Evolution of Behavior in Family Games

In 1964, the great evolutionary biologist, William Hamilton proposed that evolutionary selection would result in a population of individuals in which each acts to maximize its inclusive tness, which Hamilton de ned as a weighted average of its own survival probability and the survival probabilities of its kin, with the weights applied to relatives being proportional to their degree of relationship. Hamilton's papers were written almost 10 years before G. R. Price and John Maynard Smith introduced game theory to biologists. It is therefore not surprising that he did not model familial interactions as a game. The kind of interactions that Hamilton studied belong to a special class of games in which the e ects of actions are additive. Many economic interactions between relatives lack this additive structure and it turns out for such interactions, Hamilton's rule does not apply. This paper introduces a more general principle that does apply for a broad class of games and explains the relation between this principle and Hamilton's rule. 1 Does Hamilton's Rule Govern Kin-Selection?