Neighborhood structure and the evolution of cooperation

This paper deals with the problem of explaining the survival of cooperative behavior in populations in which each person interacts only with a small set of social 'neighbors', and individuals adjust their behavior over time by myopically imitating more successful strategies within their own neighborhood. We identify two parameters-the interaction radius and the benefit-cost ratio-which jointly determine whether or not cooperation can survive. For each value of the interaction radius, there exists a critical value of the benefit-cost ratio which serves as the threshold below which cooperation cannot be sustained. This threshold itself declines as the interaction radius rises, so there is a precise sense in which dense networks are more conducive to the evolution of cooperation.