© ISTOCK.COM/VLADSILVERFrom packs of wolves cooperating in prey capture to millions of worker ants toiling their entire lives for the benefit of their sisters and queen, cooperative behaviors pervade the animal kingdom. But such selflessness poses a major evolutionary quandary: How could natural selection favor traits that increase the reproduction of others at an apparent cost to the individuals that express them?
William D. Hamilton provided an initial solution to this problem in 1964 with his theory of kin selection. Hamilton predicted that costly altruistic behaviors could be favored if the individuals receiving help were close relatives of the helper. This is because, from the gene’s-eye view, close relatives have a greater likelihood of also possessing an allele for altruism than unrelated individuals. In fact, the probability that any two individuals share a particular allele is equivalent to their relatedness to each other. By this logic, helpers should be twice as willing to help a full sibling as a cousin, because the sibling is twice as likely to carry the altruist allele.
Indeed, helpers in most cooperative groups are offspring of the breeding pair that stay and ...
