Evolutionary Prisoner's Dilemma on heterogeneous Newman-Watts   small-world network
  We focus on the heterogeneity of social networks and its role to the emergence of prevailing cooperation and sustaining cooperators. The social networks are representative of the interaction relationships between players and their encounters in each round of games. We study an evolutionary Prisoner's Dilemma game on a variant of Watts-Strogatz small-world network, whose heterogeneity can be tuned by a parameter. It is found that optimal cooperation level exists at some intermediate topological heterogeneity for different temptations to defect. Moreover, neither the most heterogeneous case nor the most homogeneous one would favor the cooperators. At intermediate heterogeneity in degree sequences, cooperators could resist the invasion of defectors for large temptation to defect. 
Feng Fu, Lianghuan Liu, Long Wang