Claus Wedekind, 12* Manfred Milinski 1
Cooperation Through Image Scoring in Humans
Science 288. 5467 (5 May 2000): 850 - 852

The "tragedy of the commons," that is, the selfish exploitation of resources in the public domain, is a reason for many of our everyday social conflicts. However, humans are often more helpful to others than evolutionary theory would predict, unless indirect reciprocity takes place and is based on image scoring (which reflects the way an individual is viewed by a group), as recently shown by game theorists. We tested this idea under conditions that control for confounding factors. Donations were more frequent to receivers who had been generous to others in earlier interactions. This shows that image scoring promotes cooperative behavior in situations where direct reciprocity is unlikely.

1 Abteilung Verhaltensökologie, Zoologisches Institut, Universität Bern, 3032 Hinterkappelen, Switzerland.
2 Department of Biology, West Main Road, University of Utah, Salt Lake City, UT 84112, USA.
* Present address: Institute of Cell, Animal and Population Biology, University of Edinburgh, Edinburgh EH9 3JT, UK.

Contact: Claus Wedekind <>
Department of Evolutionary Ecology,
Max-Planck-Institute for Limnology
D-24306 Plön, Germany.

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