The Roots of Human Nature

IN THIS age of explosion of people and atoms man’s greatest need, more than ever before, is to understand himself. Why do we act as we do? The question becomes urgent; hence the present intensive efforts to study other living creatures that most resemble us, to reconstruct from odd-shaped stones and fossil bones the human past, and to search for the beginnings of life on other planets. Institutes for primate research are becoming established in many places, and studies of social groups of apes and monkeys in the wild, before it is too late, are therefore in vogue.

The more we see of the chimpanzee, the more we realize he is one of us. At the emotional level especially, the identity is clear. Young chimpanzees. for instance, exhibit temper tantrums all too familiar to anyone who has brought up children. And an adult chimpanzee becomes intensely disturbed on finding a live worm in its biscuit or on seeing snakes, spiders, and mice — even only the shape of a snake, although the animal may never have seen a snake before. Chimpanzees and people both have this revulsion built into their very being. Fear of the dark is also a common heritage. The sight of toy animals or a model of a human head can be terrifying to a chimpanzee. Toy animals in action can equally terrify a human infant when encountered for the first time. These fears are by no means rational, nor are they necessarily the result of childhood conditioning.

As a rule in this so-called civilization of ours man is a comparatively unemotional being, although, according to D. O. Hebb, the McGill psychologist, only because he is able most of the time to avoid situations which arouse strong emotion. For the most part, he lives in an insulated environment in which his emotional susceptibilities are well concealed, even from himself. In the same way, chimpanzees are placid in their own natural environment, but in close captivity — like a man in prison or an unemployed youth in a modern stone jungle — a chimpanzee becomes unpredictably explosive and often viciously aggressive. Hebb suggests that in the case of men and apes these emotional disturbances reflect a degree of instability which comes with a somewhat overly large brain.

Other qualities in chimpanzees make certain human traits more acceptable and perhaps better understood. Not only chimpanzees but also monkeys will work for hours at solving simple puzzles with no reward other than the satisfaction gained. In fact, a chimpanzee if he likes a learning task will work at it incessantly unless he is hungry, paying no attention to offered food, just as a man engrossed will forgo a meal. This contraverts the tradition that there is an inborn aversion to work, whether mental or physical, and that some tangible reward is required in order for work to be done. What seems to be necessary is not extrinsic reward but intrinsic interest. Just as some birds fly some of the time for the satisfaction of being in flight and some sing for the joy of song as well as to gain a mate or hold a territory, just as boys climb trees and men climb mountains because they themselves are built for climbing, so monkeys and apes and humans enjoy the skill in using their distinctive combination of eye, hand, and brain for what it is worth. Winston Churchill was expressing this when he said, “I like to learn, I don’t like to be taught.”

In 1964 Adriaan Kortlandt, of the University of Amsterdam, went to the Congo to observe wild chimpanzees. A group of forty-eight chimpanzees which occupied a banana plantation at the edge of the forest were watched from high tree blinds. Previous knowledge of chimpanzees in zoos and in the wild suggested that they normally live in small harem groups of from five to fifteen individuals, with one master of all, and it was assumed that some such state once prevailed in human or prehuman history. Now it seems that this is not so, although it is more or less true for the gorilla.

In the case of chimpanzees on the move, two forms of grouping occur: sexual groups, composed of adult males and childless females, often with a few mothers and children; and nursery groups, composed of juveniles, their mothers, and perhaps one or two adult males, showing no signs of sexual bonds or jealousy. Children up to four years of age are usually carried and are pampered. The young are tolerated and the old deferred to, with seniority conferring wisdom but never tyranny. This general pattern of social life appears to have grown out of the long and intensive care chimpanzees give their young. As a rule, however, chimpanzees in the wild act with the utmost caution, as though aware of weakness rather than collective strength. When a group emerges from dense forest onto a clearing, the adult males are always the first to appear, each looking and listening before emerging from behind a bush or tree. Once out and safe, they chase one another, shrieking, screaming, and stamping, like boys let out to play, although the females remain silent and shy.

A similar combination of sociability, family care, and curiosity has undoubtedly been characteristic of human and prehuman behavior from early times. Why then haven’t chimpanzees gone further than they have? The answer that they never came down from the trees is simply not true, for they spend much of their time on the ground, walking or running erect in order to see better or to leave hands free for carrying. Moreover, there is good evidence that they use heavy sticks as clubs either to light off leopards or for display. Gorillas, equally semiterrestrial, are known to use natural weapons in the same way, not to mention a ritual gesturing, stamping, chest-thumping, and vocalizing reminiscent of tribal warriors working up to the excitement and intimidation of a war dance. In both chimpanzees and gorillas the use of weapons is instructive, and it is reasonable to assume that the technique of armed combat emerged among the common ancestors of man and apes many million years ago and is not the peculiarly human vice it has been thought to be. So many subhuman and nearhuman creatures have gone to extinction during prehuman times that the struggle for ascendancy among the various man-apes and ape-men must have been intense.

Kortlandt suggests that it was the early invention of the spear that humanized our ancestors and dehumanized their anthropoid competitors by driving them off the savannas; that although the forest offers the best protection against spears, it has never been favorable to the evolution of the human way of life. He states that chimpanzees seize every opportunity to bring variety into their lives, are fascinated by everything new and unusual; that on one occasion an individual steadily watched an unusually beautiful sunset until almost dark; that “behind their lively, searching eyes one senses a doubting, contemplative personality, always trying to make sense out of a puzzling world.”Jane Goodall, accepted as one of themselves by the colony she studied, feels that chimpanzees are truly of the human stock. Somewhere along the line of our own past, apelike creatures ventured out from the fringes of the forest, as hesitantly as chimpanzees, as fascinated by all that was about them, as puzzled and as contemplative, but with a potential determination and decisiveness that carried the day.

THE surviving apes are few in kind and far between; monkeys are more numerous and widely spread and are sufficiently akin to apes and men to throw light on our own upbringing. At the Primate Laboratory of the University of Wisconsin, H. F. Harlow has raised infant monkeys with a surrogate mother consisting of a soft cloth-covered wire frame, complete with nursing bottle. Such infants apparently develop normally and show characteristic curiosity concerning their surroundings so long as they can run and cling to the soft mother substitute. As they grow older, they spend increasing amounts of time clinging and cuddling, although taking no more milk than do other infants supplied with the same wire and milk bottle combination without the cloth.

Infant monkeys raised with wire mothers not cloth-covered show no affection for the mother substitute and obtain no comfort; and they behave like neglected children in or out of institutions. Bodily contact with at least a simulation of the soft reality of the maternal body seems to be essential for normal emotional development. Infants raised from birth for several months with a cloth mother retain their responsiveness long after separation, but those who have known a cloth mother only after the age of eight months lose whatever responsiveness they may have shown immediately after being separated. Freud notwithstanding, the critical need is definitely not the role of the breast or the act of nursing but the clinging of infant to mother and the handling of the infant by the mother. However, it may be comforting for human mothers to know that monkey infants raised with cloth mothers, although seemingly normal as individuals, fail miserably as mothers themselves.

Monkeys also have the eye-hand kind of brain with a very subordinate sense of smell, as in humans and apes. Almost by definition, this means inquisitive fingers and a dominant sense of sight. It is not surprising that a monkey which is in captivity prefers the sight of another monkey, or almost anything that moves, such as a toy electric train, to any other form of satisfaction. There is the story of the psychologist who put a monkey in a room with various inanimate things supposedly of interest and looked through the keyhole to see its reactions, only to see a brown and lively eye peering from the other side. Watching the world go by is a pastime ingrained in us all. Any study of monkey behavior, however, as of children, should be made under natural circumstances, with the observer unobserved. This has been accomplished with baboons in Africa, with an introduced colony of old-world rhesus monkeys on an island off Puerto Rico, and with the elusive forest-dwelling monkeys of Japan.

The Japanese monkeys, with beautiful bright faces and very short tails, live in the forest in troops of up to two hundred individuals, communicating among themselves with vocal sounds relating to emotional state, movement to and from feeding grounds, defense, warning, sex, and infants. The occasional solitary monkey, however, makes no sound at all.

Within a troop, social relations become all important. Each monkey apparently knows every other monkey, its rank, status, mother-child relationship, and so on. Some of the infants, for example, are ranked high because they are children of influential mothers. In fact, at the Japan Monkey Center, established for studying these animals, a new troop was organized with monkeys collected from different natural troops. When a newcomer was added to the group, he or she was recognized at once and warmly accepted by individuals who had come from the same natural troop several months before. Each monkey troop has its own troop peculiarity and cultural trend, and each member of the troop differs from the others in personality and life history. How a distinctive culture is acquired in monkeys such as these is of considerable human import.

The Japanese scientists wished to draw their elusive subjects to a single feeding area where they could be better observed, and to do so they placed rice and sweet potato through the forest, gradually reducing the food until it was at one locality only, on the shore of the sea. Then one day a young female monkey, about eighteen months old, who had been born after the project had begun, started to wash her sweet potato in the sea before eating it, a simple action but one with considerable implication concerning monkey comprehension. Eventually the habit had been caught by all of the troop except the old and crusty males. In view of this capacity, it is perhaps surprising that the monkey world has shown so little enterprise during the multimillion years of its existence. On the other hand, man himself showed little more until relatively recent times.

In the earlier studies of both monkeys and apes, altogether too much has been read into their behavior while in confinement, for boredom affects these intelligent creatures as strongly and as disturbingly as it affects human beings under comparable conditions. Sex looms large and often perverse, while personality becomes lackluster and incurious. The role of the dominant male, polygamy, and the accentuation of brutishness with age have been overemphasized on the assumption that anthropoids in confinement behave and develop normally. The ancestors of man were outstanding, in the literal sense of the word, as venturers into open country, where danger from predators was enhanced. Of the other primates now living, only the baboon has left the woods.

Baboons are monkeys, to be sure, but they are comparatively venturesome monkeys. At some time in the monkey past they abandoned tree life for open ground, although in the last resort they climb into trees for safety, and invariably do so at night. Their special interest to man is that as monkeys they have successfully coped with a new environment of much the same sort, and in much the same way, as that of the primitive apes whose descendants we are. Like any grounded monkey, they walk and run on all fours, and use their forelimbs as arms and hands chiefly when sitting. Long jaws carry formidable teeth for fighting. Their strength is primarily collective, and their social organization is one of their principal adaptations for survival.

S. L. Washburn and I. De Vore studied the behavior of fifteen troops of baboons, troop size varying from thirteen to one hundred and eightyfive, in the Ambolesi game reserve at the foot of Mount Kilimanjaro in Kenya. They found no support for the accepted theory that sexuality provides the most important bond of the primate troop. They found that a troop, viewed at close range, is composed of strongly emotional, highly motivated, and far from neutral creatures. The basic social structure is seen when a troop moves away from the safety of trees and out onto open plains. The less dominant males occupy the van, and the older juveniles follow; in the center of the troop are the females with infants, the young juveniles, and the most dominant males; the back of the troop is a mirror image of the front. Thus without any fixed or formal order, the females and young are protected. When a predator is sighted, the females and young hurry away, but the males do not, and almost at once a platoon of males becomes interposed. Most animals leave them alone, and only the lion puts them to flight.

Much of the time the members of a troop, like most monkey folk, gather in small groups, sitting and grooming, perhaps two females and young, or an adult male and two females. Newborn infants are a center of attraction, and most dominant males sit by or walk close beside a mother. Juveniles play together in groups that persist for several years. If a juvenile is hurt and cries out, adults come running and stop the play. The security of the individual and the survival of the race lie in the strength and diversity of the social bonds. Only the stray or the outcast is vulnerable.

STUDIES of living apes and monkeys, however much they appear to give insight into our own peculiar nature, are studies of our contemporaries, not our ancestors. The assumption is that man passed through a stage similar to the existing ape, and that earlier both passed through a stage represented by existing monkeys. This may be so, but it is an assumption which needs to be verified or modified by actual evidence from the past. But efforts to reconstruct the human past have always been handicapped by the scarcity of fossil material and by the enormous extent of evolutionary time that we are concerned with. Fossilized remains are, at best, little more than signs along the road. And the primates still available for study as living creatures — four kinds of apes, the old-world and new-world monkeys, the lemurs of Madagascar, the bush babies of equatorial Africa, and the spectral tarsiers of Southeast Asia — are but a remnant of what has gone before. They do represent stages of primate evolution, although each group has had all the time until the present to diverge from a more generalized ancestral type.

The significance of recent discoveries of fossil anthropoid remains can be fully appreciated only when seen in the total perspective of primate evolution. This has been a very long process, coinciding for the most part with the evolution of the other major orders of mammals. To begin with, there was a prolonged phase represented by small primitive mammals, not unlike the present-day shrews, ancestral to all the modern orders and possessing all the particular mammalian characteristics common to mice and men. An arboreal phase followed, beginning with creatures probably similar to existing tree shrews and progressing to larger forms, such as tarsiers and lemurs, more fully adapted to the opportunities, hazards, and general requirements of arboreal existence.

Then came the anthropoids proper, with more handlike flet, better stereoscopic vision, eye-hand type of brain, great curiosity and capacity for mischief, and opportunity to chatter with impunity. There were tarsiers in the Eocene, fifty million years ago, monkeys in the Oligocene, which followed, and apes of many kinds in the Miocene forests, halfway to the present. Proconsul, an early Miocene ape of about twenty-five million years ago, a full-fledged ape of a less specialized sort than any of the present survivors, and not too well constructed for arboreal life, may have stood at the parting of the ways. At least he has a fitting name. The final phase, in any case, resulted from the grounding of apelike creatures, from which the specifically prehuman stock took a distinctive evolutionary path.

The key question is, when did this last phase begin? — as early as proconsul, or as late as the beginning of the Pleistocene a million years ago perhaps, when the Ice Age was already imminent, or sometime in between? The debate has been protracted because the evidence, although suggestive, has been too scanty and indecisive. Prehuman creatures appear to have lived in circumstances unfavorable to the preservation of their bones. Their tools are another matter, and discoveries of simple but significantly chipped pebbles have suggested the existence of humanoid beings for a longer time than their bones have indicated. When a stone that more or less fits a human hand has been flaked to a cutting edge for flensing a carcass and is found together with pieces of skull and pelvis, indicative of brain and posture, much can be surmised, and the longtime dead begin to come alive.

Modern man can be traced back only a relatively short way. Homo sapiens, self-labeled the wise, includes the Paleolithic mammoth hunters and cave painters of 20,000 years ago, and also, though belatedly admitted, the more stooped and heavybrowed Neanderthal men who lived in Europe during the last interglacial period but were missing when the glaciers finally melted. Other men, such as Peking man, known as Homo erectus, erect but not so wise, were tool-makers and fire-makers who were around during the early to middle Ice Age several hundred thousand years ago. Before that, before the initial onslaught of the Pleistocene ice, the trail until recently has been marked only by hand-flaked pebbles. New discoveries in southeastern Africa now push the fossil human story two million years into the past.

The first of these discoveries was made about forty years ago by Raymond Dart, who then and later established the existence and general nature of man-apes known as Australopithecines, about five feet tall and more manlike than apelike, who stood erect with a small, well-balanced head; who ran, hunted, used ready-made but not handmade tools or weapons, and sheltered in caves. They seem to have been widespread through southern lands and to have been closely related to the emergent human stock. That they were not themselves the actual stock is evident from discoveries made during the last few years by the Leakeys, man and wife, who had spent much of their lifetime patiently and persistently digging in and around the Olduvai Gorge in Tanzania.

The Leakeys had been challenged by the earlier discovery of unmistakably manually shaped pebbles found in East African strata of pre-Ice-Age time. At last, they were rewarded by finding remains of two kinds of beings, one of them now identified as an Australopithecine and the other a tool-maker sufficiently human to be admitted to the rank of Homo, as Homo babilus, meaning man who is able, mentally skillful, vigorous. The significance of the age of the fossilized remains is that radioactivity-dating methods place them at close to two million years, which puts the human past much further back in time than had been known before. At that time, however, the two kinds of more or less human beings were contemporary inhabitants of the earth, so that to find the true beginnings where human stock departed from the ape, we must now probe into far more ancient periods.

Fossil remains of five individuals were found, one of whom was an elderly woman, one an elevenyear-old child, and a third a young woman aged about twenty years. Homo babilus is said to have stood and walked upright. His feet and hands were similar to modern man’s. His jaw was roomy enough for a tongue to be used in speech. His teeth show him to have been as omnivorous as we are. And his skull, although small in keeping with his four-foot stature, was shaped much like our own, with room enough for a relatively well developed forebrain superior in form to all but that of modern man himself. Although the Olduvai Gorge is now a desert, during the million years Homo babilus appears to have inhabited the area the gorge was part of a wet, tropical region rich in lakes, rivers, fish, and game.

Following the announcement of the first Olduvai Gorge discoveries, John Napier, of the primatology unit of the University of London, called particular attention to the significance of the hand, pointing out that the human hand, which can achieve so much in the field of creative art and communicate such subtle shades of meaning, and on which the pre-eminence of Homo sapiens so largely depends, constitutes, in a structural sense, one of the most primitive and generalized parts of the human body. It is this aspect of the hand which has given support to the almost traditional view that the prehuman forerunners of man were equipped with a hand of essentially human form long before the brain became sufficiently well developed to exploit it. The finding of hands, tools, and skulls at the same site in the Olduvai Gorge makes correlations possible for the first time.

For all its generally primitive structure, the human hand is marvelously made, not only having an opposable thumb and rotating at the wrist, but endowed with two prehensile working arrangements. One is the power grip, such as is employed in using a screwdriver to turn a tight screw, and the other the precision grip, in which the finger and thumb tips take over. The power grip is primitive and is present in some degree in most primates, while the precision grip is the final refinement, present in man but hardly developed elsewhere. The small hand of Homo habilus appears to have been capable of a very strong power grip, but the setting of the thumb suggests that the precision grip had not attained its fullest expression. This is in keeping with the fact that their stone implements were little more than pebbles with one or more flakes struck off to produce a chopping stone. Already nearing the goal represented by modern man, the perfecting of the hand apparently kept close pace with the development of the brain.

A small but nearly perfected man inhabiting the earth almost two million years ago not only gives man a tremendous extension of his prehistoric apprenticeship but also gives his prehuman existence a much more extended past. It places the evolution of man from arboreal ape to the Leakeys’ little handyman within the long period of the Pliocene when the grasslands and the grassland fauna were evolving as the dominant living feature of die earth.

Man evolved with the creatures he lived with and hunted — not as a Johnny-come-lately pitchforked from the trees into the hostile openness of the plains when the drama of the plains had already reached its climax, but as an early adventurer, aggressive, sharp-witted, and nimble, who took to the ground because of better opportunities and broader horizons. He evolved in company, and in response to the great general environmental challenge of the age. Only his overpowering ascendancy is recent.