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British Biologist William Hamilton in 1964 explained how altruism could help an individual spread his genes; he argued that the principle explained the social life of insects.
In all ants, bees and wasps, daughters of the queen share an average of three-quarters of their genes (see diagram). Because the daughters are more related to each other than they would be to their own offspring, said Hamilton, it is in their genetic self-interest not to breed but to assist the queen in producing more daughters.
Thus the females evolved as sterile workers who cooperate socially for genetically selfish reasons.
Some years later, Trivers reasoned that if Hamilton was right about the social insects, worker ants would spend three times the energy rearing sisters as rearing brothers, because the workers are three times more closely related to their sisters than to their brothers. Trivers and his associate, Hope Hare, then analyzed thousands of ants of 20 different species and confirmed the 3-to-1 female dominance—the strongest evidence so far that organisms act as if they understand the underlying genetics.
Still, there are problems in explaining all altruism as a direct investment in one's own genes. For example, some birds give warning cries for the flock even when their young and close relatives are absent. Trivers proposed a solution in a 1971 paper on reciprocal altruism that has become a central text for sociobiologists. "In other organisms," Trivers wrote, "the evidence that altruism is genetic is rather overwhelming. It is therefore irrational to argue that the first species in which altruism has no genetic contribution is human beings." Using game theory, he concluded that natural selection produces individuals that exchange favors—in effect saying, "You scratch my back; I'll scratch yours." In other words, the favor will eventually be returned, thus improving the outlook for the genes of the first altruist. According to the theory, human charitable acts are therefore rooted in biology and gene selfishness. This theory could explain human loyalty to nation, corporation or church; these institutions can provide benefits to members that increase the chances for them to survive and propagate.
Some philosophers and theologians have been dismayed by the theory. So was one young man who had won a Carnegie Gold Medal for saving a drowning victim; he wrote Wilson a troubled letter. Recalls Wilson: "He found it difficult to grasp the notion that somehow his act was preordained through genes. I convinced him that the impulse and emotion behind his rational choice, though genetically determined, in no way detracted from the rationality and value of his altruistic act."
For many, such explanations of noble deeds are cold comfort. But Harvard Anthropologist Melvin J. Konner sees a bright side to reciprocal altruism. Sociobiologists, he says, "have in fact uplifted [human nature] by showing that altruism, long thought to be a thin cultural veneer, belongs instead to the deepest part of our being, produced by countless aeons of consistent evolution."