The Mating Mind: How Sexual Choice Shaped the Evolution of Human Nature (46 page)

The folk theorem of repeated games clearly implied that cooperation depends on the threat of punishing cheaters who do not cooperate. With contracts, punishment implies litigation. With repeated interaction, punishment can consist of withdrawing from further interaction for a while, denying the cheat the benefits of cooperation. (If both individuals were not deriving benefits from cooperating, they would not be interacting at all.) For reciprocity to evolve according to the folk theorem, you do not need the concept of a contract, or the emotion of trust or betrayal, or a conceptual understanding of the future. All that is needed is a helpful behavior on your part if the other individual cooperated last time, a punishment routine you impose if he or she fails to cooperate, plus a capacity for telling the difference. Plants, flatworms, herring, and sloths could all evolve reciprocity if they evolved these three abilities.

The idea of reciprocal altruism promised to revolutionize the study of animal behavior. In the 1970s, biologists expected to find cooperation in thousands of species being sustained through repeated interactions. Unfortunately, three decades of intense research have produced almost no clear examples of reciprocity in animals other than primates. Evolution appears to avoid reciprocity whenever possible. The only decent non-primate example occurs in vampire bats. Biologist Gerald Wilkinson found that vampire bats that have drunk well on a particular night sometimes vomit surplus blood to hungry non-relatives. These

non-relatives may vomit blood in return the next night, if they happen to have found a good vein. However, even in this often-cited case it is not clear whether generosity to particular individuals is truly contingent on their past behavior.

Social primates offer better examples of reciprocity. Primatologist Frans de Waal observed in his book
Good Natured
that chimps appear to show moral outrage if a long-term ally fails to support them in a fight. They seek out and attack the cowardly traitor. This looks like a punishment routine designed to sustain cooperation. De Waal also found good evidence of chimpanzees trading food for grooming in a truly contingent way. Higher levels of reciprocity in primates are not surprising, given that primates are good at recognizing individuals, forming social relationships with non-relatives, and giving one another social benefits such as grooming, food-sharing, and mutual defense.

Cheating for Status

In reciprocal altruism, one must be able to detect cheats who take without giving. Evolutionary psychologists Leda Cosmides and John Tooby reasoned that if humans evolved as reciprocal altruists, we must have moral capacities for detecting cheats. They have run many experiments demonstrating that the human mind is highly attuned to detecting situations where individuals take benefits without fulfilling a social requirement. Many of the situations described in their experiments do concern genuine reciprocity, in which mutual benefits are exchanged between two individuals.

However, some of their examples of detecting cheats seem more concerned with the reliability of sexual status indicators than with the maintenance of reciprocity. Consider their (fictional) example of "Big Kiku," which is often cited. A tribal chief called Big Kiku establishes the rule that an individual must have a special tattoo in order to eat cassava root, a local delicacy. When asked to identify various possible ways in which this rule could be violated by cheats, participants in the Cosmides experiments could easily see that individuals without tattoos might be cheats,

and individuals eating cassava root might be too. Yet the participants' ability to reason correctly about this problem does not necessarily depend on their understanding reciprocal altruism in Trivers's sense. If I get a tattoo, it is not giving you some benefit that you reciprocate by allowing me to eat cassava root. The tattoo is simply a costly, painful signal of tribal sexual status which entities me to enjoy the associated status display of eating cassava root.

The Cosmides experiments, often replicated and extended by other psychologists, are one of the best examples of empirical evolutionary psychology. They have revealed a specific human adaptation for detecting cheats that is distinct from general intelligence, social intelligence, or the comprehension of arbitrary social rules. But these experiments also reveal that reciprocity is not the only context in which we look for cheats. People seem to regard any status display as a benefit, and look for people who cheat by producing the display without deserving the status. They use the same mental adaptations to look for cheats who undermine fitness indicators (by pretending to a status they do not deserve) and cheats who violate reciprocity arrangements (failing to return a benefit to one who gave you a benefit).

Because the same cheater-detection module is apparently used to detect both status cheats and reciprocity cheats, evidence for cheat detection is not necessarily evidence of the importance of reciprocity in human evolution. The conventions of rank, privilege, and status are distinct from the conventions of reciprocity that yield mutual benefit. This was one of Karl Marx's key insights. A society could be based on status signals without reciprocity (a simple dominance hierarchy), or on reciprocity without status signals (an egalitarian Utopia). In either, the ability to detect cheats would be useful. Our outrage against cheats is directed at those who display deceptive fitness indicators, not just those who fail to return a kindness.

human behavior that looks initially puzzling from a survival-ofthe-fittest viewpoint. Matt Ridley made a good case for their evolutionary social, and economic significance in his book
The Origins of Virtue
. However, they hardly touch some of the moral virtues we consider most important. Parental solicitude and nepotism are widespread, adaptive, and important, but are not often praised as distinctly moral virtues. Reciprocity is certainly sensible, foresighted, and rational, but from the 1980s some scientists seem to have equated it with the whole of human morality.

For example, kinship and reciprocity have difficulty explaining charity to non-relatives. We know the difference between giving money to a nephew, lending money to a friend, and handing money to a beggar. Nor can kinship and reciprocity explain very satisfactorily other important virtues such as moral leadership, romantic generosity, sympathy, sexual fidelity, or sportsmanship. Moreover, sexual selection may cast new light on certain moral phenomena that were previously understood in terms of kinship and reciprocity.

Of course, it is possible to fit almost any human social behavior into the Procrustean bed of reciprocity, because many social interactions are repeated and many violations of social convention are frowned upon. But this does not mean that people are always giving benefits today in order to receive benefits tomorrow. Broadening evolutionary psychology's attention to aspects of morality other than kinship and reciprocity may lead to new research insights. It may also prove more appealing to those who believe that there is more to human virtue than nepotism and economic prudence.

Innate Depravity?

Some religions depict humans as born in sin and saved only through faith and good works. Some Darwinians have followed this line as well. T. H. Huxley's 1896 lecture
Evolution and Ethics
portrayed morality as a cultural invention, a sword to slay the dragon of our animal past and overcome our innate selfishness. In

Civilization and Its Discontents,
Sigmund Freud took a similar line, arguing that society depends on the renunciation of animal passions and conformity to learned social norms. One of the few points of agreement between biologists and social scientists in the 20th century was that human morality must be taught, because it cannot be instinctive.

With the rise of selfish-gene thinking in 1960s and 1970s biology the innate depravity view gained clarity and force. Biologists realized that all organisms must evolve to be evolutionary egoists in the sense of promoting the replication of their own genes at the expense of other genes. This inclined some to the view that organisms must usually be egoists in the vernacular sense as well: individually competitive, selfish, ungenerous, and ill-mannered. The evolutionary selfishness of the gene was seen as leading automatically to the selfishness of human individuals. Leading evolutionary theorists such as E. O. Wilson, George Williams, and Robert Trivers adopted this seemingly pessimistic view. In
The Selfish Gene,
Richard Dawkins followed Huxley's lead: "Be warned that if you wish, as I do, to build a society in which individuals cooperate generously and unselfishly towards a common good, you can expect little help from biological nature. Let us try to
teach
generosity and altruism, because we are born selfish."

Many critics reacted against the innate depravity view with moral outrage, sentimental anecdotes, and a failure to understand the power of the selfish-gene perspective. Confronted with an apparent conflict between modern evolutionary theory and human morality, some biologists such as Stephen Jay Gould dismissed the selfish-gene view of evolution. In reaction, selfish-gene biologists dismissed the critics as confused idealists. It has taken a couple of decades for scientists to get beyond this impasse, to accept that there are human moral instincts other than nepotism and reciprocity, and that they must have evolved somehow. Frans de Waal sounded this new note of optimism in his book
Good Matured:
"Humans and other animals have been endowed with a capacity for genuine love, sympathy, and care—

a fact that can and will one day be fully reconciled with the idea that genetic self-promotion drives the evolutionary process."

Evolutionary psychology is taking more seriously the evidence for human generosity such as evidence that sympathy develops spontaneously in young children, and experimental economics research showing "irrationally" high levels of generosity between adults playing bargaining games. Economist Robert Frank's book
Passions Within Reason
was very important in putting true sympathy and generosity back on evolutionary psychology's agenda. He analyzed the evolution of human capacities for moral commitment, showing how apparently irrational tendencies to honor promises and punish cheats could bring hidden genetic benefits. He also showed that people are pretty good at predicting who will act generously and who will not when there is a temptation to be selfish: our moral character can be reliably judged. Philosopher Elliot Sober and biologist David Sloan Wilson have also insisted on the importance of bringing psychological evidence regarding sympathy and generosity into evolutionary discussions of morality. Some evolutionary economists have even turned to Adam Smith's
A Theory of Moral Sentiments
, which presents a much rosier picture of human generosity than his more famous
The Wealth of Nations.
Human kindness is becoming accepted as an adaptation to be explained rather than a myth to be ridiculed. The new Darwinian moral optimism is much more nuanced than either the innate selfishness view of the Catholic Church and sociobiology, or the innate goodness view of Rousseau and Utopian socialism. It accepts our moral nature as we find it. But the goal remains: to find the hidden evolutionary benefits of human kindness.

Mating Well by Doing Good

Fortunately, kinship and reciprocity are not the only evolutionarily respectable ways to turn apparent altruistic costs into individual reproductive benefits. You may not be surprised to find me using the sturdy mule of mate choice to haul the cart of human nature up the mountain of morality. As we have seen before,

sexual selection can explain things that few other evolutionary forces can. It can favor attractive, elaborate indicators that incur heavy costs in every domain other than reproduction. Could our moral acts be one class of such indicators? Do our moral judgments have some overlap with mate choice?

Immoral acts are mainly those we would be embarrassed by if our boyfriend or girlfriend found out about them. Why? Because they would then hold our character in lower esteem. The esteem of sexual partners sounds like a rather trivial basis for human morality. However, those who have been divorced for their moral failings may take a more respectful attitude towards mate choice as a shaper of moral instincts. As we have seen, David Buss's findings indicate that kindness is the most desired trait in a sexual partner around the world. Other research on human mate choice consistently confirms the attractiveness of kindness, generosity, sympathy, and tenderness.

In 1995, Irwin Tessman became the first to argue that sexual selection shapes morality. He pointed out that human generosity goes beyond the demands of kinship and reciprocity. Perhaps generosity works as a Zahavian handicap that displays fitness, and thus evolved through sexual selection. Amotz Zahavi has argued since the 1970s that apparent altruism could bring hidden reproductive benefits through the social status that it inspires. Anthropologist James Boone recently combined Zahavi's handicap theory and Veblen's conspicuous consumption theory to explain costly, conspicuous displays of magnanimity. While Tessman and I focus on direct mate choice for moralistic displays during courtship, Zahavi and Boone emphasize the indirect reproductive benefits of high status. Both effects were probably important during human evolution.

In theory, mate choice could be the single most powerful moral filter from one generation to the next. It could favor almost any degree of altruism or heroism, compensating for almost any risk to survival. If, for example, all females refused to mate with any males who ate meat, any genes predisposing individuals to vegetarianism (however indirectly) would spread like wildfire.

The species would turn vegetarian no matter what survival benefits were conferred by meat-eating, as long as the sexual selection pressure against meat-eating held. Natural selection for selfishness would be impotent against sexual selection for moral behavior.