Abstract:

Social interaction networks exist at many scales of biological organization, from the level of multicellular aggregates to human societies. These networks often have an exquisite structure that promotes cooperation. The formation of social ties and cooperative interactions is endogenously driven by homophily, i.e., the phenomenon that "birds of a feather flock together." Individuals tend to bond with and cooperate with someone else who resembles themselves. Thus, one central question in evolutionary biology and the social sciences is to understand how phenotypic similarity leads to social ties ("structure") and cooperation (adaptive "function") of social networks. In this talk, I will present my recent theoretical work addressing this question. My approach combines coalescent theory in population genetics with evolutionary game theory. I will first present a brand new mathematical model to address the evolutionary origin of homophily. This model results in a surprisingly simple rule for the evolution of homophily. The population tends to evolve homophilic preferences if a > K b, where a and b are the respective payoffs for homophilic and heterophilous associations, and the term K summarizes the effects of population structure. I will then discuss how strategies of contingent cooperation evolve, that is, how individuals tend to preferentially cooperate with similar peers. My analytical results show that contingent cooperation can be favored by natural selection, provided sufficient phenotypic diversity. I will conclude my talk by proposing a general mathematical framework for studying the coevolution of homophily and cooperation in social networks.