Cooperation between non-kin in animal societies

Since Robert Trivers' seminal paper on reciprocal altruism in 1971, models of reciprocity and the Prisoner's Dilemma resource-sharing game have provided the dominant theoretical framework for explaining cooperation between unrelated individuals. Yet there is little evidence that, under natural conditions, animals other than man commonly exchange either resources or services. In a Review, Tim Clutton-Brock examines the case for reciprocal altruism in natural populations of non-human animals. The evidence is thin, he concludes, and many examples of apparent cooperation between non-kin are probably cases of mutualism or manipulation.