I study the evolution of human ultra-sociality and the role of culture in enabling it. I am especially interested in how humans evolved the capacity to cooperate with millions of genetically unrelated individuals, and how this links to the origins of moral sentiments, prosocial behavior, norms, and large-scale warfare. To address these issues, I combine formal modeling of the evolution of cooperation with fieldwork among the Turkana. The Turkana are an egalitarian pastoral society in East Africa who cooperate, including in costly inter-ethnic raids, with hundreds of other Turkana who are not kin nor close friends. Through systematic empirical studies in this unique ethnographic context, my research project here aims to provide a detailed understanding of the mechanisms underpinning cooperation and moral origins.