Running Head: The Altruism Puzzle Psychological Adaptations for Prosocial Behavior: The Altruism Puzzle

This chapter addresses the evolutionary roots of the, by and large, uniquely human capacity for helping other people who are not closely related. It is argued that prosocial tendencies have evolved through natural selection pressures associated with the need to solve critical interdependence problems, which can often be modeled as social dilemmas. Solutions to social dilemmas involve engaging in a process of social exchange with others within either dyads or groups. We address the evidence for an evolutionary-based theory of prosocial behavior by linking the concept of social exchange to several key social psychological phenomena, such as negativity effects, loyalty and commitment, forgiveness, empathy and other social emotions, social norms, group identification and xenophobia, group size and stability, and differences in prosocial dispositions. These illustrations suggest the utility of an evolutionary perspective on prosocial behavior. 2