Coevolution of extortion strategies with mixed imitation and aspiration learning dynamics in spatial Prisoner's Dilemma game

This paper investigates the mixed learning dynamics of imitation and aspiration in a spatial Prisoner's Dilemma game, and proposes a novel coevolution mechanism between individuals' learning processes and their payoffs under varying of selection intensity. By considering the evolution of three strategies (unconditional cooperation, unconditional defection, and extortion) in a square lattice, our results show that the proper selection intensity can efficiently promote the emergence of cooperative aspirators and build up a router of strategies transformation from defective imitators to extortioners and cooperators, leading to the formation of a giant cooperative component. However, both too low and too high values of selection intensity will inhibit the emergence of cooperation since the former case leads to the dominance of imitators and weakens the formation of large cooperative clusters, while in the latter case, an abundance of extortionate aspirators also suppresses the level of cooperation.