Chimpanzees are not more aggressive than bonobos but target sexes differently

The long-standing view that bonobos (Pan paniscus) are peaceful while chimpanzees (Pan troglodytes) are aggressive has shaped our understanding of primate and human social evolution. However, recent observations from the wild challenge this dichotomy, warranting standardized comparative analyses of aggression in the Pan species. Here, we examined aggressive interactions across 22 zoo-housed groups of chimpanzees (N = 9 groups, 101 individuals) and bonobos (N = 13 groups, 88 individuals) using Bayesian social network analysis. We find no species differences in overall or contact aggression rates, accounting for group size and sex ratio. However, aggression patterns diverge by sex: Bonobos exhibit higher female-to-male aggression, while chimpanzees show the reverse. Notably, absolute aggression rates varied substantially between groups within each species, reinforcing recent evidence on group-specific social structures in Pan. These findings challenge the traditional aggression dichotomy between bonobos and chimpanzees and provide insights into the evolutionary dynamics of social conflict strategies in great apes, including humans.