Evol Ecol Res 9: 1023-1041 (2007)     Full PDF if your library subscribes.

Cooperation maintained by fitness adjustment

Christine Taylor,1 Janet Chen2 and Yoh Iwasa3*

1Program for Evolutionary Dynamics, Department of Organismic and Evolutionary Biology and  2Department of Mathematics, Harvard University, Cambridge, MA 02138, USA and  3Department of Biology, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan

Author to whom all correspondence should be addressed.
e-mail: yiwasscb@mbox.nc.kyushu-u.ac.jp


Questions: Can cooperation be enhanced if players whose performance is 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 a cooperative dilemma game, and at the end of each generation those whose performance is higher than the mean are forced to pay an 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, 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 ‘envy’ is able to maintain cooperation.

Keywords: distribution of cooperation level, envy, evolution of cooperation, fitness adjustment, punishment.

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