COOPERATION MAINTAINED BY FITNESS ADJUSTMENT.

ABSTRACT

QUESTIONS Whether or not cooperation can be enhanced if players with a performance higher than the mean are forced to pay an additional cost in each generation? MATHEMATICAL METHODS: Analysis of replicator dynamics with mutation. The ESS distribution of cooperation level is obtained. KEY ASSUMPTIONS Players engage in cooperative dilemma game, and at the end of each generation, those with higher performance than the mean are forced to pay additional cost. CONCLUSIONS: Without mutation, the entire population eventually conforms to a single cooperation level determined by the initial composition of the population. With mutation, there is an equilibrium distribution of cooperation level, which has a peak at an intermediate level of cooperation. Whether it is institutionalized such as tax or just a social custom, fitness adjustment based ultimately on people's emtion of "envy" is able to maintain cooperation.