Aggression and Defense, Neural Mechanisms and Social Patterns [Reprint 2020 ed.] 9780520340190

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UCLA F O R U M IN M E D I C A L

VICTOR E . H A L L , MARTHA BASCOPÉ-ESPADA,

SCIENCES

Editor Assistant Editor

EDITORIAL BOARD

H. W. Magoun C. D. O'Malley Morton L. Pearee Sidney Roberts Emil L. Smith

Forrest H. Adams Mary A. B. Brazier Louise M. Darling Morton I. Grossman William P. Longmire Reidar F. Sognnaes

UNIVERSITY

OF C A L I F O R N I A

LOS

ANGELES

AGGRESSION AND DEFENSE NEURAL MECHANISMS AND SOCIAL PATTERNS (BRAIN FUNCTION, VOLUME V)

UCLA FORUM IN MEDICAL SCIENCES NUMBER 7

AGGRESSION AND DEFENSE NEURAL MECHANISMS AND SOCIAL PATTERNS (BRAIN FUNCTION, VOLUME V) Proceedings of the Fifth Conference on Brain Function, November 1965 Sponsored by the Brain Research Institute, University of California Los Angeles, with the support of the U.S. Air Force Office of Scientific Research

EDITORS

CARMINE D. CLEMENTE and DONALD B. LINDSLEY

UNIVERSITY

OF

CALIFORNIA

BERKELEY AND LOS ANGELES 1967

PRESS

EDITORIAL NOTE

The present volume contains the proceedings of the fifth in a series of conferences on Brain Function, supported by grants made to Dr. H. W. Magoun of the Brain Research Institute of the University of California Los Angeles. The proceedings of the first four conferences of this series have been published as Brain Function, Vol. I: Cortical Excitability and Steady Potentials; Relations of Basic Research to Space Biology (1963); Brain Function, Vol. II: RNA and Brain Function; Memory and Learning (1964); Brain Function, Vol. Ill: Speech, Language, and Communication (1966); and Brain Function, Vol. IV: Brain Function and Learning (1967).

CITATION

FORM

Clemente, C. D., and Lindsley, D. B. (Eds.), Aggression and Defense: Neural Mechanisms and Social Patterns (Brain Function, Vol. V). UCLA Forum Med. Sci. No. 7, Univ. of California Press, Los Angeles, 1967. University of California Press Berkeley and Los Angeles, California Cambridge University Press London, England © 1967 by The Regents of the University of California Library of Congress Catalog Number: 64-22268 Printed in the United States of America

PARTICIPANTS IN THE CONFERENCE D O N A L D B. L I N D S L E Y , Chairman, Co-Editor Departments of Psychology and Physiology, and Brain Research Institute University of California Los Angeles Los Angeles, California C A R M I N E D. C L E M E N T E , Co-Editor Department of Anatomy and Brain Research Institute University of California Los Angeles Los Angeles, California

J A C K D . BARCHAS

Department of Psychiatry, Stanford University Palo Alto, California S. A . BARNETT

Department of Zoology, Glasgow University Glasgow, Scotland GEORGE A .

BARTHOLOMEW

Department of Zoology, University of California Los Angeles Los Angeles, California LEONARD BERKOWITZ

Department of Psychology, University of Wisconsin Madison, Wisconsin IRWIN S. BERNSTEIN

Yerkes Regional Primate Research Center, Emory University Atlanta, Georgia JOSEPH B .

BIRDSELL

Department of Anthropology, University of California Los Angeles Los Angeles, California MARY A. B.

BRAZIER

Brain Research Institute, University of California Los Angeles Los Angeles, California

H E N R Y W . BROSIN

Department of Psychiatry, University of Pittsburgh Pittsburgh, Pennsylvania HORACE R .

CAYTON

Institute of Business and Economic Research, University of California Berkeley, California J O S É M . R . DELGADO

Department of Psychiatry, Yale University School of Medicine New Haven, Connecticut IRENAUS

EIBL-EIBESFELDT

Max-Planck-Institut für Verhaltensphysiologie Seewiesen bei Starnberg, West Germany JOHN D .

FRENCH

Brain Research Institute, University of California Los Angeles Los Angeles, California PIERRE GLOOR

Montreal Neurological Institute, McGill University Montreal, P. Q., Canada ERNST B . HAAS

Department of Political Science, University of California Berkeley, California J A M E S HEDLUND

U. S. Army Medical Research and Development Command Department of the Army Washington, D.C. B I R G E R KAADA

Institute of Neurophysiology, University of Oslo Oslo, Norway SYUNZO K A W A M U R A

Department of Biology, Osaka City University Osaka, Japan WILLIAM

KIRBY

Aberdeen Proving Grounds Aberdeen, Maryland HAROLD D .

LASSWELL

Edward J. Phelps Professor of Law and Political Science Yale School of Law, Yale University New Haven, Connecticut

Louis S. B. LEAKEY Centre for Prehistory and Palaeontology Nairobi, Kenya, East Africa H . W . MAGOUN

Dean of the Graduate Division Department of Anatomy and Brain Research Institute University of California Los Angeles Los Angeles, California KENNETH S . NOKRIS

Department of Zoology, University of California Los Angeles Los Angeles, California STANLEY C . PLOG*

President, Behavior Science Corporation (BASICO) Panorama City, California KARL H . PRIBRAM

Department of Psychiatry, Stanford University Palo Alto, California JACK H . PROSTI

Department of Anthropology, University of California Los Angeles Los Angeles, California BRYAN ROBINSON

Laboratory of Neurophysiology Yerkes Regional Primate Research Center, Emory University Atlanta, Georgia ALAN B . ROTHBALLER

Department of Neurosurgery, New York Medical College New York, New York HERMAN J . SANDER

Behavioral Sciences Division, Air Force Office of Scientific Research Washington, D.C. GEORGE SASLOW

Department of Psychiatry, University of Oregon Medical School Portland, Oregon JOHN P . SCOTT

Department of Psychology, Bowling Green State University Bowling Green, Ohio * Formerly at: Institute of Government and Public Affairs, University of California Los Angeles Los Angeles, California t Present address: Department of Anthropology, Duke University Durham, North Carolina

RICHARD T R U M B U L L

Psychological Sciences Division, Office of Naval Research Department of the Navy Washington, D.C. BRUCE L .

WELCH*

Department of Biology, College of William and Mary Williamsburg, Virginia L . YABLONSKY

Chairman, Department of Sociology, San Fernando Valley State College Northridge, California

Present address: Memorial Research Center and Hospital, University of Tennessee Knoxville, Tennessee.

FOREWORD

Man's greatest challenge in the twentieth century is the containment of his aggressive nature. Acts of violence in our cities, open hostility between nations and the potential which man has achieved for his own total annihilation demand inquiry and study of the neural mechanisms and social patterns of aggression and defense. Most animal species display overt aggressive and defensive behavior. Yet, other than in the human, fights among mammals of the same species which result in the death of a member of that same species are rare. Early man learned to arm himself for aggressive purposes and also to defend himself. With his initiation in the use of actual weapons, simple at first, he became a predator toward animals. As Louis S. B. Leakey points out, "It was possibly a natural step to extend his aggression toward other men." Most of the aggressive behavior patterns encountered in the human are found to have their counterparts in animal species. However, with his highly developed frontal brain and its exquisite control over his hands, man has far outdistanced any other species in his motivation, conception and manifestation of aggression. This book is the result of a four-day conference held in nearby Pacific Palisades, California, on November 14th to 17th in 1965. The conference, jointly sponsored by the Brain Research Institute at UCLA and the U. S. Air Force Office of Scientific Research, was the fifth in a series on the general topic of Brain Function held here in Los Angeles over the past five years. It brought together authorities in many disciplines, including anthropology, zoology, ethnology, behavioral physiology, neurophysiology, physiological and social psychology, psychiatry, sociology and law. The conference examined a variety of vertebrate animal societies for behavioral manifestations of aggression and defense and for information dealing with the nature and origins of these behaviors. This phylogenetic approach lent a good base to an examination of the underlying biological mechanisms controlling natural behavior. Human aggression and defense were examined first from an evolutionary and then from an ontogenetic position. The final two sessions of the conference examined man's aggressive behavior both as an individual and in psychiatric perspective, and in group-directed aggression. Gang warfare, riots (such as the one that had occurred recently in Los Angeles) and the social and international political framework of war and peace extended the discussions into areas of pressing current concern. The indispensable and excellent editorial assistance from Mrs. Martha Bascopé-Espada and Mrs. Amelia R. Hockings in the preparation of the xi

conference proceedings into this published form is gratefully acknowledged. The editors also extend their thanks to Mrs. Jane McConnell, who arranged all the conference details. Drs. M. A. B. Brazier, J. D. French and H. W. Magoun contributed valuable assistance in the planning and organization of the conference and, in fact, suggested this most timely subject. C.D.C. D.B.L.

Frontispiece designed and prepared by Frank Humelbaugh. Permission to reproduce its components was granted by the copyright owners and is gratefully acknowledged: Aldine Publishing Co., Chicago, 111. (from The Rat, A Study in Behavior, by S. A. Barnett); Mr. Dick Ewart, Edinburgh, Scotland ("Students Fighting at Edinburgh University"); Faber and Faber, Ltd., London, England ("Birds Fighting"); Imperial War Museum, London, England ("Kamerad!" from The War; A Concise History 1939-1945); Mrs. Ann Kehrer, UCLA Laboratory of Nuclear Medicine and Radiation Biology ("Mushroom Cloud, Nevada Test Site, 1957"); National Geographic Magazine, Washington, D.C. ("Gorilla in Berry Patch" and "American Elk Fighting"); Time-Life Books, New York, N.Y. ("Age Faces Youth" from The Primates); U.S. Library of Congress, Washington, D.C. (Plate 22 from An Album of American Battle Art, 1755-1918); Mr. Stanley Washburn, Berkeley, California ("Frilled Lizard").

CONTENTS

D E V E L O P M E N T O F AGGRESSION AS A FACTOR IN E A R L Y H U M A N AND P R E - H U M A N EVOLUTION

1

LOUIS S. B. LEAKEY A T T A C K AND D E F E N S E I N A N I M A L SOCIETIES

35

S. A. BARNETT ONTOGENETIC AND M A T U R A T I O N A L STUDIES O F AGGRESSIVE BEHAVIOR

57

IRENAUS EIBL-EIBESFELDT B R A I N M E C H A N I S M S R E L A T E D TO AGGRESSIVE BEHAVIOR

95

BIRGER KAADA AGGRESSION, D E F E N S E AND NEUROHUMORS

135

ALAN B. ROTHBALLER AGGRESSION AND D E F E N S E UNDER C E R E B R A L RADIO C O N T R O L

171

JOSÉ M. R. DELGADO AGGRESSION AS STUDIED IN T R O O P S O F J A P A N E S E M O N K E Y S

195

SYUNZO KAWAMURA AGGRESSIVE BEHAVIOR IN C E T A C E A

225

KENNETH S. NORRIS E X P E R I M E N T S ON A U T O M A T I S M AND I N T E N T I N H U M A N AGGRESSION

243

LEONARD BERKOWITZ H U M A N AGGRESSION IN PSYCHIATRIC P E R S P E C T I V E

267

HENRY W. BROSIN R E B E L L I O N IN L O S A N G E L E S : T H E W A T T S R I O T S

297

STANLEY C. PLOG T H E SOCIAL AND P O L I T I C A L F R A M E W O R K O F W A R AND P E A C E

317

HAROLD D. LASSWELL N A M E INDEX

337

S U B J E C T INDEX

343

XV

DEVELOPMENT OF AGGRESSION AS A FACTOR IN EARLY HUMAN AND PRE-HUMAN EVOLUTION LOUIS S. B. LEAKEY Centre for Prehistory and Palaeontology Nairobi, Kenya

Current findings on human evolution have brought us to the position where much of what we believed to have theoretically happened proves to be incorrect. Much that is in the textbooks, much that is still being taught in universities about human evolution is no longer true, but it continues to be taught because the implications of recent discoveries are insufficiently understood. It was principally Weidenreich (23), Le Gros Clark (3), and a few of the people of that generation, just previous to mine, who put forward and strongly defended the idea that man had gone through a very simple series of stages of evolution: the pongid stage, an Australopithecine stage, a Pithecanthropus stage, and then man as we know him today. Theoretically, this had always seemed highly unlikely to some of us, since it meant that man had done something which no other mammal had done: evolved in a single straight line instead of having one main branch, with many experimental side branches which failed to make the grade. Yet the old theory persists. Linked with it is the concept, still very, very widely taught and very widely believed, that man in the relatively near past was at a pongid or ape stage of evolution. In such a very short time, three or four million years, as the books and many of my colleagues put it, we are supposed to have lost our huge canine teeth, lost our simian shelves, lost our long, brachiating arms, ceased to dwell in the trees, and many other similar but, I fear, erroneous concepts. These were theories which in the light of current facts no longer stand up. Similarly, it was believed that man had become a tool-maker only in recent times. I regret to say I was among those who, some 14 years ago, coined the idea that "man starts at that stage of primate evolution where the creature begins to make tools to set and definite pattern." We have had to throw over that definition completely; it will not work. The new definition is so long that I will not attempt to put it to you from memory. As a result of recent discoveries in East Africa we know that far from man in the form of Homo erectus, which had evolved from an Australopithecine 1

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stage, being a direct ancestor, there was a true Homo, one morphologically much more like you and me than Homo erectus, and already present in the Villafranchian period. Two different techniques, potassium argon dating and glass fission track dating, both trace that period to nearly two million years ago. At that point we have Homo habilis side by side with and coexistent with Australopithecines in the same area, but in a different ecological niche. The latter were very strongly specialized away from man and had, indeed, become specialized for a vegetarian diet; the former had a large number of characters similar to our own and had turned towards a carnivorous diet—we can demonstrate this from different lines of evidence. This fact of two contemporary sub-families of Hominidae in the Early Pleistocene, represented by Homo habilis and an Australopithecine, completely disproves the idea that man evolved from the Australopithecines within the recent past. Somewhat higher up in geological time we have clear evidence of three contemporary types of Hominidae. Homo habilis continues into the lower part of Bed II of Olduvai; the Australopithecines are also present throughout Bed II. But in addition to this we have now found near the top of the sequence in Bed II a very good example of the African variety of Homo erectus (Pithecanthropus) while low down in Bed II we have what I consider to be a proto-Homo erectus, at approximately a million year mark. Thus, within Bed II we clearly have three entirely distinct and different members of the Hominidae, and there is also evidence of three different cultural traditions. That is a revolutionary thought but is vital to our understanding of the problems with which we are concerned. If a skull of present-day Homo sapiens is compared with the brain case of Homo habilis, one will find that the contour of the basi-occipital region of the fossil is the same as in man today. Homo habilis is, of course, much smaller, but the outline of the contour does not at all resemble that of Homo erectus, while the occipital index is within the range of Homo sapiens and outside that of Homo erectus or Australopithecus. Comparison also shows that Homo habilis, like present-day man, has the greatest width of the skull on the parietals and not lower down as in other hominids. Turning for a moment to dental characters, we find that in Australopithecines the premolars of the lower jaw are normally very wide relative to length. In contrast to this, the premolars of Homo habilis are long and narrow. Furthermore, there is a major difference in the shape of the mandibular arch of Australopithecines and Homo habilis; in the latter the arch is Ushaped, as in man today. In the East African Australopithecine Zinjanthropus there is a marked saggittal crest due to very great development of the temporal muscles. This contrasts greatly with its position in Homo habilis. Seen in profile, Zinjanihropus has a very low forehead region and an excessively long face which means that the lower jaw was probably equipped with a very high ascendency ramus. Examination of the teeth of Zinjanthropus reveals that the

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cheek teeth are of immense size and there is excessive wear on the crown surfaces, even in a young individual. Microscopic examination reveals numerous scratches caused by wear, and we may assume that these were linked with a coarse vegetarian diet. The third type of hominid in Bed II does not resemble Homo habilis or Australopithecus, but here is great resemblance to the skulls of Pekin and Java man. This is true not only of the massive brow ridges but also of contours of the occipital region. More recently we found a small skull at a low level in Bed II at Olduvai; I sent details and illustrations to my colleague von Koenigswald", and he agrees with me that this skull looks remarkablv like an ancestral form of Homo erectus. These facts about the Hominidae and the Australopithecines are strongly opposed to current textbook concepts and everything related to them which is now in the textbooks must be reconsidered. But it is not only in respect to the Pleistocene that discoveries are being made. A few years ago we found in Kenya deposits which I had provisionally called Early Pliocene, fossil remains of a creature which I named Kenyapithecus wickeri. At the time I stressed that it had a considerable number of characters which could be better described as hominid rather than pongid. The canine tooth is short; the lower molar has a strikingly hominid pattern. The upper incisor tooth, of which we have an excellent example, has been mistaken for that of primitive man by a number of human anatomists; some of them refused to believe that it could possibly be as old as it in fact is. We also found a true canine fossa of the present-day human type which, incidentally, cannot be seen in Pekin man or Java man or in any Australopithecine. The geology and the fauna indicate that it is of Upper Miocene date, which is supported by potassium argon dates. Shortly after we announced this find, Elwyn Simonsf reexamined the magnificent collection of fossils which had been brought to Yale by E. Lewis in 1934. When he reexamined Ramapithecus and found the same characters, he claimed, and rightly so, that Ramapithecus, too, represents an Upper Miocene hominid. I do not think there is any serious worker in this field today who contends that Ramapithecus and Kenyapithecus do not represent true members of the Hominidae dating back to the Upper Miocene, somewhere around 12 to 14 million years ago. The significance of this fact, as can readily be seen, is that it completely upsets all our preconceived ideas of man having been derived from a pongid ancestor in relatively recent geological time. If we examine the skull of a gorilla to see the basic characters of modern pongids we find that it is equipped with very massive canine teeth; like * Dr. G. H. Ralph von Koenigswald, Department of Paleontology, University of Utrecht, Holland. f Of the Peabody Museum, Yale University, New Haven, Connecticut.

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those of baboons and monkeys, these teeth are used in part for aggression and defense. However, the fossil ancestral stocks leading to man, Kenyapithecus and Ramapithecus, lack these long canine teeth; this distinguishes them from the pongids and links them to the hominids. In the lower Miocene of East Africa there lived a creature which is called Proconsul, and it too had characters which clearly distinguish it from modern pongids. It had a smooth rounded forehead and relatively small canine teeth, and the nature of the skull base suggests that the head was carried in a more upright position than in apes today. Let us consider briefly some of the characters of Kenyapithecus which are indicative of its links with man. Not only is the canine tooth smaller, but its root is highly compressed and not conical as in apes. The lower limit of the malar process is, moreover, set forward above the fourth premolar as in man. The only lower molar we have so far found is basically of human pattern, while the upper incisor is very hominid in pattern. At this stage the question may well arise: "If it is true that the protoHominidae were in existence back in the Upper Miocene, some 12 or 14 million years ago, how did they survive in a hostile world to go on evolving toward man if they were so unprepared by nature for either defense or aggression? What defense mechanism enabled these creatures, which were living on the ground and associated entirely with the terrestial savanna-type fauna, to survive? You say that they were not even tree climbers and thus could not escape from their enemies into the trees." My reply is that, in point of fact, trees have never helped man to escape from carnivora; even lions regularly climb trees (contrary to what the textbooks say). Obviously then, there must have been some other built-in defense mechanism, since nature had provided protoman with neither claws, long canine teeth nor great physical strength. One of my students recently looked into the literature dealing with carnivora versus man; we were repeatedly struck by very vivid tales of "man-eating tigers", "man-eating leopards" and "man-eating lions". Why is such stress laid on the term "man-eating"? Simply because such behavior is abnormal. Lions, leopards and tigers do not normally eat human flesh and therefore, when a case occurs (about one in 100,000 examples of carnivore population), it is because the animals concerned are sick, old or wounded, or their normal food has been killed off by the activities of hunters. Under any one of these conditions they turn to food which they otherwise dislike —human flesh! I myself have slept on the Serengeti plains with one African when we could not get back to camp because of a car breakdown. Five lions came and sniffed at our heads and around our faces. W e were both awake and kept very quiet, but they did not attempt to kill and eat us. They were not aggressive nor were we, and we were not considered food to eat. In 1931 I had two students in my first camp at Olduvai, and a lion came,

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sniffed at them as they lay in their cots, and walked through their tent. He was a hungry lion but he did not touch them; they were not good food. The whole of the literature makes it clear that even when a normal lion or leopard or tiger has killed a man who had been aggressive to it or had interfered with its cubs, or had wounded it, unless it is a man-eater (as psychopathic as a madman today), the animal will kill the aggressor, then turn up its nose and walk away, and not eat the dead human. I followed this up by checking on some of the other primates, such as Galagos and Pottos and quite a large number of monkeys. Most of them are not eaten by carnivores. They are ignored. The chief exception can be found among the baboon group, the Cynocephalinae, including the mandrills in West Africa, which are highly acceptable to leopards, I do not know why. When we started the investigation, I had assumed that because in the past nearly all African tribes threw out their dead to be eaten by hyenas, at least this group of carrion feeders was fond of human flesh. But we discovered that normally hyenas will not touch it until it is putrid. They prefer to wait some 36 to 40 hours after a person has died and been thrown out before eating the decaying flesh. By this time its smell has changed very considerably and is perhaps no longer recognizable as human. I seriously believe that one of the things which protected many early primates, including early man, in the defenseless days before he had weapons or tools, and when he was living on the ground, was that he was unpalatable to the carnivores. A comparable situation can be seen in the shrews: if cats or animals mistake one for a mouse, they will kill it but they will not eat it. Whether man's natural immunity to large carnivores is smell by itself—they certainly sniff at us—or whether it is a combination of smell plus knowledge of how the flesh tastes, I do not know, but I am convinced that a major defense mechanism of the earlier stages of protoman and early man was neither weapons nor canine teeth, nor claws nor physical strength, but this nature-endowed characteristic of being unpalatable, of not being good food for the large carnivores. I will now turn to the early Pleistocene period, and consider what factors forced man to make cutting tools, to eat meat and begin the morphological, physical and mental processes which led to his becoming an aggressor. Fortunately we have many fossils of other primates, such as monkeys and baboons, which were contemporary with Homo habilis and Australopithecus and later with the African Homo erectus. Those occur from Bed I upwards, high into Bed II. They were mainly giant baboons and monkeys competing for the same natural foods as Homo habilis and Pithecanthropus. As normal primates they fed upon vegetables, fruit, nuts, edible bark, edible leaves, etc., and in times of plenty there was an adequate supply of vegetable foods for all the different primates. In exactly the same way, in the Congo forest today, one can find gorillas, chimpanzees and a half dozen different species of monkey, all consuming more or less the same general-

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ized vegetable foods, without crowding each other out in a relatively small area of three or four square miles. But those primates that were contemporary with Homo habilis, who was a small creature, and with Australopithecines, who were not so small, were not ordinary primates like those of the present day. We have remains of fossil monkeys of the Colobus group whose teeth are as big as present-day man's, and whose skull is as large as that of a big baboon. These monkeys must have required a considerable quantity of vegetable foods to have an adequate intake of calories per day. We also have numerous baboons which in their limb structure are bigger than male chimpanzees; they have heavy skulls and jaws twice the size of those of present-day baboons. These were the primates that were competing for the vegetable food supply of Homo habilis and Australopithecines during the Lower Pleistocene. When climatic changes and other factors limited the amount of vegetable food available, it is scarcely surprising that protoman had to find another source of food which was not his natural one, or else perish. He had to invent ways and means of acquiring adequate sources of other foods; otherwise he would have been forced to give up the struggle for survival. He was not as strong as the gorilla-sized baboons, or as these monkeys with teeth as big as yours and mine. What, then, did he do? He started to make sharp cutting tools. These were not to be used as weapons, but simply as a means for scavenging flesh, to enable him to become a carnivore. He did this because he was driven by competition. Before we go further, let us look quickly at the creatures which were competing with Homo habilis. Both fossil and modern baboons have immensely long canine teeth despite their relatively small body size, and they use these teeth both for aggression and defense; in particular, they need this defensive weapon to protect themselves from leopards which regularly prey upon them and their young. In her study of chimpanzees, Jane Goodall* found that baboons will even use their aggressive tactics to attack chimpanzees if they are competing for the same fallen ripe fruit under a tree. The interesting point she showed was that, while the baboons relied on their huge canine teeth for aggression, the chimpanzees did not use their canine teeth as a defense mechanism, but preferred to stand upright and make violent gestures of aggression with their arms, as a man might do. This apparently worked successfully. Let us return to the question of early man's ancestors, Kenyapithecus and Ramapithecus, of some 12 to 14 millions years ago. We have seen that they lacked large canine teeth and that they were much closer to man than chimpanzees. It would seem probable therefore that they were at least as advanced and developed as chimpanzees of today, if not more so. After five years of study, Jane Goodall* has shown that chimpanzees liv* Public lecture, unpublished.

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ing in the wild make a variety of tools for specific purposes. These are clearly true tools, made by modifying and altering natural materials for specific purposes and in set patterns. These tools are, moreover, made only at certain times of the vear and are not reused until a suitable climatic situation occurs again. Jane Goodall has further shown that chimpanzees teach their young how to make the tools. She has also shown that chimpanzees, in their wild state, regularly hunt, kill and capture small mammals, including monkeys and small baboons, as well as immature pigs. Thus, it would seem that, if chimpanzees with a brain capacity of from 280 to 320 cc are capable of this, handicapped as they are by their badly developed hands and fingers, then surely we must accept at least the possibility (and I would go further, and say the likelihood) that our proto-human, Kenyapithecus, a true member of the Hominidae of some 12 to 14 million years ago, must have been doing something comparable. To me, it is inconceivable that we will not, in time, find evidence that he was at least making use of natural objects for a variety of tool purposes, even if he was not, as yet, shaping them. In Fort Teman, at the level which yielded our Kenyapithecus fossil hominid, we found the remains of an extinct antelope whose skull had been broken open to expose the brain case. While I would not say that this must have been done by Kenyapithecus, I can say I have never seen a comparable separation of the top of the skull under conditions where a carnivore had been eating a dead animal. Similarly, we found part of the skull of an extinct deer-like animal that had been separated from the rest of the skull. Nearby was the upper part of a tibia which clearly exhibits a depressed fracture on the shaft (Figure 1). I have examined this in some detail, and I am sure it was not caused by the teeth of any large carnivore. While I do not insist that these are proofs of tool-using by Kenyapithecus, they are certainly suggestive of breaking or hammering with a blunt instrument. I want to trace next the process that led from these early Hominidae to the later scavenging man-like creatures. We have not found a single tool of any kind in this Upper Miocene deposit that would suggest that it was used for breaking bones or skulls. We want to know what happened from this point until the stage where man became an actual weapon-maker and an aggressor. Protoman was not, by nature, made for aggression. Nature had given him a very good defense mechanism in the form of bad taste and smell, but no aggressive mechanism. It seems fairly clear that protoman entered the field of meat eating by reason of competition in the same way that chimpanzees are doing it today. He started, by experiment, to seek a diet for which he was not developed by the very nature of the Order of animals to which he belonged. Primates are basically vegetarians, but protoman went into a new field, initially that of a semi-carnivorous diet. Much later, we find Homo habilis, Australopithecines, etc., associated with not one or two, but literally thousands of cutting tools and artifacts made of stone. My wife has just completed her analysis (for Volume III of our work) of

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Figure 1. A broken tibia with depressed fracture; nearby is the facial part of a skull from which the back region has been broken. These may indicate meat eating activity by Kenyapithecus wickeri.

the stone tools which were found in association with Homo habilis. In a preliminary paper (11) she has explained that there are not one or two but a considerable number of different types of tools already in existence at Olduvai Bed I in the Lower Pleistocene. In our preliminary work, which I published after twenty years in 1951 (9), I stressed that the Oldowan cultures consisted mainly of chopping tools, which some of my colleagues called "the pebble culture". These Oldowan tools are not always made from pebbles, and more detailed study shows that, while chopping tools predominate on a statistical basis, there are also many flake tools of several types. There are, for example, excellent scrapers; some very small ones, some round ones and some end scrapers, which were apparently used for working skins. Many flakes show intense signs of utilization of a type which, according to experiment, results from skinning with a natural sharp edge without retouching. I have found, for example, that if the cutting edge of a stone tool accidentally touches against a bone while cutting through skin and flesh, it results in a slight damage to the edge. Repeated experiments show that these flake tools could have been very good skinning weapons, and that they show utilization of a very real nature.

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There are also some flakes which had been carefully prepared into small points. There are in all about seven different types of tools which occur repeatedly on living floors of Homo habilis in the Lower Pleistocene. Obviously, it means we should go back into the Pliocene to find the beginnings of cutting tool making, which we plan to do; we think we know where we might find them. Let us look at the picture that now emerges. First protoman scavenges without any tools, back in Upper Miocene times. Then, in all probability—I will not say this categorically—he picks up natural, sharp-edged stones and uses them to tear through the skin of an animal killed by a lion, a leopard or a cheetah. He may thus be able to cut off a hunk of meat. He then wonders, "Why should I have to carry natural stones around? Surely I can make a sharp edge by knocking two stones together." So he starts to make simple cutting tools, and then elaborates on a number of specific tools for a number of specific purposes. All this happened far earlier than we previously believed was possible for man, because we had telescoped our ideas and refused to believe in man's truly early development. Once he reached the point where he was able to scavenge for meat from carcasses killed by the lions, leopards and cheetahs, protoman could ask himself, "Why shouldn't I kill for myself?" If he had the brains for it, he would start thinking of a way to do this. What has been happening in the meantime? There has been definite selectivity. Once man turned to a flesh-eating scavenging diet, there was selectivity against having huge jaws for crushing vegetable foods, but in favor of smaller jaws with reduced masticatory muscles. This combined with selectivity in favor of increased thinking, planning powers and increased manual dexterity, and the entire selectivity processes then shifted in favor of thought and away from brute force and great muscle. There is therefore a natural survival factor in having smaller jaws and smaller temporal muscles; I stress this because the converse can be observed in the Australopithecines. In both Zinjanthropus and Paranthropus the immense temporal muscles developed to a point where they closed right over the brain case to form a saggital crest. As a result there was little possibility of major brain expansion even in young sub-adult individuals where the sutures were not yet closed. In Homo habilis at the same age, the temporal muscles ended only halfway up the left side of the parietal, exactly as in a young man today whose third molars are just erupting. The moment it is possible to reduce the size of the temporal muscle, the potential for brain expansion (not necessarily brain development in the wider sense) relative to body size is immediately developed. It becomes not only a possibility but a probability. Add to this the further selective advantage of better hands and better fingers, and one finds Homo habilis developing. The process of hominization had thus started. By the time man reached

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the stage where he began to say "Why couldn't I kill for myself instead of having to go and scavenge?", he had undoubtedly increased his brain size because of the fact that he no longer had huge compressing temporal muscles during his early childhood and youth. The brain capacity of Homo habilis in the lower part of Bed I is considerably higher (in a child of eleven years) than the greatest brain capacity of any known Australopithecine adult. Man had reached the point where, by brain development and reduction of temporal muscles as well as by any changes in the relative proportion of his teeth, he had become potentially capable of beginning to hunt and kill. I do not say that he had not made certain weapons of aggression before those that we can prove he made. Theoretically, it is highly probable that at still earlier times he had weapons of aggression made from wood and similar materials, or that he was doing as Samson did, picking up "the jawbone of an ass". But on the upper part of Bed II we find unquestionable bolas stones, and that very definitely suggests the beginning of the means to attack from a distance. Let us go back for a moment to man the scavenger. There are those who suggest that a naked, weaponless Homo habilis, or an Australopithecine, could hardly have approached a carcass when the killer lion, leopard or cheetah moved away from the unfinished meal to drink, without at once coming into conflict with the hyenas of that time. Of course, there was also competition from vultures and jackals of various types. To meet this argument, my sons and I conducted some experiments. We found that if one of us, alone, naked and unarmed except for a piece of wood picked up from under a dead tree, or a jawbone or leg bone of a giraffe, tried to drive hyenas and vultures off a kill, they sometimes stood their ground. One alone was not always enough, but if two of us went, waving natural objects in the form of weapons, we could at least temporarily drive the hyenas and other creatures off the kill. We then found that if both of us bent down to try and cut off meat, the hyenas would tend to come and attack. But if one stayed upright, threatening and waving, while the other bent down to cut off meat, it could be done. Sometimes the hyenas became so desperate that they charged in, causing us to leave. I have no doubt similar situations arose in the past and early man learned what he could do without proper weapons. From this start man began to get the idea that it might be possible to attack animals with weapons. Man was advancing fast. His brains were getting larger, and his teeth were getting smaller. In many respects he was tending more towards the Homo of today. I believe that in this development for scavenging and self-defense we have the birth of aggression. Thus we see how studies of early man help us explore the theme of this conference. Defense for man, until he had learned to make and use weapons, was the defense provided by Nature and still

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used unwittingly by us, although most of us are too frightened to risk trying it. Most present-day humans do not have that degree of faith in their own smell to ward off carnivores. As for aggression, the sequence of events in its evolution, as I see it, was as follows. First came a phase where there was no real aggression—as in the proto-hominids. Next came aggression developed against fellow scavengers of other species to drive them off the kill while man obtained meat for himself and his family; this was a very simple and utilitarian form of aggression. Then came the development of actual weapons for aggressive purposes, such as the bolas which enabled man to attack animals from a distance. W e have clear evidence that man regularly attacked and killed giant baboons at sites like Olorgesailie; having thus carried his aggression against other primates it was possibly a natural (if regretted) step to extend his aggression towards other men. Thus, from being wholly unaggressive, with nothing but a built-in defense mechanism, man eventually came to arm himself with such things as bolas, bows and arrows, guns, and then nuclear weapons. Man became a major aggressor, but notably his aggression is expressed mainly when he is armed. Discussion

Birdsell: Dr. Leakey has an entire glorious continent which he has thoroughly and scientifically exploited. I will deviate from his subject and start my discussion with models of aggression for prehistoric men derived from living people. Dr. Leakey and his sons have experimented on competing with hyenas for abandoned carcasses; Elizabeth Marshall Thomas (21), who may not be an altogether authentic reporter but is a very talented writer, described four Bushmen involved in a similar pursuit for serious purposes. They had shot a bull wildebeest with poison arrows, but since Bushman poison takes some time to work, it was several days before they caught up with their victim, only to find a large pride of 20 or 30 lions already on the carcass. These were little men, weighing perhaps 115 pounds each, and their meat was going down 400-pound cats, so they said, " W e know you are strong, Big Lions, we know you are brave, but this meat is ours and you must give it back to us." One does not harass lions with poisoned arrows which take two days to work; this is an unprofitable gambit. So they approached, throwing little stones and clods of earth and repeating, "Great Lions, Old Lions, this meat belongs to us." They walked closer, these brave and hungry four and, as they approached, the feeding lions withdrew, and in triumph the Bushmen got what was left of the wildebeest. I cannot guarantee the authenticity of this story but it suggests the dimension of flexible behavior at a vocal level, and I think the chances are quite good that the human voice used as an instrument of aggression does affect wild creatures.

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Living men are not good models for man half a million, one million, two or fourteen million years ago, but they are subject to our observation now and, hence, useful. Aggression among living hunters and collectors—we must limit ourselves to these kinds of folk—varies considerably. It is difficult to find cases of interpersonal violence among Bushmen, who are less abrupt than other people, but let me describe a story culled somewhere out of a now unidentifiable Eskimo ethnology. Wife procuring is a little irregular among Eskimos, and one of them got a wife, whom he apparently cherished all his life, by creeping into her parents' igloo and killing seven of her immediate family: mother, father, two or three sibs and a couple of collateral relatives. This apparently did not jeopardize his marriage, for, according to the reporter, they were a well adjusted couple. This is aggression at a fairly advanced level. I will quote a number of cases from a very good, detailed volume by M. J. Meggitt's Desert People (17), which deals with Walbiri tribesmen of Australia who have been undergoing acculturation for 20 to 30 years. These examples do not primarily illustrate aggression, but the interrelation of classifying relationships and how they work. "The half-brothers Donny and Yarry djabangari usually camped together in a friendly fashion. One afternoon, however, one of Donny's young sons hit Yarry's child. The mothers of both children intervened and were soon involved in a scuffle with digging-sticks.* Donny came to his wife's aid, striking her opponent several times. Yarry at once attacked Donny, and the two men, both tall and powerfully built, engaged in a vicious fight. Donny speared Yarry in the arm, but had his head split open with a club in return. Younger men, chiefly their brothers-in-law, separated them, but the quarrel quickly flared up again. Donny felled Yarry with a club, splitting his head in several places. . . . Everyone was thoroughly upset by the quarrel, which revealed the social difficulties created when close brothers fought each other" (17, p. 150). Splitting a head does not necessarily mean sundering the bones, but there is no good clinical description of what it really does mean, either. The above shows how a couple of children can set off adult tensions in a very vigorous fashion. The same principle can be illustrated further by another example from the same work: "Danny djungarai had a daughter Gladys, aged about two, by his wife Maggie nangala and a son Richard, aged about two, by his wife Mona nangala. One day Gladys attacked Richard, and Maggie slapped her lightly in the presence of Big Maggie nabangari, Maggie's own mother. Big Maggie at once split open Maggie's scalp with a digging-stick. When Lady nangala, Maggie's half-sister, heard of this, she belaboured Big Maggie with a club. By the time the amused onlookers separated the women, Big Maggie's head was split, her knee bruised, and her wrist broken." (17, p. 147.) * A digging stick is three, five, or six feet long and weighs five or six pounds.

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This is a trivial and amusing story, but although it deals with a couple of children who caused their grandmother to assault her daughter and immediately involve other women at a percussion level, Meggitt does not use it to illustrate violence but rather social relations. Australians are perhaps the most violent of living hunting and collecting people, and it would be interesting to know how frequently they seriously aggress each other. I have only a few fragments based upon my own data on the living aborigines. Upon careful examination of 27 adult Nadadjara women who were "bush" but partially acculturated, I found two with sizeable scars on their head where the hair had been cut. The hair had grown out 15 mm in one case and 20 mm in the other. The causes of the wounds, which I estimated to be 9 to 12 months old, were interesting. The first case involved a charming young woman whose husband had clubbed her twice. He had sent her a mile to the waterhole and, in her absence, their infant child had cried. What did he do? He lifted her scalp twice. She did not seem to resent it. I probed this a little bit because they were an attractive young couple, and this was rather unexpected. I also asked, "How about beating your wife?" He said, "We always do it with a glancing blow. It is not like when you hit a man." So, there is a subculture in clubbing. He really does not try to crush her skull; he simply teaches her a three-inch lesson. In the other case, a woman was in rather serious difficulty because she had fought another woman over a man. Usually a man fights a man over a woman; however, these two women had taken digging sticks and nearly knocked each other's brains out. If these figures indicate a reasonable frequency, two out of 27 in a period of one year would mean that every woman averages serious cranial blows every 14 or 15 years. If they have a life expectancy of 35 years, then one may say that selection was really giving them a cranial stressing at the rough rate of one episode in the adult life of each woman. It may have been more frequent, since they also used stones to gash their scalps in mourning, although I suspect these are fairly controlled blows, probably flesh- rather than bone-deep. But if one looks at an old woman's head in Australia, there is often more scar tissue than hair. The men do not give glancing blows and they do not show as much scarring, since death probably results from head injuries more frequently. I suggest that this is rather normal human behavior at this level. I would like to explore a rather interesting situation which has always been a little difficult to explain. The primates are not thick-vaulted, although all tool-using men are, including the Australians. I suggest that there is considerable selective pressure involved, and that survival, literally, has meant that those thin-walled vaults had a much lower chance differentially of surviving. I suggest, specifically, that human aggression over a million or two years has resulted in vault thickening which has

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only begun to reverse its direction in the last few millennia. I am told that even in modern populations there is considerable variability in vault thickness and many individuals approach Pleistocene standards. In short, the evidence suggests that man, after becoming moderately tool-using, has been persistently aggressing against other men and women. As I knew Dr. Leakey was coming, I asked Professor Raymond Dart how many of his Australopithecines were murdered, and he answered, "All of them." Leakey: I believe that the interrelationship of danger calls given by various animals, and the way they understand (to quite a considerable degree) the danger calls of other creatures would make a tremendous subject for investigation; at the present time we are completely ignorant of their significance. My experience in the last few years has very strongly suggested that there is an incredible interspecific and intergeneric and even interorder understanding of individual signals, and I think that the vocal aspects of aggression would be a most fruitful study for some would-be Ph.D. candidate. In our camp at Olduvai we have noticed again and again that, if a cat goes to a place where there are birds, such as the Masai sparrow, one of these will set up a warning call to the other sparrows, "Cat, cat, cat, danger, danger, danger." Our pet monkey, Simon, understands immediately that the birds are saying "danger", and although he does not know what the danger is because he has not seen anything himself, he too gives the danger call. When the dogs hear the monkey's warning noise they start giving a danger bark. They set off to investigate and come back looking very foolish when they find it is just the tame cat. I have been told—this is purely hearsay—that if members of the Wasanye hunting tribe down on the Tana River in Kenya want to get rid of a dangerous animal without calling attention to themselves, they imitate the danger call of birds, or the danger whistle of a bushbuck, or the screech of a tickbird. The offensive rhino or buffalo then thinks to itself, "Danger! I had better get out and fast." It occurs to me as possible (although I do not assert it) that the Bushmen described by Ann Marshall as vocalizing, "This is our meat; this is our meat" may in fact have been deliberately or subconsciously using noises indicative of danger, which the lions may have recognized. Perhaps these went away not because of the Bushmen, but because they were crying "danger" in some language which the lions could understand. Turning to Dr. Birdsell's second point regarding thickness of the vault, I would urge caution in using thickness as a primitive character; I do not believe it is necessarily valid. For example, when the fake Piltdown skull showed a thickness of 13 mm at some points, all the textbooks assumed that it must have been primitive; indeed, the forgers had chosen a thick skull because they thought this would prove it to be primitive. Some prehistoric skulls are thick and many are not; Homo habilis, both in adults and juveniles, had an extremely thin skull two million years ago. Some of the most primitive African tribes have considerably thinner brain vaults than yours or

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mine. On the whole, in a large series of specimens I measured, the Negro's parietal bone was thinner than that of the average European. I think we should be careful about generalizing from a few samples. Some of the early primitive skulls examined happened to be thick-walled and it was once laid down in textbooks that a thick skull was evidence of primitive man, but if one were to make a statistical analysis I do not think this would hold true. My third point concerns the matter of children starting fights among primitive Australian peoples. Fighting by juveniles is also a fairly frequent factor in starting aggression among primates such as monkeys or baboons. My personal observation suggests that if two youngsters are playing (not very violently), and one of them unintentionally hurts the other, the hurt child will scream. Adults will then intervene quickly, but instead of fighting the child they will fight each other. I have no idea whether the fighting is between the relative parents or random individuals, but I expect it occurs randomly. I have seen this in my pack of dogs, too: if a cat gives a cry of pain while fighting with another cat, it may start the dogs fighting among themselves. I cannot tell you why; I am just stating the observation that a cry of pain seems to touch off some aggressive factor in many different animals. The result is that a fight starts and the nearest creature gets bitten. Bernstein: I think our comments about noise and its effectiveness in driving carnivores away ought to be extended. It is quite true that many animals respond to the alarm calls of other animals; I think it is also true that many animals respond to undifferentiated loud noises. Wild animals can be chased away by making almost any loud noise or violent display. The question, of course, is whether these stimuli produce flight due to a learned association with humans as predators, or whether noise per se has this effect. Shouting and making a lot of noise perhaps serve only to call attention to one's self and to warn the animal of one's presence. On the other hand, I can think of examples in nonhuman primates where bluffing by a baboon, for example, has been reported to be effective in driving off predatory cats. My second point is that many nonhuman primates are not strictly vegetarians; they engage in a certain amount of predation and eat a large number and variety of insects. Some nonhuman primates catch birds, reptiles and other small animals, and it appears that in these cases there is more predation and hunting than scavenging. I do not see why we would have to restrict early man's first meat-eating to scavenging, and why he could not have picked up slow-moving and small animals. Leakey: Dr. Bernstein has suggested that loud noises are just as likely to cause flight or alarm in animals as warning noises. I would question this concept and suggest it is the unknown quality and not the amount of the noise that is the factor, and I doubt that it calls attention to the human. Banging on a tin will frighten an elephant; ringing a bicycle bell will drive off a lion. In addition to animals being frightened by well-known alarm sounds which they link with danger, such as those given by birds or other

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creatures, I think it is unquestionable that an unknown noise causes fear. This is true of ourselves as well: humans are most frightened of the unknown in the same way that other animals are frightened of it. Regarding Dr. Bernstein's second point, I certainly agree that other primates, besides chimpanzees, are predators to some extent. The more we study primates in detail instead of superficially, the more we find that our preconceived ideas were very far from factual. A great many people have tried to breed certain species of the Galagos unsuccessfully. They kept them in cages; the animals indulged in mating behavior but did not achieve a successful pregnancy or, if they did, it was quickly followed by an abortion. One of my colleagues in Rhodesia was, I believe, the first to discover that by feeding these species of Galagos with ample amounts of grasshoppers, in addition to fruit and honey, their diet was sufficiently complemented, and invariably mating was followed by pregnancy and good healthy births. One of our neighbors in Nairobi has been breeding Galagos regularly without any difficulty by giving them a correct diet. I would like to recommend to anyone interested in diet in primates the technique now being used at Kasakela by Jane Goodall and her team. She has an additional worker whose main task consists of washing dung, by which she established that chimpanzees are meat eaters. She had seen and filmed chimpanzees suorrounding, capturing and killing a monkey, and she had seen them coming back out of a scuffle in the bush with a dead pig or a dead juvenile bushbuck. This is not observed very often because hunting does not take place in the open but in the denser parts of the forest, so her next question was, "Let us find out whether this is a rare occurrence or a regular thing." With the technique of dung washing, there is not a week that goes by without evidence that the chimpanzee is a carnivorous mammal. Dung washing could, I believe, be applied to studies on other primates, such as the gorilla. I have never been satisfied that Schaller went far enough in his gorilla study (19). His work is comparable to what Jane Goodall did in her first 13 months, and as far as it went, it was magnificent, but he did not observe half the things Jane watched for in the last two or three years after she became completely accepted by the troop. I shall be very, very surprised if gorillas do not eat quite a lot of small game and birds and even a baby bushbuck on occasion and at certain times of the year (although Schaller says categorically they do not). At present this has not been demonstrated, but that does not mean that it does not happen. Thirdly, on the question of slow game, all the early hominids did catch and kill "slow game" in addition to scavenging. We have published this fact (10). Inevitably, in addition to mere scavenging, long before one becomes aggressive and predatory on larger herds, one catches and kills such creatures as water tortoises, juvenile animals which are particularly vulnerable to man, as well as small birds and rodents. Any creature that has developed a certain degree of mental agility can spot very quickly, indeed, whether a

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bird's nest is an old, disused one that has become the home of a rodent. If it is an old nest that has been abandoned by the birds, it rapidly becomes semitranslucent, with little holes, but if a rodent then occupies it and builds its own nest within it, the nest becomes completely opaque. Many primitive peoples have found that no time at all need be wasted testing every old bird's nest in order to catch rodents. Instead, when they see an opaque bird's nest they seize it and squeeze it, injure the animal and then take it out. We found the residue of bones of hundreds of rodents on the sites of Homo habilis. Slow game was certainly eaten, including rodents. Scott: My question concerns Dr. Leakey's material: Is there enough data on some of these different species of proto-Hominidae to warrant their description as populations? In other words, how variable are these early men? Are they, for example, as variable as modern human material? Leakey: Obviously, we are still extraordinarily short of material. We have remarkably little upon which to bis categorical regarding variation; nevertheless, spread over nearly one million years, our habilis specimens show individual variation of considerable degree. But they conform in their basic morphology, and all have major differences—major, observable, measurable differences—from any Australopithecine. Though we only have three Australopithecine specimens so far in East Africa, they clearly conform with the 70 Australopithecines from South Africa, and are clearly unlike any of our Homo habilis. As for Homo erectus, we only have two individuals, but Arambourg® has parts of three more in North Africa. Insofar as the available material shows, they are patently neither Homo habilis nor Australopithecines, but they exhibit certain comparable characters with each other. Again, there is a lot of individual variation, and one can only go as far as one's available material allows. However, I would like to say that there was a strong tendency in the early years of this century to regard any skull that was not Homo sapiens as a freak. Rhodesian man was called acromegalic, and we now know he was not a freak; the Neanderthal man was also claimed to be an acromegalic specimen or else the skull of an idiot, but it was not. It is too easy to try to bypass a difficulty by saying that this or that individual is a freak. I would prefer to believe that the mathematical chances of finding abnormality among the first few specimens is quite low. In fact, the odds are that the freak specimens will not be found. Brosin: Are there nutritional and metabolic factors, including genetic or other such schemas, relative to skull thickness? And are there any inferences regarding the function of the enormously disproportionate occipital lobe? Leakey: At the moment I am unable to answer either question. They are matters about which I have had my own worries. I can find no evidence in the literature to indicate that diet and nutrition have any effect on skull thickness; I would like evidence, but I do not know of any. Just what are • Professor Camille Arambourg, Laboratoire de Palaeontologie, Paris, France.

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the factors that produce very, very thick skulls such as those found in certain Neolithic races, fully as thick as some Pleistocene specimens? Why do we find very thin skulls in Pygmies? I do not know. I would be just as interested as anyone in knowing. As regards the occipital index, I do not think it is linked with the size of the lobes but rather with the curvature of the bone itself. There appears to be a very distinct, specific difference there, first studied in detail by my friend Phillip Tobias, * who worked out the occipital index of a vast number of Homo sapiens, covering all the available races today, and then applied the same techniques to the Australopithecines. All we can say at the moment is that there is a very definite measurable difference in both internal and external morphology, but I would not say it is linked with the brain lobes. I think that would be extrapolating too far from one thing to another. Barchas: There are certain important problems from the standpoint of molecular biology. What Dr. Leakey has done is push back the total number of generations of man that could have been selective for aggressive behavior. If the generation time was 20 years, then 12 million years allow us almost 600,000 generations, as opposed to the 100,000 generations in two million years. Assume our recent history goes back only 10,000 years which is 500 generations. When we reach 600,000 generations, we are dealing with a number of generations that even our friends who work with microbes would respect. To what extent are genetic possibilities manifested in terms of general capabilities of the brain, apart from specific behavioral aspects, that need necessarily be carried out? In other words, can one have certain attributes in neuromechanisms which will facilitate the expression of aggression without necessarily having an entire record or program for the aggressive act? Are these manifested in the neurohumoral systems or synapses? What is necessary? Robinson: I was very impressed by the skull shown by Dr. Leakey with the crest on top and the provision for large muscles, and by his idea that these muscles encased the brain and prevented it from achieving a somewhat larger size. My question is, how can one tell which mechanism comes first? How can one determine that the brain is mechanically constricted? Gloor: My comment is on the same problem. I think that, on the basis of clinical experience, a lot of us would say that the reverse is true, i.e., it is the brain that molds the skull. In a microcephalic, for example, the skull is small because the brain fails to grow, while in the hydrocephalic the skull is large because the brain pushes the case out. I would not lightly dismiss the possible role of these large occipital parts of the skull in the underlying development of the occipital lobes. I think the main factor shaping skull size is what is inside, not what is outside. ° Department of Anatomy, University of Witwatersrand, Johannesburg, South Africa.

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Magoun: Since some of us were at an earlier conference on Brain Mechanisms Underlying Speech and Language (4), and the matter of vocalization and communication has come up, I wonder if Dr. Leakey has any comments concerning the development of communication in these fascinating beings he is investigating. Leakey: It is very hard to be more than tentative and cautious when it comes to interpreting whether or not primitive primates had any degree of what we would call speech. I am inclined to suspect, but I would not put it more strongly at this stage—I certainly could not prove it—that there is inferential evidence that Homo habilis might have had speech of some sort, certainly a greater degree of speech than the Australopithecines. In speech we utilize lips and tongue to a great degree for control of different sounds and, of course, the roof of the palate or the soft palate. I do not believe that the very narrow V-shaped mandibular arch of the Australopithecines could accommodate the movements of the tongue for speech as we have it, which I believe requires a much more open arch, much more freedom. Certainly, the tubercles for attachment of the tongue muscles, and the region of the symphysis of the mandible of the Australopithecines are very different from those of man, whereas those of Homo habilis are much more like ours. Equally, I believe that, if one studied the morphology of the premaxilla and maxilla and the face of Zinjanthropus or Australopithecus africanus, one would find an absence of points of attachment for the sort of muscles that control the movement of our upper lip in speech, for using the lips as I am while speaking now. Very largely, those muscles that control the finer lip movements are rooted in our fossae caninae, which these creatures did not have. I suspect that the fossa canina in Homo sapiens and in Homo habilis, and also present in remote Kenyapithecus, may be linked with an entirely different lip structure from that of the apes who, as we know, have a very different way of moving and using their lips. Whether that is what enabled us, eventually, to have our kind of articulate speech or not, I am not yet prepared to say. I merely say there are certain things which are suggestive, and obviously deserve far more attention than they have been given so far. I would like to see some anatomist do a very intensive study (perhaps it has been done without my knowledge) of the relationship of muscle attachments on the bony structure of the lower part of the face to the function of lips in speech. Keith (7) did some work on the tongue, but I know of no literature specifically treating the area of muscle attachment in the control of the upper lips during speech. I would like to see it done. Barnett: On the subject of speech and language, there have been experiments on teaching apes to speak. They were not very successful, but I expect nearly everybody here has heard of Vicki, the young chimpanzee taught to say a few words; "mamma", "papa" and "cup", I believe, were achieved in the appropriate circumstances. This suggests that a chimpanzee

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can, in fact, make noises which we recognize as words, but the implication seems to be that it lacks the neural organization which makes proper speech possible. There is another matter regarding speech that I think is an interesting speculation, if no more. Haldane (6) has suggested that human speech as we know it is a recent development. We already know, as Dr. Leakey has said, that chimpanzees use tools, without speech. Man may have initially made and used tools with very little speech, and developed a modern type of language in the Upper Paleolithic, at a time of rapid change. Perhaps it was at that time that most imbeciles and idiots were eliminated by a kind of social selection. Haldane further suggests that the reporting of events which have happened in the past (which is confined to man) was a result of the desire of men to boast about their achievements. One of the origins of speech, according to this view, was the desire of the fisherman to report his catch. Brazier: Dr. Barnett has referred to Vicki; does he know that the obstetrician who delivered her is sitting next to him? Pribram: He was both obstetrician and undertaker. Vicki was a very good friend of mine, but I was never able to understand either "papa", "mamma" or "cup", despite what her "parents" thought. It was not too clearly expressed, and was perhaps no better than what a dog would be able to do. I think Dr. Leakey's point is well taken in general, but the neural control has to be taken into consideration also. For instance, a chimpanzee cannot sequentially move its fingers, though it certainly has the peripheral structure to do so. As has been pointed out, the temporal muscle probably cramps the brain during development. It could be that the occipital musculature does the same for the parietal lobe and thus restricts development, though such influences may be reverted. Yet I would go along with the notion that primitive speech could have come much earlier than has heretofore been thought. Eibl-Eibesfeldt: I would like to know if Vicki was verbalizing at a certain age, I think up to the fourth month, and then stopped. I remember there was a list of syllables ascribed to this animal. Is that true, was it verbalizing? Pribram: Yes. Also with respect to "cup", "papa" and "mamma", there was a period when these words were much more distinctive than later. Toilet training also developed, and then "regressed". Eibl-Eibesfeldt: Kortlandt (8) attached very great importance to Vicki's verbalizing. He took it as additional support for his hypothesis on protohominid behavior, which implies that the ancestors of the chimpanzees were cut off in their development. I do not know about other reports on rudimentary verbalization of chimpanzees. It would be a matter of great importance. Pribram: There is one other thing to be said. Vicki was not the most intelligent chimp. In a few cases one can make conjectures about heredity and environment, and in this case, I think environment at the time of her birth

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had some effect. Her mother, Vera, had experienced a similar situation with a previous baby; hence when the experimenters approached at the time of Vicki's birth, she began to take the infant away, hold it by the legs and slam its head against the cement wall. This was very effective in making us retreat and stop trying to take the baby away in this fashion. Finally, we suddenly scared her into dropping the baby and chased her into an adjacent cage, but a good deal of brain contusion had probably already been occasioned. At any rate, at least one cage-reared chimpanzee of the same age, Franz I believe it was, uniformly performed better on problem solving tests than did Vicki. Leakey: On this question of chimpanzees and Dr. Pribram's suggestion that their mental abilities vary greatly from one to another, Jane Goodall has now made detailed observations on eight chimpanzee babies born since she became familiar with the apes, and the variation in the behavior of these babies in the troop is becoming discernible. Some are more intelligent than others; one is apparently spastic. That is going to be a very interesting study by itself, abnormality in a wild primate group. I think there is no doubt that some have more and some less potential than others for doing a variety of things. Referring to Dr. Pribram's young chimpanzee that supposedly learned to say a few words, it is, I think, well known that in very young chimps and other apes, the resemblance to the human young is much greater than in later years. On the question of verbalizing, even the lip structures of a human baby and a chimpanzee baby are far more similar to each other during the first few weeks, than they are later on when one develops away from the human pattern and the other develops towards it. The further back one goes into fetal state, the more similar are the various unborn primates to each other. Clemente: I wanted to ask Dr. Leakey whether it was fair to assume that early man communicated, if he did not actually verbalize, the method of making sharp instruments. Would establishment of the fact that these instruments were created indicate that the methods in making them were taught from one individual to the next? Leakey: I would say absolutely, unquestionably, yes. Jane has shown on her films that chimpanzees teach their young to make different kinds of tools. If chimpanzees with a 280 cc brain capacity and very heavy body can do so, certainly Homo habilis must have been capable of teaching by vocal or other means. This recurrence of identical patterns of certain types of tools, very highly standardized on every floor at Olduvai even at this remote point in time, would have been impossible without "teaching". I say chimpanzees teach their young; so, for that matter, do leopards. I have watched leopard parents with three cubs go out from the thick bush to the edge of the plain and take each cub out in turn, to teach them how to stalk. Teaching is not confined to humans. Pribram: I have another story about learning and how complicated this

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sometimes seems even in the chimpanzee. At Orange Park we never saw nest-building in chimpanzees who had been taken away from their mothers and raised in the nursery. When I was at Yale we had two adult chimpanzees, then about 12 years old, who had been taken from the field when they were around two to two and one-half years old. When they had an offspring they immediately built a nest. This observation has been repeated: chimpanzees who had been taken from the wild and kept in captivity for an intervening period of ten years without a chance to observe nest-building still produce nests, whereas those who had been taken away from their mothers early do not build them. There is thus a good possibility that something is learned early which does not emerge until appropriately triggered much later. Bernstein: We can extend that. The chimpanzees had very little opportunity to build nests in Orange Park. Four years ago I tested them, and all of the wild-born ones at Orange Park produced nests; none of the laboratoryborn ones did ( 1 ) . Even after putting the laboratory-born animals with nestbuilding wild animals, where they had demonstrations, examples, etc., for two months, they did not build nests. Scott: I would like to make a suggestion which I think Dr. Eibl-Eibesfeldt would certainly second: in talking about animal species, one needs to make a clear distinction between hunting behavior or predation, which normally takes place between different species, and social aggression within the same species. For example, we find animals that will fight each other, as deer and many of the large herd animals do, but are not predatory at all. Also, we find that many of the highly social carnivores use entirely different patterns of behavior for predation and for social aggression. In our terminology as well as our thinking, we need to keep these two things clear. I think that Dr. Leakey made his meaning quite clear, and I am only criticizing his use of the term "aggression" to describe both predation against other species and fighting within the same species of hominids. His argument, therefore, implies that once early men had developed tools for hunting, they extended their predatory patterns to their own species. I can only comment that this does not seem to happen in the social carnivores; if he is right, it apparently has happened in man. Leakey: I would entirely agree that in dealing with animals which are, by nature, predators, one must clearly distinguish between predation and aggression. But I would still be inclined to suggest that when a creature, namely a hominid, who is by nature not a predator, goes into the predatory field, he does so only by virtue of having become an aggressor. That is the only point I made there. His aggression is quite different from that of the ordinary predatory animal because what he is doing is abnormal to his nature. Delgado: I would like to second Dr. Scott's comment about the differences between predatory and aggressive behavior. Aggression is expressed by territoriality, threat and attack which have a destructive purpose

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different from the food-getting aim of predation. Cats are a well-known type of predatory animal, and as they are often used for the experimental study of aggression, caution is necessary in interpreting their apparently hostile manifestations. Pribram: Dr. Leakey, do you know if there is any correlation between protection from predators and the excretion of urea versus uric acid in the urine? Leakey: I have no data on that at all. Pribram: Since man is one of the few animals that excrete urea, I wonder if this serves as protection? Leakey: The Dalmation dog does, too, strangely enough, but it is attacked by carnivores, nevertheless. Bartholomew: I wanted to comment on one of the points brought up by Dr. Scott. When talking about aggression in the general biological sense, one is almost always talking about intraspecific aggression, that is, between members of the same species and, in fact, between members of the same sex within the same species. This pattern of aggression finds its fullest development in the highly gregarious animals whose social contacts are most frequent; in other words, it is in stable, extensive groups that organized aggression reaches its fullest development. This is thrown into sharp relief, I think, in herd-forming ungulates like deer, and particularly in seals. The intraspecific aggression between male seals has favored characters enhancing aggressiveness and has led to quite a dramatic sexual dimorphism. In the Alaskan fur seal, for example, the adult male may be six to ten times bigger than the female, and this difference in size appears to have its primary relationship to intraspecific aggression. Seals and sea lions also show some interesting intraspecific social relations. The most obvious defensive reaction is flight, which is relatively easily initiated by vocal signals, not only from within the species but from without. This latter situation is well illustrated in the California sea lion because it has very poor eyesight. It is quite vulnerable when on land. A human being, on his hands and knees, can crawl up and touch one, if he wishes. It appears to depend, in this context, on the alarm note of marine birds. One bird in a group of nearby sea gulls squabbling among themselves may give an alarm note and cause several hundred sea lions to stampede into the sea. This is parallel to Dr. Leakey's point. Now I wish to return to intraspecific aggression. One of the striking things in highly gregarious and also highly aggressive animals is that a considerable amount of the overt aggression one observes is redirected, which is parallel to what Dr. Leakey mentioned about dogs. When an aggressively interacting pair of animals comes to an impasse, instead of continuing the contest, one of them will frequently fight or threaten some third and disinterested party. As a result, the actual aggressive patterns are frequently redirected, the third animal usually flees, the impasse is ended, and the two original contestants return to nonaggressive activities. Yablonsky: Regarding the distinction between predatory behavior and

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social aggression, I wonder if Dr. Leakey has some notions about the turning point between man's total involvement with the physiological gratification of continuing his existence, when aggression was geared to that particular aspect of his life, and the more contemporary refinements of violence and aggression which relate more to one's emotional gratification. In other words, would it be fair to say that a turning point between predatory behavior and social aggression is that predatory behavior is directed at some potential physiological gratification, and social aggression is related to emotional gratification within some enormous framework, such as the expectations of a culture or of a social structure? I think this has some contemporary significance, in that we have arrived at the point where violence and aggression are not confined simply to the stealing of a loaf of bread or the stealing of money to use for living; violence has become a kick-oriented or emotionally involved expression. Is there any speculation on some phase in man's evolution where he seemed to shift to violence and aggression which had some of these other dimensions, rather than predatory and physiological existence? Leakey: I think even at the chimpanzee, monkey or baboon level aggression can frequently be expressed for emotional satisfaction. There is a very definite hierarchy (pecking order, if you like) in baboons, monkeys or chimpanzees living in troops. It may vary at different times of the year as to who is boss and who is not. If a baboon boss has been away and then returns to the troop, the other baboons all tend to come up to him and in some way recognize him. This was not dealt with by Washburn (22) in as much detail as Jane Goodall did with chimpanzees, and I think it should be studied much further. If a junior within the pecking order does not behave as it should when a senior animal comes, there is very definite aggression, not necessarily actually hitting or biting, but aggression by gesture. I think that emotional aggression is undoubtedly very distinct from many of the other forms of aggression, but they can be coexistent and I should think early man probably had both. Delgado: As you probably know, there was a recent symposium on The Natural History of Aggression (2), which clarified some of the points we are discussing. Lorenz has distinguished between aggressive and predatory behavior, identifying the latter as food-getting, and he cites the case of the housewife killing a turkey for Thanksgiving, which may not be an aggressive act, but which I am not sure could be identified even as predation. Killing of animals in a slaughterhouse may be considered part of the preparation of food, in sharp contrast with killing of men during war, which is typical aggression without alimentary purpose. These comments remind me of a story about a cannibal who was discussing his savage practices with a missionary. He argued that the white man also made war and killed human beings and when the missionary replied, "Sometimes yes, but we do not eat the people," the cannibal answered with surprise, "Then why kill? What a waste!"

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Eibl-Eibesfeldt: I just wanted to add a remark to Dr. Yablonsky's proposal to distinguish predatory aggression by physiological gratification and social aggression by emotional gratification. I do not think that is feasible, since it is often observed that predators which are completely satiated will still hunt. There is a strong drive to hunt. Eating and hunting are often based on different motivational mechanisms. Pribram: Perhaps a means-end reversal takes place. As Mace (15) has suggested, whenever a society becomes affluent this sort of reversal can occur: whatever was work towards a goal tends to become a goal in and of itself. Berkowitz: In addition to this matter of the means becoming an end in itself, it seems to me that there may be an intimate connection between predatory aggression or instrumental aggression, and emotional behavior. Our research with college students indicates that under emotional arousal they can be caused to act aggressively by presenting a stimulus that is associated with aggression. Having some stimuli which are associated with predatory or instrumental aggression, and then having those stimuli present when the person is emotionally aroused can cause what Dr. Yablonsky has referred to as emotional gratification. Maybe from the early beginnings of man there may have been an intimate relationship between these two forms of aggression. Yablonsky: I would like to comment on the extreme of emotional aggression that I found among violent gangs in New York, the so-called Hell's Angels' motorcycle gang, and individuals who seem to participate in senseless violence (24). In instances of extreme alienation, which places the individual on some kind of social continuum where he is almost emotionally dead and totally disaffiliated, he uses violence to validate his existence. I feel that he has a propulsion toward an extreme act of violence and homicide (similar to the manner of violence that Camus alludes to) in order to validate his "being", to feel some participation in the human situation. Another attempt to explain this senseless violence relates, for example, to the case of a young man in a state hospital who had shot his mother and father and participated in other violence, by which he had attempted, in his words, to "break a situation". I am suggesting that, from what may be considered a logical kind of aggression in predatory behavior (related to foodgetting), we have progressed or regressed to the point where violence is intertwined and very much removed from the basic condition of living, acquiring and satisfying one's physiological needs. We seem to have moved into a twisted state of aggression and violence that is very hard to disentangle. Lindsley: In relation to Dr. Yablonsky's suggestion that predatory behavior may be a potential physiological gratification, and social aggression an emotional gratification, I would like to comment on play behavior, which is an ontogenetic phenomenon observed in many species. I do not know where play starts in evolutionary development; however, it occurs in the very young, whose play is often quite rough, it persists in one form or an-

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other to old age and, as we can observe in football and soccer games, it can be quite aggressive and damaging. It seems to arise from a need for sensory stimulation and motor activity, hence a kitten or a puppy will jump, run, curl up, roll over, and rub against objects as though in need of sensory stimulation, or in a state of "sensory hunger". Tactile stimulation by rubbing, visual stimulation by movement and orienting responses to sounds, are some of the activities that young animals seem to enjoy and strive for. Later, this becomes a joint and social enterprise, with the reactions of one stimulating the other. However, the social context is not essential, for a leaf blown along the ground provides sufficient visual, auditory and tactile stimulation to motivate self-play activities in a kitten. In his monograph, Reflexes of the Brain, published initially in 1863, Sechenov ( 2 0 ) discussed at some length the need for sensory stimulation in the young and developing organism; he may have had something like play behavior in mind. Elsewhere I have discussed the sensory need in man (12) and monkey (13) under conditions of sensory isolation and deprivation. In such experiments, humans frequently demand to be released from isolation before their agreed-upon time has been served; they also sometimes report hallucinatory-like experiences and manifest bizarre behavior. Monkeys kept in prolonged visual isolation also manifest bizarre behavior, including biting and hitting themselves, rubbing and bumping against the walls of their cage. It therefore seems that in the very young, and perhaps in the old as well, but certainly in the deprived, there is a physiological need for sensory stimulation which gives rise to activity and play behavior, and perhaps also to aggressive behavior. Eibl-Eibesfeldt: The distribution of occurrence of play is always correlated to the amount of learning that animals must undergo, hence the higher mammals play extensively, while only very few birds play. A woodpecker-finch always uses a tool to probe insects out of cracks and holes. I watched an inexperienced young male probing with a stick but, whenever it saw an insect in a hole, it threw the stick away and tried to reach it with the beak. It learned eventually, by trial and error, to use the tool properly. After satiation, my tame finches took the meal worms and hid them in cracks, but probed them out again; then they hid them in cracks and again probed them out. These birds were playing. Play behavior is in general an experimental dialogue with the environment, which serves the function of learning. All higher vertebrates must learn much and are motivated to do so by curiosity. Plog: I found Dr. Leakey's paper fascinating and also troubling because it completely invalidated some of my old notions and showed me far behind. With regard to the notion that man is basically a defenseless animal on the basis of his physiology and morphology, I would assume this incorporates his emotional characteristics; how, then, can we account for the number of situations in which man's aggression seems to be the natural outcome of an

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event? I think Dr. Berkowitz referred to this earlier in connection with some of his research, and some of the cases cited by Dr. Yablonsky follow along this line, which leads to the old and rather simple but still fairly valid notions in psychology, that frustration leads to aggression, and aggression is practically a natural outcome of things. At a higher social level, I would also refer to some of the work of McClelland on the achieving society (16), in which the most achieving individuals were those who had been at some time in their developmental period very aggressive. One can think of any society which has gained affluence and experienced a golden age, and find that previous to that time it had been aggressive by dominating other nations or cultures. Later, that aggressive drive was somehow redirected inward for the development of its own culture and its own period. My question is whether there is not a closer relationship or tie-in between aggressive behavior and innate mechanisms. I know the word "innate" is not appropriate today, especially with the people at this conference; I have been stepped on enough by my friends in ethology and I am sensitive to the word, but do not know how else to phrase it. I am using the word "innate" as more akin to emotional. Eibl-Eibesfeldt: You could say "phylogenetically adapted". Plog: That is too long. Anyhow, is it not true that aggression is natural to man himself and is adaptive to many kinds of situations, and is perhaps the result of man adapting to huge, climactic changes or other changes in the world? Leakey: First of all, somebody raised a question arising out of my very final sentence. I said, having become the maker of the bolas, and using aggression for predatory purposes, i.e., killing animals, man then moved into aggression against his fellow man. I want to make it quite clear that I do not believe one can become aggressive against his fellow man until such time as he has evolved the means to be aggressive for entirely different purposes, namely for predatory purposes. I think the essence of what I was trying to say was that man's aggression is very often purely emotional against his fellow man. He is very seldom an aggressor for cannibal purposes, but the development of emotional aggression in man only became possible as a result of his having developed weapons for purely predatory aggressive purposes. Secondly, going back one moment to Dr. Birdsell's quotation of Dart as saying "all [his Australopithecines] were murdered", I think he meant that almost all of them died from violence, which is not quite the same thing as murder. I recall that a great American newspaper accused me of saying that a Homo habilis child was evidence of the first "murder". I never used that word. The conversation went something like this. Reporter: "How did this child die?" Answer: "I don't know." Reporter: "Dr. Leakey, how did the child die?" Answer: "I don't know." Reporter: "Dr. Leakey, the child died, didn't it?" Answer: "Yes, I have the skull." Reporter: "How then did he

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die?" Answer: "I am not sure." Reporter: "Dr. Leakey, was there any sign of violence?" I had to say "yes" because there was a hole in the left parietal. Without bothering to discover whether the hole was caused by an accident or falling out of a tree or an act of aggression, it was at once called murder. Going back to Dr. Plog's question, I would like to make the point that, whereas I am fairly sure that man started in very remote times, in the Upper Miocene, as a defenseless creature (other than perhaps through smell or taste) he later became able to defend himself. This has certainly been the case for the last one-and-three-quarter million years, and that allows plenty of time for a change in pattern. Scott: I do not think we need to postulate a change in basic behavior patterns. One possibility is that early man, even before he developed tools and weapons, may have shown a certain amount of harmless and playful social fighting, such as we see among children today. For the most part, this does not result in murder. Most of the examples of acute violence in modern man, whether in Dr. Birdsell's aborigines or in our own juvenile delinquents, involve the use of weapons; in short, the behavior of modern man is consistent with Dr. Leakey's thesis. The other point I wanted to make is that the more we study well-organized animal societies in undisturbed conditions, the more we see that they actually engage in very little violence, certainly in very little destructive violence. The kind of destructive violence in human societies described by Dr. Yablonsky occurs in animal societies only when man disturbs them and produces social disorganization by breaking them up, re-grouping adult animals together and keeping them under conditions where aggressive animals cannot avoid each other and submissive animals cannot escape. It is very easy experimentally to produce destructive behavior between animals under conditions of social disorganization, and the very cases of human destructive behavior that have been mentioned here illustrate the same point: generally speaking, human destructive violence is very common in areas of social disorganization. I would also agree with Dr. Leakey that modern man is capable, under conditions of good social organization, of developing highly cooperative behavior and keeping aggressivity under very good control. We can see well-organized and peaceful behavior under most circumstances, if we just look about us; for example, nobody here at the table is going to pick up a chair and start bashing it around. I do not see why the proto-hominids might not have had capacities equal to those of modern man for developing this same kind of well-controlled behavior under conditions of well-developed and undisturbed social organization. Of course, no one knows what they could have done in cases of social disorganization. Birdsell: The violent people discussed by Dr. Yablonsky are a deviant group with no general social, normative behavior, and belong to a totally different framework from that of the Australians whose violence is required by conventional situations. The two cases I cited involved children, but the point is, in Australian society, a child is never struck nor disciplined, and

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the aggression was elicited by children setting things off among themselves. The parents responded because something had to be done and the grandmother beating up her daughter was performing a socially required act. This is not chaotic violence arising from frustrations, or from other things with which Dr. Yablonsky is working; rather, this is what a society expects, and it is aggression in a very patterned form. Yablonsky: In the violent gangs I studied, status was almost completely tied in with violence. The young gang man operating within the gang framework was very normative, although he was obviously extremely deviant within the framework of larger society. We have to look at the subcultural as well as the overall context. We have been talking essentially about aggression and violence of one organism vis-à-vis another. I would like to ask Dr. Leakey if there is any evidence of or data on suicide and, if so, at what point this began to appear. Can suicide be encompassed within the behavioral framework of learning prédation first and then becoming aggressive toward fellowmen? Leakey: I do not think we could ever find any evidence in the prehistoric period to indicate whether death was self-inflicted or inflicted by another. I am afraid the answer is, we do not know. Bartholomew: As I said earlier, conspicuous sexual dimorphism is a striking feature of many highly social mammals; it is also a striking feature of contemporary human beings. Our sexual dimorphism is of the same sort that is associated with male aggressiveness in other groups of mammals. Would Dr. Leakey comment on the presence or absence of sexual dimorphism in proto-hominids as an index to whether or not those animals (or humans) were living in an emotional and social context comparable to that with which we are now familiar? Leakey: The answer is no, we do not have enough data yet; I wish we had. Delgado: I think we should try to differentiate the physiological mechanisms of emotional display, aggression and prédation. MacDonnell & Flynn ( 14 ) have demonstrated that brain stimulation in the cat may evoke aggressive display or deadly attack separately, depending on the stimulated cerebral point, and Roberts ( 18 ) has shown that fear can be distinguished from rage experimentally. The brain probably has different neurophysiological mechanisms related to (a) display, (b) attack, and (c) emotional perception. Kaada: I would like to stress what Dr. Delgado just said. It appears from a number of stimulation experiments that the two types of aggression have different neural substrates in the brain: there is one area in the lateral hypothalamus which on stimulation produces eating responses and, on stronger stimulation, prey-killing. On the other hand, there is an area in the ventral and medial part of the hypothalamus which on stimulation elicits an emotional type of aggression. There are also areas which on stimulation inhibit aggressive behavior. Bernstein: Although we may divide aggression into several types, I think

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the types blend together so that altogether different factors may stimulate virtually the same responses. For example, in many primate societies, one of the functions of the society appears to be the protection of the members, particularly the young. If a young member of the society is in distress, most of the group may flee, which is a nonaggressive response, whereas the rest may become aggressive toward the animals which stressed the group member. In one case an extraspecific animal, a predatory bird or small cat, who attacks a young animal in the group may in turn be attacked by other members in the group. In another case a group member may attack another animal in the group and be attacked in turn by other group members. A female will frequently defend her young against extra- or conspecific aggression. Thus aggression can take place among animals within a group that is not at a stage where predation is very important, and prior to the development of tools which might inflict skull crushing blows. Human children certainly bite, slap and scratch each other and there is no reason why this kind of aggression could not have occurred in human groups before there was organized predation. Barchas: The amount, form, and degree of aggression can be described for different loci in a human society. In our studies of disturbed families who come for psychiatric help we found that aggression takes many different forms. It can range all the way from extreme physical aggression (child-battering syndrome and wife-beating syndrome) to forms which involve no physical contact but which can perhaps be described as verbal and psychological warfare. In these situations, the family sets up a local milieu, a local set of rules which may run quite counter to those set up by the larger society, and the people concerned may operate under at least two completely different sets of rules, depending upon which group they are orienting to, the family or the outside world. Even in the healthy family, there is a great range in the use of aggression for dealing with the world. I think one very important aspect is simply the way different groups, small as well as large, define what is aggression and what is helping, and to what extent and in what way aggression is channelled into either helping or non-helping situations. Delgado: Aggression is certainly a complex response and there are probably different kinds of aggression, but I hope this conference will help to clarify the welter of observations, experimental data and speculations. Aggressive performance may be considered a sequence of motor patterns which follow each other like the notes of a melody and, according to the theory of fragmental representation of behavior (5), each behavioral fragment has anatomical and functional representation within the brain, and the fragments combine into different sequences according to the different types of behavior. At the same time, the motor performance depends on previous training and skills. The aggressive purpose of a sedentary person and an athlete may be similar, but the traumatic effect of their respective

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attacks will be very different. Some problems to be investigated are whether we can relate specific motor and autonomic responses to specific cerebral structures like the motor cortex, and whether other areas of the brain such as the limbic system may be in charge of the sequential organization of the behavioral fragments. Berkowitz: It seems to me that there are various ways other than neural investigations by which this might be examined experimentally; for example, behavioral investigation, which is my own vested interest, suggests that an important distinction might be made in terms of the goal response of the activity sequence. Defined in this manner, there is experimental evidence at the human level suggesting that the goal response to aggression might be determined in terms of perception of injury to a particular object. This is perhaps one way of differentiating between instrumental aggression, in which there is a certain kind of goal response, and non-instrumental aggression, where the human being apparently achieves satisfaction by perceiving that a certain object has been injured. Leakey: I want to make a brief comment on this, relative to aggression in early man and in primates. Quite frankly, I have geared all my thoughts during this conference toward what you might call aggression against outsiders, whether outsiders in terms of animals, or outsiders in terms of other creatures of the same species. I believe that this is an entirely different pattern of aggression from that which is within the family or within the group. This is very seldom pressed beyond a certain point, and can best be regarded as play aggression, either between two juveniles, or between two chimpanzees in the same troop, or two baboons in the same troop, and even when manifested in adults. It is in part threat and in part a temporary emotional upset. I would be inclined to suggest that these types of aggressive acts must be kept entirely separate from more real aggressions directed outside the group, either toward another species or toward individuals completely out of the small group. I would like to hear the comments of Dr. Eibl-Eibesfeldt. Eibl-Eibesfeldt: Aggression within a group is normally prevented by specific buffering mechanisms. Greeting ceremonies serve this function, as can be shown in the flightless cormorant of the Galapagos islands. These birds form pairs: one is always at the nest, while the other fishes until its turn comes. Whoever approaches the nest brings a bit of seaweed, a sea star or a stick as a "present", which is grasped by the partner. If the mate returns without a present, e.g., in case we took it out of its beak, it is attacked immediately. In our everyday life greeting ceremonies serve the same function. We need only neglect to greet our closest friends for one week to experience their unbuffered aggressivity. Hedlund: It may well be that my comment is obvious and that it is unnecessary to make this point explicit, but it seems to me that we have become concerned with a number of different kinds of aggression: "predatory

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aggression" perhaps mediated by physiologic needs, at one end of the continuum, all the way to a "sublimated aggression" that has little overt similarity to our usual, common-sense construct of aggression. Yet we are using the single word "aggression" with reference to all of these, often forgetting that the different kinds of observations and operations that define them may not lead to a unitary class of phenomena. While we could continue to wallow in a common-sense and ambiguously defined notion of aggression, it seems to me that each of us should carefully specify the antecedents and characteristics of behavior he is discussing, and make explicit any relationship between that behavior and the construct of aggression. This way we will run less risk of misunderstanding each other, and stand a better chance of relating different kinds of behavior and brain function to the notion of aggression. REFERENCES

1. BERNSTEIN, I. S., Response to nesting materials of wild born and captive born chimpanzees. Anim. Behav., 1962, 10: 1-6. 2. CABTHY, J. D., and EBLING, F. J. (Eds.), The Natural History of Aggression. Academic Press, London, 1964. 3. CLABK, W . E . L., The Fossil Evidence of Human Evolution. An Introduction to the Study of Palaeoanthropology. Univ. of Chicago Press, Chicago, 1955.

4. DABLEY, F. L. (Ed.), Brain Mechanisms Underlying Speech and Language. (In press.) 5. DELGADO, J. M. R., Free behavior and brain stimulation. Intern. Bev. Neurobiol., 1964, 6: 349-449. 6. HALDANE, J. B. S., Animal communication and the origin of human language. Sci. Prog., 1955, 43: 385-401. 7. KEITH, A., The Antiquity of Man. Lippincott, Philadelphia, 1928. 8. KORTLANDT, A., Chimpanzees in the wild. Sci. Amer., 1962, 206(5): 128-138. 9. LEAKEY, L . S. B., Olduvai Gorge. Cambridge Univ. Press, Cambridge, 1951. 10. , A new fossil skull from Olduvai. Nature, 1959, 184: 491-493. 11. LEAKEY, M . D., A review of Oldowan culture from Olduvai Gorge, Tanzania. Nature, 1966, 210: 462-466. 12. LINDSLEY, D . B., Common factors in sensory deprivation, sensory distortion, and sensory overload. In: Sensory Deprivation (P. Solomon et al., Eds.). Harvard Univ. Press, Cambridge, 1961: 174-194. 13. LINDSLEY, D . B., WENDT, R. H., LINDSLEY, D . F., F o x , S. S., HOWELL, J., a n d ADEY, W . R., Diurnal activity, behavior and E E G responses in visually

deprived monkeys. Ann. N.Y. Acad. Sci., 1964, 117: 564-587. 14. MACDONNELL, M . F., and FLYNN, J. P., Attack elicited by stimulation of the thalamus of cats. Science, 1964, 144: 1249-1250. 15. MACE, C. A., Psychology and aesthetics. Brit. J. Aesthet., 1962, 2: 3-16. 16. MCCLELLAND, D . C., The Achieving Society. Van Nostrand, Princeton, 1961. 17. MEGGITT, M . J., Desert People. A Study of the Walbin Aborigines of Central Australia. Angus & Robertson, Sydney, 1962.

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23. 24.

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Rapid escape learning without avoidance learning motivated by hypothalamic stimulation in cats. J. Comp. Physiol. Psychol1958, 51: 391-399. SCHALLER, G . B . , The Mountain Gorilla; Ecology and Behavior. Univ. of Chicago Press, Chicago, 1963. SECHENOV, I. M., Reflexes of the brain. In: Sechenov: Selected Works ( A . A . Subkov, Transl. and Ed.). State Pubi. House, Moscow, 1935: 263-336. T H O M A S , E. M., The Harmless People. Knopf, New York, 1 9 5 9 . WASHBURN, S. L . , and D E V O R E , I . , The social life of baboons. Sci. Amer., 1961, 204(6): 62-71. WEIDENREICH, F., The skull of Sinanthropus pekinensis; a comparative study on a primitive skull. Palaentologia Sinica, 1943, ser. D2: No. 10. YABLONSKY, L., The Violent Gang. Macmillan, New York, 1962.

1 8 . ROBERTS, W . W . ,

19.

AS A F A C T O R

ATTACK AND DEFENSE IN ANIMAL SOCIETIES S. A .

BARNETT

Glasgow University Scotland

Anyone reading the account of the London symposium, The Natural History of Aggression (9), might be left with the impression that colleagues in Western European and North American universities regularly abuse, rob and assault each other. He would also perhaps remark a statement by Harrison Matthews (16), that there are no clear examples, in natural conditions, of fighting to the death among mammals of the same species. I discuss here conflict within animal, mainly mammalian, species. This obliges me to look critically at concepts such as "aggressive instinct". I also examine how an analytical attack on this sort of social behavior can suggest fruitful experiments—experiments which can tell us more about the behavior than can be conveniently stated in traditional terms. Finally, since this symposium is concerned principally with man, I must try to suggest how our own species fits, or does not fit, into the zoological picture. T H E N A T U B E OF A N I M A L C O N F L I C T

Buffon (7) writes of wild rats, Rattus norvegicus: ". . . in the case of a famine being occasioned by their numbers the strong kill the weak, open their heads, first eat the brains, and then the rest of the body . . . It is the same with field mice, whose prodigious increase is checked solely by their cruelties to each other when provision becomes scarce." BufFon's account is no doubt imperfect in detail, but wild animals do come into conflict. Yet some species, including those of the supposedly ferocious rats, are colonial: they live in groups, often large and thriving, and their more usual state is amicable, not hostile. These and many other species throughout the animal kingdom display both tendencies, of herding and also disruptive activity often called aggression. To name features of this behavior, I use three terms, not quite conventionally but, I hope, clearly. First, a clash is what a lawyer would call battery: it is an incident in which one individual wounds another; attack may or may not be displayed by both agonists. Second, threat is a sight, sound, odor, or contact which does not wound, but tends to prevent the approach or cause the withdrawal of another member of the same species. (It is a pity this usage is so different 35

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from the colloquial one.) Threat may be followed by attack—that is, a clash —if the opponent stands its ground. There is, however, no well-marked boundary between threat and clash: a bite, for example, might wound very slightly, and so induce withdrawal. This blurring cannot be helped: the complexities of behavior can never be matched in a few simple definitions. Third, the term nasil (4) has been coined to label social signals which do not involve conflict (that is, threat or clash); they sometimes seem to prevent it, and may even induce approach. All three types of behavior come under the heading of agonistic activities, though nasils strictly include sexual, parental and filial behavior, with which we are not concerned now. Among colonial mammals, conflict may occur between members of different groups or within one group. The first is usually territorial behavior. The term territory is used here to mean "defended region". Territorial behavior has been most studied among birds, but is general among land vertebrates, and it occurs among fish, and even invertebrates such as fiddler crabs, Uca. Despite much fascinating variety, certain generalizations are allowable (18, 21, 34): clashes are rare and hardly ever lethal, and the lay notion that the beasts are in a state of continuous harmful strife is a kind of anthropomorphism, even when applied to the apparently most ferocious species. Territories put a limit to the densities of populations, usually through the withdrawal of intruders. Rodents, which have been the most studied mammals, gurgle, chirp, purr or chatter their teeth at the approach of a stranger; their hair is raised, they often turn their flank and dance, prance or mince around their opponent (Figure 2). They may leap and bite, but serious wounding is unusual (5). Among Primates, loud sounds and conspicuous gestures are frequent (8). Many mammals, ranging from deer (Cervidae) to Carnivora, signpost their territories with scent marks which are said to have a deterrent effect on intruders (17); often the secretions are the products of special glands which evidently serve no other function. All these social signals are highly distinctive features of the species which display them; hence we can distinguish the species of many birds by their song alone, and some mammals by their sounds. Threat and attack are usually the prerogative of the territory holder: an animal, well able to threaten on his own ground, usually withdraws when caught on another's. Hence a single individual possesses the ability to perform both (a) stereotyped threat displays and ( b ) the appropriate responses to them, according to the precise circumstance. A species with a system of threats and responses which cause dispersion must also have ways of bringing individuals together, if only for mating. Colonial species further require means by which conflict within groups is prevented or controlled. Such signals, instead of releasing a response, may have an opposite effect: they have then "social inhibitors" instead of social releasers. Among wild rats, Rattus, possession of a colony odor is prob-

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Figure 2. Threat posture of a wild rat, Rattus norvegicus, on encountering a newcomer in its territory. In some circumstances this posture is performed without any subsequent clash.

ably the principal guarantee against fratricidal strife (2), but these, and probably all other species of mammals, also display postures and even sounds which seem to have a similar function. Among rodents, there is a widespread tendency for a threatened animal to lie down, shut its eyes and perhaps squeak or squeal ( 5 ) ; inevitably this has been named "submission" or "appeasement". There are also nasils which may be performed during either conflict or an entirely peaceful meeting. Wild rats crawl under each other. This is a quite distinctive, taxon-specific act: it may be performed by an adult male in a strange area on meeting a resident (territoryholder ), but also by a peaceful resident on meeting a stranger. (Juvenile rats at play crawl under any other rat that happens to be near.) Another apparent nasil is mutual grooming: this is displayed by colony members among which there is no evidence of conflict but in a clash the attacker may break off and groom the other agonist, sometimes rather vigorously. Perhaps the social role of grooming varies with the circumstances. To analyze these circumstances would be an exacting task. "Greeting ceremonies" have been described in several species of small mammals. American beavers, Castor canadensis, stand upright, shove with their forelegs, sometimes lock jaws but without wounding each other, roll over each other and finally walk off (32). Black-tailed prairie dogs, Cynomys ludovicianus, embrace, groom each other, kiss and separate (19). The en-

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counters of lemmings, Lemmus lemmus, are more strenuous, and are of the sort usually called fights: the opponents box, bite each other's snout, fall into a clinch, and kick; the outcome is flight by one agonist. Even in this species, however, serious fighting is rare in the wild ( 1 ) . The deer mouse, Peromyscus maniculatus, has a regular system of postures which indicate an attacking tendency or a submissive one ( 1 2 ) . The larger colonial mammals, notably Carnivora such as wolves, Canis lupus, and Primates, have status systems (peck orders, dominance hierarchies). By this term is here meant any social organization in which certain individuals have prior access to food, females or other amenities. Priority may be a function of age, or it may be a consequence of previous clashes. There are many kinds of status systems, and no agreed terminology for describing them. But all seem to prevent dispersive conflict among members of the same group, while the mutual intolerance of different groups keeps the population as a whole well spread out. There are good descriptions of the lives of wolves (23, 25). These handsome and fascinating, if alarming, creatures are thoroughly agreeable in their own domestic relationships. We readily understand their postures from our knowledge of our own dogs, C. familiaris. The attitude of a dominant male and that of an inferior are equally striking; so is the fact that (as usual) actual clashes hardly ever occur: agonistic behavior usually consists of formal gestures of which the most violent is snapping at air. Pairing is for life, but a small group may include unpaired males which contribute to the care of the young. Baboons, Papio, are among the Primates whose status systems have been intimately studied (6, 36, 37). Mutual grooming plays a large part in the social process, and dominance can be measured by the amount of grooming an adult receives from others; the most groomed males also have prior access to food and settling places. Dominance is achieved by clashes. Usually, there is a stable "hierarchy", in which case clashes are rare. This is partly because dominant males stop fights among other males. Washburn & DeVore (36) write: "Normally there is no fighting over females, and a male, no matter how dominant, does not monopolize a female for long." SIGNALS

Status systems are species-characteristic: on the whole, each species has its own system, though there may be diversity in detail among groups. Certainly, the social signals—postures, sounds and odors—are standardized for each species. By a signal I mean a small amount of energy or matter which induces a large change in the rate of energy-release in a system. A social signal is produced by an animal and acts on another of the same species. To what extent are we justified in thinking of agonistic signals and reactions to them in terms of stimulus and response? Among the best known studies of signalling systems are those in which models have been used to

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provoke a stereotyped reaction (33). Models abstract certain features of an animal—usually a visible pattern or a color, but sometimes a type of movement. By this means important progress has been made in the analysis of the sensory aspect of "instinctive behavior". The method can even be applied to human behavior, though only in infancy. But one disadvantage of a successful model, is that it can make analysis seem too easy. Even a young herring gull, Larus argentatus, pecking at its parent's beak, does not behave with machine-like regularity: the effects of shape, color and contrast have to be recorded as percentages of response (33); and this is a particularly simple case. The exchanges of signals between adults, especially among birds and mammals, are far more difficult to interpret. Quantitative statements on the effects of a given "social releasing stimulus", describing what response is released and how often, hardly exist. An exception is the work of Stokes on the blue tit, Parus caeruleus (31), which was watched at a winter feeding station. Crest erection and fluffing of body feathers reduced the incidence of escape by other individuals (that is, other birds flew away more often when crest and body feathers were not raised): the first reduced escape from 37 per cent of occasions to 3 per cent, the second from 34 per cent to 5 per cent. These percentages illustrate that there was no simple stimulusresponse relationship. In this example, very detailed, careful study allowed the observer to record the incidence of particular postural features and their probable effects. But, quite often, during an agonistic encounter (or, for that matter, during courtship as well) one attitude merges into another and then reappears. The "threat posture" of a wild rat, Rattus norvegicus, distinctive enough on some occasions (Figure 2), may be only imperfectly performed; and it may, by a rapid transition, become its opposite, the "submissive posture", in which the animal lies on its side. This sort of behavior makes a decision on the precise social effects of certain signals extremely difficult. Figure 3 gives examples of the ambivalence of agonistic behavior. The left of the figure refers to the incidence of three acts which are principally (or, in one instance, wholly) displayed by a "dominant" animal. In these encounters, dominance was conferred by residence in the experimental cage. On the right are shown acts more likely to be performed by an intruder, or by a subordinate animal. But each of the six acts, except the attacking jump, is performed to some extent by both kinds of rat. Residents do sometimes "submit" to an intruder, at least briefly; and intruders occasionally adopt the threat posture. A further complexity arises when we look at the development of social (including agonistic) behavior. Although social signals are species-characteristic, this does not signify that their development is always utterly fixed and preordained. The same applies to the ability to respond to them. An outstanding example is the work of Harlow and his colleagues (13,14,15) on the development of the social behavior of Macaca mulatta. The normal social

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% 60 40 'TOOTH CHATTER* 20

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Figure 3. Incidence of performance of agonistic acts during encounters by adult male wild rats, Rattus norvegicus, who are resident in a territory (checked columns), or intruding into another's territory (plain columns). (After Barnett, 2.)

behavior of these monkeys depends on their early experience with other monkeys. Males reared in isolation not only fail to mate but also attack others when released among them, instead of taking part in a stable status system. Females can be mated, but with difficulty, and they horribly neglect their young. The latter are said to be oversexed and liable to attack and injure other monkeys. This species, like all others except our own, has stereotyped signals which evidently prevent harmful clashes; but in experimen-

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tal situations the development of these signals and the responses to them can be totally disrupted. In this cursory account of animal conflict, I have tried to give fairly rigorous definitions of key terms concerning attack and defense; some of them are necessarily vernacular words put to a new use. For a subject like this, a terminology can be only provisional. For instance, I have used "threat" for acts which have a specific range of effects on other individuals. This makes possible objective statements about the behavior; but equally objective statements of a different sort are sometimes needed, because adoption of a particular posture also reflects the internal state of the performer. It is sometimes tempting, indeed, to say that posture indicates an intention but, in the absence of a physiological meaning for "intention", this temptation should be resisted. Stokes (31), in the work on blue tits previously cited, was able to state a probability that a given sign would be followed by a specific action. Erection of the crest preceded escape on 90 per cent of occasions (but absence of erect crest still had a 26 per cent probability of being followed by escape). When it came to predicting attack, probabilities were surprisingly low: the combination of (a) nape erect, (b) facing opponent, (c) body horizontal, (d) crest not erect and (e) wings not raised, gave only a 48 per cent probability that attack would follow. Many good descriptions of such behavior exist, though very few are quantitative. Often the observer is impressed by the variation in intensity with which activities such as threat or attack are performed. Sometimes intensity can be graded according to the appearance of the separate components of a complex sequence: wild rats may merely adopt a threat posture; or they may approach another rat with chattering teeth and raised hair; or they may do both and then leap; or they may do all these things and bite briefly; finally (and very rarely), they may end by biting and holding on (3). Such phenomena may be spoken of as variation in "attack drive", or even as products of an "aggressive instinct". If these phrases are defined in terms of overt behavior, then they are names. But if they are supposed to refer to internal processes, of which the behavior is an outward expression, they may seem to be explanations when none has been achieved. The growth of biology has entailed the surrender of empty phrases (such as "vital force"); instead we attempt to give accounts expressed in causal terms and based on evidence. Mendelsohn (22) has described how the doctrine of "innate heat" (calidum innatum), formerly a prominent feature of physiology, was replaced in the 17th century by an account of body heat and temperature based on the concepts of physics. The sciences of behavior are still partly in a similar, transitional stage of development. T w o PROBLEMS

Such generalizations are all very well, but the crux comes when one tries to answer some specific questions about behavior. Consider the causes of conflict. Among them might be, a priori: (i) crowding, (ii) shortage of food,

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(iii) sexual provocation. There are also the effects of conflict: these could include (a) death, (b) dispersion, ( c ) lowered fertility. I will take, as examples, one problem from causes, and one from effects. If adult male wild rats, Rattus norvegicus, strangers to each other, are crowded together in a large, unfamiliar cage with nest boxes attached, the chances are that they will settle down and live healthily together indefinitely. But if females are included, the prospect is of conflict and, in these confined conditions, death for most males in a few days or weeks. (The females will remain fit and may breed.) Yet detailed observation of the behavior of the males shows that there is no fighting for the females. Evidently, the presence of females, especially if they are coming into estrus but are not yet ready for coitus, so stimulates the males that their threshold for attack is lowered (2, 4). This has now been tested by recording attacking time, during a series of bouts with strangers, of males (a) when spending a week alone, (b) during a week in the company of two females. We have found a decisive increase in the amount of attack when females are present (Figure 4). The performance of an "irrelevant" act (attack) under sexual provocation suggests that we are dealing with "displacement" fighting. Displacement activities have in the past been described as substitutive behavior resulting from an overflow of some unidentified energy (or drive) inside the animal. Today, as discussed elsewhere (3), the original category of displacement behavior is thought to cover several kinds of response. In the present case stimulation to perform one activity evidently increases the readiness with which another can be evoked. This raises physiological questions, such as the possibility of a state of central nervous arousal which is not specific to any single act or group of related acts. Steiner (30) has shown how thirst can lower the threshold of arousal, recorded by desynchronization of the EEG. Kitai & Morin (20) have very recently recorded a similar consequence of hunger. These changes, detected by electrical means, parallel the familiar restlessness which accompanies deprivation. If we try to apply this type of analysis to agonistic behavior, we require a new physiological terminology referring to identifiable processes in the central nervous system. Fortunately, Dr. Kaada, in this symposium, points a way towards achieving this end. 0 My second example, on an effect of conflict, arises from the fact that death can result from "social stress", as indicated above. The attacks by one adult male rat on another usually lead only to the most superficial wounding at worst. Yet, the victim (usually an intruder on the other's territory ) may collapse and die, wholly without pathological signs on post mortem. This is a consequence of persistent attack in a confined space. The principal known physiological accompaniment of this collapse is greatly " See pages 95-133.

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Figure 4. Effect of presence of females on attacking time by a wild rat, Rattus norvegicus. During 4 five-day periods a strange male was presented to an adult male in his territory (a large cage) daily for 15 min. Intensity of attack was, on the average, higher when females were present. (S. A. Barnett, C. S. Evans and R. C. Stoddart, unpublished observations.)

increased activity of the adrenal cortex (4). Hence, we have here an endocrine response of the sort observed in mammals exposed to other adverse conditions, such as cold, wounding and infection. Death due to intraspecific conflict, as Buffon suggests in the passage quoted above, could be a means of regulating population growth. But encounters of lethal intensity occur in nature only under the exceedingly rare, ephemeral conditions of high population density. Probably the important effects of mutual intolerance in mammals are largely on the reproductive tract, especially of females (4) (though death may occur among adults driven from their colonies, herds or packs, or from a suitable habitat). Just as displays, rather than attack, disperse a population without clashes, so perhaps do frequent agonistic encounters lower fertility without raising the death rate among healthy adults. This type of effect has been postulated to account for the mysterious cycles of population increase and decline among small mammals such as voles, Microtus, and lemmings, Lemmus and Lagurus (10). Even at maximum density, these creatures rarely overeat their food supply. Perhaps their social behavior ensures a decline in fertility before environmental resources are exhausted. The oscillations in numbers

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could be accounted for if there were a delayed density-dependent effect, acting through crowded females on their young. Voles and lemmings either are solitary or live in pairs. Colonial mammals, such as rats and prairie dogs, display no regular fluctuations of numbers. Hence density-dependent agencies must operate on them in different ways, since in favorable conditions these species form densely populated communities. Does food shortage directly influence their social behavior? If hunger can lower the threshold of arousal, it can perhaps also increase mutual intolerance. On this everything remains to be learned. This brings us back to the causes of agonistic behavior. But, whether we are concerned with its causes or its consequences, the search leads inevitably into the central nervous system. Changes in the adrenal glands, or in the glycogen content of the liver or the hexoses in the blood, may be used as indices of the severity of stressful conditions. They are of great interest, and can perhaps lead to more profound physiological analysis than has been possible so far. But they are themselves only superficial. M A N AS A N A N I M A L ?

What has any of this to do with man? In other species we find the opposed processes of herding and dispersion. Can these be usefully compared, respectively, with society and war? In the search for valid generalizations which include man, we may take six items for comparison: Other Species

Man

Stereotyped signals Agonistic behavior Territory Peck orders Lower fertility with increasing density Death of unknown origin

Language War, murder, assault Property Social status Lower rate of reproduction with increasing prosperity Physiological effects of "social stress"

This list, I am afraid, immediately shows how little zoology has to offer to the study of conflict, animosity or dominance in human societies. The failure is not surprising. The societies of other species are founded on standardized signals and responses. The way the signals operate, and how behavior develops in each individual, may be complicated and baffling, but the stereotyped character of the behavior is certain. By contrast, except in infancy, our signals are determined by the culture in which we are reared; they are consequently immensely variable. What all human groups have in common is the ability to use a complex language: this permits reporting past events in tranquillity and suggesting possible future events—perhaps in alarm. The signals of other species usually prevent injurious clashes; so do their orders of precedence. The types of dominance relationships, and the means by which they are set up, are again species-characteristic, though they de-

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pend on the ability of each group member to learn to distinguish its companions. In human societies status may provoke, rather than prevent, conflict. The vast diversity of human custom is exemplified by the varieties of property-holding and the laws relating to it; moreover, ownership of property by man, unlike territorial behavior in other species, certainly does not prevent man from breeding too rapidly for his food supply. It is only when we come to physiology that useful parallels can perhaps be discerned. Our nervous systems and endocrine organs are constructed on the same plan as those of other mammals. A general question is: have any physiological studies in this field suggested useful comparisons between other species and ourselves? I am glad that I can leave this difficult topic to others. Perhaps, when we have discussed it, we shall decide that it is physiology that makes the whole world kin. SUMMARY

The word "aggression", in its colloquial sense, does not adequately describe conflict among animals of the same species. Encounters are usually restricted to displays, and superiority is acknowledged by withdrawal before either party is injured. Within groups, inhibitory social signals prevent or reduce conflict, often (at least among birds and mammals) in the framework of a status system. If death results from "social stress", it is due, not to wounding, but to some indirect effect of mutual intolerance. Social signals are standardized for each species. Their development may require a "learning" process, especially in early life, and their action on other individuals may vary greatly, but they do not permit much diversity of social relationships. The intensity of social interactions may vary greatly with the degree and nature of crowding. Comparisons of men with other species are most likely to be fruitful if they are phrased in physiological terms. Discussion

Scott: From a theoretical point of view, I agree with almost all that Dr. Barnett has said, and it is only in the matter of detail, and often unimportant detail, that we differ. Perhaps the most useful kind of commentary I can make on his work is to present a short film on the fighting behavior of house mice, which are a species fairly closely related to the rat. These experiments on the fighting behavior of mice were designed to test the theory that frustration, without training, will result in partially adaptive behavior. A mouse is trained to fight in the following way. We lift the pen top and dangle another mouse by the tail in front of him. This is done with four mice in succession; he attacks each one with increasing violence, and he is thus able to win four short fights without getting hurt himself—a very effective way of inducing fighting behavior in house mice. Our tests were done in a large multiple escape pen, consisting of five or-

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dinary cages connected by passageways. The trained fighter was established in one part of the pen which consisted of two small cages, and which was so constructed as to allow different subdivisions. Six barriers blocked all five passageways leading away from the fighter's portion of the pen and cut it off from the rest, so that he could safely run up and down between his two cages. We took an untrained male from the cage where he was raised, which has similar parts to the large multiple escape pen. In order to avoid handling, which has an inhibitory effect on fighting, his food was dropped through the wire, water came through a bottle, and finally he was captured by means of a cardboard box and transferred to the separate section of the multiple pen where the fighting male lived. The barriers allowed him to live in three of the small cages and to run through them in a circle, which makes escape from the attacker possible by running. He was allowed to explore the cage for a period of 24 hours. A mouse will thoroughly investigate any new passages and after only one preliminary trip is usually able to run through them at top speed and thus become familiar with all avenues of escape. We were then ready for the first experimental test. After his daily period of training against the four dangled males the fighter reached a fairly high peak of aggressiveness. The barriers were then removed, first on the side of the trained fighter and then on that of the inexperienced mouse. In most cases, the fighter immediately went through the passage toward the strange mouse. He entered the pen of his victim, investigated briefly, and attacked almost at once. Taken by surprise, the untrained mouse attempted to fight back but soon started to run, with the trained fighter pursuing him madly around three cages. The reactions of the beaten mouse were watched and recorded for a period of 30 minutes. When caught, he sometimes briefly assumed the upright posture of defense; the predominant method of adjustment, however, was obviously that of running away. The fighter was then returned to his own portion of the pen and the barrier closed. The next day his usual training was resumed. On the second day, 48 hours later, after he had had considerable rest, he was again given his daily training, after which the same untrained male was placed in the home pen of the fighter. This time, all exits were blocked and he could not escape by running. He attempted to stay away from the fighter but was soon attacked. At first he fought back, but this rarely lasted over a minute or two, and very soon he began to squeak whenever attacked, and to hold the fighter off. Unsuccessful in this, he jumped out of the way but soon resumed this posture of defense. This happened over and over again in a 30-minute period. In a typical case, a mouse assumed this defense posture 97 times in a small pen, compared with 22 times in the large pen, where he could escape by running. This same clear-cut difference occurred in all the pairs of mice we tested (26). It is obvious that frustration from the adaptive response of running produced a substitute which was a less successful but still

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partially adaptive type of adjustment—an attempt to hold the other mouse off. After a short period of comparative quiet, the attacker resumed a series of violent attacks, even chasing the losing mouse to the top of the cage. By this time the loser assumed the defensive posture whenever approached by the victor. In another mouse, more severe frustration produced this sequence: he fought back at first but soon allowed himself to be driven into one of the blocked-off passages. In this more constricted space, a still less useful type of adjustment occurred—the beaten mouse simply lay down at the end of the passage and held his four feet in the air. We checked these results with newborn mice, in which there is almost no possibility of previous training. As these mice cannot fight, we gave the tail a gentle pinch, just as the mother might give it. A succession of squeaks was heard, the young mouse thrashed violently, and finally came to rest. When placed on a surface where his feet could get some leverage, the mouse was able to move fairly rapidly over a short distance. In other words, this is actually escape behavior expressed by the very young. The next kind of agonistic behavior that appears is fighting. If this test were given to the young mouse at the time the first teeth appear at nine days of age, he would bite at the forceps, or turn around and bite the experimenter's fingers, which is defensive fighting. Attacks (aggressive fighting) between males do not appear, even under the most favorable circumstances, until early sexual maturity, between 32 and 36 days of age. I have dealt with agonistic behavior in the mouse, and Dr. Barnett has talked about agonistic behavior in the rat. Obviously, there are differences between the two species. For one thing, there is no playful fighting in the mouse as there is in the young rat; furthermore, I have never seen both mice of a pair adopt the upright defensive posture when confronting each other, although this occurs commonly in rats; it is possible that this posture has quite a different meaning in the two species. However, they are similar in that neither one seems able to develop a good dominance hierarchy. When respective groups of mice or rats are placed together and they begin to fight, what emerges is one dominant animal; all the rest are subordinate. A graduated linear hierarchy never develops in these species as far as I know; their behavior patterns just do not extend to this possibility. I would like to suggest some areas where our knowledge of agonistic behavior should be extended. There is now a large body of evidence which indicates that social disorganization is a major cause of destructive fighting in animal societies (28). This finding can be applied in many instances to fighting within human societies. Social disorganization in human beings results from immigration, family breakdowns and, in our own society, there is even a developmental period of disorganization while a young adult moves from his primary family into a family group which he has set up for himself.

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As was previously pointed out, social disorganization does not cover another major cause of human destructive behavior, namely groups organized for the purpose of destruction. This includes not only organized gangs but also the general phenomenon of warfare. W e must study warfare directly, because there is little evidence that anything strictly comparable to it ever occurs in animal societies; in other words, human warfare is either a biological or a cultural invention. Perhaps the most useful w a y to study this phenomenon, proceeding from w h a t Dr. Leakey said earlier, is to think of it as a tool. W h a t are the effects of the use of this tool? The answers, I predict, are not going to be simple: there is no single primary cause of war, and it has many varied effects. To use a psychological term, this is operant behavior on a very large scale; to use a biological term, warfare is potentially adaptive behavior by an organized group. W e can never solve the problem of warfare until w e eliminate its operant or adaptive function. Another area where w e need more information is the evolution of agonistic behavior. There is a great lack of adequate factual information on which to base any statements about this and, indeed, any generalization concerning the causes of fighting. Dr. Eibl-Eibesfeldt ( 1 1 ) has pointed out that in most of the highly social animals certain behavior patterns have evolved which reduce fighting to relatively harmless manifestations. These have become the signal systems or "nasils", as Dr. Barnett has termed them. However, Dr. Eibl-Eibesfeldt has not sufficiently emphasized that these animals possess, as a result of evolution, only the capacity for developing peaceful methods of adjustment. Members of an animal society do not inherit dominance and subordination behavior as such, but only the capacity to develop it. W e need to study the development of various kinds of adjustment and social organization in living individuals as well as in evolutionary history. The species on which thorough studies have been made include mice, rats, dogs and, to some extent, wolves, cats and chickens. These are almost all domestic animals, and thorough studies of animal societies in the wild are needed to achieve an adequate foundation for general statements. There have been, as far as I know, only t w o or three good studies which took account of the evolution of agonistic behavior in closely related species. One of these is an old study by my father ( 2 9 ) of social behavior in the sage grouse, prairie chicken, and sharp-tailed grouse, in which he found that fighting on the mating grounds is much less intense among the most highly social of these species, the sage grouse. Among these birds fighting is almost entirely reduced to signals, whereas in the others, which have a less highly organized system and smaller groupings of animals, it is much more severe. The other study is by J. B. Nelson,* who recently observed social behavior in the family Solidae, the gannets and boobies. He found that gannets, which cluster more densely in nesting areas, have developed much more * Personal communication.

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highly elaborate signal systems with respect to agonistic behavior than the boobies, which nest in more scattered groups. However, we still do not have a real foundation for general statements. Research in the future should include not only the highly social animals but also the relatively unsocial animals, in order to complete our information. The kind of study needed is now being conducted adequately in only one area—field studies on primates —and this is yielding a tremendous amount of useful information. Let me repeat that there is a need to investigate many more species in detail. The well-known cat is an unfortunate choice in many ways, because of the peculiar organization of its agonistic behavior. The cat, as everyone knows, is not a highly social animal, and one of its peculiarities is that its agonistic behavior does not seem to be very highly differentiated from its other behavioral systems. For example, it is sometimes very difficult to distinguish between its agonistic and its sexual behavior, or between predation and social fighting, because these patterns overlap, whereas in the dog and many other carnivores, quite distinct patterns can be observed. There is a tremendous amount of evidence that genetics has very important effects upon agonistic behavior between individuals within the same species, between the sexes within the same species, and between species in general, but time restricts their discussion here. The term "aggression", which is merely a convenient label for a host of practical problems (many of which have nothing to do with each other), has been replaced by the term "agonistic behavior". This can be defined as a behavioral system made up of alternate behavior patterns whose common function is adaptation to physical conflict. Dr. Barnett has already presented a very good scheme of this behavior in the rat. Agonistic behavior includes fighting, whether offensive or defensive, escape behavior, passive behavior, and patterns of dominance and subordination. These behavior patterns vary from species to species. They are elicited by different sorts of external stimuli, and are extended and supported by various internal physiological mechanisms. I would like to make a few comments about the physiology of fighting and agonistic behavior. While there is much evidence, as Dr. Barnett has shown, that fighting produces physiological changes, there is no evidence that these physiological changes necessarily precede fighting. The emotion of anger is a phenomenon of the central nervous system which is elicited by outside events and has the function of supporting and prolonging a response to such events. But there is no evidence of any mechanism, whether neural or humoral, that could act as a spontaneous internal drive for fighting (27). As Figure 5 shows, there are all kinds of places where external stimuli may enter the body and elicit fighting, but there is no physiological evidence that at any point in the nervous system there is a spontaneous accumulation of this stimulation, independent of outside events. There is no evidence that

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Figure 5. External stimulation and physiological reactions involved in fighting. Note that there is no internal organ in which stimulation originates; internal mechanisms transmit and magnify external stimulation.

the nervous system reacts like water rising in a tank or steam pressure accumulating in a boiler. We can train animals to fight and act as if they were driven, as you have seen with mice, but this learned motivation does not accumulate spontaneously. Those who advocate the existence of an internal drive have the burden of proof upon them. Through the film on experiments on fighting behavior of mice, I have shown an example of the organization of agonistic behavior, first as it develops between adult animals, and then as it develops within an infant animal. It seems to me that the organization of behavior should be the theme of this conference. Those of us who have primarily worked with behavior

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will attempt to demonstrate the organization of agonistic behavior as we observe, measure, and modify it. It is the function of the physiologists to discover and explain the physiological bases which underlie behavioral organization. To summarize, there are three major methods by which agonistic behavior is organized and, thus, controlled in animal societies. These are (a) the process of primary socialization, i.e., the formation of emotional attachments or social bonds between individuals; (b) the development of dominant-subordinate relationships; and (c) the development of relationships or attachments to the particular localities that in some instances may be defended as territories and in others not, but which in any case has an effect upon the occurrence of fighting. In the higher animals all of these methods involve the process of learning. Certain major questions arise from these phenomena. The first is: what are the situations and events which disturb the development of these controlling mechanisms? That is, what are the things that upset these mechanisms which ordinarily produce relatively peaceful behavior? The second question is highly relevant to human affairs: are there any mechanisms for controlling fighting between strange members of the same species? All of the above mechanisms work only if the individuals are known to each other and they tend to break down when strangers are brought together. Kaada: Dr. Barnett mentioned the importance of a central excitatory state in aggressive behavior and called upon one of the physiologists to comment on this problem. In the brain, the region generally thought to be of great importance in central excitatory states is the brain stem reticular formation. As will be discussed in my presentation on "Brain Mechanisms Related to Aggressive Behavior",* it has quite recently been shown that stimulation of the facilitatory region of the reticular formation lowers the threshold for eliciting sham rage behavior in hypothalamic cats. There is also a facilitatory area in the amygdaloid region of the temporal lobe. Further, there is a region which, upon stimulation, increases the threshold for provoking sham rage; this is the inhibitory part of the brain stem reticular formation. Thus, there appear to be mechanisms related to aggression which affect the central excitatory state in the same way spinal reflexes are influenced. Yablonsky: This may be a leap into the beyond, but while Dr. Barnett was talking about the rats he has studied, I was thinking of violent youth gangs in New York City. I note that some of the concepts used by Dr. Barnett (for example, territory) are very intense and meaningful matters in terms of youth gangs' operations. Another factor, status and pecking order, is also a marked characteristic of their behavior, with special emphasis on the most violent being at the top of the pack. I have also noticed, after a * Pages 95-133.

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four-year study of about 100 gangs, that when males and females get together, there is a much greater possibility for aggression and violence. I do not know exactly what this means; I never measured their adrenal weights. Bamett: May I make one point in reply to Dr. Yablonsky. The development of these acts is very different in other species. In man it is a matter of the individual responding to his own particular environment. Gangs, I take it, vary greatly from one culture to another, and this seems to me to constitute important differences which should not be obscured by these analogies. Eibl-Eibesfeldt: I would like to refer to the scheme which Dr. B a m e t t projected, comparing signals, language, etc. H e said there are no fixed action patterns in the human being, except in the child. But we have a number of movements to express rage and all sorts of different emotions which I think are signals, too. L a n g u a g e is certainly an invention of the human species but, besides language, there are inborn signalling mechanisms. W e know that children born deaf and blind smile, laugh and cry as normal children do. Bamett: Yes, I agree. The only major qualification I have is that the responses to these signals are a result of experience. When one is among quite different people, from a different culture, one finds their postures and facial expressions enigmatic. Eibl-Eibesfeldt: I must say that, unfortunately, cultural anthropologists have not yet provided us with a full repertoire of expression movements characteristic of the human species. For instance, we have no film records showing whether a Bantu child stamps his feet to indicate his intention to attack, as, for example, our children, do. This sort of cross-cultural information is not yet available, but we are now engaged in a project in which we film with a special device the facial expressions and gestures of humans without their knowledge. W e have done this in many different countries and it is surprising how close the similarities are. For example, a comparison of the flirt behavior of Karamodjos, Samoans, Peruvian Indians, Japanese, and French girls show that, in every case, there is a very fast flash of the eyes, raising of the eyebrows, a smile, and then a shy turnaway. T h e detailed expression is very delicate and yet quite similar. W e have gone to the field and filmed children smiling, raging, or hugging, and we have found the same pattern in Bantus, Japanese and Europeans. It is actually amazing to see the similarities, even in detail, of their signalling code.

Bamett: My only comment is, I am looking forward to seeing these films. Leakey: First of all, I would like to support Dr. Eibl-Eibesfeldt strongly. From my experience over many parts of Africa, with a considerable number of different tribes, ranging from Algeria, Angola, E a s t Africa, and South Africa, and from many contacts with Asians, I would say unquestionably that in the animal which we call man the basic gestures are almost universal. One can understand the basic gestures of anger, pleasure, or fear right across the

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human species, and only the more refined gestures which have been, as it were, taught into the youngsters, are enigmatic as between one people and another. Fundamentally, the basic gestures are the means of communication between species and between races, whose respective languages are not mutually intelligible. I most strongly believe that gestures are a major part of the very deep-rooted human communication system. I wanted to ask one or two questions regarding what Dr. Barnett said about "territorial mammals". As we get more and more into it, do we know of any animal or mammal that is not territorial? We thought, for example, that the Thompson gazelles in Eastern Africa were completly nonterritorial, always on the move and migrating, but recent work shows that mammals, though they may abandon territory for a short time to seek water elsewhere, return to the identical spot on the plain which they previously marked out, and any other animal which comes in is driven out. With regard to aggressive behavior in rats, which are not normally herd animals or troop animals, surely putting large numbers together will inevitably increase aggressiveness simply because an entirely abnormal situation has been created. It is not quite the same as putting an increasingly large number of gregarious animals such as wildebeests together. The more they are together, the less aggressive they are. Barnett: On the question of whether there are mammals which are not territorial, I too should like to know the answer. As for aggressive behavior in rats, there is a description of a small African rodent, Mastomys, which suggests, surprisingly, that it is non-belligerent and completely peaceable (35). A question I might ask Dr. Leakey is whether he thinks gorillas are territorial. Schaller's (24) observations suggest there is very little territorial behavior in that species. Another question deals with abnormal situations. Of course, the experiments I described on wild rats were conducted under very abnormal situations. The questions that one tries to answer in this kind of experiment concern just what stimuli and internal states provoke the behavior observed, and one cannot extrapolate in any simple way to the wild situation. One has to use extreme caution, as I think Dr. Leakey is implying, in interpreting the results of these peculiar situations in the laboratory. Leakey: I would reply to the specific point of the territoriality of gorillas with an emphatic yes. Schaller's small groups are, I think, part of a larger territorial group. Jane Goodall had the same impression when she started working with chimpanzees. She had many small troops, but she found that there were times when all 45 of them banded together as a single unit; there were subdivisions of a major troop into small groups with an occasional exchange of individuals. Brosin: In relation to whether signal systems are or are not universal, I believe with Dr. Eibl-Eibesfeldt that we all have much more in common in our humanity than we have differences. I would not think of contradicting

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that. However, the cultural systems over the world vary a great deal, and I will not even go to the exotic for an example: North Germans and South Germans have long had trouble, and the various varieties of Frenchmen still have trouble communicating with each other. Mediterraneans, indeed, do not do well with North Europeans because of their signal systems. I can give an example where one can examine the difficulty: some people in the Mediterranean area are called aggressive by North Europeans; what this may well boil down to is that they move their heads or bodies within 12 or 14 inches of the living space and thereby violate an unwritten but socially prescribed rule that one must not enter this space in public, except perhaps at political conventions. There are whole sets of behaviors like this. For clinicians, this becomes very important, and we are just becoming aware of it. When highly skilled and sophisticated European refugees went to South America, and found that the neuroses about which they were highly insightful were not very prevalent in Buenos Aires and Rio, they had to learn entirely new signal systems. Middle-class American psychiatrists, especially those who are upwardly mobile, have all kinds of troubles with the foreign groups in the metropolitan centers. The arrival in large numbers of the Spanish, Puerto Rican, and Mexican people among others, introduces many difficulties in the immediate scene. I am expanding on Dr. Leakey's learning system. There are endless errors which should not be obscured in determining which levels of signalling behavior are fairly universal, and I introduce the vexing problem of contradictory signals over much of the world. The horizontal headshake usually indicates negation, and vertical motion indicates consent, except with Arabs, who use the half-head-upward movement for negation, which causes us trouble. At the risk of being frivolous, it is said that many American soldiers in France in 1917 and 1918 misunderstood the body motions of French women. It is even more complex in other human relations. One example is the nubile, attractive, physically healthy American woman, about whom European men complain: she wears all the accouterments of seduction, and has the accompanying body motions indicating a willingness to engage in flirtation, but does not really mean to. This behavior can be extended to the Balinese and Javanese, who also may have no such intentions. Kawamura: I am interested in evolutionary processes among primates which relate to their overcoming territorial behavior or direct attack. I think there is no true sense of territory among primates. They use many methods for expressing agonistic behavior. Among anthropoid apes it appears that communication between troops is common, so that some kind of community is formed. I do not know much about the anthropoid ape, but one of my friends who recently did a study of chimpanzees in Africa found that they have some kind of family order or social pattern consisting of one male and one or two females and children. There is close contact between such

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troops. It appears possible to expand this social contact between troops so that a community relation develops beyond the borders of the troop. I hope that those processes which appear to overcome territorial behavior and direct attack will be discussed more fully in this conference. REFERENCES and KOPONEN, T . , On the aggressive behaviour of the Norwegian lemming (Lemmus lemmus) with special reference to the sounds produced. Arch. Soc. 'Vanamo', 1962, 17: 80-101. BARNETT, S. A., An analysis of social behaviour in wild rats. Proc. Zool. Soc. London, 1958, 130: 107-152. , The Rat: a Study in Behaviour. Aldine, Chicago, 1963. , Social stress. Vietvp. Biol, 1964,3: 170-218. BARNETT, S . A . , and EVANS, C . S . , Questions on the social dynamics of rodents. Symp. Zool Soc. London, 1965, 14: 233-248. BOLWIG, N., A study of the behaviour of the Chacma baboon, Papio ursinus. Behaviour, 1959, 14: 136-163. B U F F O N , G. L. L., Natural History. Cadell & Davies, London, 1812. CARPENTER, C . R., Social behavior of non-human primates. In: Structure et Physiologie des Sociétés Animales (Coll. Intern. No. 34). Centre National de la Recherche Scientifique, Paris, 1952: 227-246. CARTHY, J. D., and ERLING, F. J. (Eds.)., The Natural History of Aggression. Academic Press, London, 1964. C H I T T Y , D., Population processes in the vole and their relevance to general theory. Canad. J. Zool., 1960, 38: 99-113. E I R L - E I B E S F E L D T , I., The fighting behavior of animals. Sci. Amer., 1961, 205(6):

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J. F., Studies on the behavior of Peromyscus maniculatus gambelii and Peromyscus californicus parasiticus. Behaviour, 1962, 19: 177-207. H A R L O W , H . F., The development of affectional patterns in infant monkeys. In: Determinants of Infant Behaviour (B. M. Foss, Ed.). Methuen, London, 1961: 75-88. , The heterosexual affectional system in monkeys. Am. Psychol, 1962, 17: 1-9. , Development cf the second and third affectional systems in Macaque monkeys. In: Research Approaches to Psychiatric Problems: A Symposium (T. T. Tourlentes, S. L. Pollock and H. E. Himwich, Eds.). Grune & Stratton, New York, 1962: 209-229. HARRISON M A T T H E W S , L . , Overt fighting in mammals. In: The Natural History of Aggression (J. D. Carthy and F. J. Ebling, Eds.). Academic Press, London, 1964: 23-38. HEDIGER, H . , Wild Animals in Captivity. Butterworth, London, 1950. HINDE, R. A., The biological significance of the territories of birds. Ibis, 1956, 98 : 340-369. KING, J. A., Social behavior, social organization, and population dynamics in a black-tailed prairie dog town in the Black Hills of South Dakota. Contrib. Lab. Vert. Biol. Michigan, 1955, No. 67. EISENBERG,

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26. 27. 28. 29. 30. 31. 32.

33. 34. 35. 36.

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and M O R I N , F . , Cortical evoked potentials and appetite drive. Nature, 1965, 206: 1375-1376. LACK, D., The Natural Regulation of Animal Numbers. Clarendon, Oxford, 1954. MENDELSOHN, E . , Heat and Life. Harvard Univ. Press, Cambridge, 1 9 6 4 . M U R I E , A., The Wolves of Mount McKinley. U.S. Government Printing Office, Washington, D.C., 1944. SCHALLER, G. B . , The Mountain Gorilla; Ecology and Behavior. Univ. of Chicago Press, Chicago, 1963. SCHENKEL, R . , Ausdrucks-Studien an Wolfen. Behaviour, 1948, 1: 81-129. SCOTT, J. P . , Incomplete adjustment caused by frustration of untrained fighting mice. J. Comp. Psychol, 1946, 39: 379-390. , Aggression. Univ. of Chicago Press, Chicago, 1958. , Hostility and aggression in animals. In: Roots of Behavior (E. L. Bliss, Ed.). Harper, New York, 1962: 167-178. SCOTT, J. W., A study of the phylogenetic or comparative behavior of three species of grouse. Ann. N.J. Acad. Sei., 1950, 51: 1062-1073. STEINER, W . G . , Electrical activity of rat brain as a correlate of primary drive. EEG Clin. Neurophysiol, 1962, 14: 233-243. STOKES, A. W . , Agonistic behaviour among blue tits at a winter feeding station. Behaviour, 1962, 19: 118-138. T E V I S , L . , JR., Summer behavior of a family of beavers in New York State. J. Mammal., 1950, 31: 40-65. TINBERGEN, N., The Herring Gulls World. Collins, London, 1953. , The functions of territory. Bird Study, 1957,4: 14-27. VEENSTRA, A. J . F., The behaviour of the multimammate mouse, Rattus (Mastomys) natalensis (A. Smith). Anim. Behav., 1958, 6: 195-206. WASHBURN, S. L . and D E V O R E , I . , The social life of baboons. Sei. Amer., 1961, 204(6): 62-71. ZUCKERMAN, S., The Social Life of Monkeys and Apes. Harcourt, Brace; New York, 1932.

2 0 . KITAI, S. T . ,

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ONTOGENETIC AND MATURATIONAL STUDIES OF AGGRESSIVE BEHAVIOR IRENAUS E I B L - E I B E S F E L D T Max-Planck-Institut für Verhaltensphysiologie Seewiesen bei Starnberg W e s t Germany

Intraspecific aggression is a widespread phenomenon in vertebrates and a controversial issue for students of animal and human behavior. The points of controversy concern the extent to which phylogenetic adaptations determine this type of behavior, in particular the degree to which aggression is environmentally controlled (and thus manipulable), and the extent of its spontaneous origin in inborn drive mechanisms. I shall start by reviewing this from an ethological viewpoint. Let us first consider the phenomenon J. P. Scott (54) defined as agonistic behavior: "any sort of adaptation which is connected with a contest or conflict between two animals", subsuming under this term activities such as fighting, escaping, or "freezing". This definition incorporates intraspecific and interspecific fighting and, indeed, both have many patterns in common. There are, however, some important differences between inter- and intraspecific agonistic behavior which make a further distinction necessary. Oryx antelopes, for example, never impale a member of their species (conspecific) and fight according to certain tournament-like rules, but they do impale a predator. A giraffe uses its horns in intraspecific fighting and its hooves in interspecific conflicts. The way predators attack their prey is usually completely different from the way they attack and fight a conspecific animal. This should be emphasized, since inter- and intraspecific fighting has often been confused: Ardrey (1), for example, said that man's aggressive habits can be explained by the carnivorous habits of his ancestors, the Australopithecines; Freeman (18) followed along this line recently. But a carnivorous habit has nothing to do with intraspecific aggression—plant-eaters are by no means less aggressive than carnivores against conspecifics; bulls fight each other as viciously as dogs do.* We shall discuss here intraspecific agonistic * Kuo (34) made precisely this mistake. In order to prove that aggressive behavior is a habit, the development of which can be prevented, he raised cats, dogs and rats together, demonstrating peaceful coexistence. However, he does not distinguish between intraspecific and interspecific aggression, and unhesitatingly applies his findings on interspecific aggression to intraspecific aggression. 57

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behavior only, considering under aggressive behavior every attack or approach with threat display released by the perception of a conspecific prior to painful physical contact; defensive behaviors are the actions of the attacked. Intraspecific fighting, as I said before, is a common occurrence among vertebrates; only a very few species, such as schooling herrings, do not show this type of behavior. Whenever such a widespread phenomenon is found, we are bound to ask about its function, i.e., its selective advantages. As many authors have emphasized, the main function in territorial conflict is spacing-out to prevent overcrowding and ensure the distribution of the species (66). While some species do not fight for territory ownership but to space-out sexual rivals, both functions are combined in most cases. We would certainly be wrong in considering aggressive behavior a side-effect or a "bad habit", as is sometimes suggested. Another widespread and erroneous assumption implies that aggression is destructive, in the sense that the ultimate "goal" is the destruction of the attacked conspecific. Observation of animals fighting shows that destruction is nearly always avoided, for lethal injuries rarely result from fights between species members. Correlated with the ability to inflict damage, animals have developed special inhibitory mechanisms or changed their way of fighting in order to avoid damaging the opponent. Rattlesnakes and many

Figure 6. Fighting marine iguanas showing the ritual combat by headpushing.

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Figure 7. The loser (left) indicates his submission by lying flat on his belly, while the winner (right) waits in threat display for the rival to leave.

other poisonous snakes never bite each other but wrestle according to fixed rules. In Crotalus ruber, the male rivals raise the first third of their bodies from the ground and strike each other with their heads, but keep their mouths closed; this continues until one is exhausted and gives up, or is beaten to the ground and pressed down by a loop of the winner's body (58). Were they to bite each other, they would kill one another, and it is easy to see that this would not be advantageous to the species. Another example of aggression without lethal intent is the ritualized combat of marine iguanas. These animals occupy the rocky shores of the Galapagos Islands in large herds. During the breeding season, the males occupy territories on the shore, where they live with several females. If a male rival approaches, the territory owner shows a threat display. He opens his mouth, nods his head and walks stiffleggedly up and down in front of the rival, showing his lateral aspect with the dorsal crest erected and the gular region extended (Figure 6). If the rival answers by the same display, fighting begins and the opponents rush at each other. In spite of the feigned biting exhibited during the display, they never actually bite each other, but lower their heads instead and clash together; the horn-like scales covering the roof of their heads interlock, and they try to push each other away (Figure 7). In pauses between fights, the opponents show a frontal display, nodding with the mouth open. The struggle ends when one is pushed from the rock or surrenders by lying flat on his belly, which is the submissive posture; the

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winner stops fighting and assumes a threat display posture, waiting for the rival to leave. This fight is a highly ritualized tournament, during which the stronger wins without hurting the loser. Ritualized fighting is a widespread phenomenon and occurs in a great number of fishes, reptiles, birds, and mammals. A number of examples are listed by Lorenz (41) and Eibl-Eibesfeldt (14,15). Sometimes only parts of the entire fight are ritualized. After an introductory threat display, many mammals (such as wolves) engage in a damaging fight, during which the animals bite each other but avoid serious damage, for, after the exchange of only a few bites, the loser assumes a submissive posture by presenting its throat to the opponent, thus inhibiting further aggression. Young dogs, upon attack, even throw themselves on their backs in submission. Baboons, like the wolf, present the throat to the opponent in submission (33). Only animals without weapons or animals that can retreat easily have no such social inhibitions. Hamsters (Cricetus cricetus) bite each other viciously but, once bitten, the loser quickly retreats and the winner never follows it far. In captivity, however, species of this type kill each other easily, as do pigeons. If two rival pigeons are kept together in a cage, one will strip the other of all its dorsal feathers and finally kill it. Since the beak is not a dangerous weapon, this species has no special inhibition for its use in intraspecific fighting, and in an artificial situation where escape is prevented such species become more murderous than any wolf (41). Man belongs to a species which has special mechanisms that help prevent the killing of a conspecific. W e know from personal introspection, as well as from observation of other people, that mentally healthy people have the capacity to feel pity. This reaction is elicited by submissive acts, which have a similar function in many aspects to the submissive postures of animals. The submissive person may fall to his knees or expose his vulnerability by raising his hands to show that he is weaponless. Crying is a more specialized, typically human expression of submission. All these actions may inhibit further aggression, but they can only fulfill their function if the aggressor is not armed. Lorenz (41) has pointed out that the invention of arms has enabled man to kill a conspecific so fast that the opponent has no opportunity to appeal for pity by surrender. Our biological inhibitions cannot cope with this phylogenetically new situation to which they are not adapted, and a new moral code seems necessary to compensate for this lack. A striking phenomenon is man's warlike activity, which is very probably the expression of concerted individual aggression. The same phenomenon is expressed in some animals by group aggression, e.g., gray Norway rats gang up against each other in groups (60). It is interesting that man's aggressivity against other groups seems to be correlated with the degree of his group consciousness (52). All these observations lead to our first conclusion, that aggressive behavior serves the function of spacing-out, which is not destructive. The occur-

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rence of ritualized fighting further indicates that there is strong selection pressure in favor of aggressivity, otherwise aggressivity would have been counter-selected in species that can do damage to a conspecific. Instead, they developed the most complicated fighting techniques in order to allow fighting to occur as a spacing-out mechanism. To what extent and in which ways do phylogenetic adaptations determine aggressive behavior? From quite a number of studies on the ontogeny of behavior of animals raised under various deprivation schedules we know that these adaptations can occur on the motor side as innate skills. Certain motor patterns develop during the ontogeny of the individual. The movements follow a constant pattern and are thus species specific; they apparently develop by decoding genetically stored information, a process similar to that by which organs develop their adaptive form and function. For that reason Lorenz called them "Erbkoordinationen", translated as "fixed action patterns" by Tinbergen. Phylogenetic adaptations are also found on the receptor side, first in the capacities of the sense organs and second in the ability of the animal to respond only to perceived stimuli with species specific action patterns. These unconditioned releasing stimuli are often configurative and highly specific in regard to the evoked response. Since they "unlock" a behavior pattern, they are termed "key stimuli". They seem to act upon a specific releasing mechanism which allows the passage of the motor impulses only, following the reception of specific stimuli. Since animals not only react to impinging stimuli but also demonstrate spontaneous behavior (appetitive behavior), we have to assume specific arousal mechanisms within the animal. We finally encounter phylogenetic adaptations in the form of specific learning dispositions. Special mechanisms have evolved which ensure that an animal learns the right thing at the right time. In order to find whether an observed behavior pattern is a phylogenetic adaptation or an adaptive modification we use the deprivation experiment. It was once argued that this type of experiment is not conclusive, since one can never deprive an animal of all possible sources of information; it is always in an environment that acts upon it and the animal may learn from all sorts of environmental stimulation. The answer to such criticism is that one need not deprive an animal of all environmental stimuli. The behavior patterns in question are adapted and, for such adaptation to have occurred, information about the environmental features to which the behavior pattern is adapted must have been fed into the organisms (15, 40). This acquisition of information can take place during phylogeny or during ontogeny. Once these environmental features are known, the animal can be deprived of the patterned information about the particular environment during its ontogeny; if the adaptive behavior pattern nonetheless develops and responds to adequate releasing stimuli in a critical test, then we can conclude that this behavior pattern is phylogenetically adapted. Consider the following example. Red squirrels hide nuts with a highly

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adaptive sequence of movements: they pluck the nut, grasp it with the mouth, climb down to the ground and search for a hiding place. Usually they scratch a hole at the base of a tree or a rock with the forepaws, deposit the nut, stamp it into the ground by rapid blows of the snout, cover the nut with earth with sweeping movements of the paws, and finally pack the earth down by alternate stamping movements of the paws. It is quite easy to deprive a squirrel of the specific information needed to acquire this behavioral sequence by raising it in isolation in a wire mesh cage without earth or shavings to dig and giving it a liquid diet. Furthermore, by keeping it well fed it does not experience any food shortage. If such an animal is tested when adult, it will eat the first nuts; then, instead of dropping the last after satiation, it will climb down to the ground and search the room until it comes to a corner where it will scratch even a solid concrete floor. There it deposits the nut, stamping it down with the snout. After this is done, it performs the covering movements with the forepaws, although nothing has been dug. The whole sequence of adaptive movements is a programmed event that does not depend upon the specifically patterned information about the environmental situation toward which it is adapted. Eventually, the animals learn where it is best to hide nuts; when they perform the covering movements in vain, they often pick up the nut again and try another place. From the very beginning the inexperienced animals show a clear tendency to hide nuts at the base of vertical obstacles (bookshelves, corners of the room). This innate knowledge guides the animal in Nature to choose conspicuous landmarks such as trees which later help it in locating the hidden nut. Whereas the squirrel shows little individual variability as far as its food-hiding behavior is concerned, it proves highly individually adaptive when we study the ontogenetic development of the nut-opening technique. Here learning plays a much more important role, and even individual opening techniques can be observed (15). From numerous experiments further demonstrating phylogenetic adaptations in behavior, let me mention only a few which deal with the ontogeny of bird songs. Sauer (51) raised isolated whitethroats (Sylvia communis) in soundproof chambers where they nevertheless developed all 25 species specific calls and the three songs characteristic for this species. Konishi (30) showed that deafened chicks also develop all of their species specific calls. This is also true of juncos (Junco oregonus and J. phaeonotus) raised in soundproof chambers in isolation, but only if they can hear themselves (31). Chaffinches raised in isolation develop a song of a certain length and with a certain number of syllables, although they need to learn the characteristic patterning in three stances; interestingly enough, they demonstrate an innate knowledge of what to imitate, since when presented with a choice of different songs, they pick out the species song for imitation (64). There are many more experiments demonstrating in a similar way the existence of fixed action patterns and of an innate responsiveness to patterned

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stimuli (key stimuli). As is well known, a newly metamorphosed frog reacts with the prey-catching response whenever it perceives a small moving object; Tinbergen (65) and others repeatedly investigated this phenomenon with decoys. The male three-spined stickleback develops a brilliant red belly (which serves as a signal for other males) once it establishes a territory during the breeding season. They will attack even a very crude wax model as long as it has a red underside, but ignore the most detailed stickleback model lacking the red colors. Similarly, the male European robin attacks a bundle of red feathers but ignores a stuffed juvenile male lacking the red feathers (35), and European bluethroats react accordingly to blue feathers (46). The male lizard Sceloporus undulatus reacts to the blue stripes on the rival's belly (45). If several species of butterfly fishes (Chaetodontidae) are kept in one tank, the fish always single out species members as objects of aggression; rarely do they attack members of other species, and only if they are very similar in appearance, indicating that coloration serves as a recognition signal. Since animals fluctuate in their responsiveness to a constant stimulus situation, since they demonstrate a clear appetitive behavior (searching for a specific releasing situation) and since, if deprived of the releasing stimuli, they react less and less selectively until a behavior may even lapse in vacuo, we are led to assume that there are special built-in motivating mechanisms. These are as yet insufficiently explored, but studies on hunger, thirst, sexual behavior, and locomotion reveal that hormones, inner sensory stimuli, and the spontaneity of the central nervous system each play an important part as inner motivating factors (4, 5, 39, 49, 67, 69, 70). After the performance of a behavior pattern, there is a change in the animal's special responsiveness to stimuli, as illustrated by a recent report by Ploog (47) on sucking in babies. A group of babies received milk from nipples with a large opening, another group from nipples with a small opening. The first finished their meal in a very short time, became restless afterwards and started to cry; to quiet them down it was necessary to let them suck the empty bottle for a while. The second group drank the same amount as the first (or even less) over a longer period, since more sucking movements had to be performed; they did not cry when the empty bottles were withdrawn. Again, several mechanisms are involved in bringing a certain behavior to an end. The animal can change the stimulus situation by its activity, or end it with special switch-off stimuli. Adaptation in the releasing mechanism or a specific fatigue within the central nervous system may occur. After examining the concept of phylogenetic adaptations in behavior, we can specify our questions concerning the ontogenetic development of aggressive behavior as follows: a. Are there any motor patterns adapted to the function of intraspecific fighting (threat display, fighting techniques) that develop in every individual of the same sex and species, even if deprived of the opportunity to

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learn this pattern by imitation or by interaction with the specific environmental situation with which the behavior fits? b. What stimuli release aggressive behavior and which stimuli bring it to an end, and under what environmental conditions is the animal likely to respond to such stimuli with aggressive behavior? c. To what extent does learning influence aggressive behavior? d. Do fluctuations in the responsiveness to aggressivity-releasing stimuli occur, and what is their physiological background? Is there an appetitive behavior for fighting, and does the drive concept help us in understanding this phenomenon, or is it an unnecessary construction? In short, is aggression solely a reaction or are there indications for a spontaneous background? A number of controversial statements derive from the fact that investigators have not sufficiently specified their question but simply asked, e.g., whether aggressive behavior is an innate or an acquired habit. Once they were able to demonstrate that learning had indeed an influence, they were satisfied, and jumped to the conclusion that aggression was a product of training. However, when the question is specified, it becomes evident that heredity and environment both play important roles, and these respective roles can be exactly determined. Male rats and mice ( M u s musculus and Rattus norvegicus) are known to attack conspecifics that do not belong to their group. It has been suggested that, prior to any manifestation of aggressive behavior in the sense of an unprovoked attack, the mouse reacts with fighting responses only in defense to painful stimulation and in this way develops the habit of aggression (54); this happens during rough play and during competition for food in early youth. But Kahn (28), and more recently Banks (3), have shown that mice reared in isolation were more aggressive than those reared with litter mates and mothers, which does not exactly fit the interpretation given above. King & Gurney's (29) mice reared in isolation were also aggressive, but showed a longer latency before attack than experienced ones. One might interpret this as evidence for the need to learn an aggressive habit. King & Gurney, however, stress the fact that one does not observe aggressive fighting between litter mates; it seems to them more plausible to assume that the innate aggressive tendency of the inexperienced mice is suppressed by many new stimuli—they investigate the conspecific and finally, when they are no longer new to each other, they fight. We raised male grey Norway rats (wild stock) in isolation, taking them at 17 days of age, well before they would have started the playful wrestling typical for the species. When the isolates were six months old, the introduction of a conspecific into their territory regularly resulted in a fight within minutes, the inexperienced territory owner being the attacker. We filmed the behavior of the inexperienced animals in slow motion and compared their fighting technique and threat behavior with that of experienced fighters. In both cases, the same motor patterns of threat (e.g., clattering

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teeth, tail shaking, hairfluffing, threat jump, biting, kicking with the hindfeet, and others) were observed. Clear differences between inexperienced and experienced fighters were not seen; however, we had no trained fighters, since our control groups consisted of animals raised with their litter mates, and it is well known that there is no serious fighting between members of the same group. Thus, we compared the first fight of a socially inexperienced animal with the first fight of a socially experienced animal, and found that in order for fighting to occur in inexperienced animals they only need to be on home ground at the time of the encounter. Steiniger (59) has reported individual fighting techniques of experienced rats. Those reared with their litter mates never engaged in real fights with a group member; they occasionally pulled on the same morsel, but they never bit each other nor showed teeth-clattering. However, they vehemently attacked rats of other groups. In this context, consider striking species specific differences. Whereas one can keep a group of rats derived from one mother together over generations, this cannot be done with the European hamster (Cricetus cricetus). A hamster family regularly explodes due to the developing aggression of the litter mates; they start to attack each other in a very peculiar way—first the group attacks one member of the family and, if they are not separated they eventually kill their litter mate, then the next victim is sought, and so forth until one alone survives. In Nature, hamsters are of extremely solitary habits, whereas rats live in packs. Male red squirrels that I raised in isolation became very aggressive during the first breeding season and attacked the caretaker (or a conspecific when given the opportunity) with threat display typical of the species (laying back the ears, tail-shaking, teeth-clattering). This aggressivity faded away during the summer and the animals later invited playful wrestling without further biting or threat display. Kruijt's (32) isolated jungle-fowl cocks developed all the species specific fighting and display patterns. The isolates proved more aggressive than those reared within a group and attacked the caretaker or even their own tails as a substitute object. Studies on cichlid fishes demonstrate that every species develops its highly ritualized species specific fighting technique without the need to learn it from their partners and, likewise, three male marine iguanas which I raised from shortly after hatching, started threat display and the typical headpushing within the first year of captivity (15). It should be clear from these examples that at least a number of different vertebrate species are supplied with a number of fixed action patterns, i.e., phylogenetically adapted motor patterns that serve the function of spacing out by threat and fighting. The stimuli releasing these actions normally come from a conspecific but have been little explored. The studies of Tinbergen on sticklebacks (65), of Lack on robins (35), Peiponen on bluethroats (46), and Noble on Sceloporus lizards (45), mentioned above, indicate that often quite conspicuous simple key stimuli are involved. In mammals, smell

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plays an important role, but little is known about which components are involved." When dealing with the facts causing aggression, we have to distinguish clearly between the stimuli which release the actual acts of aggression (we have just discussed some examples) and the factors that create the species' inner disposition (readiness) to attack. Since determination of the extent to which specific responsiveness to attack is reactive or spontaneous is an object of controversy, we will discuss the arousing mechanisms, asking whether this specific readiness to react aggressively is purely environmentally controlled, or whether there are any internal contributing factors. There are certainly many facts clearly demonstrating that environmental factors have an arousing influence on aggressive behavior. Dollard et al. (13) emphasized frustration as the cause of aggression, frustration being defined as . . an interference with the occurrence of an instigated goal-response at its proper time in the behavior sequence." The evidence that aggression can be aroused by frustration is convincing, and Berkowitz is certainly right in his statement that ". . . anger is the primary, inborn reaction to thwarting" (6), meaning by anger the instigation to aggression. The question is, however: Is every case of aggression the result of frustration? If we define the term broadly enough, we can explain even the reaction to someone stepping on another's toe on this basis, but this would involve dilution of a valuable concept. There are a number of observations that favor the assumption of motivating mechanisms inside organisms, which produce a specific readiness to act aggressively. If we observe organisms, we will see fluctuations of aggressivity, as shown by the different responsiveness to the same stimuli at different times. We have already mentioned the squirrel males, where these fluctuations are induced by the changing hormone level. We could also interpret the findings of Kruijt (32) that, in the absence of conspecifics, cocks fight their own tails as an expression of an urge to fight. We further observe, as in other cases of internally driven behavior, a typical appetitive behavior for fighting. The animal wanders around restlessly, which we interpret as a search for a rival. If the environment is changed by offering food, water, nesting material, mate, or rivals, it is found that at one time the animal requires only water, at other times only food, etc., and in certain situations it only wants to fight a rival. This has also been demonstrated by von Hoist & Saint Paul (71), who were able to induce by brain stimulation typical appetitive behavior for fighting and, with adequate stimuli, fighting behavior as well; the fights were not in vacuo, and not every drive behavior resulted in this end-effect. If there is an urge to fight, the expression of aggressive behavior should be rewarding and tension-relieving, whereas suppression should heighten * The role of olfactory stimuli on aggression in mammals is further discussed in p. 70.

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aggression. Thompson (62) found that stimuli which evoke unlearned aggressive behavior act as positive reinforcers for instrumental responses. Siamese fighting fish and fighting cocks learned a task when allowed to encounter stimuli that released agonistic display. Azrin (2) used attackable inanimate objects as reinforcers: to put pigeons in an aggressive mood, they were electrically shocked, after which they learned to peck a key causing another live pigeon to appear, which they attacked; monkeys, after electrical shock, could obtain for themselves a tennis-ball to discharge aggression, which they readily did. Lorenz (40) states, that in a number of cichlid fishes, males that have been isolated cannot be paired with a female, since they attack the female as a result of their dammed-up aggression. If, however, they are allowed to fight first with another male, pairing is possible; when alone with the female again, such a male will start to attack her after a while. It is easy to succeed in breeding these animals if another pair is placed in the tank, separated by a glass plate. The males then threaten each other and do not fight their respective females. A. Rasa* repeated similar experiments with the cichlid fish Etroplus maculatus: if the males of a breeding pair had the opportunity to attack other males directly or through a glass plate, only very few attacks against the mate were counted; not given this opportunity, very intensive attacks were directed toward the mate, and the female was eventually killed. By careful motivational analysis Heiligenberg (24) proved the existence of an endogenous drive for fighting in the cichlid fish Pelmatochromis subocellatus. The performance of aggressive behavior caused action-specific fatigue but, after a period of recovery, aggression returned to its previous level. It should be emphasized that this specific fatigue is a short-term effect. As is the case in many other instinctual activities, restoration sets in, and permission of aggressive discharge brings about the long-term effect of training, that is, the animal becomes more aggressive as a result. This is important to realize for its educational implications, since it is sometimes suggested that the discharge of aggressive impulses during early childhood results in long-term cathartic effects. This is not supported by evidence from animal behavior studies. Aroused aggression is often displaced elsewhere if the arousing object cannot be attacked; this again demonstrates an urge to attack as well as a cathartic effect of aggression,f as do the observations mentioned above. Psychologists' experiments with man have demonstrated the same. Thibaut & Coules (61) made male undergraduates angry by having a peer send them insulting messages at the culmination of an exchange of notes. One " Cf. Eibl-Eibesfeldt (16). t The psychoanalysts' catharsis hypothesis contends that the expression of hostility reduces the strength of the aggressive tendencies within the individual and is thus in agreement with the ethological drive concept.

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group of subjects was allowed to reply to the provocation; the other group was told the time was up and they could not reply. Both groups had to describe the instigator's personality at the beginning and end of the study. The descriptions of the non-communicating group which had no chance to answer were less friendly than those of the communicating group, thus demonstrating residual aggression. In Feshbach's (17) study, annoyed college students were shown a 10-minute boxing film and a neutral film. Those that saw the boxing film proved less aggressive than those who saw the neutral film. The non-insulted control group showed no difference. Experiments of Hokanson & Shetler (27) amply demonstrated tension reduction resulting from the performance of aggressive behavior. The subjects (students) knew they were involved in some physiological experiments, since their blood pressure was measured, but did not know which kind. One group was made to believe that the experimenter was a low-status person, another group that he was a high-status person (a professor). The experimenter annoyed half of each group, which resulted in a rise in blood pressure, indicating the subjects' tension. Half of each of the annoyed groups was afterwards allowed to administer electrical shocks to the experimenter if he failed to guess a number the subject had in mind. The non-aggressing group simply flashed a light. It was found that aggression against the low-status person was tension-reducing, as shown by the decrease of the systolic blood pressure, which remained high in the group that was not allowed to shock the instigator. With the high-status experimenter, the systolic pressure decreased in both the non-aggression and the aggression groups, which can be interpreted by assuming that the insulted non-aggressing students had quickly given up the idea of attacking a high-status professor. The findings were supported by further experiments (26), which also showed that the opportunity to inflict verbal injuries proved tension-relieving. It may again be concluded that external as well as internal factors build up a specific responsiveness to act aggressively. This responsiveness expresses itself in an urge to attack even substitute objects, after which a relief of tension can be observed. This dynamic instinct concept of aggression, which assumed internal driving forces, had been postulated by Freud. Since he did not understand the function of aggression, he postulated a mysterious death instinct, a concept that has since changed (22) but still assumes that aggression has an internal motivation, with which ethologists agree. The reluctance to accept this as a good working hypothesis stems mainly from an idealistic background, clearly expressed, for example, in a passage from Berkowitz (6) which I should like to quote. In considering Freud's concept, Berkowitz writes: "But aside from its theoretical significance, Freud's hypothesis has some important implications for human conduct. An innate aggressive drive cannot be abolished by social reforms or the alleviation of frustrations. Neither complete parental permissiveness nor the fulfillment of every desire will eliminate in-

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terpersonal conflict entirely, according to this view. Its lessons for social policy are obvious: Civilization and moral order ultimately must be based upon force, not love and charity." I do not know if a psychoanalyst has ever arrived at this pessimistic conclusion, but I do know that ethologists never have, although they assume the existence of internal driving forces. Since a critique of this concept seems to point inevitably to the foregoing conclusion, we want to investigate its accuracy. The statement quoted above is based on the erroneous assumption that the dynamic instinct concept implies, to quote Berkowitz, " . . . a closed, entirely self-contained internal system impelling the organism to aggression" (6). But no one ever said that there are such closed systems. Even the automatism of the heart is not entirely self-contained, as every physiologist knows, although no one would doubt its automatic background. This is true for many other instinctual activities with an automatic basis, and it is certainly true for aggression. We have already mentioned a number of arousing environmental factors. Heiligenberg (23) showed that the aggressive drive even degenerates if deprived of an outlet for a long time.* This does not seem true in other species, as the experiments of Kruijt (32) on junglefowl cocks indicate. The experiments of Scott (54) have clearly demonstrated that animals can be trained to be aggressive or peaceful. Young dogs lifted from the ground whenever they showed aggressive behavior lost their aggressive habits, and the same happened to mice in a similar experiment. Scott further hopes to achieve passive inhibition of the fighting response in children by raising them in an environment lacking in stimuli eliciting fighting. This quite probably could be done; however, as McNeil (42) said, "whether such passivity would be at the cost of initiative is an unanswered question." One would really like to know what is positively related to aggression, including the implications of saying that a scientist "attacks" a problem or "sinks his teeth into it". How is the exploratory behavior of animals conditioned to peaceful habits in contrast to aggressive ones? Before we try to "cure" man of his aggressive habits we should know a little more about the possible side effects of such a "cure". And what shall we do if the side effects of non-aggressiveness are unwanted ones? Are we then to adopt a fatalistic attitude? I would say no. Close observation of animals living in groups, for example rats or a pair of cormorants, shows that the very same animals that groom each other, feed their young, and engage in other altruistic activities toward group members, are at the same time extremely hostile to strangers. That aggression does not turn against a group member is due to special mechanisms of bond formation, and it is interesting to note that those who want to control aggression have not turned to those natural aggressivity buffers that normally pre* Aggression is also influenced by other activated drives. Activation of the flight drive suppresses aggression, for example.

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vent friction within a group. A study of these buffers could help solve our problem. On the Galapagos Islands I had the opportunity to study the relieving ceremonies of the flightless cormorant. One of the adults always shelters the young or sits on the eggs, while the other is out fishing. Whenever the partner returns he brings seaweed, a sea star or a twig, which it presents to the mate, who takes it and builds it into the nestwall. Only if the mate brings such a present is it accepted. Since these animals lack the fear of man, I was able to take the present out of the beak of an approaching cormorant. It continued its way after a short hesitation, evidently unaware that there was now nothing in its beak. Its mate received it with attacks, after which it retreated, looking for something to present. On offering a twig it was accepted by the mate. Our various forms of courtesy, e.g., the greeting ceremonies, actually serve the same function, a realization easily made if one experiments by not greeting anybody for one week, not even family members: unbuffered hostility turns against one. Bond-forming behavior patterns serve the function of appeasing. When approaching the mate the blackheaded gulls turn away their black face mask, which this species uses for threat display. Modern man follows the same principle in adapting to the closely packed society of millions by hiding provocative individual display. We dress ourselves in dull colored cloth, quite in contrast to Europeans in the Middle Ages or tribal Papuans or Turkanas, who not only wear most colorful dresses or ornaments, but also display their weapons. Gestures of submission can be used in greeting; we bow, for example. But behavior patterns of the infant, or those derived from maternal or sexual activities, are also often ritualized to serve the function of appeasement. A very interesting group of bond-forming behavior patterns are those expressive movements derived from threat gestures; i.e., geese greet by ritualized threat display which differs from a threat against an enemy only by its orientation: the members of a pair do not threaten each other, but the necks are held more parallel, as if they were threatening each other. Sometimes human gestures, although learned, follow the same principle. Animals living in a group are, furthermore, often characterized by mechanisms allowing identification, thus preventing aggression against group members. In the flying opossum, Schultze-Westrum (53) found that males mark all other group members olfactorily, thus giving all members a uniting smell. The same seems to be true for Norway rats, where the male group members mark other group members, males and females alike, with their urine. This also results in a group smell, and if an individual is separated from the group for only a couple of days, it is attacked as if it were a stranger. In man, uniting symbols that allow identification also have an enormous power. The cults around flags, memorials, party emblems, uniforms, and religious symbols are well known to us, and it should be noted that the first thing a young nation does is to create symbols.

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All these observations tell us that there are control mechanisms to check aggression that at least seem effective among men and are therefore promising for further study. It is by no means a new discovery that courtesy, with its appeasing function, makes life within a group much easier. We have, furthermore, the capacity to identify ourselves with others. At the very beginning of our history, these mechanisms of identification worked only within very small groups, villages or cities, then whole tribes began to look upon each other as belonging together and created symbols accordingly. Nations and supernations evolved, and there is no reason to assume why these mechanisms should not work one day to allow identification with all mankind. This is a question of education, communication, and the creation of uniting symbols and tasks. Unfortunately, man has not yet learned very much from his history, since we are still building blocks against other blocks, and blaming each other for their effects. And once we start to argue about who is right or wrong we become emotional and, thus, blind. Lorenz (41) recently pointed out the extraordinary discrepancy of man's ability, on the one hand, to deal with the outer world—he has even solved the problem of getting close-ups from Mars—and his inability, on the other hand, to solve his social problems, such as how to get along with his neighbor or how to find the best form of government. Aggression is one of those issues about which people can become emotional, which accentuates the need to study all of its aspects sine ira et studio. SUMMARY

Intraspecific fighting serves the function of spacing-out, but observations show that there is an equally strong selective pressure at work to spare the loser. The killing of a conspecific during combat is avoided; whenever danger threatens the conspecific by poison (snakes) or sharp teeth (marine iguanas, wolves), a more or less ritualized code of fighting is developed. In many animals the entire fight becomes a tournament; in others, damaging fights occur, but are ended by a submissive posture respected by the winner. The study of ontogeny reveals the existence of phylogenetic adaptations in fighting behavior, such as fixed action patterns, innate releasing mechanisms that respond to specific releasing signals, and special motivating mechanisms. Animals demonstrate a specific readiness to react aggressively toward a foreign conspecific. This special responsiveness is built up by factors both inside and outside the organism and causes appetitive behavior, during which the animal actively seeks stimuli allowing the final discharge of aggressive impulses, which results in a relief of tension. Aggression between members of the same group is buffered by special mechanisms of bond formation and identification. Their study seems worthwhile in view of the effort to control man's destructive intraspecific aggression.

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Discussion

Lindsley: Dr. Eibl-Eibesfeldt's presentation, like those of Dr. Leakey and Dr. Barnett before him, have provided us with beautiful descriptions of behavior which illustrate manifestations of defense or withdrawal, aggression or attack, or approach with threatening gestures. When we try to make a phylogenetic review, as Dr. Eibl-Eibesfeldt has done, of commonalities in the patterns of behavior of different orders or species, we run into difficulties. Likewise, when we examine a given species ontogenetically to determine at what stages certain of these behavioral manifestations develop, or to note what transitions they go through, we also run into difficulties. Phylogenetically, the difficulties center around structure and organizational factors, as well as around environmental factors. Ontogenetically, the behavior of developing organisms progresses rapidly and passes through stages very quickly in some cases; in others the processes are quite prolonged and, as in the case of the human infant, there is an extended period of relative helplessness in motor development. Thus, phylogenetic and ontogenetic comparisons are fraught with many difficulties, but these are not insurmountable. It is encouraging to know that many varieties of phylogenetic investigations are being made by competent and experienced observers. As the title of this symposium implies, we are expected to concern ourselves not only with the behavioral and social aspects of aggression and defense, but also with brain mechanisms which underlie these processes. By way of introduction, I would like to try to sketch, briefly, some of the ontogenetic and developmental aspects of brain structure and function which bear a relation to behavioral and social development, and possibly to aggression and defense. The varying levels of complexity and the different orders of time required for maturation of the brain are certainly responsible for some of the behavioral variants observed at different phyletic levels. Although progress has not been as great as we might hope, a very considerable advance has been made in bringing together the results of behavioral studies and of brain research by means of electrical stimulation or electrical recording. By examining the results of separate studies, or by combining behavioral and electrical methods in the same experiment, a much greater understanding of these problems should evolve. Some problems related to the social and cultural aspects and determinants of aggression and defense have already been noted in this conference. Such relationships become very complex as we ascend the phylogenetic scale to man, where we deal with symbolic events and cognitive functions absent in many lower forms. Dr. Eibl-Eibesfeldt has discussed the possibilities of unlearned behavioral forms of aggression and defense as well as of learned forms. Progressively, we will become more involved with the latter, which we call the higher learned forms.

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