The Evolution of Kinship and Marriage Systems

Kinship and marriage systems represent the ways in which humans organize relatedness and reproduction. The work presented in this thesis extends the philosophical, theoretical, and methodological foundations of evolutionary biology to the study of these aspects of human social behaviour. Firstly, a game-theoretic analysis shows that the evolution of monogamous marriage can be understood within the framework of inclusive fitness theory. In this framework, the stability of monogamous marriage requires that men transfer property to their wife’s offspring; consistently, the log-linear analysis of marriage and transfer strategies across a worldwide sample of societies shows that norms stipulating the transfer of land to wife’s offspring exist in a larger proportion of monogamous than polygynous societies. Secondly, phylogenetic comparative analyses of marriage and residence strategies across societies speaking Indo-European languages reconstruct early Indo-European society as practising monogamy and prevailing virilocality with alternative neolocality. However, there is no evidence of coevolution of monogamy with neolocality in the history of these societies; thus, it cannot be excluded that the observed association between marriage and residence strategies is the artefact of a history of descent from a common ancestor. In line with the archaeological, historical, and ethnographic evidence, these findings challenge explanations that link the emergence of monogamy and neolocality to the development of idiosyncratic features of “western” social organization; such explanations dominate the social sciences. More generally, they illustrate the relevance of the evolutionary paradigm to the study of kinship and marriage systems, contributing to the development of a biologically based social anthropology.