Political Science, Department of


Date of this Version

October 2006


Cooperation has been a focus of intense interest in the biological and social sciences. Yet in spite of a tremendous effort to develop evolutionary models and laboratory experiments that explain the existence of cooperation in humans, relatively little effort has been invested in documenting the prevalence of largescale cooperation in well-mixed populations and the extent to which it may be the result of biological or social forces. In this article we study voter behaviour as a form of cooperation that bears close resemblance to theoretical models in which individuals in a large population make anonymous decisions about whether or not to contribute to a public good. Matching public voter turnout records to an adult twin registry, we compare concordance in political behaviour between monozygotic and dizygotic twins. The results show that the decision to cooperate by choosing to vote is primarily determined by genetic factors. These results suggest that humans exhibit genetic variation in their tendency to cooperate and that biological evolution has played an important role in the development of political cooperation.