The Ngogo chimpanzees of Uganda’s Kibale National Park have long been known for violent clashes with neighboring groups, often resulting in deaths — a phenomenon sometimes described as “chimpanzee warfare.”

Now, a new study led by UCLA anthropologist Brian Wood, in collaboration with John Mitani of the University of Michigan, provides the clearest evidence yet that territorial expansion after lethal conflict can directly boost reproductive success. Following a series of coordinated attacks that claimed at least 21 lives, the Ngogo group’s territory grew by 22%. In the years that followed, females gave birth more often, and their infants were far more likely to survive.