Monoamine oxidase A gene (MAOA) predicts behavioral aggression following provocation
- aDepartment of Political Science, Brown University, 36 Prospect Street, Providence, RI 02912;
- bDepartment of Politics, Princeton University, Princeton, NJ 08544;
- cDepartment of Political Science, University of California, Santa Barbara, CA 943106;
- dResearch Centre for the Study of Bioscience, Biomedicine, Biotechnology, and Society, London School of Economics, Houghton Street, London WC2A 2AE, United Kingdom and European Molecular Biology Laboratory, I-00015 Monterotondo (Rome), Italy; and
- ePolitics and International Relations, University of Edinburgh, 15a George Square, Edinburgh EH8 9LD, Scotland
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↵1R.M. and D.T. contributed equally to this work.
Edited by Raghavendra Gadagkar, Indian Institute of Science, Bangalore, India, and approved December 11, 2008 (received for review September 2, 2008)

Abstract
Monoamine oxidase A gene (MAOA) has earned the nickname “warrior gene” because it has been linked to aggression in observational and survey-based studies. However, no controlled experimental studies have tested whether the warrior gene actually drives behavioral manifestations of these tendencies. We report an experiment, synthesizing work in psychology and behavioral economics, which demonstrates that aggression occurs with greater intensity and frequency as provocation is experimentally manipulated upwards, especially among low activity MAOA (MAOA-L) subjects. In this study, subjects paid to punish those they believed had taken money from them by administering varying amounts of unpleasantly hot (spicy) sauce to their opponent. There is some evidence of a main effect for genotype and some evidence for a gene by environment interaction, such that MAOA is less associated with the occurrence of aggression in a low provocation condition, but significantly predicts such behavior in a high provocation situation. This new evidence for genetic influences on aggression and punishment behavior complicates characterizations of humans as “altruistic” punishers and supports theories of cooperation that propose mixed strategies in the population. It also suggests important implications for the role of individual variance in genetic factors contributing to everyday behaviors and decisions.
Footnotes
- 2To whom correspondence should be addressed. E-mail: dominic.johnson{at}ed.ac.uk
Author contributions: R.M., D.T., and D.D.P.J. designed research; R.M., D.T., and J.C. performed research; D.T., G.F., and D.D.P.J. analyzed data; and R.M., D.T., and D.D.P.J. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
- © 2009 by The National Academy of Sciences of the USA