New findings by researchers at the University of Montpellier, the Max Planck Institute for Evolutionary Anthropology in Leipzig, and the German Primate Center in Göttingen resolve why male-female power asymmetries vary across primate societies. Bringing together detailed observations of male-female aggression from 253 populations across 121 primate species, the study shows that clear cut dominance by either sex is rare, and highlights the conditions under which females have become socially dominant over males in primate evolutionary history.