Effects of fluctuations on the evolution of cooperation in the prisoner's dilemma game

The instabilities and fluctuations of individual fitness induced by some uncertain factors are ubiquitous in the real world. In this letter we study how the individual fitness fluctuations affect the evolution of cooperation taking place in two-dimensional square lattices and Newman-Watts small-word networks. We introduce two tunable parameters α and β to control the fluctuation scope of agents and the fluctuation amplitude of fitness, respectively. Interestingly, the cooperation can be promoted in such a situation that β is not too high and α is not too low, which indicates that the fluctuations play a significant role in the emergence of cooperation and the proper fluctuations can improve the cooperation of a system. The promotion of cooperation is explained by the feedback mechanism. Our results may be helpful in understanding the role of fluctuations in the emergence of cooperation in the real world.