Cultural tightness and social cohesion under coevolving beliefs, behaviors, and preferences.

Successful collective action on issues from climate change to the maintenance of democracy depends on societal properties such as cultural tightness and social cohesion. How these properties evolve is not well understood because they emerge from a complex interplay between beliefs and behaviors that are usually modeled separately. Here, we address this challenge by developing a game-theoretic framework incorporating norm-utility models to study the coevolutionary dynamics of cooperative behavior, expressed belief, and norm-utility preferences. We show that the introduction of evolving beliefs and preferences into the Snowdrift game and Prisoner's Dilemma leads to a proliferation of evolutionary stable equilibria, each with different societal properties. In particular, we find that reduced material benefits from cooperation can be associated with an expected increase in cultural tightness (the degree to which norms are strong and shared, so that individuals behave in accordance with widely held beliefs) and an expected reduction in social homogeneity and cohesion (the extent to which individuals belong to a single well-defined group with similar beliefs, behaviors, and preferences). Loss of social homogeneity occurs via a process of evolutionary branching, in which a population fragments into two distinct social groups with strikingly different characteristics. The groups that emerge differ not only in their willingness to cooperate, but also in their expressed beliefs about cooperation and in their preferences for conformity and coherence of their behaviors and expressed beliefs. These results have implications for our understanding of the resilience of cooperation and collective action in times of crisis.