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Science 29 October 2004:
Vol. 306. no. 5697, pp. 859 - 862
DOI: 10.1126/science.1101456
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Reports

The Evolutionary Origin of Cooperators and Defectors

Michael Doebeli,1* Christoph Hauert,1{dagger} Timothy Killingback2

Coexistence of cooperators and defectors is common in nature, yet the evolutionary origin of such social diversification is unclear. Many models have been studied on the basis of the assumption that benefits of cooperative acts only accrue to others. Here, we analyze the continuous snowdrift game, in which cooperative investments are costly but yield benefits to others as well as to the cooperator. Adaptive dynamics of investment levels often result in evolutionary diversification from initially uniform populations to a stable state in which cooperators making large investments coexist with defectors who invest very little. Thus, when individuals benefit from their own actions, large asymmetries in cooperative investments can evolve.

1 Department of Zoology and Department of Mathematics, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
2 Department of Mathematics, College of William and Mary, Williamsburg, VA 23187, USA.

{dagger} Present address: Program for Evolutionary Dynamics, Harvard University, One Brattle Square, Cambridge, MA 02138, USA.

* To whom correspondence should be addressed. E-mail: doebeli{at}zoology.ubc.ca

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