Chimpanzees are not more aggressive than bonobos but target sexes differently

The long-standing view that bonobos (<i>Pan paniscus</i>) are peaceful while chimpanzees (<i>Pan troglodytes</i>) 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 <i>Pan</i> species. Here, we examined aggressive interactions across 22 zoo-housed groups of chimpanzees (<i>N</i> = 9 groups, 101 individuals) and bonobos (<i>N</i> = 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 <i>Pan</i>. 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.