Most profoundly, children do not allow their personalities to be shaped by their parents’ nagging, blandishments, or attempts to serve as role models.24 As we shall see in the chapter on children, the effect of being raised by a given pair of parents within a culture is surprisingly small: children who grow up in the same home end up no more alike in personality than children who were separated at birth; adopted siblings grow up to be no more similar than strangers. The findings flatly contradict the predictions of every theory in the history of psychology but one. Trivers alone had predicted:
The offspring cannot rely on its parents for disinterested guidance. One expects the offspring to be preprogrammed to resist some parental manipulation while being open to other forms. When the parent imposes an arbitrary system of reinforcement (punishment and reward) in order to manipulate the offspring to act against its own best interests, selection will favor offspring that resist such schedules of reinforcement.25
That children don’t turn out the way their parents want is, for many people, one of the bittersweet lessons of parenthood. “Your children are not your children,” wrote the poet Kahlil Gibran. “You may give them your love but not your thoughts, for they have their own thoughts.”26
The most obvious prediction of the theory of parent-offspring conflict is that parents and siblings should all have different perceptions of how the parents treated the siblings. Indeed, studies of the grown members of families show that most parents claim they treated their children equitably, while a majority of siblings claim they did not get their fair share.27 Researchers call it the Smothers Brothers effect, after the comedy pair whose duller member had the signature line “Mom always liked you best.”
But the logic of parent-offspring conflict does not apply only to contemporaneous siblings. Offspring of any age tacitly compete against the unborn descendants that parents might have if they were ceded the time and energy. Since men can always father children (especially in the polygynous systems that until recently characterized most societies), and since both sexes can lavish investment on grandchildren, potential conflicts of interest between parents and offspring hang over them for life. When parents arrange a marriage, they may cut a deal that sacrifices a child’s interest for future considerations benefiting a sibling or the father. Children and adults may hold different opinions on whether a child should stick around to help the family or strike out on his or her own reproductive career. Married children have to decide how to allocate time and energy between the nuclear family they have created and the extended family they were born into. Parents have to decide whether to distribute their resources in equal parts or to the child who can make the best use of them.
The logic of parent-offspring and sibling-sibling conflict casts a new light on the doctrine of “family values” that is prominent in the contemporary religious and cultural right. According to this doctrine, the family is a haven of nurturance and benevolence, allowing parents to convey values to children that best serve their interests. Modern cultural forces, by allowing women to spend less time with young children and by expanding the world of older children beyond the family circle, have supposedly thrown a grenade into this nest, harming children and society alike. Part of this theory is surely accurate; parents and other relatives have a stronger interest in the well-being of a child than any third party does. But parent-offspring conflict implies that there is more to the picture.
If one could ask young children what they want, it would undoubtedly be the undivided attention of their mothers twenty-four hours a day. But that does not mean that nonstop mothering is the biological norm. The need to find a balance between investing in an offspring and staying healthy (ultimately to invest in other offspring) is inherent to all living things. Human mothers are no exception, and often have to resist the demands of their pint-sized tyrants so as not to compromise their own survival and the survival of their other born and unborn children. The anthropologist Sarah Blaffer Hrdy has shown that the tradeoff between working and mothering was not invented by power-suited Yuppies of the 1980s. Women in foraging societies use a variety of arrangements to raise their children without starving in the process, including seeking status within the group (which improves the children’s well-being) and sharing childcare duties with other women in the band. Fathers, of course, are usually the main providers other than the mother herself, but they have bad habits like dying, deserting, and not making a living, and mothers have never depended on them alone.28
The weakening of parents’ hold over their older children is also not just a recent casualty of destructive forces. It is part of a long-running expansion of freedom in the West that has granted children their always-present desire for more autonomy than parents are willing to cede. In traditional societies, children were shackled to the family’s land, betrothed in arranged marriages, and under the thumb of the family patriarch.29 That began to change in medieval Europe, and some historians argue it was the first steppingstone in the extension of rights that we associate with the Enlightenment and that culminated in the abolition of feudalism and slavery.30 Today it is no doubt true that some children are led astray by a bad crowd or popular culture. But some children are rescued from abusive or manipulative families by peers, neighbors, and teachers. Many children have profited from laws, such as compulsory schooling and the ban on forced marriages, that may override the preferences of their parents. Some may profit from information, such as about contraception or careers, that their parents try to withhold. And some must escape a stifling cultural ghetto to discover the cosmopolitan delights of the modern world. Isaac Bashevis Singer’s novel Shosha begins with a reminiscence of the protagonist’s childhood in the Jewish section of Warsaw at the beginning of the twentieth century:
I was brought up on three dead languages—Hebrew, Aramaic, and Yiddish…—and in a culture that developed in Babylon: the Talmud. The cheder [schoolroom] where I studied was a room in which the teacher ate and slept, and his wife cooked. There I studied not arithmetic, geography, physics, chemistry, or history, but the laws governing an egg laid on a holiday and sacrifices in a temple destroyed two thousand years ago. Although my ancestors had settled in Poland some six or seven hundred years before I was born, I knew only a few words of the Polish language…. I was an anachronism in every way, but I didn’t know it.
Singer’s reminiscence is more nostalgic than bitter, and of course most families offer far more nurturance than repression or strife. At the proximate level, Tolstoy was surely right that there are happy and unhappy families and that unhappy families are unhappy in different ways, depending on the chemistry of the people thrown together by genetics and fate. The conflict inherent to families does not make family ties any less central to human existence. It only implies that the balancing of competing interests that governs all human interactions does not end at the door of the family home.
AMONG THE COMBINATIONS of people that Trivers considered is the pair consisting of a man and a woman. The logic of their relationship is rooted in the most fundamental difference between the sexes: not their chromosomes, not their plumbing, but their parental investment.31 In mammals, the minimal parental investments of a male and a female differ dramatically. A male can get away with a few minutes of copulation and a tablespoon of semen, but a female carries an offspring for months inside her body and nourishes it before and after it is born. As they say of the respective contributions of the chicken and the pig to eggs and bacon, the first is involved, but the second is committed. Since it takes one member of each sex to make a baby, access to females is the limiting resource for males in reproduction. For a male to maximize the number of his descendants, he should mate with as many females as possible; for a female to maximize the number of her descendants, she should mate with the best-quality male available. This explains the two widespread sex differences in many species in the animal kingdom: males compete, females choose; males seek quantity, females quality.
Humans are mammals, and our sexual beha
vior is consistent with our Linnaean class. Donald Symons sums up the ethnographic record on sex differences in sexuality: “Among all peoples it is primarily men who court, woo, proposition, seduce, employ love charms and love magic, give gifts in exchange for sex, and use the services of prostitutes.”32 Among Western peoples, studies have shown that men seek a greater number of sexual partners than women, are less picky in their choice of a short-term partner, and are far more likely to be customers for visual pornography.33 But the male of Homo sapiens differs from the male of most other mammals in a crucial way: men invest in their offspring rather than leaving all the investing to the female. Though deprived of organs that can siphon nutrients directly into his children, a man can help them indirectly by feeding, protecting, teaching, and nurturing them. The minimum investments of a man and a woman are still unequal, because a child can be born to a single mother whose husband has fled but not to a single father whose wife has fled. But the investment of the man is greater than zero, which means that women are also predicted to compete in the mate market, though they should compete over the males most likely to invest (and the males with the highest genetic quality) rather than the males most willing to mate.
The genetic economics of sex also predicts that both sexes have a genetic incentive to commit adultery, though for partly different reasons. A philandering man can have additional offspring by impregnating women other than his wife. A philandering woman can have better offspring by conceiving a child by a man with better genes than her husband while having her husband around to help nurture the child. But when a wife gets the best of both worlds from her affair, the husband gets the worst of both worlds, because he is investing in another man’s genes that have usurped the place of his own. We thus get the flip side of the evolution of fatherly feelings: the evolution of male sexual jealousy, designed to prevent his wife from having another man’s child. Women’s jealousy is tilted more toward preventing the alienation of a man’s affections, a sign of his willingness to invest in another woman’s children at the expense of her own.34
The biological tragedy of the sexes is that the genetic interests of a man and a woman can be so close that they almost count as a single organism, but the possibilities for their interests to diverge are never far away. The biologist Richard Alexander points out that if a couple marry for life, are perfectly monogamous, and favor their nuclear family above each spouse’s extended family, their genetic interests are identical, tied up in the single basket containing their children.35 Under that idealization, the love between a man and a woman should be the strongest emotional bond in the living world—”two hearts beating as one”—and of course for some lucky couples it is. Unfortunately, the ifs in the deduction are big ifs. The power of nepotism means that spouses are always being tugged apart by in-laws and, if there are any, by stepchildren. And the incentives of adultery mean that spouses can always be tugged apart by cuckolds and home-wreckers. It is no surprise to an evolutionary biologist that infidelity, stepchildren, and in-laws are among the main causes of marital strife.
Nor is it a surprise that the act of love itself should be fraught with conflict. Sex is the most concentrated source of physical pleasure granted by our nervous system, so why is it such an emotional bramble bush? In all societies, sex is at least somewhat “dirty.” It is conducted in private, pondered obsessively, regulated by custom and taboo, the subject of gossip and teasing, and a trigger for jealous rage.36 For a brief period in the 1960s and 1970s people dreamed of an erotopia in which men and women could engage in sex without hang-ups and inhibitions. The protagonist of Erica long’s Fear of Flying fantasized about “the zipless fuck”: anonymous, casual, and free of guilt and jealousy. “If you can’t be with the one you love, love the one you’re with,” sang Stephen Stills. “If you love somebody, set them free,” sang Sting.
But Sting also sang, “Every move you make, I’ll be watching you.” And Isadora Wing concluded that fastener-free copulation is “rarer than the unicorn.” Even in a time when seemingly anything goes, most people do not partake in sex as casually as they partake in food or conversation. That includes today’s college campuses, which are reportedly hotbeds of the brief sexual encounters known as “hooking up.” The psychologist Elizabeth Paul sums up her research on the phenomenon: “Casual sex is not casual. Very few people are coming out unscathed.”37 The reasons are as deep as anything in biology. One of the hazards of sex is a baby, and a baby is not just any seven-pound object but, from an evolutionary point of view, our reason for being. Every time a woman has sex with a man she is taking a chance at sentencing herself to years of motherhood, with the additional gamble that the whims of her partner could make it single motherhood. She is committing a chunk of her finite reproductive output to the genes and intentions of that man, forgoing the opportunity to use it with some other man who may have better endowments of either or both. The man, for his part, may be either implicitly committing his sweat and toil to the incipient child or deceiving his partner about such intentions.
And that covers only the immediate participants. As Jong lamented elsewhere, there are never just two people in bed. They are always accompanied in their minds by parents, former lovers, and real and imagined rivals. In other words, third parties have an interest in the possible outcome of a sexual liaison. The romantic rivals of the man or woman, who are being cuckolded or rendered celibate or bereft by their act of love, have reasons to want to be in their places. The interests of third parties help us understand why sex is almost universally conducted in private. Symons points out that because a man’s reproductive success is strictly limited by his access to women, in the minds of men sex is always a rare commodity. People may have sex in private for the same reason that people during a famine eat in private: to avoid inciting dangerous envy.38
As if the bed weren’t crowded enough, every child of a man and a woman is also the grandchild of two other men and two other women. Parents take an interest in their children’s reproduction because in the long run it is their reproduction too. Worse, the preciousness of female reproductive capacity makes it a valuable resource for the men who control her in traditional patriarchal societies, namely her father and brothers. They can trade a daughter or sister for additional wives or resources for themselves, and thus they have an interest in protecting their investment by keeping her from becoming pregnant by men other than the ones they want to sell her to. It is not just the husband or boyfriend who takes a proprietary interest in a woman’s sexual activity, then, but also her father and brothers.39 Westerners were horrified by the treatment of women under the regime of the Taliban in Afghanistan from 1995 to 2001, when women were cloaked in burqas and forbidden to work, attend school, and leave their homes unaccompanied. Wilson and Daly have shown that laws and customs with the same intent—giving men control over their wives’ and daughters’ sexuality—have been common throughout history and in many societies, including our own.40 Many a father of a teenage girl has had the fleeting thought that the burqa is not such a bad idea after all.
On strictly rational grounds, the volatility of sex is a paradox, because in an era with contraception and women’s rights these archaic entanglements should have no claim on our feelings. We should be ziplessly loving the one we’re with, and sex should inspire no more gossip, music, fiction, raunchy humor, or strong emotions than eating or talking does. The fact that people are tormented by the Darwinian economics of babies they are no longer having is testimony to the long reach of human nature.
WHAT ABOUT PEOPLE who are not tied by blood or children? No one doubts that human beings make sacrifices for people who are unrelated to them. But they could do so in two different ways.
Humans, like ants, could have a gung-ho superorganism thing that prompts them to do everything for the colony. The idea that people are instinctively communal is an important precept of the romantic doctrine of the Noble Savage. It figured in the theory of Engels and Marx that “primitive communism” was the first soci
al system, in the anarchism of Peter Kropotkin (who wrote, “The ants and termites have renounced the ‘Hobbesian war,’ and they are the better for it”), in the family-of-man utopianism of the 1960s, and in the writings of contemporary radical scientists such as Lewontin and Chomsky.41 Some radical scientists imagine that the only alternative is an Ayn Randian individualism in which every man is an island. Steven Rose and the sociologist Hilary Rose, for instance, call evolutionary psychology a “right-wing libertarian attack on collectivity.”42 But the accusation is factually incorrect—as we shall see in the chapter on politics, many evolutionary psychologists are on the political left—and it is conceptually incorrect. The real alternative to romantic collectivism is not “right-wing libertarianism” but a recognition that social generosity comes from a complex suite of thoughts and emotions rooted in the logic of reciprocity. That gives it a very different psychology from the communal sharing practiced by social insects, human families, and cults that try to pretend they are families.43
Trivers built on arguments by Williams and Hamilton that pure, public-minded altruism—a desire to benefit the group or species at the expense of the self—is unlikely to evolve among nonrelatives, because it is vulnerable to invasion by cheaters who prosper by enjoying the good deeds of others without contributing in turn. But as I mentioned, Trivers also showed that a measured reciprocal altruism can evolve. Reciprocators who help others who have helped them, and who shun or punish others who have failed to help them, will enjoy the benefits of gains in trade and outcompete individualists, cheaters, and pure altruists.44 Humans are well equipped for the demands of reciprocal altruism. They remember each other as individuals (perhaps with the help of dedicated regions of the brain), and have an eagle eye and a flypaper memory for cheaters.45 They feel moralistic emotions—liking, sympathy, gratitude, guilt, shame, and anger—that are uncanny implementations of the strategies for reciprocal altruism in computer simulations and mathematical models. Experiments have confirmed the prediction that people are most inclined to help a stranger when they can do so at low cost, when the stranger is in need, and when the stranger is in a position to reciprocate.46 They like people who grant them favors, grant favors to those they like, feel guilty when they have withheld a possible favor, and punish those who withhold favors from them.47