Modeling the evolution and formation of animal friendship

Gerald G. Carter. 2024. PNAS 121 (15) e2403318121. doi.org/10.1073/pnas.2403318121

Friendship is fundamental to our health and well-being. The human capacity to form cooperative social bonds outside family has undoubtedly been a key to our survival and reproductive success over evolutionary time. Increasing evidence shows that many other animals—from chimpanzees to dolphins to crows—also build long-lasting cooperative relationships that seem analogous in form and function to human friendships (1, 2). Yet understanding friendship and social bonding from an evolutionary perspective has long been a challenge. Navigating the subtle cooperation and conflict of friendships is a cognitively complex process that violates assumptions of classic game-theory models of cooperation.