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SOCIAL SCIENCES / BIOLOGICAL SCIENCES / ECONOMIC SCIENCES / ANTHROPOLOGY
Heritability of cooperative behavior in the trust game
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*Department of Economics, Massachusetts Institute of Technology, 50 Memorial Drive, Cambridge, MA 02142; Political Science Department, University of California at San Diego, 9500 Gilman Drive 0521, La Jolla, CA 92093-0521; Department of Economics, Stockholm School of Economics, Box 6501, SE-113 83 Stockholm, Sweden; and ¶Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Box 281, SE-171 77 Stockholm, Sweden
Edited by Elinor Ostrom, Indiana University, Bloomington, IN, and approved January 15, 2008 (received for review October 23, 2007)
Although laboratory experiments document cooperative behavior in humans, little is known about the extent to which individual differences in cooperativeness result from genetic and environmental variation. In this article, we report the results of two independently conceived and executed studies of monozygotic and dizygotic twins, one in Sweden and one in the United States. The results from these studies suggest that humans are endowed with genetic variation that influences the decision to invest, and to reciprocate investment, in the classic trust game. Based on these findings, we urge social scientists to take seriously the idea that differences in peer and parental socialization are not the only forces that influence variation in cooperative behavior.
behavioral genetics | cooperation | experimental economics
Author contributions: D.C., C.T.D., J.H.F., M.J., P.L., and B.W. designed research; D.C., C.T.D., J.H.F., M.J., P.L., and B.W. performed research; C.T.D. and J.H.F. analyzed data; and D.C., C.T.D., J.H.F., M.J., and B.W. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0710069105/DC1.
|| There were several minor differences in implementation between the Swedish and U.S. experiments. In Sweden, subjects were paired with other twins (not their sibling) and paid several days later. Investors had six choices of how much to send the trustee, and trustees used the strategy method (they indicated how they would react to any possible amount sent prior to observing investor behavior). In contrast, subjects in the U.S. were paired with nontwins and paid immediately. Investors had 11 choices of the amount to send the trustee, and trustees observed investor behavior when deciding how much to send back.
** Such a conclusion rests on the assumption that it is possible to draw some evolutionary inference from economic experiments. We believe this is likely to be the case but also acknowledge that the usual caveats are in order. For instance, weak ecological validity may render such inference difficult. For a careful discussion of the various methodological problems in eliciting trust experimentally, see Cox (27).
A relatively low estimate of common environmental influences means that in the two populations studied, differences in common environment are not an important source of phenotypic variation. This finding does not justify any conclusions about the influence of environmental manipulations in general. It is, for instance, possible that the reason why the estimated effect of common environment is so low is that there is little variation in how parents transmit trust attitudes to their children.
To whom correspondence should be addressed. E-mail: jhfowler{at}ucsd.edu
© 2008 by The National Academy of Sciences of the USA
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