Cultural tightness and social cohesion under evolving norms

Abstract: 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-theoretical framework incorporating norm-utility models to study the coevolutionary dynamics of cooperative action, 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 a declining material environment can simultaneously be associated with increased cultural tightness (defined as the degree to which individuals behave in accordance with widely held beliefs) and reduced social cohesion (defined as the degree of social homogeneity i.e. the extent to which individuals belong to a single well-defined group). 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 beliefs about cooperation and in their preferences for conformity and coherence of their actions and beliefs. These results have implications for our understanding of the resilience of cooperation and collective action in times of crisis.