The theory of parent-offspring conflict says that
families
do not contain all-powerful, all-knowing parents and their passive, grateful children.
Steven-Pinker-The-Blank-Slate 1
The first edition of Richard Dawkins's The Selfish Gene contained a foreword by the biologist who originated some of its key ideas, Robert Trivers.
He closed with a flourish:
Darwinian social theory gives us a glimpse of an underlying symmetry and logic in social relationships which, when more fully comprehended by ourselves, should revitalize our political understanding and provide the intellectual support for a science and medicine of psychology. In the process it should also give us a deeper understanding of the many roots of our suffering. 1
These were arresting claims for a book on biology, but Trivers knew he was onto something. Social psychology, the science of how people behave toward one another, is often a mishmash of interesting phenomena that are "explained" by giving them fancy names. Missing is the rich deductive structure of other sciences, in which a few deep principles can generate a wealth of subtle predictions -- the kind of theory that scientists praise as "beautiful" or "elegant. " Trivers derived the first theory in social psychology that deserves to be called elegant. He showed that a deceptively simple principle -- follow the genes -- can explain the logic of each of the major kinds of human relationships: how we feel toward our parents, our children,our siblings, our lovers, our friends, and ourselves. 2 But Trivers knew that the theory did something else as well. It offered a scientific explanation for the tragedy of the human condition. "Nature is a hanging judge," goes an old saying. Many tragedies come from our physical and cognitive makeup. Our bodies are extraordinarily improbable arrangements of matter, with many ways for things to go wrong and only a few ways for things to go right. We are certain to die, and smart enough to know it. Our minds are adapted to a world that no longer exists, prone to {242} misunderstandings correctable only by arduous education, and condemned to perplexity about the deepest questions we can entertain.
But some of the most painful shocks come from the social world -- from the manipulations and betrayals of other people. According to the fable, a scorpion asked a frog to carry him across a river, reassuring the frog that he wouldn't sting him because if he did, he would drown too. Halfway across, the scorpion did sting him, and when the sinking frog asked why, the scorpion replied, "It's in my nature. " Technically speaking, a scorpion with this nature could not have evolved, but Trivers has explained why it sometimes seems as if human nature is like the fabled scorpion nature, condemned to apparently pointless conflict.
It's no mystery why organisms sometimes harm one another. Evolution has no conscience, and if one creature hurts another to benefit itself, such as by eating, parasitizing, intimidating, or cuckolding it, its descendants will come to predominate, complete with those nasty habits. All this is familiar from the vernacular sense of "Darwinian" as a synonym for "ruthless" and from Tennyson's depiction of nature as red in tooth and claw. If that were all there was to the evolution of the human condition, we would have to agree with the rock song: Life sucks, then you die.
But of course life doesn't always suck. Many creatures cooperate, nurture, and make peace, and humans in particular find comfort and joy in their families, friends, and communities. This, too, should be familiar to readers of The Selfish Gene and the other books on the evolution of altruism that have appeared in the years since. 3 There are several reasons why organisms may evolve a willingness to do good deeds. They may help other creatures while pursuing
? ? ? ? their own interests, say, when they form a herd that confuses predators or live off each other's by-products. This is called mutualism, symbiosis, or cooperation. Among humans, friends who have common tastes, hobbies, or enemies are a kind of symbiont pair. The two parents of a brood of children are an even better example. Their genes are tied up in the same package, their children, so what is good for one is good for the other, and each has an interest in keeping the other alive and healthy. These shared interests set the stage for compassionate love and marital love to evolve.
And in some cases organisms may benefit other organisms at a cost to themselves, which biologists call altruism. Altruism in this technical sense can evolve in two main ways. First, since relatives share genes, any gene that inclines an organism toward helping a relative will increase the chance of survival of a copy of itself that sits inside that relative, even if the helper sacrifices its own fitness in the generous act. Such genes will, on average, come to predominate, as long as the cost to the helper is less than the benefit to the recipient discounted by their degree of relatedness. Family love -- the cherishing of children, {243} siblings, parents, grandparents, uncles and aunts, nieces and nephews, and cousins -- can evolve. This is called nepotistic altruism.
Altruism can also evolve when organisms trade favors. One helps another by grooming, feeding, protecting, or backing him, and is helped in turn when the needs reverse. This is called reciprocal altruism, and it can evolve when the parties recognize each other, interact repeatedly, can confer a large benefit on others at small cost to themselves, keep a memory for favors offered or denied, and are impelled to reciprocate accordingly. Reciprocal altruism can evolve because cooperators do better than hermits or misanthropes. They enjoy the gains of trading their surpluses, pulling ticks out of one another's hair, saving each other from drowning or starvation, and baby-sitting each other's children. Reciprocators can also do better over the long run than the cheaters who take favors without returning them, because the reciprocators will come to recognize the cheaters and shun or punish them.
The demands of reciprocal altruism can explain why the social and moralistic emotions evolved. Sympathy and trust prompt people to extend the first favor. Gratitude and loyalty prompt them to repay favors. Guilt and shame deter them from hurting or failing to repay others. Anger and contempt prompt them to avoid or punish cheaters. And among humans, any tendency of an individual to reciprocate or cheat does not have to be witnessed firsthand but can be recounted by language. This leads to an interest in the reputation of others, transmitted by gossip and public approval or condemnation, and a concern with one's own reputation. Partnerships, friendships, alliances, and communities can emerge, cemented by these emotions and concerns.
Many people start to get nervous at this point, but the discomfort is not from the tragedies that Trivers explained. It comes instead from two misconceptions, each of which we have encountered before. First, all this talk about genes that influence behavior does not mean that we are cuckoo clocks or player pianos, mindlessly executing the dictates of DNA. The genes in question are those that endow us with the neural systems for conscience, deliberation, and will, and when we talk about the selection of such genes, we are talking about the various ways those faculties could have evolved. The error comes from the Blank Slate and the Ghost in the Machine: if one starts off thinking that our higher mental faculties are stamped in by society or inhere in a soul, then when biologists mention genetic influence the first alternatives that come to mind are puppet strings or trolley tracks. But if higher faculties, including learning, reason, and choice, are products of a nonrandom organization of the brain, there have to be genes that help do the organizing, and that raises the question of how those genes would have been selected in the course of human evolution.
The second misconception is to imagine that talk about costs and benefits {244} implies that people are Machiavellian cynics, coldly calculating the genetic advantages of befriending and marrying. To fret over this picture, or denounce it because it is ugly, is to confuse proximate and ultimate causation. People don't care about their genes; they care about happiness, love, power, respect, and other passions. The cost-benefit calculations are a metaphorical way of describing the selection of alternative genes over millennia, not a literal description of what takes place in a human brain in real time. Nothing prevents the amoral process of natural selection from evolving a brain with genuine big-hearted emotions. It is said that those who appreciate legislation and sausages should not see them being made. The same is true for human emotions.
So if love and conscience can evolve, where's the tragedy? Trivers noticed that the confluence of genetic interests that gave rise to the social emotions is only partial. Because we are not clones, or even social insects (who can share up to three-quarters of their genes), what ultimately is best for one person is not identical to what ultimately is best for another. Thus every human relationship, even the most devoted and intimate, carries the seeds of conflict. In the movie AntZ, an ant with the voice of Woody Allen complains to his psychoanalyst:
It's this whole gung-ho superorganism thing that I just can't get. I try, but I just don't get it. What is it, I'm supposed to do everything for the colony and . . . what about my needs?
The humor comes from the clash between ant psychology, which originates in a genetic system that makes workers more closely related to one another than they would be to their offspring, and human psychology, in which our
? ? genetic distinctness leads us to ask, "What about my needs? " Trivers, following on the work of William Hamilton and George Williams, did some algebra that predicts the extent to which people should ask themselves that question. 4
The rest of this chapter is about that deceptively simple algebra and how its implications overturn many conceptions of human nature. It discredits the Blank Slate, which predicts that people's regard for their fellows is determined by their "role," as if it were a part assigned arbitrarily to an actor. But it also discredits some nai? ve views of evolution that are common among people who don't believe in the Blank Slate. Most people have intuitions about the natural state of affairs. They may believe that if we acted as nature "wants" us to, families would function as harmonious units, or individuals would act for the good of the species, or people would show the true selves beneath their social masks, or, as Newt Gingrich said in 1995, the male of our species would hunt giraffes and wallow in ditches like little piglets. 5 Understanding the patterns of genetic overlap that bind and divide us can replace simplistic views of all kinds {245} with a more subtle understanding of the human condition. Indeed, it can illuminate the human condition in ways that complement the insights of artists and philosophers through the millennia.
~
The most obvious human tragedy comes from the difference between our feelings toward kin and our feelings toward non-kin, one of the deepest divides in the living world. When it comes to love and solidarity among people, the relative viscosity of blood and water is evident in everything from the clans and dynasties of traditional societies to the clogging of airports during holidays with people traveling across the world to be with their families. 6 It has also been borne out by quantitative studies. In traditional foraging societies, genetic relatives are more likely to live together, work in each other's gardens, protect each other, and adopt each other's needy or orphaned children, and are less likely to attack, feud with, and kill each other. 7 Even in modern societies, which tend to sunder ties of kinship, the more closely two people are genetically related, the more inclined they are to come to one another's aid, especially in life-or-death situations. 8
But love and solidarity are relative. To say that people are more caring toward their relatives is to say that they are more callous toward their nonrelatives. The epigraph to Robert Wright's book on evolutionary psychology is an excerpt from Graham Greene's The Power and the Glory in which the protagonist broods about his daughter: "He said, 'Oh god, help her. Damn me, I deserve it, but let her live forever. ' This was the love he should have felt for every soul in the world: all the fear and the wish to save concentrated unjustly on the one child. He began to weep. . . . He thought: This is what I should feel all the time for everyone. "
Family love indeed subverts the ideal of what we should feel for every soul in the world. Moral philosophers play with a hypothetical dilemma in which people can run through the left door of a burning building to save some number of children or through the right door to save their own child. 9 If you are a parent, ponder this question: Is there any number of children that would lead you to pick the left door? Indeed, all of us reveal our preference with our pocketbooks when we spend money on trifles for our own children (a bicycle, orthodontics, an education at a private school or university) instead of saving the lives of unrelated children in the developing world by donating the money to charity. Similarly, the practice of parents bequeathing their wealth to their children is one of the steepest impediments to an economically egalitarian society. Yet few people would allow the government to confiscate 100 percent of their estate, because most people see their children as an extension of themselves and thus as the proper beneficiaries of their lifelong striving.
Nepotism is a universal human bent and a universal scourge of large organizations. It is notorious for sapping countries led by hereditary dynasties {246} and for bogging down governments and businesses in the Third World. A recurring historic solution was to give positions of local power to people who had no family ties, such as eunuchs, celibates, slaves, or people a long way from home. 10 A more recent solution is to outlaw or regulate nepotism, though the regulations always come with tradeoffs and exceptions. Small businesses -- or, as they are often called, "family businesses" or "Mom-and-Pop businesses" -- are highly nepotistic, and thereby can conflict with principles of equal opportunity and earn the resentment of the surrounding community.
B. F. Skinner, ever the Maoist, wrote in the 1970s that people should be rewarded for eating in large communal dining halls rather than at home with their families, because large pots have a lower ratio of surface area to volume than small pots and hence are more energy efficient. The logic is impeccable, but this mindset collided with human nature many times in the twentieth century -- horrifically in the forced collectivizations in the Soviet Union and China, and benignly in the Israeli kibbutzim, which quickly abandoned their policy of rearing children separately from their parents. A character in a novel by the Israeli writer Batya Gur captures the kind of sentiment that led to this change: "I want to tuck in my children at night myself. . . and when they have a nightmare I want them to come to my bed, not to some intercom, and not to make them go out at night in the dark looking for our room, stumbling over stones, thinking that every shadow is a monster, and in the end standing in front of a closed door or being dragged back to the children's house. "11
? ? ? ? ? ? ? ? ? ? It is not just recent dreams of collectivism that are subverted by kin solidarity. The journalist Ferdinand Mount has documented that the family has been a subversive institution throughout history. Family ties cut across the bonds connecting comrades and brethren and thus are a nuisance to governments, cults, gangs, revolutionary movements, and established religions. But even a thinker as sympathetic to human nature as Noam Chomsky does not acknowledge that people feel differently about their children from how they feel about acquaintances and strangers. Here is an excerpt of an interview with the lead guitarist of the rap metal group Rage Against the Machine:
rage: Another unquestionable idea is that people are naturally competitive, and that therefore, capitalism is the only proper way to organize society. Do you agree?
chomsky: Look around you. In a family for example, if the parents are hungry do they steal food from the children? They would if they were competitive. In most social groupings that are even semi-sane people support each other and are sympathetic and helpful and care about other people and so on. Those are normal human emotions. It takes plenty of training to drive those feelings out of people's heads, and they show up all over the place. 12 {247}
Unless people treat other members of society the way they treat their own children, the answer is a non sequitur: people could care deeply about their children but feel differently about the millions of other people who make up society. The very framing of the question and answer assumes that humans are competitive or sympathetic across the board, rather than having different emotions toward people with whom they have different genetic relationships. Chomsky implies that people are born with fraternal feelings toward their social groups and that the feelings are driven out of their heads by training. But it seems to be the other way around. Throughout history, when leaders have tried to unite a social group they have trained their members to think of it as a family and to redirect their familial emotions inside it. 13 The names used by groups that strive for solidarity -- brethren, brotherhoods, fraternal organizations, sisterhood, sororities, crime families, the family of man -- concede in their metaphors that kinship is the paradigm to which they aspire. (No society tries to strengthen the family by likening it to a trade union, political party, or church group. ) The tactic is provably effective. Several experiments have shown that people are more convinced by a political speech if the speaker appeals to their hearts and minds with kinship metaphors. 14
Verbal metaphors are one way to nudge people to treat acquaintances like family, but usually stronger tactics are needed. In his ethnographic survey, Alan Fiske showed that the ethos of Communal Sharing (one of his four universal social relations) arises spontaneously among the members of a family but is extended to other groups only with the help of elaborate customs and ideologies. 15 Unrelated people who want to share like a family create mythologies about a common flesh and blood, a shared ancestry, and a mystical bond to a territory (tellingly called a natal land, fatherland, motherland, or mother country). They reinforce the myths with sacramental meals, blood sacrifices, and repetitive rituals, which submerge the self into the group and create an impression of a single organism rather than a federation of individuals. Their religions speak of possession by spirits and other kinds of mind melds, which, according to Fiske, "suggest that people may often want to have more intense or pure Communal Sharing relationships than they are able to realize with ordinary human beings. "16 The dark side of this cohesion is groupthink, a cult mentality, and myths of racial purity -- the sense that outsiders are contaminants who pollute the sanctity of the group.
None of this means that nonrelatives are ruthlessly competitive toward one another, only that they are not as spontaneously cooperative as kin. And ironically, for all this talk of solidarity and sympathy and common blood, we shall soon see that families are not such harmonious units either.
~
Tolstoy's famous remark that happy families are all alike but every unhappy family is unhappy in its own way is not true at the level of ultimate {248} (evolutionary) causation. Trivers showed how the seeds of unhappiness in every family have the same underlying source. 17 Though relatives have common interests because of their common genes, the degree of overlap is not identical within all the permutations and combinations of family members. Parents are related to all of their offspring by an equal factor, 50 percent, but each child is related to himself or herself by a factor of 100 percent. And that has a subtle but profound implication for the currency of family life, parents' investment in their children.
Parental investment is a limited resource. A day has only twenty-four hours, short-term memory can hold only four chunks of information, and, as many a frazzled mother has pointed out, "I only have two hands! " At one end of the lifespan, children learn that a mother cannot pump out an unlimited stream of milk; at the other, they learn that parents do not leave behind infinite inheritances.
To the extent that emotions among people reflect their typical genetic relatedness, Trivers argued, the members of a
? ? ? ? ? ? ? ? family should disagree on how parental investment should be divvied up. Parents should want to split their investment equitably among the children -- if not in absolutely equal parts, then according to each child's ability to prosper from the investment. But each child should to want the parent to dole out twice as much of the investment to himself or herself as to a sibling, because children share half their genes with each full sibling but share all their genes with themselves. Given a family with two children and one pie, each child should want to split it in a ratio of two-thirds to one-third, while parents should want it to be split fifty-fifty. The result is that no distribution will make everyone happy. Of course, it's not that parents and children literally fight over pie or milk or inheritances (though they may), and they certainly don't fight over genes. In our evolutionary history, parental investment affected a child's survival, which affected the probability that the genes for various familial emotions in parents and in children would have been passed on to us today. The prediction is that family members' expectations of one another are not perfectly in sync.
Parent-offspring conflict and its obverse, sibling-sibling conflict, can be seen throughout the animal kingdom. 18 Littermates or nestmates fight among themselves, sometimes lethally, and fight with their mothers over access to milk, food, and care. (As Woody Allen's character in AntZ pointed out, "When you're the middle child in a family of five million, you don't get much attention. ") The conflict also plays out in the physiology of prenatal human development. Fetuses tap their mothers' bloodstreams to mine the most nutrients possible from her body, while the mother's body resists to keep it in good shape for future children. 19 And it continues to play itself out after birth. Until recently, in most cultures, mothers who had poor prospects for sustaining a {249} newborn to maturity cut their losses and abandoned it to die. 20 The fat cheeks and precocious responsiveness in a baby's face may be an advertisement of health designed to tilt the decision in its favor. 21
But the most interesting conflicts are the psychological ones, played out in family dramas. Trivers touted the liberatory nature of sociobiology by invoking an "underlying symmetry in our social relationships" and "submerged actors in the social world. "22 He was referring to women, as we will see in the chapter on gender, and to children.
The theory of parent-offspring conflict says that families do not contain all-powerful, all-knowing parents and their passive, grateful children. Natural selection should have equipped children with psychological tactics allowing them to hold their own in a struggle with their parents, with neither party having a permanent upper hand. Parents have a short-lived advantage in sheer brawn, but children can fight back by being cute, whining, throwing tantrums, pulling guilt trips, tormenting their siblings, getting between their parents, and holding themselves hostage with the threat of self-destructive behavior. 23 As they say, insanity is hereditary: you get it from your children.
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 {250} 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, {251} 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 {252} 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 behavior 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. {253} 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 Jong'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 {254} 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. {255}
~
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 social 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 {256}
An ethos of reciprocity can pilot not just one-on-one exchanges but contributions to the public good, such as hunting animals that are too large for the hunter to eat himself, building a lighthouse that keeps everyone's ships off the rocks, or banding together to invade neighbors or to repel their invasions. The inherent problem with public goods is captured in Aesop's fable "Who Will Bell the Cat? " The mice in a household agree they would be better off if the cat had a bell around its neck to warn them of its approach, but no mouse will risk life and limb to attach the bell. A willingness to bell the cat -- that is, to contribute to the public good -- can nonetheless evolve, if it is accompanied by a willingness to reward those who shoulder the burden or to punish the cheaters who shirk it. 48
The tragedy of reciprocal altruism is that sacrifices on behalf of nonrelatives cannot survive without a web of disagreeable emotions like anxiety, mistrust, guilt, shame, and anger. As the journalist Matt Ridley puts it in his survey of the evolution of cooperation:
Reciprocity hangs, like a sword of Damocles, over every human head. He's only asking me to his party so I'll give his book a good review. They've been to dinner twice and never asked us back once. After all I did for him, how could he do that to me? If you do this for me, I promise I'll make it up later. What did I do to deserve that? You owe it to me. Obligation; debt; favour; bargain; contract; exchange; deal. . . . Our language and our lives are permeated with ideas of reciprocity. 49
Studies of altruism by behavioral economists have thrown a spotlight on this sword of Damocles by showing that people are neither the amoral egoists of classical economic theory nor the all-for-one-and-one-for-all communalists of Utopian fantasies. In the Ultimatum Game, for example, one participant gets a large sum of money to divide between himself and another participant, and the second one can take it or leave it. If he leaves it, neither side gets anything. A selfish proposer would keep the lion's share; a selfish respondent would accept the remaining crumbs, no matter how small, because part of a loaf is better than none. In reality the proposer tends to offer almost half of the total sum, and the respondent doesn't settle for much less than half, even though turning down a smaller share is an act of spite that deprives both participants.
Darwinian social theory gives us a glimpse of an underlying symmetry and logic in social relationships which, when more fully comprehended by ourselves, should revitalize our political understanding and provide the intellectual support for a science and medicine of psychology. In the process it should also give us a deeper understanding of the many roots of our suffering. 1
These were arresting claims for a book on biology, but Trivers knew he was onto something. Social psychology, the science of how people behave toward one another, is often a mishmash of interesting phenomena that are "explained" by giving them fancy names. Missing is the rich deductive structure of other sciences, in which a few deep principles can generate a wealth of subtle predictions -- the kind of theory that scientists praise as "beautiful" or "elegant. " Trivers derived the first theory in social psychology that deserves to be called elegant. He showed that a deceptively simple principle -- follow the genes -- can explain the logic of each of the major kinds of human relationships: how we feel toward our parents, our children,our siblings, our lovers, our friends, and ourselves. 2 But Trivers knew that the theory did something else as well. It offered a scientific explanation for the tragedy of the human condition. "Nature is a hanging judge," goes an old saying. Many tragedies come from our physical and cognitive makeup. Our bodies are extraordinarily improbable arrangements of matter, with many ways for things to go wrong and only a few ways for things to go right. We are certain to die, and smart enough to know it. Our minds are adapted to a world that no longer exists, prone to {242} misunderstandings correctable only by arduous education, and condemned to perplexity about the deepest questions we can entertain.
But some of the most painful shocks come from the social world -- from the manipulations and betrayals of other people. According to the fable, a scorpion asked a frog to carry him across a river, reassuring the frog that he wouldn't sting him because if he did, he would drown too. Halfway across, the scorpion did sting him, and when the sinking frog asked why, the scorpion replied, "It's in my nature. " Technically speaking, a scorpion with this nature could not have evolved, but Trivers has explained why it sometimes seems as if human nature is like the fabled scorpion nature, condemned to apparently pointless conflict.
It's no mystery why organisms sometimes harm one another. Evolution has no conscience, and if one creature hurts another to benefit itself, such as by eating, parasitizing, intimidating, or cuckolding it, its descendants will come to predominate, complete with those nasty habits. All this is familiar from the vernacular sense of "Darwinian" as a synonym for "ruthless" and from Tennyson's depiction of nature as red in tooth and claw. If that were all there was to the evolution of the human condition, we would have to agree with the rock song: Life sucks, then you die.
But of course life doesn't always suck. Many creatures cooperate, nurture, and make peace, and humans in particular find comfort and joy in their families, friends, and communities. This, too, should be familiar to readers of The Selfish Gene and the other books on the evolution of altruism that have appeared in the years since. 3 There are several reasons why organisms may evolve a willingness to do good deeds. They may help other creatures while pursuing
? ? ? ? their own interests, say, when they form a herd that confuses predators or live off each other's by-products. This is called mutualism, symbiosis, or cooperation. Among humans, friends who have common tastes, hobbies, or enemies are a kind of symbiont pair. The two parents of a brood of children are an even better example. Their genes are tied up in the same package, their children, so what is good for one is good for the other, and each has an interest in keeping the other alive and healthy. These shared interests set the stage for compassionate love and marital love to evolve.
And in some cases organisms may benefit other organisms at a cost to themselves, which biologists call altruism. Altruism in this technical sense can evolve in two main ways. First, since relatives share genes, any gene that inclines an organism toward helping a relative will increase the chance of survival of a copy of itself that sits inside that relative, even if the helper sacrifices its own fitness in the generous act. Such genes will, on average, come to predominate, as long as the cost to the helper is less than the benefit to the recipient discounted by their degree of relatedness. Family love -- the cherishing of children, {243} siblings, parents, grandparents, uncles and aunts, nieces and nephews, and cousins -- can evolve. This is called nepotistic altruism.
Altruism can also evolve when organisms trade favors. One helps another by grooming, feeding, protecting, or backing him, and is helped in turn when the needs reverse. This is called reciprocal altruism, and it can evolve when the parties recognize each other, interact repeatedly, can confer a large benefit on others at small cost to themselves, keep a memory for favors offered or denied, and are impelled to reciprocate accordingly. Reciprocal altruism can evolve because cooperators do better than hermits or misanthropes. They enjoy the gains of trading their surpluses, pulling ticks out of one another's hair, saving each other from drowning or starvation, and baby-sitting each other's children. Reciprocators can also do better over the long run than the cheaters who take favors without returning them, because the reciprocators will come to recognize the cheaters and shun or punish them.
The demands of reciprocal altruism can explain why the social and moralistic emotions evolved. Sympathy and trust prompt people to extend the first favor. Gratitude and loyalty prompt them to repay favors. Guilt and shame deter them from hurting or failing to repay others. Anger and contempt prompt them to avoid or punish cheaters. And among humans, any tendency of an individual to reciprocate or cheat does not have to be witnessed firsthand but can be recounted by language. This leads to an interest in the reputation of others, transmitted by gossip and public approval or condemnation, and a concern with one's own reputation. Partnerships, friendships, alliances, and communities can emerge, cemented by these emotions and concerns.
Many people start to get nervous at this point, but the discomfort is not from the tragedies that Trivers explained. It comes instead from two misconceptions, each of which we have encountered before. First, all this talk about genes that influence behavior does not mean that we are cuckoo clocks or player pianos, mindlessly executing the dictates of DNA. The genes in question are those that endow us with the neural systems for conscience, deliberation, and will, and when we talk about the selection of such genes, we are talking about the various ways those faculties could have evolved. The error comes from the Blank Slate and the Ghost in the Machine: if one starts off thinking that our higher mental faculties are stamped in by society or inhere in a soul, then when biologists mention genetic influence the first alternatives that come to mind are puppet strings or trolley tracks. But if higher faculties, including learning, reason, and choice, are products of a nonrandom organization of the brain, there have to be genes that help do the organizing, and that raises the question of how those genes would have been selected in the course of human evolution.
The second misconception is to imagine that talk about costs and benefits {244} implies that people are Machiavellian cynics, coldly calculating the genetic advantages of befriending and marrying. To fret over this picture, or denounce it because it is ugly, is to confuse proximate and ultimate causation. People don't care about their genes; they care about happiness, love, power, respect, and other passions. The cost-benefit calculations are a metaphorical way of describing the selection of alternative genes over millennia, not a literal description of what takes place in a human brain in real time. Nothing prevents the amoral process of natural selection from evolving a brain with genuine big-hearted emotions. It is said that those who appreciate legislation and sausages should not see them being made. The same is true for human emotions.
So if love and conscience can evolve, where's the tragedy? Trivers noticed that the confluence of genetic interests that gave rise to the social emotions is only partial. Because we are not clones, or even social insects (who can share up to three-quarters of their genes), what ultimately is best for one person is not identical to what ultimately is best for another. Thus every human relationship, even the most devoted and intimate, carries the seeds of conflict. In the movie AntZ, an ant with the voice of Woody Allen complains to his psychoanalyst:
It's this whole gung-ho superorganism thing that I just can't get. I try, but I just don't get it. What is it, I'm supposed to do everything for the colony and . . . what about my needs?
The humor comes from the clash between ant psychology, which originates in a genetic system that makes workers more closely related to one another than they would be to their offspring, and human psychology, in which our
? ? genetic distinctness leads us to ask, "What about my needs? " Trivers, following on the work of William Hamilton and George Williams, did some algebra that predicts the extent to which people should ask themselves that question. 4
The rest of this chapter is about that deceptively simple algebra and how its implications overturn many conceptions of human nature. It discredits the Blank Slate, which predicts that people's regard for their fellows is determined by their "role," as if it were a part assigned arbitrarily to an actor. But it also discredits some nai? ve views of evolution that are common among people who don't believe in the Blank Slate. Most people have intuitions about the natural state of affairs. They may believe that if we acted as nature "wants" us to, families would function as harmonious units, or individuals would act for the good of the species, or people would show the true selves beneath their social masks, or, as Newt Gingrich said in 1995, the male of our species would hunt giraffes and wallow in ditches like little piglets. 5 Understanding the patterns of genetic overlap that bind and divide us can replace simplistic views of all kinds {245} with a more subtle understanding of the human condition. Indeed, it can illuminate the human condition in ways that complement the insights of artists and philosophers through the millennia.
~
The most obvious human tragedy comes from the difference between our feelings toward kin and our feelings toward non-kin, one of the deepest divides in the living world. When it comes to love and solidarity among people, the relative viscosity of blood and water is evident in everything from the clans and dynasties of traditional societies to the clogging of airports during holidays with people traveling across the world to be with their families. 6 It has also been borne out by quantitative studies. In traditional foraging societies, genetic relatives are more likely to live together, work in each other's gardens, protect each other, and adopt each other's needy or orphaned children, and are less likely to attack, feud with, and kill each other. 7 Even in modern societies, which tend to sunder ties of kinship, the more closely two people are genetically related, the more inclined they are to come to one another's aid, especially in life-or-death situations. 8
But love and solidarity are relative. To say that people are more caring toward their relatives is to say that they are more callous toward their nonrelatives. The epigraph to Robert Wright's book on evolutionary psychology is an excerpt from Graham Greene's The Power and the Glory in which the protagonist broods about his daughter: "He said, 'Oh god, help her. Damn me, I deserve it, but let her live forever. ' This was the love he should have felt for every soul in the world: all the fear and the wish to save concentrated unjustly on the one child. He began to weep. . . . He thought: This is what I should feel all the time for everyone. "
Family love indeed subverts the ideal of what we should feel for every soul in the world. Moral philosophers play with a hypothetical dilemma in which people can run through the left door of a burning building to save some number of children or through the right door to save their own child. 9 If you are a parent, ponder this question: Is there any number of children that would lead you to pick the left door? Indeed, all of us reveal our preference with our pocketbooks when we spend money on trifles for our own children (a bicycle, orthodontics, an education at a private school or university) instead of saving the lives of unrelated children in the developing world by donating the money to charity. Similarly, the practice of parents bequeathing their wealth to their children is one of the steepest impediments to an economically egalitarian society. Yet few people would allow the government to confiscate 100 percent of their estate, because most people see their children as an extension of themselves and thus as the proper beneficiaries of their lifelong striving.
Nepotism is a universal human bent and a universal scourge of large organizations. It is notorious for sapping countries led by hereditary dynasties {246} and for bogging down governments and businesses in the Third World. A recurring historic solution was to give positions of local power to people who had no family ties, such as eunuchs, celibates, slaves, or people a long way from home. 10 A more recent solution is to outlaw or regulate nepotism, though the regulations always come with tradeoffs and exceptions. Small businesses -- or, as they are often called, "family businesses" or "Mom-and-Pop businesses" -- are highly nepotistic, and thereby can conflict with principles of equal opportunity and earn the resentment of the surrounding community.
B. F. Skinner, ever the Maoist, wrote in the 1970s that people should be rewarded for eating in large communal dining halls rather than at home with their families, because large pots have a lower ratio of surface area to volume than small pots and hence are more energy efficient. The logic is impeccable, but this mindset collided with human nature many times in the twentieth century -- horrifically in the forced collectivizations in the Soviet Union and China, and benignly in the Israeli kibbutzim, which quickly abandoned their policy of rearing children separately from their parents. A character in a novel by the Israeli writer Batya Gur captures the kind of sentiment that led to this change: "I want to tuck in my children at night myself. . . and when they have a nightmare I want them to come to my bed, not to some intercom, and not to make them go out at night in the dark looking for our room, stumbling over stones, thinking that every shadow is a monster, and in the end standing in front of a closed door or being dragged back to the children's house. "11
? ? ? ? ? ? ? ? ? ? It is not just recent dreams of collectivism that are subverted by kin solidarity. The journalist Ferdinand Mount has documented that the family has been a subversive institution throughout history. Family ties cut across the bonds connecting comrades and brethren and thus are a nuisance to governments, cults, gangs, revolutionary movements, and established religions. But even a thinker as sympathetic to human nature as Noam Chomsky does not acknowledge that people feel differently about their children from how they feel about acquaintances and strangers. Here is an excerpt of an interview with the lead guitarist of the rap metal group Rage Against the Machine:
rage: Another unquestionable idea is that people are naturally competitive, and that therefore, capitalism is the only proper way to organize society. Do you agree?
chomsky: Look around you. In a family for example, if the parents are hungry do they steal food from the children? They would if they were competitive. In most social groupings that are even semi-sane people support each other and are sympathetic and helpful and care about other people and so on. Those are normal human emotions. It takes plenty of training to drive those feelings out of people's heads, and they show up all over the place. 12 {247}
Unless people treat other members of society the way they treat their own children, the answer is a non sequitur: people could care deeply about their children but feel differently about the millions of other people who make up society. The very framing of the question and answer assumes that humans are competitive or sympathetic across the board, rather than having different emotions toward people with whom they have different genetic relationships. Chomsky implies that people are born with fraternal feelings toward their social groups and that the feelings are driven out of their heads by training. But it seems to be the other way around. Throughout history, when leaders have tried to unite a social group they have trained their members to think of it as a family and to redirect their familial emotions inside it. 13 The names used by groups that strive for solidarity -- brethren, brotherhoods, fraternal organizations, sisterhood, sororities, crime families, the family of man -- concede in their metaphors that kinship is the paradigm to which they aspire. (No society tries to strengthen the family by likening it to a trade union, political party, or church group. ) The tactic is provably effective. Several experiments have shown that people are more convinced by a political speech if the speaker appeals to their hearts and minds with kinship metaphors. 14
Verbal metaphors are one way to nudge people to treat acquaintances like family, but usually stronger tactics are needed. In his ethnographic survey, Alan Fiske showed that the ethos of Communal Sharing (one of his four universal social relations) arises spontaneously among the members of a family but is extended to other groups only with the help of elaborate customs and ideologies. 15 Unrelated people who want to share like a family create mythologies about a common flesh and blood, a shared ancestry, and a mystical bond to a territory (tellingly called a natal land, fatherland, motherland, or mother country). They reinforce the myths with sacramental meals, blood sacrifices, and repetitive rituals, which submerge the self into the group and create an impression of a single organism rather than a federation of individuals. Their religions speak of possession by spirits and other kinds of mind melds, which, according to Fiske, "suggest that people may often want to have more intense or pure Communal Sharing relationships than they are able to realize with ordinary human beings. "16 The dark side of this cohesion is groupthink, a cult mentality, and myths of racial purity -- the sense that outsiders are contaminants who pollute the sanctity of the group.
None of this means that nonrelatives are ruthlessly competitive toward one another, only that they are not as spontaneously cooperative as kin. And ironically, for all this talk of solidarity and sympathy and common blood, we shall soon see that families are not such harmonious units either.
~
Tolstoy's famous remark that happy families are all alike but every unhappy family is unhappy in its own way is not true at the level of ultimate {248} (evolutionary) causation. Trivers showed how the seeds of unhappiness in every family have the same underlying source. 17 Though relatives have common interests because of their common genes, the degree of overlap is not identical within all the permutations and combinations of family members. Parents are related to all of their offspring by an equal factor, 50 percent, but each child is related to himself or herself by a factor of 100 percent. And that has a subtle but profound implication for the currency of family life, parents' investment in their children.
Parental investment is a limited resource. A day has only twenty-four hours, short-term memory can hold only four chunks of information, and, as many a frazzled mother has pointed out, "I only have two hands! " At one end of the lifespan, children learn that a mother cannot pump out an unlimited stream of milk; at the other, they learn that parents do not leave behind infinite inheritances.
To the extent that emotions among people reflect their typical genetic relatedness, Trivers argued, the members of a
? ? ? ? ? ? ? ? family should disagree on how parental investment should be divvied up. Parents should want to split their investment equitably among the children -- if not in absolutely equal parts, then according to each child's ability to prosper from the investment. But each child should to want the parent to dole out twice as much of the investment to himself or herself as to a sibling, because children share half their genes with each full sibling but share all their genes with themselves. Given a family with two children and one pie, each child should want to split it in a ratio of two-thirds to one-third, while parents should want it to be split fifty-fifty. The result is that no distribution will make everyone happy. Of course, it's not that parents and children literally fight over pie or milk or inheritances (though they may), and they certainly don't fight over genes. In our evolutionary history, parental investment affected a child's survival, which affected the probability that the genes for various familial emotions in parents and in children would have been passed on to us today. The prediction is that family members' expectations of one another are not perfectly in sync.
Parent-offspring conflict and its obverse, sibling-sibling conflict, can be seen throughout the animal kingdom. 18 Littermates or nestmates fight among themselves, sometimes lethally, and fight with their mothers over access to milk, food, and care. (As Woody Allen's character in AntZ pointed out, "When you're the middle child in a family of five million, you don't get much attention. ") The conflict also plays out in the physiology of prenatal human development. Fetuses tap their mothers' bloodstreams to mine the most nutrients possible from her body, while the mother's body resists to keep it in good shape for future children. 19 And it continues to play itself out after birth. Until recently, in most cultures, mothers who had poor prospects for sustaining a {249} newborn to maturity cut their losses and abandoned it to die. 20 The fat cheeks and precocious responsiveness in a baby's face may be an advertisement of health designed to tilt the decision in its favor. 21
But the most interesting conflicts are the psychological ones, played out in family dramas. Trivers touted the liberatory nature of sociobiology by invoking an "underlying symmetry in our social relationships" and "submerged actors in the social world. "22 He was referring to women, as we will see in the chapter on gender, and to children.
The theory of parent-offspring conflict says that families do not contain all-powerful, all-knowing parents and their passive, grateful children. Natural selection should have equipped children with psychological tactics allowing them to hold their own in a struggle with their parents, with neither party having a permanent upper hand. Parents have a short-lived advantage in sheer brawn, but children can fight back by being cute, whining, throwing tantrums, pulling guilt trips, tormenting their siblings, getting between their parents, and holding themselves hostage with the threat of self-destructive behavior. 23 As they say, insanity is hereditary: you get it from your children.
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 {250} 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, {251} 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.
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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 {252} 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 behavior 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. {253} 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 Jong'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 {254} 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. {255}
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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 social 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 {256}
An ethos of reciprocity can pilot not just one-on-one exchanges but contributions to the public good, such as hunting animals that are too large for the hunter to eat himself, building a lighthouse that keeps everyone's ships off the rocks, or banding together to invade neighbors or to repel their invasions. The inherent problem with public goods is captured in Aesop's fable "Who Will Bell the Cat? " The mice in a household agree they would be better off if the cat had a bell around its neck to warn them of its approach, but no mouse will risk life and limb to attach the bell. A willingness to bell the cat -- that is, to contribute to the public good -- can nonetheless evolve, if it is accompanied by a willingness to reward those who shoulder the burden or to punish the cheaters who shirk it. 48
The tragedy of reciprocal altruism is that sacrifices on behalf of nonrelatives cannot survive without a web of disagreeable emotions like anxiety, mistrust, guilt, shame, and anger. As the journalist Matt Ridley puts it in his survey of the evolution of cooperation:
Reciprocity hangs, like a sword of Damocles, over every human head. He's only asking me to his party so I'll give his book a good review. They've been to dinner twice and never asked us back once. After all I did for him, how could he do that to me? If you do this for me, I promise I'll make it up later. What did I do to deserve that? You owe it to me. Obligation; debt; favour; bargain; contract; exchange; deal. . . . Our language and our lives are permeated with ideas of reciprocity. 49
Studies of altruism by behavioral economists have thrown a spotlight on this sword of Damocles by showing that people are neither the amoral egoists of classical economic theory nor the all-for-one-and-one-for-all communalists of Utopian fantasies. In the Ultimatum Game, for example, one participant gets a large sum of money to divide between himself and another participant, and the second one can take it or leave it. If he leaves it, neither side gets anything. A selfish proposer would keep the lion's share; a selfish respondent would accept the remaining crumbs, no matter how small, because part of a loaf is better than none. In reality the proposer tends to offer almost half of the total sum, and the respondent doesn't settle for much less than half, even though turning down a smaller share is an act of spite that deprives both participants.
