The evolution of monogamous marriage

The majority of human societies allow polygynous marriage, and the prevalence of this practice is readily understood in evolutionary terms. Why some societies prescribe monogamous marriage is however not clear: current evolutionary explanations --- that social monogamy increases within-group co-operation, giving societies an advantage in competition with other groups --- conflict with the historical and ethnographic evidence.

In this talk, I present two case studies investigating the evolution of monogamous marriage. Firstly, I use an inclusive fitness model to show that where wealth is transferred across generations this marriage strategy may be advantageous because it concentrates resources in a limited number of heirs, and because females are likely to grant higher fidelity to husbands who invest exclusively in their offspring. Secondly, I use phylogenetic comparative methods on linguistic phylogenies and cross-cultural data to reconstruct the history of marriage strategies in societies speaking Indo-European languages, and show that early Indo-European society practised monogamous marriage.

In line with the archaeological, historical, and ethnographic evidence, these findings challenge explanations that link the emergence of monogamous marriage 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 our understanding of human social behaviour.