Nature 437, 1291-1298 (27 October 2005) | doi:10.1038/nature04131

Evolution of indirect reciprocity

Martin A. Nowak1 & Karl Sigmund2,3


Natural selection is conventionally assumed to favour the strong and selfish who maximize their own resources at the expense of others. But many biological systems, and especially human societies, are organized around altruistic, cooperative interactions. How can natural selection promote unselfish behaviour? Various mechanisms have been proposed, and a rich analysis of indirect reciprocity has recently emerged: I help you and somebody else helps me. The evolution of cooperation by indirect reciprocity leads to reputation building, morality judgement and complex social interactions with ever-increasing cognitive demands.

  1. Program for Evolutionary Dynamics, Department of Organismic and Evolutionary Biology, Department of Mathematics, Harvard University, Cambridge, Massachusetts 02138, USA
  2. Faculty for Mathematics, University of Vienna, A-1090 Vienna, Austria
  3. IIASA, A-2631, Laxenburg, Austria

Correspondence to: Karl Sigmund2,3 Correspondence should be addressed to K.S. (Email:


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