Sarah Mathew: UCLA Department of Anthropology

Knowledge of the nature and scale of cooperation in acephalous societies is important for understanding the evolution of human sociality. I will present data showing that the Turkana, an acephalous pastoral society in East Africa, sustain costly large scale cooperation in warfare through informal sanctions against free riders, and that Turkana norms regulating warfare benefit the ethno-linguistic group, not smaller social units. The findings shed light on the equilibrium selection processes that have shaped human sociality and suggest that large scale cooperation may have been common for a long period of human evolutionary history.