A historical-genetic reconstruction of human extra-pair paternity

Paternity testing using genetic markers has shown that extra-pair paternity (EPP) is common in many pair-bonded species. Evolutionary theory and empirical data show that extra-pair copulations can increase the fitness of males as well as females. This can carry a significant fitness cost for the social father, who then invests in rearing offspring that biologically are not his own. In human populations, the incidence and correlates of extra-pair paternity remain highly contentious. Here, we use a population-level genetic genealogy approach to reconstruct spatiotemporal patterns in human EPP rates. Using patrilineal genealogies from the Low Countries spanning a period of over 500 years and Y-chromosomal genotyping of living descendants, our analysis reveals that historical EPP rates, while low overall, were strongly impacted by socioeconomic and demographic factors. Specifically, we observe that estimated EPP rates among married couples varied by more than an order of magnitude, from 0.4...