Effect of asymmetry on cooperation in spatial evolution.

Asymmetry is omnipresent in human society and nature and the reasons causing asymmetry are multiple. To think about the impact of asymmetries on the cooperation systems, we focus on a typical model of great asymmetric traits-the boxed pigs game-and extended the one-to-one interaction to the interaction in population. We consider the asymmetry of payoff and the spatial structure of the two populations in space. Our results have shown that the almost equal abundance and strength of two populations kills cooperative behavior. The single increase of either strength-asymmetry or abundance-asymmetry promotes cooperation. But high levels of both asymmetries would inhibit cooperative behavior, making the powerful mechanism of cooperation broken.