title: 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.
authors.affiliation: Program for Evolutionary Dynamics, Department of Mathematics, Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, U.S.A., Email: taylor4@fas.harvard.edu.
authors.forename: Christine
authors.initials: C
authors.lastname: Taylor
authors.forename: Janet
authors.initials: J
authors.lastname: Chen
authors.forename: Yoh
authors.initials: Y
authors.lastname: Iwasa