Cooperation through Imitation and Exclusion in Networks

We develop a simple model to study the coevolution of interaction structures and action choices in prisoners' dilemma games. Agents are boundedly rational and choose both actions and interaction partners via payoff-biased imitation. The dynamics of imitation and exclusion yields polymorphic outcomes under a wide range of parameters. Whenever agents hold some information beyond their interaction neighbors defectors and cooperators always coexist in disconnected components. Otherwise polymorphic networks can emerge with a center of cooperators and a periphery of defectors. Any stochastically stable state has at most two disconnected components. Simulations confirm our analytical results and show that the share of cooperators increases with the speed at which the network evolves, increases with the radius of interaction and decreases with the radius of information.