Parochial Cooperation in Humans: Forms and Functions of Self-Sacrifice in Intergroup Conflict

Although cooperation between groups is not unusual, most forms of human cooperation are in-group bounded and, sometimes, motivated by the desire to ward-off and subordinate rivaling out-groups. Building on evolutionary perspectives and models, we propose that humans evolved a capacity for parochial cooperation, which entails (1) in-group love: the tendency to cooperate with and extend trust toward those others who are similar, familiar rather than unfamiliar, and belong to one's own group; and (2) out-group hate: a willingness to fight against rivaling out-groups. This chapter reviews our own work, and that of others, showing that parochial cooperation (1) emerges especially when it benefits individuals' within-group reputation, (2) affects one's within-group status, (3) is more prominent among individuals with chronic prosocial rather than proself value orientation, and (4) is sustained and motivated by oxytocin, an evolutionary ancient hypothalamic neuropeptide pivotal in social bonding, pair–bond formation, and empathic responding. Across the board, findings resonate well with relatively recent evolutionary theory on (inter)group relations and add to classic theory in social psychology.