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Science 5 May 2000:
Vol. 288. no. 5467, pp. 819 - 820
DOI: 10.1126/science.288.5467.819
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Perspectives

Also see the archival list of Science's Compass: Enhanced Perspectives

SOCIAL SCIENCE:
Enhanced: Shrewd Investments

Martin A. Nowak and Karl Sigmund

Why do we help others? There are two principal reasons according to evolutionary biologists: kin selection (we help those who are most closely related to us) and reciprocal altruism (we give to receive). Reciprocal altruism can be divided into direct reciprocity (the donor is rewarded by the recipient) and indirect reciprocity (the donor is rewarded by third parties). As Nowak and Sigmund explain in a Perspective, a psychology experiment in which students are asked to play a game where they donate money to others in the group demonstrates indirect reciprocity in action (Wedekind and Milinski,). Knowing the overall generosity score of their co-players (but not the individuals to whom co-players had been generous) students donated most often to the more generous individuals and less often to those with low scores.

M. A. Nowak is at the Institute for Advanced Study, Princeton University, Princeton, NJ 08540, USA. E-mail: nowak{at}ias.edu K. Sigmund is at the Institut fuer Mathematik, Universitaet Wien and International Institute for Applied Systems Analysis, Laxenburg, Austria. E-mail: karl.sigmund{at}univie.ac.at

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