Cultural Evolution and the Deep Roots of Cooperation: A Unified Perspective

This essay frames the evolution of human cooperation as a two-layer process. A foundational layer, rooted in subsistence and ecological pressures, shaped cooperative dispositions unevenly, whereas an expansionary layer, rooted in conflict, political stratification, and shared infrastructure, generated largescale, institutionalized cooperation. The first evolutionary layer unfolded over the grand arc of human evolution, reinforcing the capacity for small-scale cooperation in hunter-gatherer societies while favoring traits complementary to cooperation only in some sedentary societies. The second evolutionary layer emerged as rising population density heightened external threats, fostered coercive centralized authority, and raised the returns to public infrastructure. In environments where cooperative traits had already evolved, warfare, extraction, and infrastructure provision reinforced these predispositions, scaling them into durable collective institutions. Yet in regions where such cultural foundations were absent, large-scale collective action was more challenging, and conflict was often destabilizing, magnifying division and political fragility. Recognizing the profound global heterogeneity in this foundational layer of cooperative behavior is essential for identifying the origins of large-scale cooperation and the conditions under which conflict enhanced this capacity.