In-group defense, out-group aggression, and coordination failures in intergroup conflict.
Intergroup conflict persists when and because individuals make costly contributions to their group's fighting capacity, but how groups organize contributions into effective collective action remains poorly understood. Here we distinguish between contributions aimed at subordinating out-groups (out-group aggression) from those aimed at defending the in-group against possible out-group aggression (in-group defense). We conducted two experiments in which three-person aggressor groups confronted three-person defender groups in a multiround contest game (n = 276; 92 aggressor-defender contests). Individuals received an endowment from which they could contribute to their group's fighting capacity. Contributions were always wasted, but when the aggressor group's fighting capacity exceeded that of the defender group, the aggressor group acquired the defender group's remaining resources (otherwise, individuals on both sides were left with the remainders of their endowment). In-group defense appeared stronger and better coordinated than out-group aggression, and defender groups survived roughly 70% of the attacks. This low success rate for aggressor groups mirrored that of group-hunting predators such as wolves and chimpanzees (n = 1,382 cases), hostile takeovers in industry (n = 1,637 cases), and interstate conflicts (n = 2,586). Furthermore, whereas peer punishment increased out-group aggression more than in-group defense without affecting success rates (Exp. 1), sequential (vs. simultaneous) decision-making increased coordination of collective action for out-group aggression, doubling the aggressor's success rate (Exp. 2). The relatively high success rate of in-group defense suggests evolutionary and cultural pressures may have favored capacities for cooperation and coordination when the group goal is to defend, rather than to expand, dominate, and exploit.
Institute of Psychology, Leiden University, 2333 AK Leiden, The Netherlands; Center for Experimental Economics and Political Decision Making, University of Amsterdam, 1018 WB Amsterdam, The Netherlands; c.k.w.de.dreu@fsw.leidenuniv.nl.
Carsten K W
CK
De Dreu
Institute of Psychology, Leiden University, 2333 AK Leiden, The Netherlands; Center for Experimental Economics and Political Decision Making, University of Amsterdam, 1018 WB Amsterdam, The Netherlands;
Jörg
0000-0002-5403-9475
J
Gross
Humanities, Arts and Social Sciences, Singapore University of Technology and Design, Singapore 487372;
Zsombor
Z
Méder
Institute of Psychology, Leiden University, 2333 AK Leiden, The Netherlands;
Michael
M
Giffin
Institute of Psychology, Leiden University, 2333 AK Leiden, The Netherlands;
Eliska
E
Prochazkova
Center for Experimental Economics and Political Decision Making, University of Amsterdam, 1018 WB Amsterdam, The Netherlands;
Jonathan
J
Krikeb
Department of Experimental and Applied Psychology, Vrije Universiteit Amsterdam, 1081 BT Amsterdam, The Netherlands.
Simon
0000-0003-1546-955X
S
Columbus
D000374:Aggression / Q000523:psychology*; D000533:Altruism; D000818:Animals; D001522:Behavior, Animal; D003220:Conflict, Psychological; D003299:Cooperative Behavior; D005260:Female; D006791:Hostility; D006801:Humans; D007398:Interpersonal Relations; D008297:Male; D002679:Pan troglodytes / Q000523:psychology; D011678:Punishment / Q000523:psychology; D012919:Social Behavior; D019596:Wolves / Q000523:psychology
collective action; competition; coordination; intergroup relations; parochial altruism