The genetical evolution of social preferences: where the categorical imperatives of Hamilton, Kant and Nash meet.

This paper models the genetical evolution of individual behavioral rules that guide the choice of strategies in pairwise assortative interactions under incomplete information. Building on results at the crossroads of evolutionary theory and game theory, it is first shown that in an uninvadable population state of behavioral rule evolution, individuals are compelled to use strategies that are Nash equilibria of a lineage fitness game. Thus, choice behavior evolves to be representable as the maximization of a utility function, as if each individual holds a personal preference that orders both their own and their interaction partner's strategies. Second, the paper contrasts two representations of personal utility that are found to be uninvadable. The first is semi-Kantian in form. This preference averages a fitness self-interest with a relatedness weighted Kantian interest. The latter interest evaluates the consequence of own behavior for own fitness, assuming the interaction partner adopts the same behavior as self. The second preference is a personal inclusive fitness. This preference combines a self-regarding interest with a relatedness weighted other-regarding interest. Each such interest takes the form of an average effect, which evaluates the consequence of expressing own behavior, instead of average population behavior, on a statistical average fitness to self and the interaction partner.