Adaptations for Reasoning About Social Exchange

NISA AND TOMA were hunter-gatherers, !Kung San people living in Botswana’s inhospitable Kalahari desert during the 1960s. Their way of life was as different from that in an industrialized, economically developed society as any on earth, yet their sentiments are as familiar and easy to comprehend as those of your neighbor next door. They involve social exchange, interactions in which one party provides a benefit to the other conditional on the recipient’s providing a benefit in return (Cosmides, 1985; Cosmides & Tooby, 1989; Tooby & Cosmides, 1996). Among humans, social exchange can be implicit or explicit, simultaneous or sequential, immediate or deferred, and may involve alternating actions by the two parties or follow more complex structures. In all these cases, however, it is a way people cooperate for mutual benefit. Explicitly agreed-to forms of social exchange are the focus of study in economics (and are known as exchange or trade), while biologists