Gene-culture coevolution of complex social behavior: human altruism and mate choice.

The hypothesis is examined that genes bias the development of complex social behavior in one direction over alternatives. Studies of altruism and political attitudes in twins estimate that approximately 50% of the variance is associated with direct genetic inheritance, virtually 0% with the twin's common family environment, and the remainder with each twin's specific environment. Studies of human marriages show that spouses choose each other on the basis of similarity, assorting on the most genetically influenced of a set of homogeneous attributes. These data imply a genetic canalization of social influences such that, within the constraints allowed by the total spectrum of cultural alternatives, people create environments maximally compatible with their genotypes.