Coevolutionary Dynamics of Cultural Markers, Parochial Cooperation, and Networks

The emergence and institutionalization of cooperation in sizable groups without reciprocity receives considerable attention in game-theoretical modeling. Agents in our study play the Prisoner's Dilemma game cooperating with tolerably similar neighbors. They may imitate cultural markers (tags) and tolerance from more successful neighbors. Alternatively, they break ties to out-group neighbors. New partners are selected either from neighbors' neighbors (clustering) or randomly. Variations in network plasticity (the likelihood of changing partners rather than being influenced) and clustering are explored. With high plasticity and high clustering, networks tend to fragment. With low plasticity and low clustering, networks tend toward global cooperation, but with severe losses of cultural diversity and tolerance. Cooperation in such regimes also proves to be vulnerable to defection. Between, there is a space displaying relatively stable and widespread cooperation with diversity and tolerance. We note some important structural characteristics of the networks evolving in this space.