Intergroup Conflict May Inhibit Coalescing of Large Human Groups and Decrease Returns from Cooperation

Recent theoretical advances and quasi-experimental evidence from modern conflict areas suggest that intergroup conflict and ostracism play a pivotal role in the evolution of cooperation. However, relatively little is known about the role of intergroup conflict and ostracism on group formation and human migration. Here, we show that intergroup conflict may inhibit coalescing of large human groups and decrease net returns from cooperative behaviors. Moreover, we find that competitive pressure between groups decreases the likelihood of being punished through ostracism. Our results suggest the importance of stable group boundaries on the evolution of human cooperation through intergroup conflict and point to the dangers of implementing group contests to foster human cooperation