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. [ABSTRACT FROM AUTHOR]