Natural cooperators: food sharing in humans and other primates.

The study of cooperation is rich with theoretical models and laboratory experiments that have greatly advanced our knowledge of human uniqueness, but have sometimes lacked ecological validity. We therefore emphasize the need to tie discussions of human cooperation to the natural history of our species and its closest relatives, focusing on behavioral contexts best suited to reveal underlying selection pressures and evolved decision rules. Food sharing is a fundamental form of cooperation that is well-studied across primates and is particularly noteworthy because of its central role in shaping evolved human life history, social organization, and cooperative psychology. Here we synthesize available evidence on food sharing in humans and other primates, tracing the origins of offspring provisioning, mutualism, trade, and reciprocity throughout the primate order. While primates may gain some benefits from sharing, humans, faced with more collective action problems in a risky foraging niche, expanded on primate patterns to buffer risk and recruit mates and allies through reciprocity and signaling, and established co-evolving social norms of production and sharing. Differences in the necessity for sharing are reflected in differences in sharing psychology across species, thus helping to explain unique aspects of our evolved cooperative psychology.