The interface of unidirectional rewards: Enhanced cooperation within interdependent networks

As a way to induce cooperation more effectively, positive incentives have emerged in social species forefront to negative incentives. To assess their effects in cooperation networks, we simulated a social scenario in which reward behaviors are dispensed unilaterally. To do so, we let evolve asymmetric rewards within two specular, interdependent networks, whose individuals in an upper layer have the right to reward corresponding players displaying, likewise, cooperative or defective behavior in the lower layer. With this setup, rewarded players in the lower layer can obtain a payoff equivalent to the amount of the cost of granting reward from the upper layer. Peculiarly, we find that cooperators survive for larger reward values regardless of how high the temptation to defect is. Notably, cooperators in the upper network thrive even if the temptation to defect is pretty high. By further analyzing the nature of social interactions, we find that defection is the winning strategy when rewards originated pro-socially, and that cooperation instead wins by invading the whole system when rewards originated anti-socially. These results are consistent when crosschecked to a theoretical analysis here purposely drawn up. Our work highlights the need of including complex network structures when analyzing asymmetric incentives in the evolution of cooperation, both in human and non-human species.