Chimpanzee Friendship and Social Rules

A controlled scientific study published on September 1, 2026, in Evolution and Human Behavior by researchers from the University of California, Berkeley, reveals that chimpanzees treat close social companions differently during conflicts over resources. By observing 26 chimpanzees at the Ngamba Island Chimpanzee Sanctuary in Uganda and setting up controlled pineapple theft experiments, researchers discovered that animals were less likely to steal from strongly bonded partners compared to nonfriends. The study authors, including lead author Oded Ritov and principal investigator Jan Engelmann, emphasize that friendship among chimpanzees leads to specific social expectations and restraint regarding antisocial behavior. When thefts did occur between friends, both parties exhibited distinct emotional patterns where agitation subsided more quickly than interactions involving nonfriends. These findings provide groundbreaking evidence that relationship-specific expectations exist outside of human societies, suggesting that the foundational building blocks of human cooperation, friendship, and moral principles evolved from ancient primate social dynamics. Researchers conclude that studying these behavioral nuances helps bridge the evolutionary gap between basic social preferences and large-scale human moral systems, highlighting how mutual expectations within close animal partnerships scaled up into generalized societal norms over evolutionary time.