Sherlock abduced, on the basis of the evidence available to him, that a single perpetrator was unlikely to be the solution to his mystery. So have I, though it took me a lot longer. A single-perpetrator explanation doesn’t fit the evidence in this case any better than it did in Sherlock’s. I have come to the conclusion that there are some previously unsuspected psychological mechanisms involved in children’s social development. I posit three mechanisms, distinguishable by their different goals, by the different sorts of information they receive from the environment, and by the different ways they process that information. Only one of them can be held accountable for the differences between reared-together identical twins, but all three are needed to explain environmental effects on personality and behavior.
It was the trial-and-error process of natural selection that produced the design for the human mind. The design specs were worked out over eons of time: the two or three million years during which hominid head size was expanding and our remote ancestors were doing increasingly sophisticated things—using tools, making tools, acquiring language, creating art, developing cultures. The components of the mind of the modern human were road tested under rigorous conditions: the conditions that prevailed in the Paleolithic, prior to the end of the last ice age (around 10,000 B.C.) and the invention of agriculture. If the human mind hadn’t passed that road test, we wouldn’t be here. Our ancestors succeeded in becoming our ancestors because they had what it took to survive and reproduce. Along the way, millions of less successful hominids—the also-rans in the competition—bit the dust. We are the descendants of the winners.
To appreciate what it took to make a go of it back then, it helps to have an understanding of what “back then” was like. It wasn’t like an endless camping trip, because there were no compasses, matches, sleeping bags, tents, metal knives or axes, pots or pans, bottles of water, chocolate bars, or cell phones. And it wasn’t like the first part of Robinson Crusoe’s sojourn on the island, before he met Friday, because our ancestors were hardly ever alone. Being alone was too dangerous for the members of a species as flimsy as ours. There was safety in numbers, so they traveled in groups. They wandered around looking for something to eat, fearful of predators, fearful of rival groups, fearful of straying too far from a source of water. The latter two concerns made them more or less territorial. They had to move fairly often—if you don’t plant crops or raise domesticated animals, a small piece of land will soon be exhausted of its edibles—but most movement probably followed an annual circuit and the land they moved over was familiar.23
It’s hard to imagine what it was like to raise a child under such conditions. A baby had to be carried everywhere for three or four years, until it could walk well enough to keep up with the group. Through rain and wind and darkness of night, you’d have to schlep this wet, dirty, hungry little creature wherever you went. It took tremendous effort just to keep a child alive, and yet our ancestors must have done it, because here we are. Some mental module provided them with enough motivation to see the job through. Anyone who thinks that humans don’t have instincts needs to have his head examined.
Aside from the certainty that at least some children survived, we have no direct knowledge of what childhood was like in the Paleolithic. But anthropologists have studied societies that maintained a hunter-gatherer lifestyle into the twentieth century, and there is plenty of information on other traditional human societies—tribal and small village societies that, at the time of the anthropologists’ visit, had had little or no exposure to Western culture. The commonalities among these societies serve as clues to ancient patterns.
Under ancestral conditions, the effort involved in rearing a new infant could jeopardize its mother’s chances of survival and those of her previous children as well. Therefore, the first thing a baby had to do after drawing a breath was to win its mother’s commitment. Should she keep it and rear it? If food or water was scarce, if her previous child wasn’t old enough to be weaned, or if there was anything iffy about the newborn itself, the answer might be no. Such decisions could never have been easy; they were made with sadness and regret.24
Once the decision was made to keep the baby, the mother’s commitment was wholehearted. The baby was carried everywhere, nursed whenever he whimpered. By night he slept by his mother’s side. For three or four years the mother and the child were in almost constant physical contact.
Then his mother had another baby. If he hadn’t already been weaned from the breast, weaning would come as an abrupt shock, without apology or explanation. The new baby was now the center of the mother’s attention and her previous child, three or four years old, became a member of a coterie of children. He still knew who his parents were, of course, and would return to them at night and occasionally during the day for food or comfort, but decreasingly often as he grew older. Even at three or four, most of his daylight hours would be spent in the company of other children.
At the age when they graduate to the children’s play group, children in traditional societies are about a year behind American babies in learning to talk. Mothers in these societies are very concerned about the physical well-being of their babies, but they don’t talk to them much because they don’t believe that babies can understand a word of what is said to them.25 The children learn the local language the same way they learn the local rules of social behavior: from other children, a little older than themselves. Here’s the German ethologist Irenäus Eibl-Eibesfeldt describing early childhood in the hunter-gatherer and tribal societies he studies:
Three-year-old children are able to join in a play group, and it is in such play groups that children are truly raised. The older ones explain the rules of play and will admonish those who do not adhere to them, such as by taking something away from another or otherwise being aggressive. Thus the child’s socialization occurs mainly within the play group…. Initially the older children behave very tolerantly toward the younger ones, although eventually they place definite limitations on behavior. By playing together in the children’s group the members learn what aggravates others and which rules they must obey. This occurs in most cultures in which people live in small communities.26
Nowadays parenting is a job that lasts at least eighteen years and parents are held responsible for every aspect of their children’s development. In the old days, parents had more worries about keeping their children nourished and healthy, but almost everything else was seen as the child’s job. Children were expected to acquire the skills they would need in adulthood by observing adults or older children and eventually performing the tasks themselves. They were admonished for minor mistakes and beaten for major ones, but no explanations were given. Parents in traditional societies do not, as a rule, give long-winded lectures to their offspring. The adult’s conversational partners are other adults; the child’s are other children.27
But some things haven’t changed. Modern children can’t count on their families’ remaining intact until they have made it through childhood and it was no better in the old days. An anthropologist who studied the Yanomamö (Amazonian Indians who live in the rainforests of Venezuela and Brazil) reported there was only a one-in-three chance that a child of ten would still be living with both parents. Though the rate of marital breakup was low compared to ours—about 20 percent—the death rate was considerably higher.28 The Yanomamö get their meat from hunting but they also plant some crops; they lead a less precarious existence than people who rely entirely on foraging. In the Paleolithic, the chances that a child would still have both parents by the age of ten was probably less than one in three.
Children couldn’t rely on their parents for companionship, teaching, or conversation, and they couldn’t count on them to stick around for long. But the loss of one or both parents, though it lowered a child’s chances of surviving, wasn’t a death warrant because he was a member of a group. He was surrounded by other relatives who might be willing to look after him. Only if he lost his entire group did his chances plummet
to zero. The survival of a small, peripatetic band of humans couldn’t have been anything close to a sure thing in the Paleolithic, but it was a better bet than the survival of any particular individual.
Though the world held many dangers—predators, starvation, disease—the greatest threat to the survival of a hunter-gatherer group was probably the group next door. Group warfare is not a human invention; we share the willingness to engage in it with a variety of other creatures, including ants. That doesn’t mean we inherited this propensity from ants; it evolved independently in the social insects. But we did inherit a taste for warfare from our primate ancestors. As Jane Goodall discovered, chimpanzees can be just as bloodthirsty as humans: they, too, engage in systematic efforts to wipe out other groups of their own species.29 The main difference is that chimpanzees have to pick off their enemies one by one, whereas humans, with the aid of technology or cunning, can do it in one fell swoop.
According to the evolutionary psychologist Robin Dunbar, human hunter-gatherer and tribal societies are organized in tiers: “overnight groups” of 30 or 35 people, clans of about 150, and tribes of around 1,500 to 2,000.30 The membership of overnight groups is unstable; their numbers vary according to local conditions and personal preferences. These groups remain in close contact with each other and people frequently switch from one to another, so within a clan everyone has a chance to get to know everyone. Contact is also maintained between clans, for the purposes of trade, finding marriage partners, and mutual defense. Between tribal groups, relationships are likely to be predominantly unfriendly. But war may also break out within a tribe, between clans. Someone might decide that he got cheated in a trade, or accuse another man of seducing his wife, and the matter could escalate, causing the tribal group to split up into feuding clans.
When a human group splits in two and the two new groups occupy adjacent territories, war between them is likely to be sporadic rather than continuous. There will be truces during which goods are traded and marriages arranged. Nonetheless, if the two groups remain distinct, cultural differences between them will inevitably emerge, due to what I call “group contrast effects.”31 These effects work in the opposite way to that of Richard Dawkins’ “memes.” Cultural transmission by memes is analogous to genetic transmission by genes: bits of culture are passed from one generation to the next, with successful variations promulgating themselves and unsuccessful ones dying out. That’s a reasonable description of what happens within a group, but to explain what happens between groups we need the concept of anti-memes.32
Anti-memes can come into play very quickly. In The Nurture Assumption I described an experiment in social psychology, done in Oklahoma in the 1950s, called the Robbers Cave study. Twenty-two boys, matched in every important demographic attribute, were divided into two groups and treated to a couple of weeks in a summer camp, in a wilderness area known as Robbers Cave. Hostility between the two groups broke out almost immediately and was quickly followed by the development of contrasting customs. The boys in one group gave up using naughty words and started saying prayers together, while those in the other group cursed like troopers and acted rough and tough.33
“Humans show a strong inclination to form such subgroups which eventually distinguish themselves from the others by dialect and other subgroup characteristics and go on to form new cultures,” Eibl-Eibesfeldt observed. “To live in groups which demarcate themselves from others is a basic feature of human nature.” Human groups demarcate themselves from one another by adopting different styles of dress, different norms of behavior, and different dialects. A stranger who dresses, behaves, or speaks differently is regarded with suspicion or hostility. “Xenophobia,” lamented Eibl-Eibesfeldt, “is a universal quality.”34
It’s universal and it shows up early. Babies around the world begin to show a wariness of strangers at around six months of age. By then, in a typical hunter-gatherer or tribal society, they will have had a chance to meet most of the members of their clan and many of their tribe. An unfamiliar face alerts the baby: this person might be dangerous. If the stranger approaches too quickly and tries to pick up the baby, the baby will protest vigorously.35
But the appearance of a solitary stranger from another tribe would be a rarity in such a society. “To venture out of one’s territory,” explained evolutionary biologist Jared Diamond, “was equivalent to suicide.” Diamond was describing tribal life in the interior highlands of New Guinea before the arrival of Europeans. Most New Guinea highlanders, he said, spent their lives within ten miles of where they were born.36
When human groups cease to have friendly contact with each other, cultural development proceeds independently. Each valley in New Guinea, Diamond reported, had its own culture and its own language. When Europeans first ventured into the interior of New Guinea—an area about the size of Texas—they found it was a Tower of Babel: nearly a thousand different languages were spoken, most of them mutually unintelligible.37
Many tribal societies refer to themselves by a word that translates as “the people.” The implication is that anyone who is not a member of their tribe is not a person. One Amazonian group, the Wari, go even further. Their language has a term that means “an edible thing” and they apply it to anyone who is not a Wari. My reaction, when I read about the Wari,38 was indelicate, I’m afraid. Instead of going tsk-tsk, I wrote a little poem about them.
In the Wari dictionary
Food’s defined as “not a Wari.”
Their dinners are a lot of fun
For all but the un-Wari one.
You see, babies have good reason to be afraid of strangers.
I meant, of course, adult strangers. Babies are not afraid of other babies or of children—on the contrary, they are attracted to them. This means that babies not only distinguish familiar individuals from strangers: they also distinguish children from adults.
Months before they acquire the physical and social skills that will enable them to play with one another, babies show an interest in other babies.39 Their interest increases as they get older. For a child, the sight or sound of other children is an irresistible invitation to come and play. This is true in all primate species. Young monkeys leave their mothers for sessions of rollicking play with their peers as soon as they can move around well on their own. One that is unable to find playmates in its own troop may go in search of them. The attraction of playmates transcends troop boundaries and even the boundaries between species: Goodall saw young chimpanzees playing with young baboons in Tanzania.40
Adults’ quarrels can cause groups to split up, but children’s desire for playmates—especially in places where there aren’t many of them—can cause new groups to form. This, too, has been observed in chimpanzees. A young chimpanzee who hears other young chimpanzees playing in the distance will try to persuade his mother to move in that direction, and eventually she may give in to his pestering.41
Thus, children in ancestral times were not limited to the handful of playmates available in their overnight group: probably all the children in the clan played with each other at one time or another, and some friendships—especially among older children—might have transcended clan boundaries. Where life expectancy is short, the number of babies and children in a population far exceeds the number of adults,42 so a clan of 150 or so would have contained plenty of children.
When they have a choice, children prefer to play with other children of their own sex and roughly their own age. Wherever there are enough children and adults don’t interfere, children split up into sex-segregated groups. They do this in populous traditional societies and on school playgrounds in modern industrialized societies. But in places where there are fewer children—in sparsely settled neighborhoods in modern societies, for instance—they will play with whoever is available. Thus, neighborhood play groups often include both sexes and a range of ages.43 It was probably much the same in the Paleolithic. When there weren’t many children around, play groups would be mixed-sex and multi-age. When overnig
ht groups coalesced into larger ones, the children might divide into three groups: younger kids, older girls, and older boys.
A child in a traditional society who enters the younger kids’ play group will at first be watched over by an older child. Typically the one who is charged with this responsibility will be his next-older sibling, a child only three or four years older than himself. This is the very child whose place he usurped in their mother’s arms, and yet the older sibling will show genuine concern for the younger one’s well-being and will defend him against teasing or bullying by other children. In traditional societies (and in chimpanzee societies too), siblings are allies and generally remain so all their lives.44
But they do not remain playmates, because the age gap of three or four years will separate them before long. The older sibling will graduate to a group of older girls or boys and leave the younger one behind in the little kids’ group. And then, at around fifteen or sixteen, the older one will become an adult.
In the majority of traditional human societies, males generally remain with the group they were born into, while females more often “marry out.” They may be wooed away or the switch may be made involuntarily. A girl may be given in marriage to someone in another clan, or stolen in a raid by another tribe, and she may not see her parents and siblings again for a long time, if ever. It’s less common today, but there are still places where a nubile young woman is regarded as something that can be bought, sold, stolen, or given to seal an alliance. The man who mistook his wife for a hat had a rare neurological disorder; the man who mistook his wife for a chattel is an anthropological commonplace.45
For boys there are other hazards: they are expected to participate in the defense of their group. A boy just past puberty may not be old enough to win a wife, but he is considered old enough to die for his group.46
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