Conditional neutral punishment promotes cooperation in the spatial prisoner's dilemma game

Punishment plays an important role in promoting cooperation. In real society, individuals tend to punish other players based on certain conditions rather than punish them directly. Thus, we introduce a conditional neutral punishment mechanism and study how this mechanism affects the evolution of cooperation. Namely, an individual can punish his/her neighbors with the opposite strategy when his/her payoff is lower than the average payoff of his/her neighbors. The simulation results show that this mechanism promotes cooperation effectively even with antisocial punishment. By adopting such a mechanism, cooperative punishers form shields to protect cooperators inside, while defective punishers hide behind defectors without punishing anyone. (C) 2019 Elsevier Inc. All rights reserved.