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.
Aristophanes' play Lysistrata of 411 B.C. illustrated the moral power of female sexual choice. Lysistrata convinced the other women of Athens to stop having sex with their men until the men stopped waging the Peloponnesian war. The women barricaded themselves in the Acropolis, while (in the original staging of the play) the sex-starved men wandered around with ever-larger leather phalluses, gradually realizing that military victory becomes meaningless without the prospect of sex. Although some women were also tempted to break the sex strike—one even tried to sneak off to a brothel—they outlasted the men. Lysistrata's sex-strike succeeded in forcing the Athenian men to make peace with the Spartans. Her strategy would have worked equally well over evolutionary time: female sexual preferences for peace-keepers could have reduced male belligerence and aggressiveness.
This "better morality through mate choice" hypothesis prompts several questions. Why would mate choice mechanisms evolve to favor displays of generosity, fair play, good manners, or heroism? Why do we consider such displays especially "moral," as compared with other courtship displays? Why do our judgments of different courtship displays feel so different? Bodily ornaments seem to provoke lust, artistic displays induce aesthetic feelings, and moralistic displays attract admiration. This chapter does not answer all these questions, but may chart some new territory in the evolution of human morality. We'll start with a simple example of how mate choice can favor costly behaviors that provide for the common good.
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