On the Role of External Constraints in a Spatially Extended Evolutionary Prisoner’s Dilemma Game

Abstract. We study the emergency of mutual cooperation in evolutionary prisoner’s dilemma games when the players are located on a square lattice. The players can choose one of the three strategies: cooperation (C), defection ( D) or “tit for tat” ( T) , and their total payoffs come from games with the nearest neighbors. During the random seqtfential updates the players adopt one of their neighboring strategies if the chosen neighbor has higher payoff. We compare the effect of two types of external constraints added to the Darwinian evolutionary processes. In both cases the strategy of a randomly chosen player is replaced with probability P by another strategy. In the first case, the strategy is replaced by a randomly chosen one anlong the two others, while in the second case the new strategy is always C. Using generalized mean-field approximations and Monte Carlo simulations the strategy concent,rations are evaluated in the stationary state for different strength of external constraints characterized by the probability P