Predicting the patterns of kinship dynamics in human societies

Abstract

By shaping the inclusive fitness effects of behaviours, kinship environments have important implications for social evolution, and studies across non-human animal societies have shown that the patterns of kinship dynamics individuals experience as they age can be predicted by simple demographic parameters relating to sex-specific dispersal patterns, the extent of extra-group mating, and the age-specific patterns of mortality and fertility. However, it remains unclear whether these insights apply within our own species, where we see both extended lifespans in which kinship dynamics can play out, and remarkable variations in cultural practices relating to marriage and residence that influence the patterns of inter-individual relatedness. Here, using a newly developed model of kinship dynamics, we explore how marriage practices and post-marital residence rules, along with the typical survival and fertility schedules of our own species, can predict the emergent patterns of female and male kinship dynamics in human societies. By showing evidence that the model successfully captures the patterns of female and male kinship dynamics underlying human societies, we demonstrate that, despite the diversity in human social organisation, a relatively simple set of parameters relating to male and female rates of dispersal and the prevalence of extra-group mating suffices to capture the qualitative patterns of human kinship dynamics. Given the inclusive fitness implications kinship dynamics have for sex- and age-linked variations in behaviours, our study thus generates new insights into human social evolution.