Emergence of Altruism in Spatially Structured Populations

Spatial structure of an otherwise random and uniform population impacts on the emergence of cooperation among selfish and rational individuals. In the ensembles of structured populations constrained by the combinations of degree distribution, assortativity, and clustering coefficient, we try to map the comprehensive ???cooperativity landscape??? in the context of game theory. To explore the structure space with varying degrees of assortativity and higher-order degree-degree correlations, we employ a Monte Carlo algorithm for the degree-preserving rewiring and produce the statistical ensemble of thermally annealed graphs retaining the major characteristics of empirical social networks. We find that the effects of the clustering on the sustained cooperation are not monotonic whereas the higher assortativity is disfavored in general. We discuss the individual-based reinforcement strategies for the enhanced cooperativity in a variety of real-world social networks