Coren Apicella and Joan Silk
Current Biology, Volume 29 (11), pp 447-450.
Darwin viewed cooperation as a perplexing challenge to his theory of natural selection. Natural selection generally favors the evolution of behaviors that enhance the fitness of individuals. Cooperative behavior, which increases the fitness of a recipient at the expense of the donor, contradicts this logic. William D. Hamilton helped to solve the puzzle when he showed that cooperation can evolve if cooperators direct benefits selectively to other cooperators (i.e. assortment). Kinship, group selection and the previous behavior of social partners all provide mechanisms for assortment (Figure 1), and kin selection and reciprocal altruism are the foundation of the kinds of cooperative behavior observed in many animals. Humans also bias cooperation in favor of kin and reciprocating partners, but the scope, scale, and variability of human cooperation greatly exceed that of other animals. Here, we introduce derived features of human cooperation in the context in which they originally evolved, and discuss the processes that may have shaped the evolution of our remarkable capacity for cooperation. We argue that culturally-evolved norms that specify how people should behave provide an evolutionarily novel mechanism for assortment, and play an important role in sustaining derived properties of cooperation in human groups.
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Cooperative foraging and breeding provide the evolutionary backdrop for understanding the evolution of cooperation in humans, as the returns from cooperating in these activities would have been high in our hunter-gatherer ancestors. Still, explaining how our ancestors effectively dealt with the problem of free-riders within this context remains a challenge. Derived features of human cooperation, however, give us some indication of the mechanisms that could lead to assortativity. These derived features include: first, the scope of cooperation — cooperation is observed between unrelated and often short-term interactors; second, the scale of cooperation — cooperation extends beyond pairs to include circumscribed groups that vary in size and identity; and third, variation in cooperation — human cooperation varies in both time and space in accordance with cultural and social norms. We argue that this pattern of findings is best explained by cultural evolutionary processes that generate phenotypic assortment on cooperation via a psychology adapted for cultural learning, norm sensitivity and group-mindedness.
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