Evolution of Indirect Reciprocity by Image Scoring / The Dynamics of Indirect Reciprocity

The question of cooperation is crucial for understanding Darwinian evolution. Theories of cooperation have been based on kin selection, group selection, and reciprocal altruism. The idea of reciprocal altruism usually involves direct reciprocity: repeated encounters between the same individuals allow for the return of an altruistic act by the recipient. Here we present a new theoretical framework, which is based on indirect reciprocity and does not require the two individuals ever to meet again. Individual selection can nevertheless favor cooperative strategies directed towards recipients that have helped others in the past. Cooperation pays because it confers the image of a valuable community member. We present computer simulations and analytic models to specify the conditions for evolutionary stability of indirect reciprocity. In particular we show that the probability of knowing the image of the recipient must exceed the cost-to-benefit ratio of the altruistic act. We argue that the emergence of indirect reciprocity was a decisive step for the evolution of human societies