R. H., 1963, Social learning and personality ment. New York, Holt, Rinehart, & Winston. Benedict, R., 1955, Urformen der Kultur. Hamburg, Rowolt. Berkowitz, L., Corwin, R., & Heironimus, M., 1963, Film violence and subsequent aggressive tendencies. Public Opinion Quarterly, 27:217-229. Boas, F., 1895 (reprint 1970) The social organization and the secret societies of the Kwakiutl indians. New York, Johnson's Reprint Corp. Bullock, T. H., & Horridge, G. A., 1965, Structure and function in the nervous system of invertebrates. Vol. I & II. San Francisco, W. H. Freeman. Cullen, E., 1960, Experiments on the effects of social isolation on reproductive behavior in the three-spined stickleback. Animal Behavior, 8:235. Denker, R., 1966, Aufklärung über Aggression: Kant, Darwin, Freud, Lorenz. Stuttgart, Kohlhammer. Dollard, J., Doob, L., Miller, N., Mowrer, O., & Sears, R., 1939, Frustration and aggression. New Haven, Conn., Yale University Press. Eibl-Eibesfeldt, I., 1955, Der Kommentkampf der Meerechse (Amblyrhynchus cristatus Bell) nebst einigen Notizen zur Biologie dieser Art. Zeitschrift Tierpsychologie, 12:49-62. (see also wiss. Film der Encycl. einem., E 591. Göttingen, Inst. wiss. Film, 1964.) Eibl-Eibesfeldt, I., 1970, Liebe und Hass. Zur Naturgeschichte elementarer Verhaltensweisen. Munich, Piper.

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of aggression

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Eibl-Eibesfeldt, I., 1972a, Grundriss der vergleichenden Verhaltensforschung. 3rd. edition. Munich, Piper. Eibl-Eibesfeldt, I., 1972b, Die !Ko-Bushmanngesellschaft: Aggressionskontrolle und Gruppenbindung. Monograph of Human Ethology, 1. Munich, Piper. Eibl-Eibesfeldt, I., 1973, Expressive behavior of the deaf-and-blind-born. In M. von Cranach and I. Vine (Eds.), Social communication and movement. London, Academic Press. Esser, A. H., 1970, Interactional hierarchy and power structure on a psychiatric ward. In S. J. Hütt & C. Hütt (Eds.), Behavior studies in psychiatry. Oxford, Pergamon Press. Felipe, N. J. & Sommer, R., 1966, Invasions of personal space. Social Problems, 14:206-214. Feshbach, S., 1961, The stimulating versus cathartic effects of a vicarious aggressive activity. Journal of Abnormal and Social Psychology, 63:381-385. Feshbach, S., & Singer, R., 1971, Television and aggression. San Francisco, JosseyBass. Freud, S., 1950, Gesammelte Werke. 18 vols. London, Imago. Gibbs, F. A., 1951, Ictal and nonictal psychiatric disorders in temporal lobe epilepsy. Journal of Nervous and Mental Disorders, 113:522-528. Hall, E. T., 1966, The hidden dimension. New York, Doubleday. Heinz, H. J., 1972, Territoriality among the Bushmen in general and the !Ko in particular. Anthropos, 67:405-416. Helmuth, H., 1967, Zum Verhalten des Menschen: Die Aggression. Zeitschrift Ethnologie, 92:265-273. Hokanson, J. E., & Shetler, S., 1961, The effects of overt aggression on physiological tension level. Journal of Abnormal and Social Psychology, 63:446449. Hollitscher, W., (Ed.), 1973, Aggressionstrieb und Krieg. Stuttgart (dva). Holst, E. v., & Saint Paul, U. v., 1960, Vom Wirkungsgefüge der Triebe. Die Naturwissenschaften, 18:409-422. Jolly, A., 1972, The evolution of primate behavior. New York, Macmillan. Jouvet, M., 1972, Le Discous biologique. La Revue de Médecine, 26-27:10031063. Konishi, M., 1963. The role of auditory feedback in the vocal behavior in the domestic fowl. Zeitschrift Tierpsychologie, 20:349-367. Konishi, M., 1964, Effects of deafening on song development in two species of juncos. Condor, (56:85-102. Konishi, M., 1965, Effects of deafening on song development of American robins and black-headed grosbeaks. Zeitschrift Tierpsychologie, 22:584-599. Kortlandt, A., 1972, New perspectives on ape and human evolution. Stichting voor Psychobiologie. Zoologie Lab. Amsterdam. Kruijt, J., 1964, Ontogeny of social behavior in Burmese red jungle fowl. (Gallus gallus spadiceus). Behavior Supplement, 12. Kruijt, J., 1971, Early experiencè and the development of social behavior in jungle fowl. Psychiatria Neurologia Neurochirurgia, 74:1-20. Kunz, H., 1946, Aggressivität und Zärtlichkeit. Bern. Kuo, Z. Y., 1960, Studies on the basic factors in animal fighting. Journal of Genetic Psychology, 96:201-239. Kuo, Z. Y., 1961, Studies on the basic factors in animal fighting. Journal of Genetic Psychology, 97:181-209. Lack, D., 1943, The life of the robin. Cambridge, University Press.

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Lagerspetz, K., 1969, Aggression and aggressiveness in laboratory mice. In S. Garattini & E. B. Sigg (Eds.), Aggressive behavior. Amsterdam, Excerpta Medica. Lawick-Goodall, J. v., 1963, My life among the wild chimpanzees. National Geographic, 125(8):272-308. Lepenius, W., & Nolte, H., 1971, Kritik der Anthropologie. Munich, Hauser. Livingstone, F. B., 1971, Auswirkungen des Krieges auf die Biologie des Species Mensch. In M. Fried, M. Harris, & R. Murphy (Eds.), Der Krieg, zur Anthropologie der Aggression und des bewaffneten Konflikts. Conalika humana. Frankfurt/Main, S. Fischer. Lorenz, K., 1961, Phylogenetische Anpassung und adaptive Modification des Verhaltens. Zeitschrift Tierpsychologie, 75:139-187. Lorenz, K., 1963, Das sogenannte Böse. Wien, Borotha-Schoeler. Lorenz, K., 1966, On aggression. New York, Harcourt, Brace & World. Lumsden, M., 1970, The instinct of aggression: Science or ideology? Futurum, Z. für Zunkunftsforschung, 3:408-419. Mark, V. H., & Ervin, F. K., 1970, Violence and the brain. New York, Harper & Row. Moyer, K. E., 1969, Internal impulses to aggression. Transactions of the New York Academy of Sciences, Ser. II, 37:104-114. Moyer, K. E., 1971a, Experimentale Grundlagen eines physiologischen Modells aggressiven Verhaltens. In A. Schmidt-Mummendey & H. D. Schmidt (Eds.), Aggressives Verhalten. Munich, Juventa. Moyer, K. E., 1971b, The physiology of aggression. Chicago, Markham Press. Montagu, M. F. A., 1968, Man and aggression. New York, Oxford University Press. Noble, G. K., & Bradley, H. T., 1934, The mating behavior of lizards. Natural History, 34:1-15. Palluck, R. J., & Esser, A. H., 1971, Controlled experimental modification of aggressive behavior in territories of severely retarded boys. American Journal of Mental Deficiency, 76:23-29. Plack, A., 1968, Die Gesellschaft und das Böse. 2nd edition. Munich, List. Rasa, O. A. E., 1969, The effect of pair isolation on reproductive success in Etroplus maculatus (Cichlidae). Zeitschrift Tierpsychologie, 26:846-852. Rasa, O. A. E., 1971, Appetence for aggression in juvenile damsel fish. Beiheft 7, Zeitschrift Tierpsychologie. Berlin, Parey. Rattner, J., 1970, Aggression und menschliche Natur. Olten/Schweiz, Walter. Roeder, K. D., 1955, Spontaneous activity and behavior. Scientific Monthly, Washington, 80:362-370. Roper, M. K., 1969, A survey of evidence for intrahuman killing in the pleistu cene. Current Anthropology, 70:427-459. Sauer, F., 1954, Die Entwicklung der Lautäusserungen vom Ei ab schalldicht gehaltener Dorngrasmücken (Sylvia c. communis Latham). Zeitschrift Tierpsychologie, 77:1-93. Schenkel, R., 1966, Zum Problem der Territorialität und des Markierens bei Säugern - am Beispiel des schwarzen Nashorns und des Löwen. Zeitschrift Tierpsychologie, 23:593-626. Schjelderup, H., 1963, Einführung in die Psychologie, Bern, Huber. Schmidbauer, W., 1972, Die sogenannte Aggression. Hamburg, Hoffman & Campe. Schmidt-Mummendey, A., & Schmidt, H. D., 1971, Aggressives Verhalten.

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Munich, Juventa. Scott, J. P., 1960, Aggression. Chicago, University of Chicago Press. Selg, H., 1971, Zur Aggression verdammt? Stuttgart, Kohlhammer. Skinner, B. F., 1971, Beyond freedom and dignity. New York, A. Knopf. Sweet, W. H., Ervin, F., & Mark, V. H., 1969, The relationship of violent behavior to focal cerebral disease. In S. Garattini & E. B. Sigg (Eds.), Aggressive behavior. Amsterdam, Excepta Medica. Szondi, L., 1969, Gestalten des Bösen. Bern, Huber. Tellegen, A., & Horn, J. M., 1972, Primary aggressive motivation in three inbred strains of mice. Journal of Comparative and Physiological Psychology, 2:297-304. Thompson, T. I., 1963, Visual reinforcement in Siamese fighting fish. Science, 141:55-57. Thompson, T. I., 1964, Visual reinforcement in fighting cocks. Journal of the Experimental Analysis of Behavior, 7:45-49. Tinbergen, N., 1951, The study of instinct. Oxford, Oxford University Press. Walther, F. R., 1966, Mit Horn und Huf. Berlin, Parey. Weidkuhn, P., 1968/1969, Aggressivität und Normativität. Über die Vermitlerrolle der Religion zwischen Herrschaft und Freiheit. Ansätze zu einer kulturanthropologischen Theorie der sozialen Norm. Anthropos, 63/64. Wickler, W., 1971, Die Biologie der zehn Gebote. Munich, Piper.

ABSTRACT In the service of aggression, phylogenetic adaptations evolved in many animal species in the form of motor patterns, releasing and motivating mechanisms. Motor patterns of anger mature in the deaf and blind born as also does stranger repulsion. Stranger rejection seems to be a basic inborn reaction in man. Cross-cultural comparison reveals this reaction to be found in all cultures and furthermore establishes the existence of universal motor patterns of fighting and threat and of universal fighting inhibitions. The question whether an inborn aggression drive exists is hotly disputed. Neurophysiological evidence is in favor of the inborn drive concept. Certainly cultural factors foster or repress the expression of aggressive acts, but a basis is provided by phylogenetic adaptations.

RÉSUMÉ Dans le domaine de l'agression, il apparaît chez de nombreuses espèces animales certaines adaptations phylogénétiques sous la forme de patterns moteurs, de mécanismes déclenchants et motivants. Les patterns moteurs de la colère arrivent à maturation chez les sourds et aveugles de naissance, au même titre que la répulsion pour l'étranger. Ce rejet de l'étranger semble être une réaction innée chez l'homme et dans toutes les cultures comme le montrent les études interculturelles qui prouvent en outre l'existence de patterns moteurs universels de combat et de menace ainsi que des inhibitions correspondantes. La question de savoir s'il existe une tendance innée à l'agression fait l'objet de discussions passionnées. La neuro-physiologie est en faveur de l'idée d'une tendance innée. Les facteurs culturels encouragent ou répriment certainement la manifestation des actes agressifs, mais la base en est fournie par les adaptations phylogénétiques.

Factors facilitating development of aggressive behavior in chimpanzees and humans* D A V I D A. H A M B U R G JANE VAN L A W I C K - G O O D ALL Stanford

University

School of

Medicine

Evolution and learning The contemporary human species is capable of profound cooperation, attachment, tenderness and compassion but also of hatred, cruelty, destruction and violence. It is scarcely useful to portray man as saint or sinner but far more useful to investigate the conditions under which various behavior patterns are likely to occur. The human species has a biological heritage of its vertebrate-mammalian-primate history. This heritage includes some features of brain and behavior. It may well include some anlage of aggressive tendencies, transmitted genetically yet requiring environmental stimulation for full development. Aggressive behavior between man and man, between man and animals and between human groups has been a prominent feature of human experience for a very long time (Bigelow, 1972). Such behavior has been easily learned, practiced in play, encouraged by custom and rewarded by most human societies for thousands of years. Surely it is reasonable to keep an open mind to the possibility that such behavior may be shaped in our own species by both social and biological transmission. In any event, the mechanisms of transmission remain largely for future research to determine. One worthwhile line of inquiry is to determine whether the human organism early in life is 'primed' to acquire certain elementary * We are very grateful to Anneliese Korner and Anke Ehrhardt for valuable assistance in the preparation of this paper.

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behavior patterns with relative ease. Is there a special facility for learning along lines that have been adaptively valuable for the species over a very long time in the course of its evolution? For any species, some patterns of behavior are easy to learn, some difficult and some impossible. In general, it seems likely that learning in such adaptively significant spheres as behavior oriented to food, water and reproduction would have high biological priority; and aggression can serve in the implementation of these adaptive requirements. So it is plausible that the inherited 'wiring diagram' of the brain would in some way reflect the long-term selective advantage of facility in learning such behavior (Hamburg, 1963). For example, simple preferences on the part of the infant or young child might draw its attention to a certain class of stimuli or reward its engagement in a particular kind of activity. Once drawn in this direction early in life by an inherited preference, a great deal of complex learning could ensue, fully taking account of cultural instructions. This line of inquiry may in future years link evolutionary and developmental approaches toward the understanding of human aggressiveness. From an anthropological perspective, this viewpoint has recently been well stated by Raleigh and Washburn (1973): 'Man easily learns the kinds of behavior that were important during his evolution. The feedback relation between successful behavior and biological structures produced brains that learn certain behaviors far more easily than others. Human beings learn to walk proficiently, but few learn to swim effectively because walking was important during human evolution and swimming was not. Throwing and hunting represent two behaviors that were critical in the history of man and their acquisition illustrates what is known as the ease of learning principle.' It has been a significant contribution of ethological research to relate the processes of learning to the problems of survival in natural habitats and hence to the pressures of natural selection over very long time spans in the evolutionary history of a species. Their findings indicate that heredity and learning are not utterly separate realms, but rather that one way in which genes may operate is by facilitating an organism's ability to acquire certain patterns of behavior in preference to others. For example, in an important new book, Hinde (in press) makes the following statement: 'The demonstration that aggressive behavior is influenced by genes tells us little about how differences in aggressiveness between strains arise. The genetic effects may be in-

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direct - mediated for instance by differences in body size, strength, weapons, activity level, sensory capacities and so on, or by differences in the ease with which aggressive responses are learned, as well as through changes in the immediate central nervous determinants of aggression' (emphasis ours). Similarly, in a discussion of aggressive behavior, Tinbergen (1968) remarked, 'There are also behavior patterns which do appear in the inexperienced animal, but in an incomplete form, and which require additional development through learning . . . By far the most interesting aspect of such intermediates between innate and acquired behavior is the fact that learning is not indiscriminate, but is guided by a certain selectiveness on the part of the animal' (emphasis ours). In this vein, Eibl-Eibesfeldt (1970) concluded, . . it is clear that various species of animals are equipped with various innate dispositions to learn . . . Learning is not the result of a passive reception of stimuli by an organism. All observations support the view that there are often quite specific learning dispositions and internal motivating mechanisms, the latter being expressed in curiosity and play behavior.. . The animal seems to learn things that are of use to it in its later life, and the development of some behavior patterns seems to include "preprogrammed" play activities . . . ' . We believe the concepts of these three distinguished ethologists are directly pertinent to the observations we shall present on certain aspects of the development of aggressive behavior in chimpanzees and humans. The biologically oriented approach to learning processes has recently elicited fresh interest among experimental psychologists. A newly published volume pulls together a substantial body of recent experimentation and conceptualization in this field. Seligman and Hager (1972) conclude: 'Animals, man included, learn some things easily, others only painstakingly, and still others not at all. Some species learn particular things better than other things and better than other species. Within a species, some individuals can learn particular things better than other things. Further, an individual will learn some things better at one stage of development than at another stage. Some of these differences are environmental, others evolutionary.. . For in the real world animals learn not only random contingencies but also about contingencies their species has faced for eons. And this learning may be different in kind.'

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In the present paper, when we refer to ease of learning, or propensity to learn, we are referring to a simple pattern of behavior that gets an organism going in a certain direction, increasing the probability of following a path; but any path toward aggressive behavior has many branches that may or may not be followed later in life. We wish to give some examples of ways in which such a process might work. These examples are intended to be pertinent to the development of aggressive behavior in chimpanzees and perhaps in humans as well. We certainly do not believe that there is anything like definitive evidence on these matters at the present time. Rather, we are trying to construct plausible models that would help to stimulate and guide inquiry on factors facilitating the development of aggressive behavior in chimpanzees and humans.

Observation of fighting Three fundamental processes that have powerful bearing upon learning in higher primates are attention, motivation and the inclination to learn from models. All three have a very long history in primate evolution (Hamburg, 1968). They are not human inventions. Any situation that draws the attention of young primates and taps into relatively strong motivations and provides vivid models is likely to be a situation about which much will be learned. Fighting is such a situation. In a chimpanzee community, fighting draws attention. It is a higharousal condition. There is much screaming and rapid movement, and most if not all chimpanzees in the vicinity look to see what is going on. Given the powerful evidence from laboratory experiments and field observations on observational learning in a social context, it seems to us highly probable that chimpanzees and humans must learn a great deal about aggressive behavior from observing actual and imminent fighting episodes (Bandura, 1973). In the Gombe chimpanzee community, infants do not seem to take much interest in encounters of this kind during the first few months of life, indeed during a good deal of the first year. The mother, however, responds strongly. If the infant happens to be off her body at the time such an episode begins, she rapidly collects the infant and moves away. In the age range ten to fourteen months, the infant apparently bccomes afraid when a fighting

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episode begins and quickly goes to his mother, usually into the ventral position. Thus, in the early months of life, avoidance reactions under these conditions are mainly on the initiative of the mother, but by one year of age the infant is also showing strong initiative in this respect. It is worth considering the possibility that there is a phenomenon here similar to that observed by Sackett (1966) in rhesus monkeys - i.e., a sensitive period for responsiveness to threat stimuli. But we are not aware of any observations comparable to Sackett's on isolation-reared chimpanzees. Perhaps in the latter part of the first year of life, central nervous system maturation in the chimpanzee has reached a point where some aspects of the stimuli associated with threat and fighting have a particularly strong emotional impact. In any event, the immediately ensuing period is one in which infant chimpanzees make many observations, frequently at close range, of the behavioral sequences involved in threat, attack, submission and reassurance.

Tantrum behavior Our next example of processes that may facilitate the learning of aggressive behavior in chimpanzees and humans can best be introduced by a comment of Hebb's (1972): 'Neither a human nor a chimpanzee baby needs to learn how to have a temper tantrum. The behavior is complex but quite characteristic in form, so that no experienced observer has any difficulty in identifying it. The baby does not have to practice it (nor to see how others do it) in order to produce, on the first try, a first-class sample. It is therefore "unlearned". But it is not independent of learning'. Tantrums in chimpanzees resemble the tantrums of young children. The chimpanzee pattern is characterized by intense screaming with glottal cramps, crouching, grabbing at objects such as a tree stump, hurling self on the ground, rolling, running and occasionally attacking the mother. The usual duration is between one-half minute and two minutes. Occasionally they continue up to five minutes. What are the contexts in which tantrums are likely to occur? The earliest tantrum we have observed occurred in an infant born into one of our captivity groups during the first week of life. The mother, although adequate in maternal behavior by captivity standards, was inexperienced and sometimes held the infant off her body. When this

62 David A. Hamburg and Jane van Lawick-Goodall happened, the infant would begin intense screaming, with flailing arm and leg movements. Although the infant's coordination was immature, the patterns were essentially those of a tantrum. Observers described the behavior as having a frenzied quality. When the mother would move the infant back onto her body, the tantrum would stop. Thus, deprivation of tactile contact was presumably an important factor in precipitating these tantrums at a very early point in life. The tantrum behavior appeared disturbing to the mother, roused her to action, and the result of her action was typically rewarding to the infant. In the natural habitat at Gombe, tantrums have been observed around age eight to nine months, when the infant is just beginning to walk. At such times, the infant will sometimes lose sight of the mother and look around frantically. Then, failing to see the mother, the infant may go into a tantrum. In the framework of the mother-infant relationship, the immediate issue seems to be deprivation of visual contact. Starting at about one year of age in the natural habitat, and extending for several years thereafter, a relatively common precipitating context for tantrum behavior is the mother's unwillingness to share food, especially premium food, with the infant. In the period between about age four and age six, when weaning is occurring, tantrums are common. They are typically precipitated by the mother's unwillingness to permit nursing. There is much individual difference in frequency of tantrums from one infant to another. In this period, tantrums are sometimes precipitated by a mother's refusing to allow her infant to ride on her. It sometimes happens that the infant cannot get across a gap in the trees when it is on its own, though the mother is not far away. Tantrums occasionally occur in this context. A young chimpanzee may have a tantrum if hurt in play. This behavior continues into adolescence. Beyond infancy, and for many years thereafter, even sometimes into adult life, a chimpanzee may have a tantrum after being attacked. An adolescent may have a tantrum if, in response to his intensive and repeated submissive signals, a higher-ranking individual does not reassure him. Rarely, tantrums are observed among adults when repeated efforts to obtain a premium food by begging have been unsuccessful. It is not yet possible to delineate with confidence the components of the above interactions that are crucial in precipitating tantrums, especially in the absence of experimental analysis. Nevertheless it

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seems likely that deprivation in any of several spheres may precipitate tantrums in chimpanzees: tactile contact, visual contact, food, sucking and movement; also, tantrums apparently may be precipitated by pain, fear and rejection. One way. of viewing these precipitating contexts is to consider them basic frustrations. That is, they appear to be elements of adaptive behavior that are thwarted. When thwarted, the likelihood of a tantrum response is increased. When the tantrum response occurs, it tends in turn to elicit a response from a significant other individual, usually the mother. In fact, the mother's response is usually to do what the infant apparently wants to have done. The mother's tendency is to respond in a way that corrects the deficiency and comforts the infant. To be sure, there are striking individual differences in this regard. Some females will go 100 to 200 yards to a juvenile offspring who is having a tantrum, will take some specific corrective action and/or hold the infant close. Thus, if the tantrum is viewed as a very simple form of aggressive behavior, or at least as a precursor of aggressive behavior, then the model is reward for aggression. It is worth noting that the tantrum and the charging display that develops fully in adolescence are both singularly uninhibited. They are both characterized by a kind of overwhelming intensity. In either the tantrum or the charging display, the individual may break through ordinary constraints and in so doing elicit rewarding responses. We now turn our attention to tantrums in the human species. We refer to behavior appearing in the first few months of life characterized by intense crying, flailing of the limbs, clenched fists and red face. In the beginning, the pattern is diffuse and poorly coordinated; it conveys to observers a forceful sense of dissatisfaction on the part of the infant. At this stage, it is often precipitated by food deprivation; the infant has not been fed for some hours, and the tantrum is promptly terminated by feeding. Later in infancy and early childhood, the pattern becomes more adequately coordinated, and there are unmistakeable signs of intense, diffuse anger. The tantrum has scarcely been a major object of study in child development. The recent edition of Carmichael's manual of child psychology, a definitive compendium of information on the subject, includes well over 2,000 pages of text by leading scientists in the child development field (Mussen, 1970). We were able to find only three mentions of tantrums in these two volumes (Feshbach, 1970). Neverthe-

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less, some information is available, enough to be suggestive for the purpose of our present inquiry. The landmark study in this field was published more than forty years ago (Goodenough, 1931). Tantrums were found to be a common expression of anger in the first year of life. In the second year of life, there was some shift of emphasis to more directed motor and language responses, these becoming prominent by the age of two. She collected data from 45 mothers who recorded 1,878 anger outbursts in their children during a one-month period. The children ranged in age from seven months to eight years. Attention was given to the precipitating circumstances. Prominent among these in children under two years of age were the following: Being forced to remain on the toilet, being required to wear restrictive clothing, being put to bed, being refused permission to carry out some desirable play activity or being physically restrained from such activity and quarreling with playmates. Also prominent were hunger, fatigue and illness. All of these seemed more likely to occur when there were visitors in the home occupying the attention of the mother and perhaps other family members as well. Often, though not always, the parents yielded in infancy to the urgent demands of the tantrum. Goodenough remarks: 'Such apparently unserviceable acts as those of screaming, kicking, or holding the breath may have proved themselves to be the most effective means for getting one's own way.' Thus, tantrums may be viewed from a social perspective as well as a biological one. We do not know how often tantrums occur in the absence of a beholder. Most often, the tantrum conveys information to another person - when language is not yet established or fails under the impact of intense anger. In effect, the message is 'pay attention' or 'do something' or 'correct whatever is wrong'. Other scholars in the field of behavior development have recently commented on circumstances likely to precipitate tantrums. Harlow (1971) says, 'arbitrary and inconsistent parental demands may present the child with an unsolvable, and hence frustrating, discrimination problem'. Stone and Church (1973) remark, 'sometimes a conflict of wills, or excessive pressure on the child, will result in tantrums'. They are speaking about the toddler era - 15 to 30 months of age. They consider ways in which parents respond to the toddler's tantrums. They believe that parental retaliation may intensify tantrums. 'It is those adults who douse the toddler with cold water, or threaten him with loss of love or abandonment, who stoke the fires of tantrums.'

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Tantrums are usually experienced as very unpleasant by parents; hence, they are strongly motivated to find ways of terminating each episode. Goodenough found that a variety of techniques were used by parents. Generally, they could bring the tantrum to an end by removing interferences with the child's motivated activities. This included such techniques as granting the child's desire, removing the source of difficulty, diverting the child's attention, providing a substitute activity, ignoring the tantrum and briefly isolating the child. Reasoning, scolding, coaxing and soothing were less effective. Thus, parents learn ways of turning off each episode and thereby relieving their own distress as well as the child's. However, there remains the problem of long-run consequences. It is possible that some methods of terminating the immediate distress may inadvertently increase the frequency of such episodes in the future. This indeed seems to be the case. When the parents consistently yield to the child, give him his own way, the frequency of tantrums seems to increase over time. It is exceedingly difficult for parents to avoid rewarding the tantrum at least occasionally. This is particularly so because rewards may take diverse forms in this context. Bandura (1973) points out that young children often resort to aggressive ways of securing attention when they lack alternative means of gaining it. Their repertoire in this respect is quite limited early in life. Bandura comments, in a recent review of systematic studies on efforts to diminish aggressive outbursts in children, 'negative attention-forcing behavior is highly resistant to change because, to a child of limited skills who desires the recognition of others, even reprimands serve as rewards'. He describes various studies in which a systematic program directed toward minimizing rewards for tantrum behavior may lead to a marked decrease in such outbursts. In our view, similar processes occur in normal development. As tantrums are diminishingly rewarded, and as alternative coping skills are learned, the frequency of tantrums diminishes, and they are extinguished in due course. But the model of reward for aggression is established in the child's behavioral repertoire. Gradually, more sophisticated modes of aggressive behavior are acquired and replace tantrums. In some cases, perhaps rare in the general population but common in psychiatric experience, dangerous tantrum equivalents may reoccur years later, even after a long interval largely free of tantrums. When this happens, the risks are likely to be high in circumstances that permit ready availability of weapons.

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Stevenson (1970), in a recent review of learning and reinforcement effects in child development, points out the difficulty of extinguishing tantrums: 'If the child finds that tantrums never lead to reward, tantrums will be extinguished; but if the parent at times succumbs to his child's wailing (intermittent reinforcement), the child will repeat the act many times before giving it up as a means of controlling parental responses.' Similarly, Anthony (1970) says, 'temper tantrums can be reinforced both by reactions of solicitude and annoyance; the parents, on advice to ignore the behavior, tend to break down at times and respond, thus establishing a pattern of partial reinforcement, highly resistant to extinction. Probably no more than ten percent reinforcement could lead to recalcitrance'. Thus, the tantrum appears to be an early form of aggressive behavior, or at least a precursor of aggressive behavior, which occurs universally in the human species. It tends to be triggered by basic frustrations and to elicit a high level of parental attention, often accompanied by caretaking responses, sometimes by retaliatory anger. The extraordinary attention elicited by the tantrum appears to have reinforcing properties. Even with sustained parental effort, it is difficult to avoid some reinforcing effects. A pattern of intermittent reinforcement is established that tends to maintain the behavior. Nevertheless, it is likely to be channeled into increasingly focussed and sophisticated expressions as the child matures and learns. Based on her pioneering study, Goodenough says, 'with advancing age, the forms of behavior displayed during anger become more definitely directed toward a given end, while the primitive bodily responses of the infant and young child are gradually replaced by substitute reactions commonly of a somewhat less violent and more symbolic character'. Presumably such learning extends over many years, involving long sequences and complex processes of observation, reinforcement and problem solving. We believe that it is based upon and influenced by a period of about a year in infancy when tantrums and tantrum-like activity have established the model of reward for aggression on a very simple basis. This elementary pattern of behavior, presumably built into the central nervous system through its effectiveness in adaptation over millions of years, gives the infant remarkable power in eliciting responses from others. In this respect, it may not only be an important precursor of aggressive behavior but of competence as well - for it is one of the earliest ways in which the infant can produce strong

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effects on its environment. In our view, it is at least possible that the simple early lesson of aggressive efficacy is not lost on the developing child. As he matures this lesson can be applied in many contexts and shaped by many influences in the family, subculture and culture. To the extent that the learning of aggressive behavior is easy for the human species, these early experiences may well play a facilitative role.

Rough-and-tumble

play

Recently, Dolhinow and Bishop (1972) have reviewed the development of motor skills and social relationships through play in nonhuman primates. They point out that, in many species of nonhuman primates, play in infancy and the juvenile era prominently features chasing, hitting, wrestling and biting. In early infancy, these patterns are not associated with injury. In older infants and juveniles there is a clear increase in the frequency with which such play goes over into serious fighting. This behavior is to some extent sex-differentiated. 'Both human and nonhuman primate play studies indicate that roughand-tumble play is an activity of young males and that females tend to withdraw from play groups during the juvenile stage when the play becomes too aggressive for them.' In respect to chimpanzee play in the natural habitat, considerable information has accumulated over the past decade at Gombe, though there has not yet been a specialized study on this topic (van LawickGoodall, 1968). During the early months of life, there is little play; much of the time is spent alone with the mother, and, even when other animals are present, little direct contact takes place. However, by the second year of life there is considerable play. If infancy is divided into two phases, the first from zero to two years of age and the second from two to four years of age, then frequency analysis shows that the second half of infancy is characterized by much more play than any other phase of the life cycle. Second in frequency, at about the same level, are the first half of infancy and the juvenile era. The structure of the chimpanzee community is such that there is considerably less opportunity for the young chimpanzee to play with age mates than is the case in a troop of baboons or rhesus macaques. Nevertheless, there is much play in infancy, and infants show considerable initiative in this respect. A two-year-old infant commonly initiates play by walk-

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ing slowly to a younger infant and reaching out to pat it or tickle it. The same animal, when initiating play with a peer or older infant is likely to run up in a vigorous 'play walk' or gambol, to fling itself into the other infant, hitting, mock-biting, flailing or kicking. Chasing, on the ground and especially through the trees, is common. Older infants often chase wildly through the trees, leaping from branch to branch or even from one tree to another. If the pursuer catches the other animal, there is often a bout of wrestling. This is simple on the ground but requires special adjustments in the trees; for example, one chimpanzee infant hanging down from a branch by one arm while sparring or grabbing the other with his free arm and legs. Often, one chimpanzee kicks back at the chimpanzee behind, sometimes with considerable force. Very young infants sometimes play 'tug-of-war' with twigs. They may hit each other with long grasses or twigs. Infants two or three years of age may also direct rough-and-tumble play toward adults who tolerate it consistently. Such infants may leap onto the adult, biting or pulling his hair, hitting him or dangling above the adult and kicking downward. Play between infants sometimes ends with one of them screaming and hitting the other in an intense, vigorous way. The other is then likely to hit back relatively hard. Under these conditions, one of the mothers is likely to intervene by threatening her offspring's playmate. Occasionally, the higher-ranking of the two mothers will attack the lower-ranking one. Indeed, a good deal of female aggression occurs in the context of such quarrels between their infants. Overall, rough-and-tumble play is common in Gombe chimpanzees from about age one to age seven. Beyond that, in adolescence, such encounters get very rough, especially between males (Pusey, personal communication). Throughout infancy the sex difference in rough-andtumble play appears modest, certainly less striking than in the Gombe baboons (Owens, personal communication). Both sexes appear to find such play rewarding, though in the long run this is more impressive for males. We have also observed pygmy chimpanzees (Pan paniscus) in the San Diego Zoo engage in rough-and-tumble play patterns similar to those observed at Gombe. A pair of infants, between two and three years of age, showed vivid precursors of aggressive patterns in their play: Pushing, pulling, grabbing, dragging, raising arms over head, biting, jumping on the other, rolling, pressing down the other. In short,

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they frequently engage in a kind of intensive wrestling which is similar to the rough-and-tumble play of other higher primate species. What about the human species? Are there play patterns early in life that can reasonably be considered precurors of aggressive behavior? If so, do these patterns show appreciable resemblance to the roughand-tumble play of the higher nonhuman primates? Hartup (1970) has recently published a comprehensive, informative review of peer interactions and social organization. Although there is a paucity of research on play in human infancy, his review provides some useful clues. From present evidence, it appears that infants show little interest in other infants during the early months of life; but toward the end of the first year, such interest tends to increase considerably and to become vigorous thereafter. In observing infant-infant interaction, it appears that fighting reaches a peak between nine and thirteen months and decreases thereafter; the fighting is mostly over toys. However, among institutionalized infants, the peak of fighting seems to occur at about fifteen months and does not diminish till after two years of age. Toward the middle of the second year, infants generally attend positively to peers once conflicts involving play materials have been resolved. From several observational studies examining aggressive behavior in infancy and early childhood, there is some indication that the total frequency of aggressive peer interaction increases between the ages of two and four, and then declines. Of course, the modes of aggression change with age and experience. They are related to changes in sensory-motor capacities, cognitive skills and the development of impulse controls. Stone and Church (1973), defining the toddler era as ranging from fifteen to thirty months of age, indicate that the toddler prefers largemuscle activity to small-muscle activity, that he is more likely to send his whole body hurtling through space than to engage in sensitive manipulation of small objects. His play begins with social-affective play. This involves his relations with adults as well as with infants and children. When other babies are present, there is keen curiosity, often accompanied by poking, pinching, stroking and pulling. The other baby is likely to respond in kind. In the period around twenty-four to thirty months, the child makes a transition from play that is largely solitary to parallel play, in which the concomitant activities of the two children are occasionally punctuated by a tug-of-war over a premium play object.

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Social-affective play continues into the preschool years in a more elaborate, complex form. One prominent feature of such play, especially in boys, involves motor patterns similar to those observed in the higher nonhuman primates: Pushing, pulling, hitting, chasing, wrestling. Recent cross-cultural studies suggest that these patterns occur in many cultures in different parts of the world, with different value orientations, and at quite different stages of technological development (Whiting, 1972). There is consistency too in the observation that these patterns occur more frequently in boys than in girls. During the preschool years, boys express more aggression than girls in both play and fantasy. Temper tantrums, quarreling, destruction of objects, physical attacks and serious fighting are all more common in boys than in girls. Indeed, during the early years of life, even verbal aggression is more common in boys than in girls, though this situation changes in later childhood. In the comprehensive survey of sex differences in behavior undertaken by Maccoby and her colleagues, one of the most consistent findings across a variety of studies was that of sex differences in aggressive behavior (Maccoby, 1966). Utilizing a variety of measures at different age levels of childhood and adolescence, the consistent (though not quite universal) finding was that boys are more physically aggressive than girls. The principal concentration of these studies was on the age range of three to six years. There is a great need for direct studies, utilizing systematic observational techniques, of aggressive behavior and its precursors in human infancy and early childhood. From the limited evidence available at present, it appears that precursors of aggressive behavior are indeed present in infancy and early childhood, that some of them show considerable resemblance to the rough-and-tumble play of higher nonhuman primates, and that they are present in both sexes though more prominently in males. In these respects, there appears to be some evolutionary continuity between ourselves and our ancestors. But we are well aware of the differences, not only in the biological nature of the organisms but also in the immense complications that lie ahead in the long course of human development as aggressive propensities are subjected to environmental influences. We shall have more to say on this later.

Factors facilitating development of aggression Sex hormones and aggressive

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inclinations

Early hormonal influences upon brain organization affect later aggressive and sexual behavior. Pioneering work was done with rodents and then extended to monkeys (Goy, 1968). The administration of a rather large dose of testosterone to a pregnant monkey during roughly the second quarter of gestation tends to masculinize a female fetus in some anatomical and behavioral respects - one of the behavioral effects being to make these females somewhat more aggressive than untreated females. Using reliable scoring systems, it has been established that they engage more in rough-and-tumble play and initiate social threat more than females who have not been exposed to high levels of testosterone in utero. Of course, over the years of growth and development many influences can modify the expression of these aggressive patterns that have been influenced by testosterone. Therefore, it is interesting that there is some tendency toward persistence of these hyper-aggressive characteristics into adult life in the female monkeys whose mothers were exposed to testosterone in pregnancy. Is there any evidence that testosterone may have similar effects on behavior development in man? Some years ago when the findings in monkeys were first reported we accumulated some cases of androgenexposure during pregnancy in humans, but too few for an adequate study. Fortunately, the pediatric endocrine clinic at Johns Hopkins has a large resource of such patients. Money and Ehrhardt (1968) were able to study twenty-five girls, mostly in late childhood and early adolescence, whose mothers had been exposed to androgens before their births. Those of them who, as newborns, had shown striking anatomical abnormalities underwent surgical correction shortly after birth. With interviews and projective tests, data were obtained from each girl, at least one parent and some other informants, in several behavioral categories. The research design undertook to control for observer bias. The results indicated that the early-androgenized girls, as contrasted with a control group, tended to be described by self and others as 'tomboys', to engage in outdoor sports requiring much energy and vigor, to prefer rough play and to prefer toys ordinarily chosen by boys - such as guns. The possibility that sex hormones play a significant role in mediating the development of human aggressive behavior, especially in respect to rough-and-tumble play patterns, has been strengthened by two very

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Lawick-Goodall

recent studies which we now wish to summarize. The first of these deals with the later effects of prenatal androgens. Ehrhardt, who collaborated with Money in the earlier work at Johns Hopkins, is conducting a new study with Baker in Buffalo (1973). Their first paper on the new study essentially confirms and extends the previous work. They are interested in assessing major trends of childhood behavior over many years. This assessment is undertaken through interviews with the children and their mothers, utilizing a semi-structured interview schedule covering items on general development, play behavior and sex-related behaviors such as toy preference, aggression, rehearsal of adult roles and clothing preferences. Rating scales were developed to permit quantitative estimates of behavioral items. The investigators were able to locate 27 of the 31 patients who had been seen in the history of their clinic with the disease congenital adrenal hyperplasia. At the time of study, the offspring ranged from about four years to the early twenties, with most in middle childhood and early adolescence. For comparison, a sample of unaffected siblings consisting of eleven females and sixteen males with comparable age ranges was obtained. All children were receiving corrective hormonal therapy, with most having begun this therapy very early in life. The therapy had been effective. The findings are based on comparison with same-sex siblings. In this disease, the fetus is exposed to exceptionally large amounts of selfgenerated androgens during pregnancy. The fetally androgenized girls showed a clear preference for vigorous, intense, physical activity. From an early point in their lives, they had sought rough outdoor play. However, there was no significant difference between the androgenized girls and their unaffected siblings in the frequency of starting fights, either verbal or physical. If given a choice of playmates during childhood, the androgenized girls more frequently preferred boys over girls in comparison with the unaffected siblings. The androgenized girls also showed a tendency to choose toys ordinarily associated with boys, such as guns. Their interest in dolls was very low, and significantly more often than the unaffected siblings they showed indifference or aversion to small infants. A majority of the androgenized girls were regarded by themselves and others as a 'tomboy' throughout their childhood, in marked contrast to the unaffected siblings. Overall, Ehrhardt and Baker report: 'The results presented are almost in complete agreement with the earlier studies at Johns Hopkins in which

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patients were compared with normal matched girls from nonpatient families. Thus, even in sibling comparisons, when social class, intelligence of parents, number of brothers and other family characteristics are matched to a high degree for both patients and sibling controls, clearcut behavior differences were found.' They believe that one of the principal findings is the difference in rough-and-tumble play. In their view, the preference for playing with boys and the toys associated with boys is secondary to the basic temperamental trait expressed in the enjoyment of rough-and-tumble play. They comment: 'If you play more rough games, you will find more boys to do it with.' A new feature of the Buffalo study is the inclusion of males. Thus, fetally hyper-androgenized males are compared with unaffected (normally androgenized) male siblings. The only significant difference between the two groups is that boys with a history of excess androgen show an exceptionally strong preference for vigorous, rough, outdoor activities. This finding is similar to the fetally androgenized girls. Also, the excessively androgenized boys are more likely than their normal brothers to initiate fighting, both physically and verbally. A group of our colleagues in the Department of Psychiatry at Stanford has just reported a novel study of prenatal exposure to female hormones in humans (Yalom, Green & Fisk, 1973). They have examined the effects of intrauterine estrogen and progesterone on psychosexual development in boys. They studied twenty sons of diabetic mothers who were given moderately high doses of estrogen and progesterone during pregnancy. These boys were compared with two relevant groups: (1) Sons of diabetic mothers who were not given exogenous estrogen or progesterone; and (2) sons of nondiabetic mothers. Both comparison groups were matched as carefully as possible to the experimental group in several respects: (1) Age, (2) social class, (3) living in the same community, (4) attending the same schools. Behavioral assessment was undertaken on a double-blind basis to the maximum extent possible. It appears to have been successful in respect to boys who are assessed at six years of age but only partially successful at the sixteen-year-old level. At age six, there is only a slight difference between the groups. According to the teachers' ratings (which were indeed made without knowledge of prior conditions), the experimental boys were significantly less assertive than boys in the two comparison groups. They did not, however, differ in more dramatic variables of aggressive

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behavior. It might be anticipated that such slight differences between the groups would be largely attenuated by age sixteen in light of a decade's experience with all of its cultural and sub-cultural influences. The finding is quite the contrary. At age sixteen, the experimental boys are not only less assertive than both comparison groups but distinctly less aggressive over a broad range of situations. This applies to assessments of recent anger, history of anger intensity, physical toughness, fights and adventuresome attributes. In other words, the boys exposed prenatally to female hormones showed less of these aggressive characteristics than the comparison boys, regardless of whether the estimates were derived from self-ratings, ratings by other people, systematic interviews, or a projective test (Thematic Apperception Test). So far as we know, this is the first evidence derived from a specifically designed research study indicating that early exposure to female hormones may diminish aggressiveness in human males. This study raises many questions, only one of which we will comment on here. In other contexts, we are investigating the psychobiology of adolescence in chimpanzees and humans (Lund & Hamburg, 1972). We are inclined to believe that the hormonal changes of puberty, especially in males, may facilitate the learning of aggressive behavior (but space does not permit our pursuing this theme here). Therefore we are struck by the possibility that, in addition to the early effects of the female hormones on the developing brain, the nature of puberty may have been modified in these boys by prenatal exposure to large amounts of female sex hormones. We raise this question primarily because the findings are more striking at age sixteen than at age six. However, there is no gross evidence of pubertal abnormality, and the behavioral finding may have other roots. Still, it is possible that the upsurge of androgen that normally occurs in male adolescents may have been diminished by the early hormone exposure, or that the brain's response to such an upsurge was modified by the early exposure to female hormones. In any event, these two new studies, both done more carefully than most clinical investigations, give us reason to believe that even in the human species, aggressive behavior may be influenced in the early course of its development by exposure of the fetal brain to sex hormones. We suspect that such effects might well operate through the shaping of an early interest or preference of the developing organism,

Factors facilitating development of aggression 75 such that a slight bias toward the environment is established. This bias increases the probability that learning will proceed in certain directions; but it does not require that this happen, and indeed environmental influences may overcome it. In summary, rough-and-tumble play appears to be rewarding for many primate species early in life. Moreover, there is a sex difference in the prominence of rough-and-tumble play. In the rhesus macaque, this is clearly apparent within the first year of life. In the Gombe baboons, it is clearly apparent around the end of the first year of life. It is our impression that chimpanzees show a sex difference in this regard, appearing somewhat later than in baboons. Human studies in a variety of cultures suggest that rough-and-tumble play is also rewarding for young humans, and again more so for boys than for girls. Recent evidence indicates that the early preference for this type of activity is mediated in part by androgens, not only in monkeys but in humans as well. In any event, if rough-and-tumble play is considered a very simple form of aggressive behavior, or at least a clear precursor of aggressive behavior, then we have here a model of a biologically determined early preference which involves the organism in rewarding aggressive activity. In seeking out opportunities for this activity, the organism will be drawn to others who share his preference. In the main, these will be males. This will then provide opportunity to learn a great deal about other interests, preferences and salient characteristics of male organisms. The male play group devoted to rough-andtumble activities will, in effect, provide a pool of information about the male way of life.

Attachment and the development of aggressive behavior There are other aspects of human development, derived from the evolutionary history of the species, that may make aggressive behavior easy to learn. Indeed, the ease-of-learning paradigm may be useful in several fundamental spheres of child development (Bruner, 1972, 1973). We have already mentioned the hormonal changes of adolescence and their possible behavioral concomitants (Hamburg, 1971a). Beyond this, we are impressed with the similarities of form and context of many - though certainly not all - aggressive patterns in chimpanzees and humans. We have described these elsewhere (van

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Lawick-Goodall, 1971; Hamburg, 1971b). We have also undertaken an analysis of other similarities in the forms and contexts of chimpanzee and human behavior (van Lawick-Goodall & Hamburg, in press). While there are certainly enormous differences as well, the trend of evidence over the past decade has been to diminish the gulf between human and nonhuman primates, especially chimpanzees. Of all these similarities, none interests us more than the deep and enduring quality of attachments in the higher primates, perhaps reaching a culmination in chimpanzee and human interpersonal bonds. Gombe research has revealed that the affectionate bonds between chimpanzee mothers and their offspring and between siblings are often strong and long-lasting. The young male associates very closely with his mother until he is nine or ten years of age. Moreover, all five of the males we observed whose mothers were alive during their adolescence continued to associate with them frequently during that period. We have now been able to make detailed observations on the relationships between three old females and their socially mature sons - that is, males more than fifteen or sixteen years of age. One of these females had two such sons, the others one each. All these young males associated quite frequently with their mothers, and during such times social grooming between mother and son was frequent. Moreover, on a few occasions mothers were observed to hurry to the assistance of adult as well as adolescent sons; similarly, sons sometimes assisted their mothers. Females tend to remain closely associated with their mothers for even longer than males but to date we have been able to follow the development of a relationship between a mother and her daughter into the latter's adulthood in only one case; in other cases either the mother or the daughter died before the daughter became an adult. Observations on two pairs of brothers suggest that long-term bonds, similar to those observed between a mother and her son, may typically be formed between brothers. To date we have been able to study the relationship between only one pair of chimpanzee sisters, the eldest of whom is close to social maturity and the other approaching adolescence. These two associate with their mother almost all the time, and the bond between all three is very close. As complex organisms have evolved, behavior has become an exceedingly important way of meeting adaptive tasks which contribute

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to species survival - tasks such as finding food and water, avoiding predators, achieving fertile copulation, caring for the young and preparing the young to cope effectively with the specific requirements of a given environment. These are behavioral endeavors that contribute crucially to species survival. The role of behavior in adaptation is not bnly a function of individuals, but of groups as well. This is strikingly true of higher primates. Recent studies of nonhuman primates and of hunting-and-gathering human societies in their natural habitats suggest that group living has conferred a significant selective advantage upon the more highly developed primates. This selective advantage derived from social organization has probably included: a) Protection against predators, b) meeting nutritional requirements, c) protection against climatic variation, d) dealing with injuries, e) facilitating reproduction, f) preparing the young to meet the requirements and utilize the opportunities of a given environment whatever its characteristics may be. Both nonhuman primates and early man have been organized into small societies (Washburn & Harding, in press). These societies provide, among other things: (1) Intimate, enduring relationships with mutual assistance in difficult circumstances; (2) clear guidelines for individual behavior, highly relevant to survival requirements in a given environment. More than a decade ago, one of us wrote: 'The adaptive function of primate groups should alert us to look for processes in the individual that facilitate the development of interindividual bonds. In seeking such processes, we may find useful guidance in the principle that individuals seek and find gratifying those situations that have been highly advantageous in survival of the species. That is, tasks that must be done (for species survival) tend to be quite pleasurable; they are easy to learn and hard to extinguish. Their blockage or deprivation leads to tension, anger, substitutive activity and (if prolonged) depression. Such blockage is often accompanied by emergency-type physiological responses that support actions necessary to correct the situation. In the post-infancy human, a remarkable variety of coping behavior may be mobilized by such blockage or deprivation, determined in substantial part by cultural patterning. 'In view of the extreme dependence on learning in the human species, such bonds would most likely be greatly strengthened through learning. Selection may operate on differential readiness for learning

78 David A. Hamburg and Jane van Lawick-Goodall responsiveness and attachment to others of the same species' (Hamburg, 1963). Since that was written, new research on human infancy has suggested pathways through which powerful and enduring attachments are formed (Yarrow & Pedersen, 1972; White, 1971). Biological derivatives of our history as a species, built into the central nervous system (presumably because they had selective advantage in evolution) lead human infants to interact in certain ways with their environments; in most circumstances, these interactions make attachments easy to learn. Much has been clarified during the past decade about the earliest period of human infancy, thanks to careful, systematic, direct observation of infants and the development of ingenious techniques (Kessen, Haith & Salapatek, 1970; Stone & Church, 1973). One of the main thrusts of this work has been to show that the capacities of the human infant in the first few months of life, indeed in the neonatal period, are greater than had been generally supposed. We regret that there is not room in this paper for a substantial summary of this work as it pertains to our main theme (Jeffrey, 1970). Suffice it to say that in our view, a conjunction of simple behavior patterns very early in life fosters the formation of interpersonal bonds. A perceptual preference in the visual sphere (for the human face), another preference in the auditory sphere (for the human voice) and a simple motor pattern (the smile) come together in such a way as to elicit caretaking, affectional responses from the mother and to facilitate a transaction between mother and infant that deepens the bond between them over time. Our view is similar to Bowlby's (in press) comprehensive formulation of attachment. He emphasizes infant behavior patterns that tend to attain proximity with the mother and to elicit nurturance responses from her. These patterns include following, clinging, crying, calling, greeting and smiling. They functioned as adaptive mechanisms and have been maintained because of their survival value. We especially value Bowlby's effort to integrate data and concepts from ethology, developmental psychology and clinical psychiatry. But what does all this have to do with aggression? One connection is emphasized by Bowlby; and we wish to conclude by pointing out others. Bowlby is concerned with anger as one of the common responses to unwilling separation and threats of separation. His main

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focus is on the child's anger towards its mother, though he recognizes that other targets are possible. To the extent that the mother-infant relationship is a prototype for all subsequent human relationships, anger experienced in this context early in life may pave the way for anger later in life in the context of jeopardy to an intimate bond. This brings us to a final consideration of some ways in which our evolutionary history as a species may influence our susceptibility to environmental events. Both biological and psychological theories of human aggressiveness indicate that modifying major frustrations might be an important point of leverage in changing development in such ways as to reduce hatred and violence. What sorts of frustrations are most effective in eliciting severe aggressiveness in contemporary populations? One major category of frustration, at all times and places, is survival threat: Clear and present danger to survival. It seems likely that this has an evolutionary linkage. In nonhuman primates in their natural habitats, recent research has shown that for survival it is important to be an integrated member of a social group; moreover, anthropological studies highlight the crucial role of group membership in the evolution of early man. In all likelihood, for millions of years, man's survival has been greatly facilitated by attachment to other humans and by belonging in organized groups - groups oriented toward meeting the tasks of adaptation. The next fundamental motivation, frustration of which heightens probability of hatred and violence, is self-esteem, or a sense of personal worth. This need must be related in evolution to the adaptive value of having a place in the group. On the average over long time spans, survival and reproduction must have been facilitated by being recognized and respected by others. Such respect must have been enhanced by demonstrated competence appropriate to one's age-sex class. Behavior directed towards establishment and maintenance of selfesteem, of dignity, of self-worth, has great cross-cultural generality, even though there are differences among cultures in what it is that constitutes a severe threat to self-esteem. One significant sub-category in the self-esteem area is threat to self-esteem of young males - especially the issue of manliness in young males who have been so important historically in warlike activities. A third major category of frustration that is very important in eliciting aggression in contemporary man has to do with crucial interpersonal relationships. These are the primary relationships for group

80 David A. Hamburg and Jane van Lawick-Goodall membership and are highly significant in the evolution of our species along the lines we have already sketched. Finally, and very closely related, is a threat to the sense of belonging - belonging to a larger group, beyond the intimate few, but a group with which one identifies. It may be a subculture, an ethnic group, a nation, a tribe, a political entity or an occupational unit - but in any event, a group which makes some contribution to the selfesteem of its members and provides guidelines for adaptation. These four major, overlapping categories of motivation are so salient in most cultures that frustration or threat to them significantly raises the probability of aggressive behavior. Threat to these fundamental motivations may elicit non-hateful, non-violent ways of coping - and indeed usually do so. Hostile responses are not the only way to cope with such threats. A serious frustration may lead to hateful, destructive, violent attitudes and actions; however, it may also lead to assertive behavior, personal initiative, vigorous and persistent efforts toward problem-solving that may be aggressive in some popular sense but not aggressive in the sense of being hateful and destructive. Such nondestructive, vigorous, persistent efforts at problem-solving may be more difficult, complicated and tedious in the short run but much more rewarding in the long run, and perhaps even essential for our survival as a species.

REFERENCES Anthony, E. J., 1970, Behavior disorders. In P. H. Müssen (Ed.), Carmichael's manual of child psychology. New York, Wiley. Bandura, A., 1973, Aggression: A social learning analysis. Englewood Cliffs, New Jersey, Prentice-Hall. Bigelow, R., 1972, The evolution of cooperation, aggression and self-control. Nebraska symposium on motivation. Lincoln, University of Nebraska Press. Bowlby, J., in press, Attachment theory, separation anxiety and mourning. In D. Hamburg & K. Brodie (Eds.), American handbook of psychiatry, Vol. 6, New frontiers. New York, Basic Books. Bruner, J. S., 1972, Nature and uses of immaturity. American Psychologist, 27 \ 1-22. Bruner, I. S., 1973, Organization of early skilled action. Child Development, 44:1-11. Dolhinow, P., & Bishop, N., 1972, The development of motor skills and social relationships among primates through play. In P. Dolhinow (Ed.), Primate patterns. New York, Holt, Rinehart and Winston.

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Ehrhardt, A. A., & Baker, S. W., 1973, Hormonal aberrations and their implications for the understanding of normal sex differentiation. Presented at the Society for Research in Child Development, Philadelphia, March. Eibl-Eibesfeldt, I., 1970, Ethology: The biology of behavior. New York, Holt, Rinehart and Winston. Feshbach, S., 1970, Aggression. In P. H. Müssen (Ed.), Carmichael's manual of child psychology. New York, Wiley. Goodenough, F. L., 1931, Anger in young children. Minneapolis, University of Minnesota Press. Goy, R. W., 1968, Organizing effects of androgen on the behavior of rhesus monkeys. In R. Michael (Ed.), Endocrinology and human behavior. London, Oxford University Press. Hamburg, D., 1963, Emotions in perspective of human evolution. In P. Knapp (Ed.), Expression of the emotions in man. International University Press. Hamburg, D., 1968, Evolution of emotional responses: Evidence from recent research on nonhuman primates. In J. Masserman (Ed.), Animal and human. New York, Grune and Stratton. Hamburg, D., 1971a, Recent research on hormonal factors relevant to human aggressiveness. International Social Science Journal, 23:36-47. Hamburg, D., 1971b, Aggressive behavior of chimpanzees and baboons in natural habitats. Journal of Psychiatric Research, 8:385-398. Harlow, H. F., 1971, Learning to love. San Francisco, Albion. Hartup, W. W., 1970, Peer interaction and social organization. In P. H. Müssen (Ed.), Carmichael's manual of child psychology. New York, Wiley. Hebb, D. O., 1972, Textbook of psychology. Philadelphia, Saunders. Hinde, R., in press, Biological bases of social behavior. New York, McGraw-Hill. Jeffrey, W. E., 1970, Perception, attention and curiosity. In T. D. Spencer & N. Kass (Eds.), Perspectives in child psychology. New York, McGraw-Hill. Kessen, W., Haith, M. M., & Salapatek, P. H., 1970, Infancy. In P. H. Müssen (Ed.), Carmichael's manual of child psychology. New York, Wiley. Lunde, D. & Hamburg, D., 1972, Techniques for assessing the effects of sex hormones on affect, arousal, and aggression in humans. Recent progress in hormone research, 28:627-663. Maccoby, E. (Ed.), 1966, The development of sex differences. Stanford, Stanford University Press. Money, J., & Ehrhardt, A. A., 1968, Prenatal hormonal exposure: Possible effects on behavior in man. In R. Michael (Ed.), Endocrinoloy and human behavior. London, Oxford University Press. Müssen, P. H. (Ed.), 1970, Carmichael's manual of child psychology, 2 volumes. New York, Wiley. Owens, N. Research on play behavior of Gombe baboons. Personal communication. Pusey, A. Research on adolescent behavior of Gombe chimpanzees. Personal communication. Raleigh, M. J., & Washburn, S. L., 1973, Human behavior and the origin of man. Impact of Science on Society, 23:5-14. Sackett, G. P., 1966, Monkeys reared in isolation with pictures as visual input: Evidence for an innate releasing mechanism. Science, 154:1468. Seligman, M. E., & Hager, J. L., 1972, Biological boundaries of learning. New York, Appleton-Century-Crofts. Stevenson, H. W., 1970, Learning and reinforcement effects. In T. D. Spencer &

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N. Kass (Eds.), Perspectives in child psychology. New York, McGraw-Hill. Stone, L. J., & Church, J., 1973, Childhood and adolescence, 3rd edition. New York, Random House. Tinbergen, N., 1968, On war and peace in animals and man. Science, 160:14111418. van Lawick-Goodall, J., 1968, The behavior of free-living chimpanzees in the Gombe stream reserve. Animal Behavior Monographs, 7:161-311. van Lawick-Goodall, J. 1971, Some aspects of aggressive behavior in a group of free-living chimpanzees. International Social Science Journal, 23:89-97. van Lawick-Goodall, J., & Hamburg, D., in press, New evidence on the origins of human behavior, D. Hamburg & K. Brodie (Eds.), American handbook of psychiatry, Vol. 6, New frontiers. New York, Basic Books. Washburn, S. L., & Harding, R. S., in press, Evolution and human nature. In D. Hamburg & K. Brodie (Eds.), American handbook of psychiatry, Vol. 6, New frontiers. New York, Basic Books. White, B., 1971, Human infants. Englewood Cliffs, New Jersey, Prentice-Hall. Whiting, B., 1972, Presentation at conference on the biocultural bases of sex role differentiation. Palo Alto, California, June. Yalom, I. D., Green, R., & Fisk, N., 1973, Prenatal exposure to female hormones: Effect on psychosexual development in boys. Archives of General Psychiatry, 28:554-561. Yarrow, L. J., & Pedersen, F. A., 1972, Attachment: Its origins and course. In W. W. Hartup (Ed.), The young child: Reviews of research, Vol. 2. Washington, O.C., National Association for the Education of Young Children.

ABSTRACT Several similarities in the forms and contexts of chimpanzee and human aggressive behavior suggest ways in which evolution may have facilitated the learning of such patterns. Simple sensory and motor preferences early in life draw the organism in certain directions. Once so drawn, much complex learning ensues, taking account of group norms. Several aspects of early experience are considered in this perspective: (1) Observation of imminent and actual fighting; (2) tantrum behavior - its forms, precipitating contexts, reinforcements and derivatives; (3) rough-and-tumble play - its forms in nonhuman primates and children, sex differences, reinforcements and derivatives. Recent research indicates that early exposure of the developing primate (including human) brain has some influence on early preferences pertinent to later aggressive behavior, especially rough-and-tumble play. New studies on intrauterine hormone variations are cited, involving (a) exposure of female fetus to high androgens and (b) exposure of male fetus to high estrogens and progesterone. The ease-of-learning paradigm applies to attachment behavior also. The evolutionary significance of attachments within the primate group help to clarify circumstances in contemporary societies that are likely to elicit aggressive behavior.

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RÉSUMÉ Certaines ressemblances entre les comportements agressifs du chimpanzé et de l'homme permettent de mieux comprendre comment est facilité l'apprentissage de certains patterns dès le début de la vie. Plusieurs aspects de cette expérience précoce sont considérés ici dans cette perspective: (1) observation d'une lutte imminente et réelle; (2) comportement de colère: formes, contextes déclenchants, renforcements et dérivés; (3) combat ludique: ses formes chez les primates non-humains et les enfants, différences selon le sexe, renforcements, dérivés. De récentes recherches indiquent que l'exposition précoce du cerveau en développement du primate (y compris l'homme) à certains stimuli a une influence sur le comportement agressif ultérieur, en particulier le combat ludique. De nouvelles études sur les variations hormonales intra-utérines sont citées: (a)exposition du fœtus femelle à des taux élevés d'androgènes; (b) exposition du fœtus mâle à des taux élevés d'œstrogènes et de progesterone. Le principe de facilitation dans l'apprentissage s'applique également ici. l'évolution des rapports au sein du groupe des primates aide à voir plus clair dans les circonstances qui, dans nos sociétés contemporaines, font probablement apparaître le comportement agressif.

Aggressive behavior and its brain mechanisms (as exemplified by an experimental analysis of the rat's mouse-killing behavior)* PIERRE Université

KARLI

Louis Pasteur,

Strasbourg

As this paper will focus on a certain kind of aggressive behavior, two general remarks should be made by way of introduction: 1. Internal milieu factors (glycemia, osmolarity, sexual hormone levels) play an essential role in the elicitation of behaviors (eating, drinking, sexual and maternal behaviors) which form an integral part of some basic biological regulation. The detection of humoral fluctuations plays a preponderant part in the processes giving rise to the relevant 'specific arousals' or 'drive states' (hunger, thirst, sexual and maternal 'drives'). In many instances of aggressive behavior, there does not seem to exist any such humoral factor which could be held responsible for the production of a specific drive state ('aggressiveness') arising internally. Social behavior is often shaped essentially by the life-history, by both the general and the more specific history of reinforcement. There are intimate relations between emotional and social responsiveness, in their progressive shaping during ontogenesis as well as in their behavioral expression in the adult organism. This notion should not lead one to minimize the part taken by humoral factors in the elaboration of any kind of behavioral response. Internal milieu fluctuations as well as changes in the turnover rates of brain neurohumors do affect one or the other of the various aspects of an * This research has been supported since 1966 by grants from the Direction des Recherches et Moyens d'Essais du Ministère des Armées (DRME) and from the Institut National de la Santé et de la Recherche Médicale (INSERM). The major part of the experimental work referred to in this paper was done in collaboration with M. Vergnes, F. Eclancher, J. P. Chaurand and P. Schmitt.

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organism's responsiveness. As regards the brain neurohumors, it must be added that our knowledge of neurochemical correlates of behavior is expanding rapidly; but only very seldom are we able at the present time to uncover clear causal relationships between neurochemical and behavioral changes. 2. It is widely accepted among biologists that any unitary concept of aggressiveness and aggressive behavior is to be avoided. There are a number of different motivational states which may express themselves in different kinds of aggressive behavior. Many factors take part in the elicitation, in the facilitation or in the suppression of an aggressive behavior, and behavioral as well as neurophysiological analyses show that the relative importance of these factors may be quite different from one case to another. If we turn now to a given kind of aggressive behavior, namely the rat's mouse-killing behavior, important questions arise: Is this mousekilling behavior itself something unitary; is it always elicited or facilitated by the same factors; are the same neural mechanisms always brought into play? The answer to these questions is no. Under experimental conditions, one is led to distinguish between at least two different types of mouse-killing behavior, with a different biological significance. First, stimulation of lateral hypothalamic (Vergnes & Karli, 1969; De Sisto & Huston, 1971; Panksepp, 1971; Woodworth, 1971) and a number of ventral tegmental sites (Chaurand, 1973) elicits a kind of 'cold-blooded' killing similar to the killing spontaneously shown by the experienced killer rat (the aggression is a well-oriented one; the rat searches after the mouse; there is but a poor emotional display). This behavior is mainly elicited in killer rats which kill regularly with a more or less prolonged delay but rarely in natural non-killers. The effective stimulation sites are also self-stimulation sites. If the rat is presented with both a self-stimulation lever and a mouse, he leaves the lever at some time (in spite of the highly rewarding effects of the self-stimulation), he kills the mouse and then resumes selfstimulation. In this case, the elicited (or rather facilitated) mousekilling may be considered as an approach behavior, the underlying motivation being of an appetitive nature. Second, stimulation of medial hypothalamic (Vergnes & Karli, 1970) and of a few periaqueductal sites (Chaurand, Vergnes, & Karli, 1972) elicits a different kind of mouse-killing: The 'affective' kind of ag-

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gression with an important emotional display (the aggression is a poorly oriented one - the rat does not search after the mouse; it attacks only when the mouse comes close to him). This behavior is readily elicited in the natural non-killer. The effective stimulation sites are in every case 'switch-off sites. Once the rat has learned to put an end to the brain stimulation either by fleeing or by pressing a lever (*switch-off' response), he may not be induced readily to kill a nearby mouse. In this case, the elicited mouse killing may be considered as a defense behavior, as a kind of active avoidance behavior, killing being instrumental in putting an end to an aversive experience. Such a distinction between an appetitively motivated attack behavior and an aversively motivated defense behavior may have its counterpart in the distinction made by Wasman and Flynn (1962) between the 'quiet biting' type and the 'affective' type of attack elicitated in the cat. The latter distinction was based at first on the mere observation of the behavior induced in the stimulated cat; but it appeared in later experiments that a learned escape response (escape from tail shock by jumping onto a stool) could be transferred to hypothalamic stimulations that yielded 'affective' attack accompanied by vocalization, but never to those stimulations that yielded 'quiet biting' attack (Adams & Flynn, 1966). If we leave the behavior induced by brain stimulation, the question now arises: How about the natural, spontaneous mouse-killing behavior? The two kinds of motivation may well follow each other in time, and they may also overlap and interact to some extent. 1. In the experienced killer rat, the appetitive motivation is certainly largely preponderant. This appears clearly in the following facts: (a) In the experienced killer, the availability of a mouse for killing can serve as a reinforcer in instrumental learning situations (Myer & White, 1965; Van Hemel, 1972). The observation (Myer, 1967) that killing experience increases the resistance of the behavior to the suppressive effects of punishment lends further support to the proposition that killing is self-strengthening. Positive reinforcement of killing may well derive particularly from the repeated association of the aggressive behavior with eating of part (most usually the brain) of the killed mice, (b) The 'latency' of the killing response decreases with experience (Karli, 1956), and there is also a progressive decline of the emotional components of the aggressive response, (c) Food depriva-

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tion induces immediate killing in rats that used to kill regularly with a more or less prolonged delay (unpublished observations), (d) An experienced killer rat goes on searching after the mouse and killing it, even when he has been deprived of olfactory, visual and auditory afferents (Karli, 1961), or when his reactivity has been considerably lowered by doses of chlorpromazine or of reserpine as high as 15-20 mg/kg (Karli, 1959). 2. But which are the determinants that induce some rats (and only some of them) to kill the mouse when they are presented with an animal of this species for the very first time? Anticipation of a reward, of a positive reinforcement, may in some instances play a part in the elicitation of the killing response (by reference to previous experiences with situations somehow relevant to the mouse presentation situation). But the observation of the rat's behavior shows that he is usually quite excited and seems to be 'upset' by the presence of the mouse in his cage. His aggressive behavior may then aim mainly at getting rid of something that is new, strange, aversive. If that is the case, a rat's initial mouse-killing behavior (under natural conditions as well as following a number of brain lesions) might in most instances stand for an aversively motivated defense or active avoidance behavior. Although one has to bear in mind the somewhat schematic character of the outlined distinction, it is of interest to examine within such a framework the neural mechanisms underlying each one of these two different (in fact opposed) motivational states with their behavioral expression.

Appetitively

motivated killing behavior (in the experienced killer rat)

We may briefly examine the part taken by three central nervous structures: The lateral hypothalamus, the amygdala, the ventral mesencephalic tegmentum. Lateral hypothalamus Electrical stimulation of various sites (mostly in the region of the medial forebrain bundle, in the posterior two-thirds of the lateral hypothalamus) elicits an immediate killing response in the rat which usually kills with a more or less prolonged delay (Vergnes & Karli, 1969). Conversely, bilateral lesions placed within this region entail a

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long-lasting abolition of the killing response (Karli & Vergnes, 1964). In most cases, there is a profound behavioral deficit affecting various kinds of motivated behavior. This is due to the fact that the lateral hypothalamus (and the fiber systems running through it) are involved in many processes that give rise together to an appetitive motivation. So an activation of the lateral hypothalamic area may bring simultaneously into play: (a) A selective facilitation of the reception and transmission of sensory information arising from relevant goal objects. In relation to attack behavior, it was shown that a lateral hypothalamic stimulation induces a very sensitive field around the muzzle in the cat (MacDonnell & Flynn, 1966) as well as in the rat (Smith, 1972). On the other hand, a unilateral lesion of this site entails an ipsilateral sensory deficit the nature of which is not yet clearly understood (Marshall, Turner, & Teitelbaum, 1971; Turner, 1973). (b) A non-specific behavioral arousal as well as a non-specific descending facilitation of the spinal reflexes which, in their turn, facilitate both the appetitive and the consummatory phases of any kind of motivated behavior, (c) More or less specific processes of positive reinforcement, be the reward effects anticipated or actually derived from an already ongoing behavior. It may be recalled here that the effective stimulation sites (as regards elicitation of 'cold-blooded' killing) are also self-stimulation sites. Amygdala Bilateral lesions limited to the centromedial region of the amygdala entail a long-lasting abolition of the killing response; amygdaloid lesions sparing this centromedial region have little or no effect upon the killing behavior (Karli & Vergnes, 1965; Karli, Vergnes, Eclancher, Schmitt, & Chaurand, 1972). Seemingly at variance with the results of the lesion experiments is the fact that an electrical stimulation of the amygdala results regularly in an immediate inhibition of any ongoing killing response, the killer rat resuming its aggressive behavior almost immediately when the stimulation is discontinued. But it must be added that the stimulations which inhibit the killing behavior always prove to be epileptogenic, so their inhibitory effect results most probably from an interference of the seizure discharge with the normal functioning of the amygdala (Vergnes & Karli, 1969). Thus it appears that the centromedial amygdala exerts an important

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facilitating influence upon the release of the killing behavior. As to the mechanisms underlying such an influence, the following suggestions can be offered: The amygdala may play an important part in the anticipation of any reward to be derived from mouse killing, through reference to the laid-down traces of past experiences; furthermore, the amygdala seems to be an important link in the chain of mechanisms through which intracentral as well as peripheral excitatory feedback amplifies and prolongs an emotional response with its possible consequences upon social behavior. Ventral mesencephalic tegmentum The 'cold-blooded' type of mouse-killing behavior can be elicited by electrical stimulation of ventral tegmental sites which are also selfstimulation sites (Chaurand, 1973). Conversely, lesions of the ventromedial tegmentum entail a transient abolition of mouse killing as well as a transient suppression of self-stimulation at lateral hypothalamic sites (Chaurand, Schmitt, & Karli, 1973).

Aversive motivations and their behavioral

expression

First of all, it must be stressed that an aversive experience can have two rather opposed behavioral effects, according to its nature and to its intensity. On the one hand, it may induce the 'affective' kind of mouse-killing behavior standing for a defense or active avoidance behavior; but on the other hand, it may well induce a tendency to retreat or to flee, and such a tendency would obviously interfere with an ongoing appetitively motivated killing response. When examining the brain mechanisms mediating the behavioral effects of aversive experiences, one has to take into consideration at least three closely related groups of factors and mechanisms, namely those concerning: (a) A general level of non-specific responsiveness; (b) the more specific emotional responsiveness to aversive experiences; and (c) behavioral-emotional adaptations shaped by the life-history. The interpretation of the results obtained in both lesion and stimulation experiments is not an easy one, as we probably interfere in most experiments with more than one of these schematically separated processes and underlying mechanisms.

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91

The rat's nonspecific responsiveness It so happens that most if not all of the brain lesions that may elicit mouse-killing behavior in the natural non-killer are also lesions that entail some kind of hyperreactivity (the precise nature of which can be quite different from one case to another). Destruction of the following structures is in this respect more or less effective: Olfactory bulbs (Vergnes & Karli, 1963; Karli, Vergnes & Didiergeorges, 1969), septum (Miczek & Grossman, 1972), ventromedial hypothalamus (Eclancher & Karli, 1971), dorsomedial thalamus (Eclancher & Karli, 1968), raphe nuclei (Grant, Coscina, Grossman & Freedman, 1973; Vergnes, Mack & Kempf, 1973), mesencephalic central grey (Chaurand et al., 1972). The hyperreactivity of the rat deprived of its olfactory bulbs may be due to a great extent to the sudden loss of behavioral-emotional adaptations based on olfactory information. The mere loss of olfactory information as such emanating from the mouse (following destruction or removal of the nasal mucosa) is not sufficient to elicit mouse killing (Alberts & Friedman, 1972; Spector & Hull, 1972). Thus it appears that the role played by the olfactory bulbs goes beyond the mere transmission of olfactory cues. The increased elimination of urinary catecholamines in the bulbectomized rat may also be an indication of the loss of some emotional adaptations (Jund, Canguilhem & Karli, 1971). The non-killer deprived of olfactory bulbs starts killing only if he is kept in isolation after the operation. If the bulbectomized animals are kept in groups, vicarious behavior adaptations can develop on the basis of social interactions and sensory information other than olfactory, thus preventing the appearance of mouse-killing behavior (Karli et al., 1969, 1972). The septal lesioned rats are clearly hyperreactive. But the lesion induces killing behavior only in rats having had little or no experience with mice (Miczek & Grossman, 1972); in rats accustomed to the presence of a mouse in their cage, the septal lesion never induces mouse-killing behavior (Karli, 1960). On the other hand, painful electric shock which does not elicit mouse killing in the intact rat (Karli, 1956) proves effective when combined with a septal lesion (Miley & Baenninger, 1972). Most of the rats lesioned in the ventromedial hypothalamus are again clearly hyperreactive and often difficult to handle; but only about one-third of them start killing mice, the proportion being

92 Pierre Karli significantly higher when the hypothalamic lesion has been made at an early age (Eclancher & Schmitt, 1972). There is no correlation between the postoperative development of a more or less important hyperphagia and the display of mouse-killing behavior (Eclancher & Karli, 1971). Furthermore, the lesioned animals show decreased aggressive interactions in a food competition situation but a clear facilitation of both pain-induced aggression and acquisition as well as performance of active avoidance responses (Grossman, personal communication). Taken together, these facts suggest that the lesioned rat is not induced to go for a new source of food and to engage in an appetitively motivated mouse-killing behavior; his interspecific aggressiveness may rather result from an enhanced responsiveness to aversive stimulations. The last structure to be taken briefly into consideration, namely the mesencephalic central grey, will best help us to make the transition from the simple notion of an increased responsiveness (regardless of the precise nature of the latter) to the more specific notion of an altered emotional responsiveness to aversive experiences (which in fact has already been touched upon). The central grey lesioned animals are hyperactive in the open field (Vergnes & Chaurand, 1973) which indicates some kind of increased responsiveness. But the lesion very seldom induces mouse-killing behavior in natural non-killers. As a matter of fact, the central grey lesion has another obvious effect: It greatly reduces the fear responses (the animals defecate much less in the open field as well as upon handling; vocalization upon handling is often completely abolished), and it clearly facilitates the killing behavior in animals that, prior to the operation, used to kill with a more or less prolonged delay. As the same animals show hyperphagia (Chaurand et al., 1972) as well as a lasting facilitation of lateral hypothalamic self-stimulation (Schmitt, 1972), one is tempted to conclude that a decreased emotional responsiveness to aversive experiences brings about a general facilitation of various appetitively motivated behaviors. Conversely, as we shall see in a moment, a central grey stimulation with aversive effects inhibits in most instances any ongoing killing response in the experienced killer rat; it may well be that an aversively motivated tendency to avoid and to retreat interferes here with the appetitively motivated tendency to approach and to kill. The rat's emotional responsiveness to aversive experiences Some of the above-mentioned structures (namely, the ventromedial

Aggressive behavior and its brain mechanisms in rats

93

hypothalamus, the dorsomedial thalamus and the mesencephalic central grey) seem to constitute a medial periventricular system which has aversive effects when activated. The rat learns readily to switch off any stimulation affecting one or the other of these periventricular structures. But it also appears that the behavioral effects of the electrical stimulation may be quite different from one site to another. At a number of medial hypothalamic sites (Vergnes & Karli, 1970) and at a few sites in the immediate vicinity of the aqueduct (Chaurand et al., 1972), the stimulation elicits the 'affective' type of mouse killing in the natural non-killer. At many more sites, the stimulation inhibits regularly an ongoing killing response in the killer rat. But even this inhibitory effect is somewhat different from one structure to another. Central grey stimulations inhibit an ongoing aggression and they provoke flight responses at slightly higher intensities; in the absence of a mouse (in the absence of any appetitive motivation?), the lower stimulation intensities may already provoke a clear flight response. Dorsomedial thalamic stimulations entail an immediate inhibition of the killing behavior, but they do not induce flight responses even at higher stimulation intensities (Vergnes & Karli, 1972). Finally, medial hypothalamic stimulations often provoke flight responses which of course interrupt an ongoing aggression; but the flight response is usually not preceded by an actual inhibition of the killing behavior. A precise and coherent understanding of the mechanisms mediating the differential behavioral effects of these brain stimulations to which the rat learns readily to put an end by pressing a lever remains one of the major problems to be solved in this field. Developmental factors The rat's life-history is important in determining whether or not an adult rat will display mouse-killing behavior. By repeatedly exposing the animals to both food deprivation and competition for food, the incidence of mouse-killing behavior can be increased in a group of rats (Heimstra, 1965), whereas early social contacts with mice reduce greatly the incidence of the killing response in the adult rat (Denenberg, Paschke, & Zarrow, 1968; Myer, 1969). Sexual hormones control to some extent the shaping of socialemotional adaptations through intraspecific social interactions. For example, androgenic hormones play a trivial role in the control of mouse-killing behavior in the adult experienced killer rat; but they

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are important in the development and in the initial release of this interspecific aggressive behavior (Karli et al., 1969). The amygdala seems to play a key role in mediating the effects of early social interactions upon the development of behavior traits, in the progressive shaping of social-emotional adaptations during ontogenesis, and more specifically in the inhibition (or the nondevelopment) of mouse-killing behavior. The experimental evidence shows that lesions of the amydgala made at an early age greatly interfere with the inhibition (or the nondevelopment) of the killing behavior during ontogenesis in each one of the three following instances: (a) In the otherwise intact rat 90 out of 100 of the amygdaloid-lesioned rats kill mice, as compared with 15 out of 100 killer rats in the control group (Eclancher & Schmitt, 1972); (b) in the rat deprived of olfactory bulbs and kept in a group the postoperative social interactions do not prevent the development of mouse-killing behavior; they do not compensate in the amygdaloid-lesioned animal for the loss of adaptations based on olfactory information (unpublished observations); and (c) in the rat brought up together with a mouse, in about 60 out of 100 of the amygdaloid-lesioned animals, early social contacts between the two species do not prevent the rat from becoming a killer rat (unpublished observations). There seems to be little doubt that the amygdala plays an important part in the control of mouse-killing behavior both during ontogenesis and in the adult animal. This has led us to collaborate with the biochemists of the Centre de Neurochimie with the aim of uncovering in the amygdala neurochemical correlates of various aspects of the rat's mouse-killing behavior. The following recent result is worth mentioning: The activity of choline-acetyl-transferase is higher in the amygdala of the killer rat than in the amygdala of the non-killer; if the latter is converted into a killer rat through an ablation of the olfactory bulbs, the local activity of the enzyme goes up to the level which characterizes the natural killer rat's amygdala (Ebel, Mack, Stefanovic, & Mandel, 1973). It has been pointed out previously how difficult it is to establish precise causal relationships between behavioral and neurochemical differences. But it is in this direction that important contributions can be made to the study of the basic problem of what roles genetic and experiential factors play in the development of aggressive behavior. Our knowledge of the brain mechanisms underlying aggressive be-

Aggressive

behavior and its brain mechanisms in rats

95

havior is still quite fragmentary; yet it has come to a point where it appears both possible and most desirable to study these mechanisms in a developmental perspective with an interdisciplinary approach.

REFERENCES Adams, D., & Flynn, J. P., 1966, Transfer of an escape response from tail shock to brain-stimulated attack behavior. Journal of the Experimental Analysis of Behavior, 9:401-410. Alberts, J. R., & Friedman, M. I., 1972, Olfactory bulb removal but not anosmia increases emotionality and mouse-killing. Nature, 255:454-455. Chaurand, J. P., 1973, Etude de la participation fonctionnelle de certaines structures mésencéphaliques au déterminisme du comportement d'agression interspécifique Rat-Souris. Thèse de Doctorat-ès-Sciences, Université Louis Pasteur de Strasbourg. Chaurand, J. P., Schmitt, P., & Karli, P., 1973, Effets de lésions du tegmentum ventral du mésencéphale sur le comportement d'agression Rat-Souris. Physiology and Behavior, 10:507-515. Chaurand, J. P., Vergnes, M., & Karli, P., 1972, Substance grise centrale du mésencéphale et comportement d'agression interspécifique du Rat. Physiology and Behavior, 9:475-481. Denenberg, V. H., Paschke, R. E., & Zarrow, M. X., 1968, Killing of mice by rats prevented by early interaction between the two species. Psychonomic Science, 11:39. De Sisto, M. J., & Huston, J. P., 1971, Aggression and reward from stimulating common sites in the posterior lateral hypothalamus of rats. Communications in Behavioral Biology, Part A, 6:295-306. Ebel, A., Mack, G., Stefanovic, V., & Mandel, P., 1973, Activity of cholineacetyl-transferase and acetylcholinesterase in the amygdala of spontaneous mouse-killer rats and in rats after olfactory lobe removal. Brain Research, 57:248-251. Eclancher, F., & Karli, P., 1968, Lésion du noyau dorso-médian du thalamus et comportement d'agression interspécifique Rat-Souris. Comptes Rendus de la Société de Biologie, Paris, 762:2273-2276. Eclancher, F., & Karli, P., 1971, Comportement d'agression interspécifique et comportement alimentaire du Rat: effets de lésions des noyaux ventromédians de l'hypothalamus. Brain Research, 26:71-79. Eclancher, F., & Schmitt, P., 1972, Effets de lésions précoces de l'amygdale et de l'hypothalamus médian sur le développement du comportement d'agression interspécifique du Rat. Journal de Physiologie, Paris, 65:231 A. Grant, L. D., Coscina, D. V., Grossman, S. P., & Freedman, D. X., 1973, Muricide after serotonin depleting lesions of midbrain raphe nuclei. Pharmacology, Biochemistry and Behavior, 7:77-80. Heimstra, N. W., 1965, A further investigation of the development of mousekilling in rats. Psychonomic Science, 2:179-180. Jund, A., Canguilhem, B., & Karli, P., 1971, Catécholamines urinaires et comportement d'agression interspécifique du Rat. Comptes Rendus de la Société de Biologie, Paris, 765:1998-2004.

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Karli

Karli, P., 1956, The Norway rat's killing-response to the white mouse. An experimental analysis. Behaviour, 10:81-103. Karli, P., 1959, Action de substances dites tranquillisantes sur l'agressivité interspécifique Rat-Souris. Comptes Rendus de la Société de Biologie, Paris, 755:467-469. Karli, P., 1960, Effets de lésions expérimentales du septum sur l'agressivité interspécifique Rat-Souris. Comptes Rendus de la Société de Biologie, Paris, 754:1079-1082. Karli, P., 1961, Rôle des afférences sensorielles dans le déclenchement du comportement d'agression interspécifique Rat-Souris. Comptes Rendus de la Société de Biologie, Paris, 155:644-646. Karli, P., & Vergnes, M., 1964, Dissociation expérimentale du comportement d'agression interspécifique Rat-Souris et du comportement alimentaire. Comptes Rendus de la Société de Biologie, Paris, 158:650-653. Karli, P., & Vergnes, M., 1965, Rôle des différentes composantes du complexe nucléaire amygdalien dans la facilitation de l'agressivité interspécifique du Rat. Comptes Rendus de la Société de Biologie, Paris, 159:754-756. Karli, P., Vergnes, M., & Didiergeorges, F., 1969, Rat-mouse interspecific aggressive behavior and its manipulation by brain ablation and by brain stimulation. In S. Garattini & E. B. Sigg (Eds.), Aggressive Behaviour. Amsterdam, Excerpta Medica. Karli, P., Vergnes, M., Eclancher, F., Schmitt, P., & Chaurand, J. P., 1972, Role of the amygdala in the control of mouse-killing behavior in the rat. In B. E. Eleftheriou (Ed.), The neurobiology of the Amygdala. New York Plenum Press. Mac Donnell, M. F., & Flynn, J. P., 1966, Control of sensory fields by stimulation of hypothalamus. Science, 252:1406-1408. Marshall, J. F., Turner, B. H., & Teitelbaum, P., 1971, Sensory neglect produced by lateral hypothalamic damage. Science, 174:523-525. Miczek, K. A., & Grossman, S. P., 1972, Effects of septal lesions on inter- and intraspecies aggression in rats. Journal of Comparative and Physiological Psychology, 79:37-45. Miley, W. M., & Baenninger, R., 1972, Inhibition and facilitation of interspecies aggression in septal lesioned rats. Physiology and Behavior, 9:379-384. Myer, J. S., 1967, Prior killing experience and the suppressive effects of punishment on the killing of mice by rats. Animal Behaviour, 15:59-61. Myer, J. S., 1969, Early experience and the development of mouse-killing by rats. Journal of Comparative and Physiological Psychology, 67: 46-49. Myer, J. S., & White, R. T., 1965, Aggressive motivation in the rat. Animal Behaviour, 25:430-434. Panksepp, J., 1971, Aggression elicited by electrical stimulation of the hypothalamus in albino rats. Physiology and Behavior, 6:321-329. Schmitt, P., 1972, Effets de lésions de la substance grise centrale du mésencéphale sur les réponses de 'switch-off' et d'autostimulation au niveau de l'hypothalamus. Journal de Physiologie, Paris, 65:501 A. Smith, D. A., 1972, Increased perioral responsiveness: A possible explanation for the switching of behavior observed during lateral hypothalamic stimulation. Physiology and Behavior, 8:617-621. Spector, S. A., & Hull, E. M., 1972, Anosmia and mouse-killing by rats: A nonolfactory role for the olfactory bulbs. Journal of Comparative and Physiological Psychology, 50:354-356.

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Turner, B. H., 1973, Sensorimotor syndrome produced by lesions of the amygdala and lateral hypothalamus. Journal of Comparative and Physiological Psychology, 82:37-41. Van Hemel, P. E., 1972, Aggression as a reinforcer: Operant behavior in the mouse-killing rat. Journal of the Experimental Analysis of Behavior, 17:231245. Vergnes, M., & Chaurand, J. P., 1973, Effets comportementaux de lésions de la partie postérieure de la substance grise periaqueducale. Comptes Rendus de la Société de Biologie, 167:351-356. Vergnes, M., & Karli, P., 1963, Déclenchement du comportement d'agression interspécifique Rat-Souris par ablation bilatérale des bulbes olfactifs. Action de l'hydroxyzine sur cette agressivité provoquée. Comptes Rendus de la Société de Biologie, Paris, 757:1061-1063. Vergnes, M., & Karli, P., 1969, Effets de la stimulation de l'hypothalamus latéral, de l'amygdale et de l'hippocampe sur le comportement d'agression interspécifique Rat-Souris. Physiology and Behavior, 4:889-894. Vergnes, M., & Karli, P., 1970, Déclenchement d'un comportement d'agression par stimulation électrique de l'hypothalamus médian chez le Rat. Physiology and Behavior, 5:1427-1430. Vergnes, M., & Karli, P., 1972, Stimulation électrique du thalamus dorsomédian et comportement d'agression interspécifique du Rat. Physiology and Behavior, 9:889-892. Vergnes, M., Mack, G., & Kempf, E., 1973, Lésions du raphé et réaction d'agression interspécifique Rat-Souris. Effets comportementaux et biochimiques. Brain Research, 57:61-14. Wasman, M., & Flynn, J. P., 1962, Directed attack elicited from hypothalamus. Archives of Neurology, 6:220-227. Woodworth, C. H., 1971, Attack elicited in rats by electrical stimulation of the lateral hypothalamus. Physiology and Behavior, 6:345-353.

ABSTRACT The rat's mouse-killing behavior provides a tool for studying the neural mechanisms underlying the appetitively motivated attack behavior (in the experienced killer rat) as well as the neural mechanisms involved in the elicitation of the 'affective' kind of attack standing for an aversively motivated defense or active-avoidance behavior (when the rat is presented with a mouse for the first time, under natural conditions or following a number of brain lesions). The life-history takes an important part in determining whether or not an adult rat will display mouse-killing behavior. The amygdala appears to play a key role in mediating the effects of early social interactions in the progressive shaping of social-emotional adaptations during ontogenesis and more specifically in the inhibition (or the nondevelopment) of the rat's mouse-killing behavior.

RÉSUMÉ Le comportement d'agression interspécifique Rat-Souris permet d'étudier non seulement les mécanismes nerveux qui participent au déterminisme d'une réac-

98

Pierre Karli

tion d'attaque sous-tendue par une motivation de nature appétitive (chez le rat tueur qui a l'expérience de ce comportement), mais également ceux qui sont responsables du déclenchement d'une agression dont la motivation est de nature aversive et qui a la signification d'un comportement de défense ou d'évitement actif (chez le rat confronté avec une souris pour la première fois, soit dans des conditions naturelles, soit à la suite d'une lésion nerveuse centrale). Le 'vécu' de l'animal détermine pour une large part son comportement vis-à-vis de l'espèce Souris à l'âge adulte. Les données expérimentales montrent que l'amygdale joue un rôle essentiel dans l'élaboration des adaptations socio-émotionnelles tout au long de l'ontogenèse, et plus particulièrement dans l'inhibition (ou le nondéveloppement) de l'agressivité interspécifique du rat.

The genesis of aggressive criminality: Implications of a study of crime in a Danish twin study K A R L O. C H R I S T I A N S E N University

of

Copenhagen

Criminality may by definition be considered expressions of aggressiveness. Most crimes can be described as 'crimes against...'. Sutherland and Cressey (1966), in their well-known criminological textbook, define crime in this way: 'Crime may be considered... to involve three elements: a value which is appreciated by a group or a part of a group which is politically important; isolation of or cultural conflict in another part of this group so that its members do not appreciate the value or appreciate it less highly and consequently tend to endanger it; and a pugnacious resort to coercion decently applied by those who appreciate the value to those who disregard the value' (p. 15-16). Later Cressey added a fourth point: 'Political declaration that behavior endangering the value is henceforth to be a crime' (Sutherland & Cressey, 1970, pp. 11-12). This definition implies that a crime is an attack on more or less generally accepted social values. The same point is emphasized in several other general descriptions or definitions of crime. Crimes are asocial or antisocial acts which are harmful, immoral and universally condemned (Void, 1958). The two French sociologists, Emile Durkheim and Paul Fauconnet, have described crime in a way which makes its aggressive character explicit. In Fauconnet's (1920) book, La résponsabilité, it is expressed more or less like this: Crime threatens social solidarity. A theft does not result in a financial loss alone, for then it would be enough to pay compensation. It also hurts one of the strongest human feelings embodied in the right to possess; crime is an attack on honest people's belief in the community, and therefore it is necessary to punish.

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Karl O. Christiansen

A strong element of aggressiveness is obviously present in crimes against the person, most clearly, perhaps, in crimes of violence, but sexual offenses and even normal sexual behavior often reveal aggressive strains. There is also a certain association between aggressiveness and the severity of punishment. The most aggressive crimes will as a rule be punished by the most severe sanctions, and vice versa: The most harsh punishments are, in Western cultures, generally inflicted on persons who have committed the most aggressive crimes. On the other side, it must be added that the length of sentence is not a simple function of the cruelness and aggressiveness demonstrated when the criminal act was committed. The association exists, but it is of a general character. The aggressive element in offenses against property may be less evident, but in many cases it is clearly demonstrated. Theft is defined in Danish law as an act which is performed for the sake of gain, but among so-called 'thefts with atypical motive', i.e., thefts in which the acquisitive element, at least apparently, is absent, aggressiveness often plays an important role. In a small study of such thefts the author found a number of cases where revenge had played an important role in the genesis of the crime (Christiansen, 1946). Thefts described as 'stealing for the sake of stealing' are often of an aggressive nature (Healy, 1915; Healy & Bronner, 1936). In two cases (Christiansen, 1946) fraud and embezzlement were committed at different times against the same 70-year-old merchant by two frustrated employees who, without knowing each other, apparently acted from a more or less overt motive for revenge. The youngest of the two employees revealed also a clear and more overt acquisitive element. Probably irrational motives with elements of aggression are contributory causes of most crimes against property, even if the acquisitory purpose is a dominating element in the planning and perpetration of the crime.

Early twin studies of criminality The German psychiatrist, Johannes Lange (1929), was the first who performed a thorough study of criminality among twins. An investigation of 30 same-sexed pairs yielded results which he interpreted as conclusive evidence of the dominating influence which heredity exerts on crime. Among 13 monozygotic pairs he found 10 concordant pairs

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101

and among 17 dizygotic pairs only two concordant pairs when concordance was defined as offenses sanctioned by imprisonment. This difference is significant, and Lange formulated his conclusions as follows: 'As far as crime is concerned, monozygotic twins on the whole react in a definitely similar manner; dizygotic, however, behave quite differently. In accordance with the significance of the twin method we must conclude from this that heredity plays a quite preponderant part among the causes of crime' (Lange, 1929: 14). This conclusion has been repeated, with relatively minor modifications by later students (Legras, 1932; Rosanoff, Hardy & Rosanoff, 1934; Stumpfl, 1936; Kranz, 1936; Borgstrom, 1939; Yoshimasu, 1941, 1965). Although the frequencies in some of the studies differ greatly from his findings, Lange's conclusion, on the whole, holds true. Only four of the 10 samples studied display a statistically significant difference between monozygotic (MZ) and dizygotic (DZ) pairs with respect to delinquency or crime. The results of the earlier investigations appear in Table 1. Table 1. Concordance rates in previous criminological twin studies Monozygotic No. of Concordance pairs (percent) Lange (1929) Legras (1932) Kranz* (1936) Stumpfl* (1936) Borgstrom (1939) Rosanoff et al. (1941) Juv. delinq. males Juv. delinq. females Adult crime, males Adult crime, females Yoshimasu (1961) Total

Dizygotic No. of Concorpairs ance (percent)

P

13 4 31 18 4

76.9 100.0 64.5 61.1 75.0

17 5 43 19 5

11.8 0.0 53.5 36.8 40.0

—

MMMZ

MMDZ

FFMZ

FFDZ

325 71 25 0.521 0.148 3.53

611 120 15 0.222 0.110 2.01

328 14 3 0.353 0.026 13.62

593 27 2 0.138 0.025 5.64

M-MF

F-MF

MMUU

FFUU

1547* 172* 6* 0.250

1547* 24* 6* 0.035 0.016 2.25

112 40 10 0.400 0.223 1.79

70 6 0

0.111 2.25

0.000

0.043 -

* Persons

The comparison of the twin coefficients under (b) above yields the opposite result of the comparison of concordance rates: In twins, female criminality is more heritable and/or more directly or indirectly communicable than male criminality. The comparisons under (c) and (d) likewise lead to conclusions which are rather different from the corresponding conclusions based on comparison of the concordance rates. Expressed in another way: Being a twin influences female MZ pairs most, then female DZ pairs, male MZ pairs, MF pairs and male DZ pairs. Male pairs of unknown zygocity come somewhat lower. Such results illustrate how important it is to relate the concordance rates to the frequency of crime within the various subgroups of twins. The twin coefficient in various population groups The problem of variations in the twin coefficient in different population groups shall not be treated in detail here. However, as the results may be of some interest for the discussion on aggression and crime they are summarized below. 1. Monozygotic male pairs show higher twin coefficients with

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109

respect to crime than do dizygotic male pairs in six out of six mutually independent subgroups, defined by year of birth, place of birth and social class of father. The results are the same when the analysis is based on the wider concept of offenses (crime proper + minor offenses). 2. Monozygotic female pairs show higher twin coefficients with respect to crime than do dizygotic female pairs in five out of the six subgroups, defined above. The same is true for offences. 3. Monozygotic female pairs show higher twin coefficients for crime than do monozygotic male pairs in six out of six possible subgroups. The results are the same for the total group of offenses. 4. Dizygotic female pairs show higher twin coefficients for crime than do dizygotic male pairs in six out of the six subgroups. The same is true for offenses. 5. Male-female pairs in all subgroups show lower twin coefficients than female DZ pairs and higher coefficients than do male DZ pairs. The same holds true for offenses. 6. Male pairs of unknown zygocity show a lower twin coefficient for crime than do monozygotic male pairs in six out of six subgroups. The results are the same for offenses. 7. Male pairs of unknown zygocity show lower twin coefficients with respect to crime than do dizygotic male pairs in five out of six subgroups. The same is true for offenses in six out of six subgroups. 8. Twin pairs born between 1881 and 1895 show higher twin coefficients for crime than do pairs born between 1896 and 1910 in six out of six possible, mutually independent subgroups, defined by sex and zygocity. The results are the same for offenses. 9. Twin pairs born in rural districts show higher twin coefficients with respect to crime proper than do pairs born in towns in five out of six possible subgroups, as defined above. With respect to offenses, the same is true in three out of six possible subgroups. 10. Twin pairs coming from higher social classes show higher twin coefficients with respect to crime than do pairs coming from lower social classes in five out of six subgroups, as defined above. The same holds true for offenses in all six subgroups. 11. The twin coefficients are higher for crime proper than for offenses (crime proper + minor offenses) in 32 out of 36 possible subgroups, defined by sex, zygocity, birth year, birth place and social class of father.

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Karl O.

Christiansen

A possible explanation Before turning to the question of the occurrence of crime against the person among twins it might be expedient to look at these results from a criminological point of view. Criminology is a relatively young science, and it is impossible to point to a commonly accepted general theory. There exists, however, a number of middle-range theories or hypotheses which are based on different scientific methods and cover partly different fields of criminology. The analysis of the present material has clearly demonstrated that the twin coefficient, which in the last analysis is a function of inheritance and environment, is different in twin pairs of different zygocity and in twin pairs with different environmental backgrounds. It is easy to illustrate these results in Table 5. Table 5. Key diagram of subgroups of twin coefficient Higher TwCf

of twin pairs, according

to size

Lower TwCf

MMMZ FFMZ

Monozygotic

Dizygotic

MMDZ FFDZ

FFMZ FFDZ

Females

Males

MMMZ MMDZ

Older generations

Younger generations

Rural born

Urban born

Father: Higher social class

Father: Lower social class

Crime

Offenses

Sellin (1938) discusses the concept of group resistance to crime. This concept may throw some light on the problem of crime among twins. The group resistance against breaches of accepted norms is partly expressed through legal sanctions, but conduct norms are not necessarily embodied in law. Conduct norms also come from institutions such as the family, the church, colleagues and so on, and are effective through the actual attitude of the community to the individuals, through ridicule, estrangement, ostracism and the like. Group resistance may also be defined as the group's publicly expressed disapproval of violation of the norm. Group resistance, then, will depend on at least the following conditions: (a) The number of

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persons in the group who directly or indirectly disapprove of the violation of the norm; (b) the emotional strength of resistance of such individuals; (c) the stronger or weaker organization of the persons who take part in the group resistance; and (d) the way in which the disapproval is expressed (privately, informally or publicly, officially). In this sense, group resistance may be regarded as a sociological term combining several closely integrated social factors which influence the rate of criminality. Strong group resistance involves, other things being equal, a smaller number of criminal acts and weak group resistance involves a greater number of criminal acts. Group resistance also seems to have an influence on the selection of persons who become criminals. Sellin (1938) recommends that criminological research concentrate on persons who have violated norms (a) with high resistance potentials, (b) incorporated as personality elements, (c) which possess strong emotional tone. 'Offenders who have overcome the greatest and most pervasive group resistance probably exhibit more clearly than others the personality types which have significance for our research purposes' (Sellin, 1938, p. 44). Consequently we may postulate that, all other things being equal, strong group resistance involves a greater frequency of socially or psychologically deviating persons, and weak group resistance involves a selection of offenders who, socially and psychologically, come closer to the average population. This implies that strong group resistance is more easily overcome by persons who because of mental deviations feel the resistance less strongly, or by persons who due to unfortunate social conditions are living under special pressure. When the twin coefficient for certain subgroups of twins is high, the co-twins will be more alike than those in subgroups where the twin coefficient is low. This is true, not only with respect to criminal behavior, but also with respect to background factors. Therefore we may expect that subgroups with high twin coefficients (placed on the left side of the vertical line in the key diagram) have acted against greater group resistance than their counterparts (on the right side of the line). Is this assumption founded in fact? The answer, for most of the subgroups, is affirmative. Resistance against deviating behavior, and particularly crime, is considerably higher in the country than in towns, within older generations than within younger, in higher social classes than lower, for women than for men and against crime than against minor offenses.

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Several investigations support the assumption. Inghe (1941), in a study based on forensic psychiatric statements on persons convicted of various crimes in Sweden, concludes that mental deviations of convicted persons are found more frequently in women than in men, in the old than in the young, in rural than in urban populations, among sexual offenders and persons convicted of the more serious crimes of violence and arson rather than among other types of offenders. In a similar way Dahlberg (1948) has proved, also from Swedish data, that the frequency of mental deviations is higher among criminals in the country than in the towns, among women than among men and in the age groups where the risk of criminality is small, i.e., among older offenders than in high-risk age groups, i.e., among juvenile delinquents. In a study of Danish citizens who collaborated with the Germans during World War II, a similar connection between group resistance, frequency of collaboration and frequency of social deviations in various population groups was found (Christiansen, 1968). So far the hypothesis regarding the influence of group resistance on the frequency of deviating norm breaches and on the twin coefficient has gained support. We must reject, however, the assumption that group resistance against criminality is higher in the milieu of monozygotic than in the milieu of dizygotic twins. The group's attitude towards criminality may exert a different influence on co-twins in MZ pairs, and especially in DZ pairs, but this does not imply that the general attitude within the milieu of the two zygocity groups is different. Other factors must be decisive. We are brought back to the classical problem of inheritance and environment. The twin coefficient is not supposed to be a measure of heredity. It is an index which expresses something about the impact of environmental factors and factors in the personality, which is basically a product of heredity and environment. A greater frequency of concordance among MZ than among DZ pairs only means that similar hereditary factors and/or environmental conditions result in greater likelihood of similarity in social behavior. The first condition for discriminating between the two sets of basic factors is, according to Gottesman and Shields (1972), that MZ twins are not especially predisposed to criminality. It is definitely not fulfilled. In MZ pairs, the frequency of crime is 14.8 %; in DZ pairs it is 11.0%. This source of error, however, is eliminated by comparing MZ and DZ pairs with respect to the twin coefficient, a fraction in which

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the frequency of criminal persons in the corresponding twin population is introduced as the denominator. The second condition, that possible crime factors in the environments of MZ co-twins are not systematically more alike than those of DZ co-twins, is probably not fulfilled. At any rate, it has hitherto not been possible to demonstrate that it must be the case. Offenses according to degree of aggressiveness Thus far, criminality has been classified into two main categories: Minor offenses against the Special Laws, and crimes which are offenses against the Criminal Code. We shall now introduce a subdivision of the latter category. The concept of 'minor offenses' is retained as a subgroup so that three types of offenses will be analyzed: (a) Violence and sexual offenses (VS) occurring alone (about three-fifths of the cases) or together with other offenses (two-fifths); (b) other offenses against the Criminal Code (P + ), almost exclusively property offenses; and (c) offenses against the Special Laws (SL). In this classification the VS crimes, which are also called crimes against the person, are offenses which display the aggressive element of criminality most clearly, and they are, in most societies, considered the most grave and dangerous breaches of the law. The SL type crimes are the most benign and, with the exception of some alcohol offenses, as a rule do not betray any open aggression. The P + type crimes which include property offenses and a few crimes without violence against the person are placed somewhere on the line between the two ends of the scale, for instance, destruction of property close to the aggressive pole and embezzlement among the least-aggressive criminal acts. Thus we assume that crimes against the person provoke the highest group resistance and special law offenses the lowest, some of these norm violations now and then being regarded as quite acceptable behavior. According to what was demonstrated about the correlation between group resistance and the twin coefficient, the coefficient should be highest for VS type, lower for P + type and lowest for SL type offenses. Table 6 shows the distribution of the three kinds of offenses among the co-twins in male monozygotic and male dizygotic twin pairs. Among 18 MZ pairs registered for violence or sexual offenses five are concordant (registered for the same type of offense). This gives a pairwise concordance rate of 28 % and a proband concordance rate of

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Table 6. Male MZ pairs and male DZ pairs, according to type of offense: Violence and/or sexual offenses (VS), other Criminal Code offenses (mostly property offenses P + ), Special Law offenses (SL), and no offenses (No Off.), in the co-twins MZ Pairs TWIN I T W I N II

VS P+ SL No Off. Total

VS 5 2 1 2 10

P+ 2 15 5 11 33

SL 0 8 12 23 43

No Off. 6 7 33 0 46

Total 13 32 51 36 132

SL 2 6 5 36 49

No Off. 5 33 39 0 77

Total 11 51 53 76 191

DZ Pairs TWIN I T W I N II

VS P+ SL No Off. Total

VS 3 3 2 11 19

P+ 1 9 7 29 46

44 %. Among 27 DZ pairs, three are concordant, resulting in pairwise and proband concordance rates of 11% and 20%, respectively. Within 50 MZ pairs with property offenses, etc., 15 are concordant, with pairwise and proband concordance rates of 30% and 46% respectively. Within 90 DZ pairs, nine are concordant which gives pairwise and proband concordance rates of 10% and 18% respectively. Eighty-two MZ pairs with special law offenses include 12 concordant pairs; the pairwise and proband concordant rates are 15% and 26%, respectively. Ninety-seven DZ pairs count five concordant pairs, the pairwise and proband concordance rates being 5 % and 9 % respectively. A summary of the results is presented in Table 7 which also includes data on the expected offense rates and the twin coefficients. Pairwise and proband concordance rates are higher in MZ than in DZ pairs for all types of offenses. In both MZ and DZ pairs they are higher for VS and P + offenses which are on the same level and lower for SL offenses. It might be reasonable, therefore, to conclude that hereditary or environmental factors exert a certain influence on all three types of

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Table 7. Number of criminal and concordant pairs, pairwise concordance rates (PWCR), proband concordance rates (PRCR) and twin coefficients, according to type of offense among 325 male MZ and 611 male DZ twin pairs MZ Pairs No Crim No Cone PWCR PRCR Expected TwCoef

VS 18 5 0.278 0.435 0.035 12.43

P+

50 15 0.300 0.463 0.100 4.62

SL 82 12 0.146 0.255 0.145 1.77

DZ Pairs VS 27 3

0.111 0.200 0.025 8.00

P+

88 9 0.102 0.186 0.079 2.35

SL 97 5 0.052 0.098 0.083 1.17

offenses, but apparently greater influence on offenses against the Criminal Code than on offenses against Special Laws. If, however, one looks at the twin coefficient, which tells how much the proband concordance rate increases in relation to the probability of one of the twins becoming a criminal, the picture changes. Then it becomes obvious that both M Z and DZ pairs with crimes against the person show higher coefficients than pairs with other crimes against the Criminal Code (P + ), and, at the bottom, we find pairs with Special Law offenses. The twin coefficient is higher for M Z than for DZ pairs within all three types of offenses. These results concerning the type of offenses are in accordance with the group-resistance theory, but let it be repeated that they do not imply anything about the mutual influence of inheritance and environment on the genesis of crime. However, the investigation has established that the combined influence of heredity and environment is greater for crimes of violence than for property crimes. Or, expressed in another way, aggressiveness is more heritable or more communicable (either directly or indirectly) or both than is acquisitiveness. Some speculative generalizations The group resistance model can be applied to all breaches of norms. This has been shown for aggressiveness insofar as it is unacceptable behavior. It is evident that a number of expressions of aggression are highly condemned outright, others are criticized, some are quite acceptable, and some are considered to express valuable human qualities. They can be arranged on a continuum, with the most cruel

116 Karl O. Christiansen crimes at one pole, some types of nonpunishable roughness (e.g., in sport) around the middle and the ambitious quest for power or unremitting courage in a justified struggle at the other pole. The tolerance of various forms of aggression differs with time and place, i.e., with culture. On the basis of experiences in the field of criminology it should be expected that the most frequent occurrence of the more acceptable forms of aggression committed by the more normal section of the population will appear in cultures which demonstrate a tolerant attitude towards overt expressions of aggressiveness. On the other hand, a low incidence of the more serious forms of violence committed by a group which includes many deviants should occur in cultures characterized by high group resistance towards aggression. Cross-cultural comparisons may be one of the methods to use in such studies, but experiments may also be useful. We have quite reliable methods to assess dominating attitudes within population groups, and one would expect that psychologists nowadays are able to determine and change attitudes experimentally within small groups. Finally, it might be appropriate to draw attention to two questions which require further investigation. It would be important to have more detailed knowledge about the elements of aggression in different types of crime, particularly of the role of aggression in property offenses, preferably based on intensive studies of larger samples of offenders. This is, admittedly, a difficult field because the favorite victim of criminologists, the prisoner, frustrated by his prison environment, cannot be used as the subject of an experiment or an interview. The second question deals with the occurrence of acceptable forms of aggressiveness in relation to the dominant attitude of the group. What determines the incidence of such acts? How does the dominant attitude of the group determine which people behave in such a positive way? Probably social psychologists could help in solving these problems, if they do not have the answers already at hand.

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REFERENCES Allen, G., Harvald, B., & Shields, J., 1967, Measures of twin concordance. Acta Genetica et Statistica Medica, Basel, 77:475-481. Borgström, C. A., 1939, Eine Serie von kriminellen Zwillingen. Archiv für Rassen und Gesellschaftsbiologie, 5:334-343. von Bracken, H., 1934, Mutual intimacy in twins: Types of social structure in pairs of identical and fraternal twins. Character and Personality, 2:306. Burlingham, D., 1952, Twins: A study of three pairs of identical twins. London, Imago. Christiansen, K. O., 1946, Theft with atypical motive. In Opuscula psychiatriconeurologica Hjalmaro Helweg dedicata, Cph. 1946. Acta Psychiatrica et Neurologica, 21 (Fase. 1-3). Christiansen, K. O., 1968, Recidivism among collaborators. In M. Wolfgang (Ed.), Crime and culture: Essays in honor of Thorsten Sellin. New York, John Wiley. Dahlberg, G., 1948, A new method in crime statistics applied to the population of Sweden. Journal of Criminal Law and Criminology, 39:317-341. Dencker, S. J., 1963, Closed head injury in monozygotic twins. Lunds Universitets aarsskrift. N. F. avd. 2. Vol. 58, No. 15. Fauconnet, P., 1920, La résponsabilité. Paris, Librairie Félix Alcan. Gottesman, I., & Shields, J., 1972, Schizophrenia and genetics. New York, Academic Press. Harvald, B., & Hauge, M., 1965, Genetics and the epidemiology of chronic diseases. Washington, D.C., Public Health Service. Hauge, M., Harvald, B., Fischer, M., Jensen, K. G., Nielsen, N. J., Raebild, I., Shapiro, R., & Videbaek, T., 1968, The Danish twin register. Acta Geneticae Medicae et Gemellogiae, 77:315-332. Healy, W., 1915, The individual delinquent. Boston, Little. Healy, W., & Bronner, A. F., 1939, New light on delinquency and its treatment. New Haven, Yale University Press. Husén, T., 1959, Psychological twin research. 1. A methodological study. Stockholm, Almqvist & Wiksell. Inghe, G., 1941, Mental abnormalities among criminals. Acta Psychiatrica et Neurologica, 7(5:421-458. Kranz, H., 1936, Lebensschicksale krimineller Zwillinge. Berlin, Springer. Lange, J., 1929, Verbrechen als Schicksal. Leipzig, Georg Thieme. Legras, A. M., 1932, Psychosen en criminaliteit bij tweelingen. Utrecht, Kemink en Zoon N.V. Lehtovaara, A., 1938, Psychologische Zwillingsuntersuchungen. Helsinki, Suomalainen Tiedeakatemia. Luxenburger, H., 1930, Psychiatrische-Neurologische Zwillingspathologie. Zentralblatt für die gesamte Neurologie und Psychiatrie, 56:146, 153, 164. Mosher, L., & Feinsilver, D., 1970, Special report on schizophrenia. Rockville, Md., National Institute of Mental Health. 0stlyngen, E., 1946, Psykologisk tvillingforskning og dens problemer. Oslo, Gyldendal. Rosanoff, A. J., Hardy, L. M., & Rosanoff, I. A., 1934, Criminality and delinquency in twins. Journal of Criminal Law and Criminology, 24:932. Sellin, T., 1938, Culture conflict and crime. New York, Social Science Research Council.

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Stott, D. H., 1966, Commentary on 'The genetic determinants of differences in intelligence: A study of monozygotic twins reared together and apart' by Cyril Burt: Congenital influences on the development of twins. British Journal of Psychology, 57:423-429. Stumpfl, Fr., 1936, Die Ursprünge des Verbrechens. Dargestellt am Lebenslauf von Zwillingen. Leipzig, Georg Thieme. Sutherland, E. H., & Cressey, D. R., 1966, 1970, Principles of criminology, (6th and 7th eds.). Philadelphia, Lippincott. Void, G. B., 1958, Theoretical criminology. New York, Oxford University Press. Yoshimasu, S., 1941, Psychopathie und Kriminalität. Die Bedeutung der Erbanlage und Umwelt f ü r die Entstehung von Verbrechen im Lichter der Zwillingsforschung. Psychiatria Neurologia Japonica, 45:455-531. Yoshimasu, S., 1961, The criminological significance of the family in the light of the studies of criminal twins. Acta Criminologicae et Medicinae Legalis Japonica, 27:117-141. Yoshimasu, S., 1965, Criminal life curves of monozygotic twin pairs. 1 and 2. Acta Criminologicae et Medicinae Legalis Japonica, 31{4): 144-153; 52(5-6): 190-197. Zazzo, R., 1960a, La méthode des jumeaux. Paris, University of France Press. Zazzo, R., 1960b, Les jumeaux, le couple et la personne. Paris, University of France Press.

ABSTRACT The paper starts with some remarks on the general aggressive character of criminality and points to the existence of aggression in property offenses as well as in crimes against the person, but it focuses on results f r o m a study of crime in an unselected sample of 3,856 twins born in 1881 to 1910. Checking two registers showed that in 799 pairs at least one of the twins had been registered for offenses, 467 for offenses against the Criminal Code. The pairwise concordance rate was 35 % in M Z twins and 13 % in D Z twins, significantly lower than in previous studies. It was also shown that the twin coefficient (the ratio between the proband concordance rate and the expected frequency of crime in the corresponding twin population) was higher for older generations than for younger, higher for rural than for urban born pairs, and higher for pairs from higher social class homes than for pairs from lower class homes, higher for pairs with crimes against the person than for pairs with property offenses and higher f o r pairs with property offenses than for pairs with offenses against the Special Laws.

RÉSUMÉ L'article débute par quelques remarques sur le caractère agressif général de la criminalité et souligne l'existence de l'agression dans les atteintes à la propriété aussi bien que dans les crimes contre la personne, puis il se centre sur les résultats d'une étude du crime dans un échantillon tout venant de 3 856 jumeaux nées entre 1881 et 1910. L'exploitation de deux registres a montré que pour 799 paires au moins l'un des jumeaux a été enregistré pour délit, dont 467 pour contravention au Code Criminel. Le taux de concordance était de 35 % chez les

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jumeaux homozygotes et de 13% chez les hétérozygotes, significativement plus bas que celui de les études précédentes. Les résultats ont montré également que le 'coefficient de jumelage' (rapport entre le taux de concordance entre jumeaux et la fréquence probable de crimes dans la population correspondante de jumeaux) était plus élevé pour les générations les plus anciennes, pour les paires nées en milieu rural, pour les jumeaux provenant de classes sociales plus élevées, pour les crimes contre la personne plutôt que contre la propriété, enfin pour les paires portant atteinte à la propriété plutôt que celles contrevenant aux Lois Spéciales.

The hostile and instrumental functions of human aggression* BRENDAN GAIL RULE University of Alberta

Although aggression is a topic which has interested laymen, philosophers and scientists for many years, there remain several unresolved issues concerning the definition, and thereby the antecedents of aggression. Recently, in an extensive review of the literature, Johnson (1972) has suggested that there are many different kinds of aggressive behavior and hence there may be no single definition of aggression. Although this latter possibility can be entertained, such a position may lead to a needless proliferation of apparently unrelated ideas and results. To avoid this proliferation, a definition of aggression that encompasses the various phenomena which have been considered as manifestations of human aggression will be adopted in this paper. Because the common underlying attribute of all aggression is injury, an injurious response is considered as the defining characteristic of aggression. However, injurious responses are further classified according to the purpose served by the response. By considering the functions of aggression, issues are raised especially with regard to the aggressor's interpretation of the situation. The antecedents of focus in this approach are what many authors refer to as cognitive, rather than as* Preparation of this paper was facilitated by a Canada Council Leave Fellowship to the author who was on leave at the Developmental Division, University of Nijmegen, Nijmegen, Netherlands. The author's research reported in the paper was supported by Canada Council Grants. The author is indebted to Pieter Duker and Ad Van Assow who generously contributed bibliographic assistance and to Robert Carey, Allen Dobbs, Ronald Dyck, Willard Hartup, Gerry Leger, Andrew Nesdale and Dolf Ryks for insightful comments and helpful criticisms on various issues discussed in this paper.

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sociative, although the latter are recognized as important determinants of some aggressive responses. Definitions of aggression have differed primarily on the basis of whether or not intentions are specified by the definition. Since the inception of the frustration-aggression hypothesis, aggression has often been defined as behavior to which the goal response is injury to the person toward whom it is directed (Dollard, Doob, Miller, Mowrer & Sears, 1939; Berkowitz, 1962). While this definition is clearly based on the intentions underlying the aggressive response, other writers have attempted to eliminate intentions from their definition. For example, in his earlier work, Buss (1961) argued that aggression is simply the delivery of noxious stimuli to a victim. Similarly, Bandura and Walters (1963) have minimized the importance of intentions by defining aggression as the delivery of high intensity noxious stimuli which differ quantitatively rather than qualitatively from other responses. Bandura and Walters have admitted, however, that since aggression is really based on a social judgment by an observer, inclusion of intent for understanding socially significant behavior is appropriate. However, going beyond its appropriateness, arguments can be made for the necessity of considering intentions (Kaufmann, 1970). For example, without concern for intentions, it is not clear how accidental aggressive acts can be separated from other aggressive acts. Noting this and related problems, Feshbach (1964, 1970) pointed out that aggression may serve several functions for humans and identified the expressive, accidental, hostile and instrumental purposes of aggression. It was Feshbach's view that while aggression can be defined as injury at the descriptive level, in the interests of clarification, some form of typing of aggression is necessary at the construct level. According to Feshbach (1970), 'unintentional aggressive acts are those acts which, although resulting in injury, were not contingent upon their injurious consequences' (p. 161). Thus, unintended aggressive acts are accidental. Intentional aggressive acts, which are contingent on their injurious consequences, are not considered necessarily as conscious 'but only that the aggressive component of this behavior is an essential part of its function' (p. 161). Those intentional aggressive acts which have been given the most attention in current theory and research are those which serve either hostile or instrumental functions. Hostile aggressive behavior is that which is directed primarily at injuring another person whereas instrumental aggressive behavior is that which is directed

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toward attaining a nonaggressive goal. In instrumental aggression, the reinforcer may be obtained from the victim or from some source external to the victim. In the latter case, injury is perpetrated for money or for prestige or to gain approval from a source other than the victim (Bandura, 1969; Buss, 1961; Milgram, 1963; Silverman, 1971; Borden, Bowen & Taylor, 1971). In agreement with Feshbach's view, Buss (1971) has reversed his former position by noting that intent can be inferred by reference to the antecedents and consequences of the behavior being studied. Accordingly, he distinguishes angry aggression and instrumental aggression, a distinction which closely parallels the distinction between hostile and instrumental aggression. More recently, Feshbach (1971) has drawn a distinction between personally and socially motivated aggression, particularly as it pertains to moral judgments. He classified hostile and instrumental goals directed toward achieving one's own goal as being personally motivated aggression. In addition, he noted that many acts of aggression serve socially oriented functions. Presumably, judgments of the morality of aggression are based upon whether the aggressive response is socially versus personally motivated. However, as will be explicated in this paper, this more recent distinction has relevance not only for understanding judgments of the morality of aggression but also for understanding some of the antecedents of aggressive responses. In this paper, aggression is defined as a response resulting in injury. The response is considered hostile when the injury to the victim is the primary goal but is considered instrumental when the injury is secondary to the acquisition of a goal other than an injury to the victim. Instrumental aggression may be personally motivated or socially motivated and will be hereafter referred to as personal-instrumental and social-instrumental aggression, respectively. The usefulness of this latter distinction as well as the implications for theory depend upon whether the causes and efforts other than the injury per se differ for the functionally different aggressive responses. Although some authors have stressed the relevance of distinguishing between hostile and personal-instrumental goals (Feshbach, 1964; Buss, 1966), it is contended that the distinction between personally motivated and socially motivated aggression is a more important one. In order to support this contention, the empirical and theoretical bases for both the dichotomy between hostile and personal-instrumental aggression and that between personally versus socially motivated aggression will be presented.

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Personal-instrumental

and hostile aggressive responses

In drawing attention to the distinction between personal-instrumental and hostile aggression, Feshbach (1964, 1970) has argued that they can be distinguished primarily on the basis of their differing reinforcers. If a person's goal is attainment of an object, retrieval of the object from the victim is reinforcing, whereas if a person's goal is to hurt a victim, then the pain of the victim is reinforcing. Feshbach, Stiles and Bitter (1967) have provided some evidence for the latter aspect of this argument. In their experiment, they demonstrated that observing the pain of a provoker was reinforcing after a person had been angered. This demonstration was achieved by conditioning the verbal behavior of women after they had been angered or not angered. The women constructed sentences while observing their partners being shocked. Each time the subjects emitted a 'we' or a 'they', their partner showed evidence of pain. For the control conditions, each time the subject constructed a sentence using 'we' or 'they', a light went on. It was found that the provoked women increased the use of the word 'they' when they observed the provoker being shocked. Although other experiments (Baron, 1971a, 1971b; Geen, 1970) have failed to show that pain cues increase expression of aggression after anger arousing procedures, Baron (1973) has recently provided some supporting evidence. In his study, which minimized social altruistic goals in aggressing, subjects used greater shock 1 after being attacked when their attacker showed signs of pain. The specification of differing reinforcers implies that differing antecedents precipitate the aggressive response. If the reinforcement is attainment of an object, then the relevant antecedent condition is deprivation of that object, not attack by a provoker (Feshbach, 1970). The possibility that different stimulus conditions lead to responses whose functional significance varies has been raised in the context of controversy over the frustration-aggression hypothesis. Proponents of the frustration-aggression hypothesis (Berkowitz, 1962, 1969; Dollard, Doob, Miller, Mowrer & Sears, 1939) have defined frustration broadly 1. In experiments where shock is used as a measure of aggression, no shocks are actually administered to the other participant. Although subjects are led to believe that shocks are being delivered to their partner, the apparatus is not functional. The procedures are fully described to subjects immediately following the experimental session.

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to include among others, withholding objects, anticipated deprivation and insult. These varying antecedents are viewed as leading to functionally equivalent responses primarily aimed at injury. However, such a view has been disputed. For example, Buss (1966) has argued that attack instigates aggression which serves primarily to relieve anger, whereas pure goal blocking instigates aggression which is primarily oriented toward reducing the frustration or achieving the blocked goal. Buss (1966) specifically designed an experiment to test the hypothesis that pure goal blocking leads to aggression particularly when the aggressive response has instrumental value in achieving the goal. He found no evidence to support the notion that goal blocking led to aggression even when the aggressive response was instrumentally valuable. In his most recent treatment of these issues, Buss (1971) has claimed that the instigators of angry aggression, which is similar to Feshbach's notion of hostile aggression, are annoyers, attack and insult, whereas the instigators of non-angry instrumental aggression are competition and possession of a desired object by a target person. The latter are instances of pure goal blocking. The issue, then, appears to be to what extent different instigating conditions such as attack or pure goal blocking produce clearly differentiated effects. One way in which this issue can be clarified is to examine whether these differing conditions produce similar feelings on the part of the aggressor toward the instigation and the instigator. A study conducted in our laboratory (Rule & Percival, 1971) provided relevant data. We examined the effects of pure goal blocking and insult on aggressive responses as well as on the aggressor's feelings about the victim who instigated the aggression. The subject's personal motivation was aroused by saying that he would be judged according to his ability to teach a partner a list of nonsense syllables. Frustration was induced by the learner's failing to learn a list of nonsense syllables or was not induced by the learner's successful performance. In addition, the learner either insulted or did not insult the teacher who was administering electrical shocks as punishment for errors. The results indicated that goal blocking enhanced aggression, as did unjustified insult. Moreover, the frustration and insult manipulations produced virtually identical perceptions on the part of the subjects. In comparison to control conditions, regardless of whether he was insulted or frustrated, the subject reported that he was more annoyed, that the learner's performance was not good, that the learner did not improve his performance and that the learner's

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personal attributes were unfavorable. In this experiment, however, the functions of aggression were not separated. Increasing shock could both harm the victim as well as enable the subject to reach his goal. Nonetheless, it is evident that the antecedents which presumably differentiate the two types of aggression lead to the same internal feelings of annoyance and the same negative evaluations of the victim and his performance. The fact that similar perceptions are engaged by the two different sources of instigation is consistent with the frustration-aggression hypothesis. According to that formulation, the degree to which the instigator is perceived as the source of frustration, regardless of the specific instigating condition, enhances the likelihood of aggressive responses. However, it is possible and necessary to go beyond the frustration-aggression hypothesis to deal with the aggressor's inferences about the source of the frustration or insult. A person's inferences in any situation depend on the nature of the interaction. If a person is concerned with personal goal attainment, he will be sensitized to particular features of the situation. According to Jones and Thibaut (1958), when personal goal attainment is the interaction goal, the perceiver's primary focus is on the consequences of the other's behavior for the perceiver. The perceiver's concern is with what the other person is doing to, or for, him. Because of this, the perceiver reacts to the other person's behavior in terms of whether that person is the causal locus of his behavior. In particular, the perceiver responds to his assessment of the other person's intentions in behaving as he did. In a situation where the perceiver has been frustrated or insulted, he uses information about the extent to which the other person intended harm. Jones and Davis (1965) have referred to this as judging the degree of personalism involved in another's behavior. Judgments of personalism may include considerations of whether the harm-doer had other alternatives available, could have foreseen the consequences of his act, or know his behavior would deprive the other person of benefit or would actually harm him, each of which presumably affects the perceived appropriateness of retaliation. It is assumed that prior knowledge that the harm-doer had choice, could have foreseen the consequences, or knew harm would befall the victim increase instigation and subsequent retaliation. If the perceiver makes inferences about intentions after the harm is done (and this is likely to occur only if he is not too highly aroused), differences in aggressive retaliation are

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probably due to differential suppression of the response. Regardless of which process underlies its effect, personalism is likely to affect the expression of aggression. Some experiments bear on the assumption that personalism affects aggressive response. Jones and DeCharms (1957) found that when subjects were failing to achieve a goal because an unmotivated partner was doing poorly, they evaluated the partner more negatively than when he was apparently trying to succeed. Similarly, Lanzetta and Hannah (1969) demonstrated that subjects who themselves were trying to succeed administered more shock to a failing partner who lacked effort rather than ability. It is evident that behaviors which indicate choice in harming the actor induce aggressive retaliation. Along similar lines, Jones and Davis (1965) have proposed that apparently chronic indiscriminate aggression (Jones, Hestor, Farina & Davis, 1959) reduces aggressive retaliation. The retaliator may assume that indiscriminately aggressive or emotionally maladjusted people have no choice or are unaware of the consequences of their behavior. And, if a perceiver assumes that the attacker knew that his behavior would affect the perceiver, he is likely to retaliate (Jones & Davis, 1965). Studies on the intentions underlying aggressive acts are directly related to this issue. Pepitone and Sherberg (1957) found that subjects evaluated a harm-doer more favorably when they perceived that the harm-doer wanted to help rather than to hurt a victim (good versus bad intentions). Pieter Duker and I (Rule & Duker, 1973) found that children reported being more angry when an aggressor's intentions were to severely hurt the victim (bad) rather than to teach the victim not to transgress again (good). And, in experiments on direct physical aggression, several investigators (Epstein & Taylor, 1967; Hendrick & Taylor, 1971) have provided subjects with information that an opponent intended to deliver either a high or a low level of shock to the subject. Subjects retaliated with more shocks when the opponent intended to deliver a higher level of shock. Moreover, as Masselli and Altrocchi (1969) have suggested, the perception of the opponent's intention may actually be a more important determinant of retaliation than is actual physical attack (Greenwell & Dengerink, 1973). Finally, studies with the arbitrariness of frustration (Burnstein & Worchel, 1962; Cohen, 1955; Pastore, 1952; Rothaus & Worchel, 1960) have revealed that frustration which is apparently arbitrary increases aggression. In these studies, arbitrariness was usually manipulated by

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the frustrator's awareness that harm would befall the victim or by his choice in harming the victim. From a theoretical perspective, and supported by data, frustration or attack is judged not only by whether the instigator is perceived as the cause of the harm but also by whether he intended the harm. The factors affecting the perception of intention, which in turn determine the expression of aggression, are the same regardless of whether the instigation is goal blocking or insult. Additionally, Feshbach (1964, 1970) has noted that hostile and personal-instrumental motivations are often difficult to disentangle experimentally and in real life. Moreover, Feshbach has observed that continued expression of aggression for whatever reasons may reduce empathy toward the victim. Consequently, the noxious consequences of aggression presumably influence the subsequent behavior of the aggressor, even in personal-instrumental aggression. Combining these considerations with the evidence by Rule and Percival (1971) that the antecedent conditions which presumably differentiate these two types of aggression lead to the same feelings and perceptions, it can be concluded that the distinction is not very important. It appears that although there is some basis for distinguishing between hostile and personal-instrumental motivation by considering their specific reinforcers, especially when factors extrinsic to the victim affect the response, other considerations blur the discrimination. Only Feshbach's (1970) contention that goal blocking and insult may be differentially important for children at varying ages remains a possible but untested basis for continuing to consider the distinction.

Personally motivated and socially motivated aggressive responses Although the distinction between hostile and personal-instrumental aggressive responses blurs when the attributions, feelings and consequences other than the injury itself are considered, another function of instrumental aggression is important. Instrumental aggressive responses not only serve personal goals but also more socially oriented ones. Sears (1961) discussed prosocial aggression as 'aggression used in a socially approved way for purposes that are acceptable to the moral standards of the group'. Such aggression includes socially acceptable controls and discipline. These are injurious responses which are only a

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by-product of trying to reach a goal for another person or society. However, relatively little theoretical or empirical attention has focused on such aggression. In fact, arguments have been raised against considering injuries serving a social purpose as aggressive (Buss, 1961, 1971; Feshbach, 1964). For example, Buss (1971) has indicated that punishment is conventionally excluded from concern if it is in the context of a socially approved role such as parent, teacher, judge or dentist. In his view, of course, if the appropriate intensities are exceeded, the punishment is then labelled aggressive. Similarly, in his earlier work Feshbach (1964) referred to the dentist as engaging in accidental aggression, a view which eliminates the need to search for its antecedents. However, is can be argued that the view that dentists do not appear to be engaged in aggressive behavior may only reflect the fact that their behavior is not labelled aggressive because their 'good' intention which is to help, not to harm, the patient is recognized. The prosocial nature of the dentist's injury has been widely accepted as such and is almost a culturally accepted truism. It would be interesting to see how young children who may not yet distinguished intentions view the dentist. It may be that very young children dislike the dentist, whom they see as aggressive. Only when they separate the motivations underlying his response should they like him and then perhaps dislike only his office or what he does. If one does not define aggression in terms of its hostile connotation, but rather as an injurious response which serves different functions, injurious responses directed towards a socially approved goal are appropriately labelled as aggressive. When a prosocial aggressive response is invariably fulfilling a specialized role, and no alternative responses are available (e.g., the dentist) there is little theoretical or practical interest in ascertaining its antecedents. However, there are many role-related prosocial responses which allow for variable responses whose antecedents are of concern. Judges, parents and teachers sanction when there are other alternatives available. There are also non-role-related interpersonal situations which may engage a prosocial aggressive response. For example, one person may criticize another person in order to motivate him or one adolescent may tattle on another to prevent an even greater punishment from befalling the other adolescent. The antecedents of prosocial aggression are seen as those pertaining to the perceived norms about the value of aggression. According to Jones and Thibaut (1958), sanctions are applied in an effort to attain

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a goal which is consistent with societal norms. A parent punishes a child or a teacher punishes a pupil in order to achieve some goal that is deemed desirable for the victim. Thus, a person's perceptions of norms about the appropriateness of the aggressive response and whether it is potentially beneficial induces prosocial instrumental responses. Jones and Thibaut (1958) have referred to the perceptual orientation in punishment situations as situation matching sets. They have postulated that the causal locus of behavior may not be as relevant for information processing in such cases as it is in situations where personal goal attainment is the major interaction goal. Ascertaining the norm and how it applies in the situations is considered especially important for sanctioning behavior which occurs within the constraint of a role. Along similar lines, Kelley (1971) has suggested that when a person punishes another person there may be some limitation on the relation between attributions about intent and the aggressive response. In particular, he has claimed that while a person may take intentions into account to determine how much punishment is appropriate, he also considers some element of the act's future avoidability. Thus, Kelley has argued that judgments related to ethical considerations also serve the purpose of discouraging similar acts in the future. According to both Kelley's and Jones and Thibaut's positions, if a person is engaging in prosocial aggression, such as in sentencing a criminal for the protection of society, then attributions about the criminal's intentions may be relatively unimportant, compared with the influence of the norms about punishment and insuring that similar behavior will not occur again. Although this may be true when the norms about the aggressive responses are unambiguous, intentions are often considered as important when the norms are ambiguous. Furthermore, frequently the norms about punishment are intimately tied with consideration of intentions. Nonetheless, the mediating role of attributions of intent may be more restricted in the case of prosocial-instrumental aggression than it is in the case of hostile or personal-instrumental aggression. When acts of injury serve goals for prosocial reasons, normative concerns are likely to be more important determinants of the response. If aggression serving social goals is considered as functionally different from aggression serving personal goals, then the basic question is whether the antecedents and consequences other than the aggressive response vary for these functionally different aggressive responses. In order to examine this issue, I will discuss research in which personal

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motivation and social motivation are engaged within the design of the same experiment. In one experiment conducted in our laboratory, Lynn Hewitt and I (Rule & Hewitt, 1971) manipulated low-, medium- and high-frustration conditions in a study where subjects could administer electrical shocks as punishment for errors. In the first phase of the experiment, the subject participated as a learner. Low frustration was accomplished by the subject successfully learning a list of nonsense syllables, moderate frustration by the subject's lack of success in learning a list of nonsense syllables and high frustration by the subject's lack of success in learning a list of nonsense syllables while being berated by a peer. After the frustration manipulation, the subject participated as the teacher for the final phase of the experiment. The results demonstrated that subjects administered the most shock to their partner following high- and low-frustration conditions. We (Rule & Hewitt, 1971) interpreted these results as showing that aggressive responses in the same situation occurred for different reasons, apparently related to salience of the functions served by the aggressive response. In our study, as in other studies using this paradigm (e.g., Buss, 1966), shock could be used to harm physically and also to help the other person reach a goal. The shock administered under highfrustration conditions was interpreted as reflecting anger because these responses were accompanied by elevated cardiac activity and annoyance ratings. The data in the low- and moderate-frustration conditions provided no indications that subjects were angered or physiologically aroused. The low-frustrated subjects delivered a relatively high number of shocks similar in number to those delivered in the high-frustration condition, apparently assuming that the shocks would facilitate the other person's goal achievement. On the other hand, moderately frustrated subjects using previous failure as a comparison, apparently assumed that punishment would contribute little to the other's goal achievement and hence delivered fewer shocks. Our interpretation was that the salient function of delivering shocks may have been determined by the context in which they occurred. Shock may have been determined to hurt physically an insulting partner or to promote learning if learning seemed feasible on the basis of the subject's past experience. In this experiment, as well as in others using a similar paradigm, the effects of increasing shock levels may provide a conflict, depending on

132 Brendan Gail Rule the aggressor's predominant goal. Thus, although the teacher may wish to harm the learner by increasing the amount of shock, he also increases the learner's chances of success on the task. Alternatively, if the teacher wants a learner to succeed, he must administer more noxious shocks. Apparently, as shown in the Rule and Hewitt study, the experimental context provides a set which makes one of the conflicting goals dominant and thereby reduces the conflict. In an attempt to infer more unambiguously the aggressor's intent and to establish specific antecedents leading to one or the other use of shock, another experiment was conducted by myself and a colleague, Andrew Nesdale (Rule & Nesdale, 1973). In this experiment, situations which maximized either the motivation to help or to hurt the learner were created, thereby unconfounding the hostile and socially motivated instrumental value of aggressive acts. The subject participated as a teacher who was supposed to deliver instant electrical shock feedback to reinforce the learner's performance. However, the shocks could vary in intensity and number and duration and the teacher was told that increasing shock inflicted pain which was described in one half of the conditions as a help to performance but in the other half of the conditions as a hindrance to performance. Although the teacher's own performance carried no evaluative or monetary incentive, the learner either succeeded or failed on his task thereby winning or losing a reward himself. Moreover, the learner either insulted or did not insult the teacher. Table 1. Mean intensity of shocks as a function of the confederate's insult and the value of the aggressive responsea Geometric mean * intensity N o insult Insult Instrumental Hostile

81.82 79.95

101.25 70.94

a. Data from Rule and Nesdale (1973). Note: Higher scores indicate higher intensity shock. * These measures were computed by adding the value of 1 to all scores before log transformation and subtracting the value of 1 after the antilog was taken. Data analysis was based on log (x -f 1).

Table 1 presents the mean shock values for the insult and non-insult conditions under helping (instrumental) or hindering (hostile) instructions.

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As expected, subjects administered shock levels according to both the value of aggression and their partner's insult. Examination of the mean scores revealed that the greater intensity of shock was administered by insulted, rather than non-insulted, subjects when they were told that the shock would hurt the victim, but a lower intensity of shock was administered by insulted, rather than non-insulted, subjects when they were told that the shock would help the victim learn the syllables. Other data confirmed the nature of the motivation aroused in the situation. As can be seen in Table 2, the insulted men were more upset when the shock helped rather than hindered their provoker's performance, whereas the non-insulted men were more upset when shock hindered rather than helped their partner's performance. Table 2. Mean rating 'Upset' item as a function of the insult and the value of the aggressive responsea Insult Instrumental Hostile

3.63 2.44

confederate's

No insult 1.31 1.81

a. Data from Rule and Nesdale (1973). Note: Higher scores indicate a greater number of shocks.

Table 3 presents the mean shock values for the success and failure conditions which were presumed to potentiate prosocial instrumental aggression. The specific expectations were partially supported by the data. More shocks were administered to successful learners when the shock facilitated rather than hindered performance. However, more shocks were given to failing learners when the shock hindered rather than helped performance. It may be that failing to help another over a series of trials is in itself frustrating. In spite of the fact that the failure of the learner induced hostile aggression on the part of the teacher, the results were consistent with the idea that the antecedent conditions of the different types of aggressive response varied. The results of these experiments have important implications for procedures in the study of aggression. The introduction of the learning paradigm as a ruse for studying aggression (Buss, 1961) provided participants with the opportunity to administer physically harmful responses in a socially-sanctioned situation. However, it is clear that

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Table 3. Mean number of shocks as a function of the confederate's performance and the value of the aggressive responsea Geometric mean * intensity Success Failure Instrumental Hostile

1.08 0.98

0.96 1.31

a. Data from Rule and Nesdale (1973). Note: Higher scores indicate more unfavorable ratings. * These measures were computed by adding the value of 1 to all scores before log transformation and subtracting the value of 1 after the antilog was taken. Data analysis was based on log (x + 1).

the subjects may use shock in different ways, depending on the subject's particular set in the situation. Ambiguities in interpreting the data can thereby be introduced. In some experimental contexts, increasing shock could reflect motivation to help, rather than to hurt, when the latter is what the experimenter intended. In other situations, there may be unintended systematic differences within and between conditions which engage either the motivation to help or the motivation to hurt, thereby cancelling out expected effects. It is clear that far more attention must be given in the experimental situation to the subject's motivations and his cognitions about the effect that increasing shock has on the other person. Apart from assessing whether varying antecedents actually precipitate functionally different aggressive responses, another approach to examining the basis for the functional distinction is to ascertain observers' reactions to aggression motivated for different reasons. In particular, as postulated by Feshbach (1971), one might expect that observers would view personally motivated (hostile or personalinstrumental) aggressive responses differently from socially motivated aggressive responses. Several experiments in our laboratory have supported this idea. In these studies, subjects read a transcript of an interview which described an interviewee who engaged in a fight for one from among several different reasons. In two studies (Nesdale & Rule, 1973; Nesdale, Rule & McAra, 1973), the interviewee engaged in a fight in order to return a wallet to its rightful owner (socially motivated aggression) or to keep the wallet for himself (personally motivated aggression). Tables 4 and 5 present the mean ratings for

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Table 4. Mean moral judgments of personally versus socially motivated aggression1 Personal-instrumental Right-wrong Deserves punishment

1.98 3.11

Social-instrumental 4.74 5.47

1. Data from Nesdale and Rule (1973). Note: Higher scores indicate more positive judgments.

Table 5. Mean moral judgments of personally versus socially motivated aggression1 Personal-instrumental Right-wrong Deserves punishment

1.25 2.72

Social-instrumental 4.48 5.08

1. Data from Nesdale, Rule and McAra (1973). Note: Higher scores indicate more positive judgments.

these comparisons. The interviewee was judged as right and not deserving of punishment when he had aggressed for a socially oriented reason, in comparison to when he did so for a personal reason. In another study, we (Rule, Dyck & McAra, 1973) described the interviewee's aggression as motivated by the desire either to hurt the victim (hostile aggression) or to return a wallet to its rightful owner (social-instrumental) or to keep the wallet for himself (personalinstrumental). The results are presented in Table 6. An aggressor who hit for either hostile or personal-instrumental reasons was judged more wrong and more deserving of punishment whereas an aggressor who hit for prosocial instrumental reasons was judged more right and less deserving of punishment. From an observer's perspective, personal-instrumental and hostile aggression elicited similar judgments. In a second experiment which was almost identical to our latter study, we (Rule, Dyck & McAra, 1973) used tenth- and eleventh-grade lower-middle-class high school students as participants. The mean ratings for the different motivations are presented in Table 7.

136 Brendan Gail Rule Table 6. University student's mean moral judgments of aggression based on differing motives1

Right-wrong Deserves punishment

Hostile

Socialinstrumental

Personalinstrumental

1.70b 3.10 b

4.90„ 5.30 a

1.40b 3.00h

1. Data from Rule, Dyck and McAra (1973). Note: Higher scores indicate positive judgments. Cells having different subscripts across rows are significantly different at less than .05 level by Duncan's multiple range test.

Table 7. High school student's mean moral judgments of aggression based on differing motives1

Right-wrong Deserves punishment

Hostile

Socialinstrumental

Personalinstrumental

3-14. 3.96 a

4.96 b 5.19 b

2.12 c 3.30 c

1. Data from Rule, Dyck & McAra (1973). Note: Higher scores indicate more positive judgments. Cells having different subscripts across rows are significantly different at less than the .05 level by Duncan's multiple range test.

As can be seen in Table 7, prosocial aggression was judged as more right and less deserving of punishment than was either hostile or personal-instrumental aggression. However, in this study, personalinstrumental aggression was judged as more wrong and deserving more punishment than was hostile aggression. These latter results may be due to two major related factors. The first is that in the personal-instrumental condition, the aggressor may be seen as not only aggressing for personal reasons, but also as engaging in additional counter-normative behavior. Keeping someone else's wallet represents stealing which may provide an increment to the negative moral judgment, especially for the lower-middleclass high school students, who also perceived that the aggressor hit harder in the personal-instrumental condition than in either of the other two conditions. Although the intention underlying the response affects moral judgments, other factors such as justification and norms

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relevant to the other goals in the situation can modify the judgment of an observer. For example, negative evaluations of a personalinstrumental aggressive act are likely to be reduced if the act occurs in the service of self-protection. The second reason why the results are somewhat different between the two studies may be that the age of the participants varied. Younger persons may rely more on specific norms rather than on more general principles relating to intentions to form their judgments. Thus, the high school students may have weighted the counter-normative of the stealing goal in the personal-instrumental condition more heavily than did the college students. On the other hand, the college students may have weighted the intentional dimension more heavily than did the high school students. In summary, the results from this series of experiments on moral judgments have shown that observers' attitudes toward the same aggressive act are based to a great extent on the purpose of the aggression. Aggression committed for prosocial reasons is consistently evaluated more positively than aggression committed for personal reasons. Reactions to hostile versus personal-instrumental aggression may be affected by the age of the observers and the weighting given to other features of the situation in which the aggression occurred.

Conclusions Controversy about the definition and functions of aggression has fostered a one-sided treatment of aggressive phenomena. This treatment has focused on hostile aggression or personal-instrumental aggression, both of which are personally motivated. Although personally motivated aggression should continue to be of theoretical and empirical interest, the determinants and consequences of prosocial aggression must be investigated. By avoiding consideration of this function of aggression, phenomena such as sentencing behavior and punishment, which are of pervasive concern, have been ignored. Recognition that some aggression may be perceived as right does not, of course, support the view that it is right. The data presented in this paper have demonstrated that the distinction between personally and socially motivated aggression is a viable one. The determinants and concomitants of each differ from the

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other since expressing a given level of aggression may reflect primarily either personal or social motivation. The control of aggression depends on knowing why it was expressed. Although personal and social goals may, in many cases, overlap, one motivation rather than the other often predominates depending on the situation. The social context may enhance the salience of one goal and the relevance of the aggressive response to that goal. For example, the rhetoric of violence frequently highlights the prosocial rather than the hostile function of aggressive behavior. If aggression is directed toward improving the lot of blacks, control of aggression is more readily achieved by altering the social conditions rather than by curtailing the activity of persons presumed to be chronically hostile. In dealing with the antecedents of aggression, the aggressor's perception of the situation is considered to be very important, especially in personally motivated aggression. Personally motivated aggression can, of course, be activated by factors other than attribution in the situation. A considerable amount of work on the factors underlying impulsive aggression has demonstrated that personally motivated aggression is elicited by cues in the environment (Berkowitz, 1964, 1965, 1973), disinhibited by observation of another's aggression (Bandura & Walters, 1963), or inhibited by anticipated social sanctions (Bandura & Walters, 1963). Personally motivated aggressive responses can be shaped by reinforcement and may be habitual responses. However, aside from these factors, the aggressor's interpretation of the situation is often a crucial determinant of the level of aggression expressed. Specifying the nature of inferences, as well as their underlying processes, in aggressive situations is essential in order to attain a more complete understanding of attitudes toward, and expression of, aggression.

REFERENCES Bandura, A., 1969, Principles of behavior modification. N e w York, Holt, Rinehart & Winston. Bandura, A., & Walters, R. H., 1963, Social learning and personality development. N e w York, Holt, Rinehart & Winston. Baron, R. A., 1971a, Magnitude of a victim's pain cues and level of prior anger arousal as determinants of adult aggressive behavior. Journal of Personality and Social Psychology, 17:236-243. Baron, I. A., 1971b, Aggression as a function of magnitude of victim's pain cues,

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level of prior anger arousal, and aggressor-victim similarity. Journal of Personality and Social Psychology, 25:48-54. Baron, R. A., in press, Aggression as a function of victim's pain cues, level of prior anger arousal and exposure to an aggressive model. Journal of Personality and Social Psychology. Berkowitz, L., 1960a, Some factors affecting the reduction of overt hostility. Journal of Abnormal and Social Psychology, 60:14-21. Berkowitz, L., 1960b, Repeated frustrations and expectations in hostility arousal. Journal of Abnormal and Social Psychology, 60:522-529. Berkowitz, L., 1962, Aggression: A social psychological analysis. New York, McGraw-Hill. Berkowitz, L., Aggressive cues in aggressive behavior and hostility catharsis. Psychological Review, 77:104-122. Berkowitz, L., 1965, The concept of aggressive drive: Some additional considerations. In L. Berkowitz (Ed.), Advances in experimental social psychology, Vol. 2. New York, Academic Press. Pp. 301-329. Berkowitz, L., 1969, The frustration-aggression hypothesis revisited. In L. Berkowitz (Ed.), Roots of aggression. New York, Atherton Press. Pp. 1-28. Berkowitz, L., 1973, Words and symbols as stimuli to aggressive responses. In J. F. Knutson (Ed.), Control of aggression: Implications from basic research. Chicago, 111., Aldine. Borden, R. J., Bowne, R., & Taylor, S. P., 1971, Shock setting behavior as a function of physical attack and extrinsic reward. Perceptual and Motor Skills, 33:563-568. Burnstein, E., & Worchel, P., 1962, Arbitrariness of frustration and its consequences for aggression in a social situation. Journal of Personality, 30:528540. Buss, A. H., 1961, The psychology of aggression. New York, Wiley. Buss, A. H., 1966, Instrumentality of aggression, feedback and frustration as determinants of physical aggression. Journal of Personality and Social Psychology, 3:153-162. Buss, A. H., 1971, Aggression pays. In J. L. Singer (Ed.), The control of aggression and violence. New York, Academic Press. Pp. 7-19. Cohen, A. R., 1955, Social norms, arbitrariness of frustration and status of the agent of frustration in the frustration-aggression hypothesis. Journal of Abnormal and Social Psychology, 51: 222-226. Dollard, J., Doob, L. W„ Miller, N. E„ Mowrer, O. H., & Sears, R. R., 1939, Frustration and Aggression. New Haven, Yale University Press. Epstein, S., & Taylor, S. P., 1967, Instigation to aggression as a function of degree of defeat and perceived aggressive intent of the opponent. Journal of Personality, 35:265-289. Feshbach, S., 1964, The function of aggression and the regulation of aggressive drive. Psychological Review, 71: 257-272. Feshbach, S., 1970, Aggression. In P. H. Mussen (Ed.), Carmichael's manual of child psychology (Rev. Ed.). New York, Wiley. Pp. 159-259. Feshbach, S., 1971, Dynamics and morality of violence and aggression. Some psychological considerations. American Psychologist, 2(5:281-292. Feshbach, S., Stiles, W. B., & Bitter, E., 1967, The reinforcing effect of witnessing aggression. Journal of Experimental Research in Personality, 2:133-139. Geen, R. G., 1970, Perceived suffering of the victim as an inhibitor of attackinduced aggression. Journal of Social Psychology, 81:209-215.

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Greenwell, J., & Dengerink, H. A., 1973, The role of perceived versus actual attack in human physical aggression. Journal of Personality and Social Psychology, 26:66-71. Hendrick, C., & Taylor, S. P., 1971, Effects of belief similarity and aggression on attraction and counter-aggression. Journal of Personality and Social Psychology, 77:342-349. Johnson, R. N., 1972, Aggression in man and animals. Philadelphia, W. B. Saunders. Jones, E. E., & Davis, K. E., 1965, From acts to dispositions. In L. Berkowitz (Ed.), Advances in experimental social psychology, Vol. 2, New York, Academic Press. Pp. 220-266. Jones, E. E., & deCharms, R., 1957, Changes in social perception as a function of the personal relevance of behavior. Sociometry, 20:75-85. Jones, E. E., & Thibaut, J. W., 1958, Interaction goals as bases of inferences in person perception. In R. Taguiri & L. Petrullo (Eds.), Person perception and interpersonal behavior. Stanford, California, Stanford University Press. Jones, E. E., Hester, S. L., Farina, A., & Davis, K. E., 1959, Reactions to unfavorable personal evaluations as a function of the evaluators perceived judgment. Journal of Abnormal and Social Psychology, 59:363-370. Kaufmann, H., 1970, Aggression and altruism. New York, Holt, Rinehart & Winston. Kelley, H. H., 1971, Attribution in social interaction. New York, General Learning Press. Lanzetta, J. T., & Hannah, T. E., 1969, Reinforcing behavior of 'naive' trainers. Journal of Personality and Social Psychology, 11:245-252. Masselli, M. D., & Altrocchi, J., 1969, Attribution of intent. Psychological Bulletin, 71: 445-454. Milgram, S., 1963, Behavioral study of obedience. Journal of Abnormal and Social Psychology, (57:371-378. Nesdale, A. R., & Rule, B. G., 1973, Effects of an, aggressor's characteristics and an observer's accountability on judgments of aggression. Presented at Canadian Psychological Association, Victoria, B.C., (Abstract). Nesdale, A. R., Rule, B. G., & McAra, M., 1973, Effects of an aggressor's attractiveness, intentions and consequences of his aggression on judgments. Unpublished manuscript. Pastore, N., 1952, The role of arbitrariness in the frustration-aggression hypothesis. Journal of Abnormal and Social Psychology, 47:728-731. Pepitone, A., & Sherberg, J., 1957, Intentionality, responsibility and inter-personal attraction. Journal of Personality, 25:757-765. Rothaus, P., & Worchel, P., 1960, The inhibition of aggression under nonarbitrary frustration. Journal of Personality, 28:108-117. Rule, B. G., & Duker, P., 1973, Effects of intentions and consequences on children's evaluations of aggressors. Journal of Personality and Social Psychology, 27:184-189. Rule, B. G., & Hewitt, G. L., 1971, Effects of thwarting on cardiac response and physical aggression. Journal of Personality and Social Psychology, 19:181189. Rule, B. G., & Nesdale, A. R., in press, Differing functions of aggression. Journal of Personality. Rule, B. G., & Percival, E., 1971, The effect of frustration and attack on physical aggression. Journal of Experimental Research in Personality, 5:111-118.

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Rule, B. G., Dyck, R, & McAra, M., 1973, Judgments of aggression serving personal versus pro-social purposes. Unpublished manuscript. Sears, R. R., 1961, Relation of early socialization experiences to aggression in early childhood. Journal of Abnormal and Social Psychology, 65:466-492. Silverman, W. H., 1971, The effects of social contact, provocation and sex of the opponent upon instrumental aggression. Journal of Experimental Research in Personality, 5:310-316.

ABSTRACT Aggressive responses may be directed primarily toward injuring the victim (hostile aggression) of primarily toward attaining a non-aggressive goal (instrumental aggression). The latter may reflect a desire to obtain a personal goal (personal-instrumental) or a prosocial goal (social-instrumental). Although the distinction between hostile and personal-instrumental aggression has been emphasized in previous theory and research, it is argued that the distinction between personally motivated aggression, which includes hostile and personalinstrumental aggression, and socially motivated aggression is more important for understanding aggressive phenomena. The theoretical and empirical bases for the various distinctions are reviewed.

RÉSUMÉ Les réactions agressives peuvent avoir pour but principal de blesser une victime (agression hostile) ou d'atteindre un objectif non vulnérant (agression instrumentale). Ce dernier type peut traduire le désir d'obtenir un gain personnel ou social. Bien que la distinction entre agression hostile et agression instrumentale personnelle ait été mise en évidence au cours de recherches antérieures, la différence entre agression personnellement motivée - qui inclut l'agression hostile et agression instrumentale personnelle - et agression socialement motivée est plus importante pour la compréhension des phénomènes agressifs. L'auteur passe en revue les fondements théoriques et empiriques de ces distinctions.

External determinants of impulsive aggression*

L E O N A R D University

of

B E R K O W I T Z

Wisconsin

Several years ago a veteran homicide detective in Dallas, Texas, made an observation about many of the murders he had encountered: 'Murders', he said, 'result from little ol' arguments about nothing at a l l . . . Tempers flare. A fight starts, and somebody gets stabbed or s h o t . . ( c i t e d in Mulvihill & Tumin, 1969, p. 230). His point, of course, was that most of the killings were 'spontaneous acts of passion' caused by trivial issues rather than the results of a thought-out determination to kill. In this paper I will consider some of the conditions that appear to influence this kind of violent outburst.

Impulsive and instrumental

aggression

The impulsive nature of many of these murders suggests that they shouldn't be regarded as instrumental aggression. If, with Feshbach (1964, p. 25), we define instrumental aggression as that intentional action that injures others but which, nonetheless, is 'directed towards the achievement of nonaggressive goals' (i.e., whose primary aim isn't to do harm), we'd be hard-pressed to say what nonaggressive purposes are served in many of these killings.1 More often than not, I suspect, if * The author's research reported in this paper was carried out under grants from the National Institute of Mental Health. 1. According to Toch (1969), many criminally violent men are enraged by threats to their self-esteem and presumably strike at those whom they think are challenging them in order to protect their image or reputation. But even if most

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the murderers wanted anything at the time they struck their victim, they wanted to hurt or perhaps even to destroy him. The behavior, in Feshbach's terminology, was hostile aggression and was controlled primarily by anticipations of the actions' injurious outcome. Some theorists dispute this view of a specifically aggressive goal. In his recent book on aggression Bandura (1973) emphasizes the essential similarity between violent and nonviolent actions. In both cases, he argues, the behavior is strongly controlled by its consequences. The individual attacks someone, just as he engages in nonviolent conduct, largely because he expects his action to have positive benefits. But although these expected outcomes govern all types of behavior, according to Bandura, positive incentives are especially important in aggression. The person who fights knows he risks some injury or punishment from others (or even from himself). 'Rewards become increasingly important as the costs of aggression become greater' (p. 184). Moreover, in contrast to Feshbach and the position taken here, Bandura also suggests that essentially the same types of incentives regulate aggressive as well as nonaggressive behavior. He doubts the necessity of invoking a special instigation to inflict pain when discussing aggression (p. 196), contending that signs of suffering generally inhibit aggression (p. 198). If the victim's pain does function as a positive reinforcement on occasion, it is presumably only because the aggressor's behavior had produced some tangible benefits (such as the elimination of the provocation). 'In other words, the alleviation of aversive treatment from an injured oppressor rather than his suffering may be the primary source of satisfaction' (p. 198). Later on in this paper I'll present some evidence indicating that an angry person's aggression is reinforced when he learns that he had injured his enemy. Right now I'd like to limit the proposition that positive incentives govern all aggression. Some violent outbursts are too impulsive, too quick and involuntary, to be greatly affected by the aggressor's belief as to what will be the result of his behavior, beyond the simple idea that he will hurt his victim. This is especially true of homicides, and, indeed, the threat of capital punishment is a com-

murderers are concerned with enhancing or maintaining their self-concepts, and there's little good evidence that this is the case, did they have to kill to do this? In most cases at least, their action was excessive. This paper attempts to suggest why.

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paratively ineffective deterrent because most murderers don't think of the possible consequences. In their rage they strike out without much thought. In many instances a single action has both instrumental and impulsive components. This is often the case in laboratory measures of aggression. The subject in the typical experiment in this area knows he has to administer electric shocks to a fellow student and presses the shock button at the appropriate time at least partly because he wishes to obtain the rewards controlled by the experimenter. The punishment he inflicts is instrumental to getting these benefits. But the vigor of his response and how long he holds the button down are probably less affected by these expected outcomes. These aspects of the subject's behavior are governed to a greater extent, comparatively speaking, by the impulsive processes. I also contend that these latter determinants contribute substantially to the number of times he presses the button in a brief interval (if, as in many Wisconsin experiments, he is instructed to administer a number of shocks) and also to the intensity of the shocks he quickly decides to deliver (if the Buss procedure is employed).2 Generally speaking, the faster the individual's action and the less he thinks about or is aware of what he is doing, the greater is the relative contribution of the impulsive components over the instrumental ones (Kimble and Perlmuter, 1970). Emotional behavior in natural settings can also be a composite of these instrumental and impulsive (or expressive) features. Think of a young soldier in wartime who has just entered a village he believes is controlled by the enemy. From his perspective the aggression he displays as he shoots at an apparently menacing stranger might produce some tangible benefits: He might be protecting himself as well as his comrades; he is doing his duty and being a good soldier; and so on. However, since he is highly aroused emotionally, he is also very susceptible to other influences operating on him in a fairly involuntary fashion. He might then fire wildly at almost every moving object, not stopping to differentiate civilians from enemy troops. He might even 2. I suspect that the usual procedure in these psychological experiments also facilitates the operation of involuntary determinants. Very frequently the subject expects to attack someone later so that he is set to aggress at the time he is exposed to the given stimulus conditions. Since he is also shielded from distracting influences, aggression is a relatively dominant response and is comparatively easily elicited by environmental stimuli.

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be stimulated by the weapon in his hands so that he shoots more than he otherwise would have intended.

Impulsive aggression elicited by aggressive stimuli In a series of papers over the years (Berkowitz, 1962, 1964, 1965a, 1971, 1973) I have suggested that these impulsive aspects of aggression can be likened to a conditioned response that is evoked by internal and external stimuli. External stimuli are particularly important. The expressive reaction (in the present sense of this term) is not simply produced by an 'overflow' of emotional excitement as Darwin (1873) and others had thought but is also affected to a considerable degree by environmental stimuli. Simply put, these stimuli elicit the responses that are most strongly associated with them. Internal excitation isn't necessary for this to occur but facilitates the process; with Hull and Spence, we can say that the arousal (or general drive) 'energizes' the individual's habitual reactions to the environmental stimuli. The 'weapon effect' Applying this reasoning to aggression, Berkowitz and LePage (1967) demonstrated that the mere presence of guns heightened the punishment angry men administered to their tormentor. These provoked students evidently wanted to hurt the person who had insulted them, and they also knew that they were expected to give him at least some shocks. But on seeing the nearby weapons and thinking of them as 'aggressive' objects (i.e., used to intentionally injure someone or something), the guns elicited semantically associated reactions within them which then added to the strength of their attacks; the evoked impulsive responses 'rode along' with instrumental components of the behavior, intensifying the aggression. Before proceeding any further, I should say a bit more about the 'weapon effect'. Although the Berkowitz and LePage findings have been replicated and extended (Fraczek & Macaulay, 1971), some investigators (e.g., Page & Scheidt, 1971; Buss et al., 1972) have failed to confirm the earlier results. It's clear that guns don't always stimulate increased aggression. One reason for the failure has to do with the person's interpretation of the weapons. What effect the occurrence has depends on how he thinks of it, what meaning it has for him (Lazarus

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& Alfert, 1964; Berkowitz & Alioto, 1973). If he thinks of a gun primarily as a dangerous or terrible object, it's likely to evoke stronger anxiety than aggression. Then too, the internal reactions elicited at the sight of a gun are probably fairly weak in most cases so that the weapon doesn't heighten open aggression unless the individual is highly aroused and set to attack. The evoked aggressive responses can also be easily masked by situationally induced inhibitions. Turner and Simon (1973) have recently shown how both evaluation apprehension and the subject's awareness of the importance of the guns in the room can depress aggressive reactions to the presence of weapons. Evaluation apprehension was created in half of the experimental subjects by informing them that the research would determine how well-adjusted they were. Then, after all of the men were deliberately insulted by one confederate, a second accomplice, posing as a student who had just served in the study, made some remarks about the procedure. His comments created one of three levels of awareness about the weapons the actual subject would soon see. In the high awareness group he said the experimenter 'probably' expected that the guns would 'change' the subject's reactions. After getting this information the subject entered the room from which he was supposed to administer the shocks, saw the weapons on a nearby table3 and gave the first confederate a number of shocks as his judgment of that person's work on an assigned task. Figure 1 shows the mean number of shocks given in each condition and in a control group not seeing any weapons and not given any apprehension or awareness information. As the findings clearly indicate, the subjects who believed their adjustment was being tested administered fewer shocks than did the men not having this view of the study. Further, the more aware they were that the experimenter was interested in their reaction to the guns, the less aggressive they were in the presence of the weapons. The 'weapons effect' apparently can only be detected in subjects who aren't suspicious about the weapons. The least apprehensive group not specifically alerted to the importance of the guns were actually more punitive in their presence than were the control subjects not seeing any weapons. 3. The experimenter told the subject that someone else involved in another study had left the guns there.

148 Leonard Berkowitz Figure 1. Aggression as a function of awareness of gun's importance -7.0

• LOW ELEVATION • HIGH EVALUATION • NO WEAPONS

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We also have an interesting extension of the 'weapons effect' in an experiment carried out by Leyens and Parke (1973) at Louvain. Instead of displaying actual guns, they exposed their university students to a series of five slides, each portraying a certain type of object. Judges had previously rated these objects as either highly aggressive (e.g., a machine gun), moderately aggressive (e.g., pincers) or nonaggressive in nature. Then, after viewing the slides, each subject indicated the level of shock intensity he wanted to give to the other person who had previously either insulted him or treated him in a neutral fashion. This intended punishment was affected by both the insult treatment and the content of the slides. Consistent with the Berkowitz and LePage results, only the provoked men were more aggressive after seeing the highly aggressive slides.4 4. However, if we generalize from other research (e.g., Berkowitz & Alioto, 1973), viewers are less apt to be affected by these slides if they regard the pictures as make-believe as they look at them.

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Table 1. Mean intensity of punishment the subjects have chosen to deliver in each group Nature of slides shown to subject before Highly aggressive Moderately Non-aggressive (e.g., machine aggressive (e.g., box of gun, bayonet) (e.g., pincers, dessert) matches) Insulted 5s Non-insulted Ss

71.1

46.7

45.0

12.2

12.8

13.1

These data had yielded a significant interaction (F = 4.06). Source: Leyens and Parke, 1973.

Aggression in the mass media This last-mentioned study is one of a good many demonstrations of the aggression-heightening effects of media violence. Whether the observer sees weapons or a fight, on a printed page, on a screen, or 'in the flesh', there is now a greater chance than before that he will be openly aggressive (Berkowitz, 1971, 1973). Moreover, the more aroused he happens to be at the time, the stronger is his violent reaction. So, Geen and O'Neal (1969) had half of their subjects hear moderately unpleasant white noise right after they had watched either a brief prize fight or a nonaggressive film and found that the noise had increased the aggressive impact of the fight movie. The noiseengendered arousal had evidently intensified the aggressive reactions elicited by the witnessed aggression, thereby strengthening the subject's attacks upon the available target.

Characteristics of the aggression-evoking stimulus Up to this point I had been arguing that an external object or event is capable of evoking impulsive aggressive reactions to the extent that it has aggressive meaning, i.e., is associated with aggression. In line with this reasoning, several of our experiments sought to determine if the available target's connection with aggression, and particularly with the witnessed media violence, would heighten the punishment given him. The point here is that a person can also serve as a conditioned stimulus

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Figure 2. Aggressive reactions to movie stimuli as a function of arousal level (data from Geen & O'Neal, 1969)

AGGRESSIVE SCENE

NONAGGRESSIVE SCENE

TYPE OF FILM AGGRESSIVE REACTIONS TO MOVIE STIMULI AS A FUNCTION OF AROUSAL LEVEL DATA FROM GEEN AND O'NEAL CI969)

to aggression. If he has the appropriate characteristics, he can also evoke impulsive aggressive reactions strengthening the aggressive responses elicited by the violent scene. The first experiment along these lines (Berkowitz, 1965b) varied the target-person's stimulus characteristics in terms of his social role. A confederate was introduced to each subject as either a college boxer (this was in the days when the university still had a boxing team) or a speech major. This person then either insulted the subject or acted neutrally towards him, and the subject watched either our standard prize fight scene or a neutral movie.

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Our theoretical expectations were upheld. For one thing, the boxer was punished more severely than the same person labeled as a speech major. But more particularly, the provoked subjects attacked the confederate most strongly when they had seen the fight film and the confederate had been described as a boxer. The target's role-mediated association with the observed aggression had apparently heightened his ability to evoke impulsive aggressive reactions. But what was the exact nature of this connection? Was he associated with the idea of aggression per se or was there a tie-in with a particular aspect of the witnessed fight? Geen and Berkowitz (1966) provided some information about this connection with the boxing movie. This time, instead of manipulating the insulting confederate's role in the university, his name was systematically altered. In introducing him to the subject at the start of the session, the experimenter gave him the name of the actor (Kirk) or the character (Kelly) who was beaten in the fight movie, or the name of the fight winner (Dunne), or assigned him a name that didn't appear in the boxing film (Riley). The confederate then provoked the subject, after which the subject watched either the boxing film or a nonaggressive but exciting movie of a track race. Figure 3 shows the mean number of shocks administered to the confederate at the conclusion of the film. The results indicate that the confederate drew the strongest attacks when the subjects had seen the violent film, and he had the same name as the fight loser (Kirk or Kelly). Since the movie character was portrayed in an unfavorable manner, the beating he received in the film was generally regarded as deserved. This means the accomplice was associated with the victim of 'good' or perhaps even rewarding aggression. Can it be that he was connected with rewarded aggression, and that this enhanced his ability to evoke impulsive aggression? Research with animals (e.g., Ulrich, Johnston et al., 1963) has demonstrated how a neutral stimulus can become a discriminative stimulus for aggression by pairing it with rewards for fighting. At the human level, Geen and Stonner (see Geen, 1972, pp. 13-14) also reported that stimuli associated with rewarded aggression can elicit relatively intense aggression. Data from an unpublished experiment by Lang and Berkowitz can also be interpreted in this way. In the first part of this study the subjects were told to shock one person when a certain signal (the discriminative stimulus) appeared, and they were implicitly rewarded (by

152 Leonard Berkowitz Figure 3. Number of shocks given to confederate (data from Geen & Berkowitz, 1966)

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