Conditional punishment resolves social dilemma in spatial network

Social punishment, a mechanism that cooperative individual spends a little cost to penalize defector, is verified to be an effective mechanism for promoting the evolution of cooperation. In this paper, we introduce conditional punishment, the willingness to punish p, which decides whether to carry out penalty. It is shown that cooperative behavior is significantly enhanced when punishers are taken into account and the frequency of cooperation increases with p. In addition, we find out the protective effect of punishers on evolution of cooperation from a micro point of view. We hope our work may shed light on understanding of cooperative behavior in society.