Abstract

This article studies the evolution of altruism. We consider a model in which a population of agents are assortatively matched to play some asymmetric two-player game, and evolution operates at the level of behavior rules. We find that the relationship between the evolutionarily stable level of altruism and the index of assortativity of matching is determined by two novel features: whether the total payoff function of the game exhibits complementarity or substitutability; whether the two players’ strategies affect each other’s fitness in the same direction or the opposite. These two features combined generalize the stability conditions related to Hamilton’s rule to a class of asymmetric games.