Monetary Punishment Promotes Cooperation in Complex Networks

In cooperation dilemmas, for cooperation to emerge, a mechanism for the evolution of cooperation is needed. We propose a costly monetary punishment model based on the spatial prisoner’s dilemma game and complex networks, specifically, cooperators sanction defective behaviors by applying a punishment fine to defectors directly, and all cooperators share the punishment cost. We mainly focus on how the monetary punishment mechanism affects the evolution of individuals’ strategy behaviors under different network structures. Results show that cooperation is significantly promoted even for quite small initial fractions of cooperators in square lattice and small-world network. Furthermore, we find out that when the mechanism is turned off, cooperation drops to a comparatively lower level in small-world network, while there is no change in square lattice. Additionally, the mechanism promotes the average payoff of the population.