Research Article ‘‘In-Group Love’ ’ and ‘‘Out-Group Hate’ ’ as Motives for Individual Participation in Intergroup Conflict A New Game Paradigm

ABSTRACT—What motivates individual self-sacrificial be-havior in intergroup conflicts? Is it the altruistic desire to help the in-group or the aggressive drive to hurt the out-group? This article introduces a new game paradigm, the intergroup prisoner’s dilemma–maximizing difference (IPD-MD) game, designed specifically to distinguish be-tween these two motives. The game involves two groups. Each group member is given a monetary endowment and can decide how much of it to contribute. Contribution can be made to either of two pools, one that benefits the in-group at a personal cost and another that, in addition, harms the out-group. An experiment demonstrated that contributions in the IPD-MD game are made almost ex-clusively to the cooperative, within-group pool. Moreover, preplay intragroup communication increases intragrou