Evolution of cooperation: The analysis of the case wherein a different player has a different benefit and a different cost

The existence of cooperation demands explanation in terms of natural selection. Prisoner’s dilemma is a framework often used when studying the evolution of cooperation. In prisoner’s dilemma, most previous studies consider the situation wherein an individual who cooperates will give an opponent an amount b at a personal cost of c, where b > c > 0 while an individual who defects will give nothing. This model setting is convenient; however, previous studies have not considered the case wherein a different player has a different benefit and different cost while in reality, it is natural to consider that a different player has a different benefit and different cost. Here, we raise the following question: Taking that a different individual has a different benefit and a different cost into consideration, what strategy is likely to evolve? In this paper, we focus on the direct reciprocity and analyze the case wherein a different player has a different benefit and a different cost. We obtain the condition for the evolution in the general case. And in addition, we have revealed that under a specific condition as the interaction repeats longer and the benefit-to-cost ratio is larger and the cooperating probability is more sensitive to the benefit the opponent provides, the establishment of cooperation is more likely.