The long-term evolution of social and economic inequality in human societies appears to have followed a zig-zag pattern. Our closest primate relatives are characterized by dominance hierarchies, yet early human groups were highly egalitarian. With the advent of agriculture larger-scale, more hierarchical and unequal societies emerged. The Axial Age saw yet another turn, a move towards greater egalitarianism. In this project we seek to understand what caused these fluctuations in inequality, and how societies balance the pros and cons of hierarchical organization. Religion may have played an extremely important, yet little appreciated role in these processes. The goal of the proposed research is to test this idea by analyzing the role of religion, social equity norms, and inter-societal competition in the evolution of egalitarianism. Our theoretical framework for addressing these issues is modern cultural evolutionary theory. To accomplish our goal we will construct a large historical database using an innovative approach that will assemble the specialized knowledge of experts on the characteristics of past human societies. A range of competing hypotheses will be tested using rigorous, quantitative statistical analyses. The results of our analyses will be disseminated via multiple high-impact, high-profile publications . A workshop involving policy makers will help translate the empirical findings of our investigations into practical measures that help create more inclusive and cohesive societies. The project will create a new, interactive, open-access database that in the long term will enable many other important questions to be addressed. The establishment of our database will create an enduring impact on the way research into human societies is conducted, making it easier to to share and collate knowledge in order to test hypotheses about the past quantitatively and rigorously, and helping to bridge the gap between the humanities and the sciences.