The evolution of morality did not have to get us over some ethical hump to move us from spiteful animal to generous human. We started in the middle, already sitting on the ethical fence, neutral and apathetic. We just needed some kind of selection pressure capable of favoring kindness. Any good evolutionary theory of human morality must convert the apparent costs of helping others into a realistic benefit to one's genes, by turning material costs into survival or reproductive benefits. If it cannot do that, it cannot explain how moral behaviors like kindness or generosity could evolve. The rules of evolutionary biology demand that we find a hidden, genetically selfish benefit to our altruism.
Some philosophers, theologians, and journalists are unhappy with this hidden-benefit requirement. They wish to define morality as purely selfless altruism, untainted by any hidden benefit. In their view, only the morality of the celibate saint qualifies as worthy of evolutionary explanation. But to my way of thinking, a moral theory of saints explains little about human nature, because saints are rare. Of the 15 billion or so humans who have lived since the time of Jesus Christ, the Catholic Church has canonized only a few thousand. Saints are literally one in a million. They may be instructive as moral ideals, but they are statistically irrelevant as data about real human moral behavior. Moral philosophers are sometimes not clear about whether they are developing a descriptive explanation of human moral behavior as it is, or an ideal of saintly moral behavior as it should be. My interest here is in finding an evolutionary explanation of ordinary human kindness, not in accounting for the outer limits of saintly goodness.
One step down from theologians, but still high above the rest of us, sit the economists. They appear to explain human morality as they explain all behavior, in terms of rationally pursued preferences. If we are kind, we must have a taste for kindness, to which we attach some "subjective utility." If we give money to charity, that must be because the subjective utility we derive from giving exceeds the subjective utility that we would derive from holding on to the money. Most economists understand perfectly well that this "revealed preferences" principle is circular. It is a statement of the axioms that they use to prove theorems about the emergent effects of individual behavior in markets. It should not be confused with a psychological explanation of behavior, much less an evolutionary explanation.
Psychologists sometimes fail to understand how circular it is to "explain" moral behavior in terms of moral preferences. Of course, one can always say that we are kind because we choose to be kind, or it feels good to be kind, or we have brain circuits that reward us with endorphins when we are kind. Such responses beg the question of why those moral preferences, moral emotions, and moral brain circuits evolved to be standard parts of human nature. A costly behavior cannot evolve just because it happens to feel good. Feeling good must have evolved to motivate the behavior, which must have some hidden benefit.
Most evolutionary psychologists have agreed that kindness and generosity bring two major kinds of hidden benefit. One kind of benefit comes when the generosity is directed towards blood relatives. In such cases, the cost to one's own genes can be outweighed by benefits to copies of those genes in the bodies of relatives. This is the theory of kin selection, and it explains generosity toward kin. The other kind of benefit comes when generosity is directed toward individuals who are likely to reciprocate in the future. Today's altruism may be repaid tomorrow. This is the theory of reciprocal altruism, which, it has been claimed, explains most instances of kindness to non-relatives.
Kinship and reciprocity are certainly important in human affairs, and we have evolved many psychological adaptations to deal with them. They go a long way in explaining many aspects of human moral behavior. For example, kinship theory puts into an evolutionary context the Confucian virtues of family obligation, while reciprocity helps to explain prudence, loyalty, guilt, and revenge. However, there is a lot left over. Human morality includes a great variety of behaviors and judgments that are hard to explain through kinship and reciprocity. Let's have a closer look at their limitations, and then see whether there are any other hidden evolutionary benefits to kindness.
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