Groups and alliances

Abstract

Few species cooperate as readily with non-relatives as humans do, and this chapter examines the evolved mechanisms that make large-scale group living possible. It draws on evidence from non-human primates and hunter-gatherer societies to show how kin-based and reciprocal alliances structure social hierarchies, regulate access to resources, and enhance survival in the face of predation, disease, and intergroup conflict. The chapter then explores the cognitive and emotional architecture that sustains cooperation, including theory of mind, social emotions, gossip, reputation, and cheater detection, showing how these mechanisms work together to enforce norms and deter free-riding. It considers the costs of group living alongside its benefits, addressing pathogen transmission, resource competition, and the tragedy of the commons as countervailing pressures. Finally, the chapter presents reciprocal altruism and norm enforcement as the evolutionary foundations of the trust and cohesion that characterise human social life.