Some political scientists have argued in recent years that twin research shows that genetic factors play an important role in shaping political attitudes, ideologies, and behavior. Moreover, some researchers claim to have identified genes for political traits at the molecular level. The author argues that the main theoretical assumption of the twin method, which holds that monozygotic and dizygotic twin pairs experience equal environments, is untenable. Therefore, the results of twin studies can be completely explained by nongenetic factors. The author also argues that recent gene discovery claims in political science are unlikely to be replicated. He concludes that because genetic interpretations of twin study results are confounded by environmental factors, political scientists have no reason to revise previous socialization theories of political traits.
Keywords: behavioral genetics; equal environment assumption; genetics; political science; twin study; molecular genetics; voting
Since at least 2005, political scientists Alford, Funk, and Hibbing (2005) and others have argued that differences in political orientation and behavior have an important genetic basis (others making such claims include Alford, Funk, & Hibbing, 2008a, 2008b; Bell, Shermer, & Vernon, 2009; Fowler, Baker, & Dawes, 2008; Fowler & Dawes, 2008; Hatemi, Alford, Hibbing, Martin, & Eaves, 2009; Hatemi, Medland, & Eaves, 2009; Hatemi, Medland, Morely, Heath, & Martin, 2007; Medland & Hatemi, 2009; Hatemi et al., 2010). Intuitively, we might reject such an idea out of hand, yet the past few years have seen claims that the link between genes and political behavior and attitudes has been established by twin research. This has led to the creation of the nascent field of "genopolitics" and to the claim that there is a "developing consensus that genes play an important role in political behavior" (Settle, Dawes, & Fowler, 2009, p. 601).
It is my understanding that political scientists take quantitative empirical methodology very seriously. Thus, one can only welcome a thorough evaluation of twin research by this field. This does not usually occur in psychiatry and psychology, where journals regularly publish the results of behavioral genetic research with little or no critical analysis. Conversely, genetic theories and claims have sparked a debate in political science on the validity of twin research (for criticism of twin research in political science, see Beckwith & Morris, 2008; Charney, 2008a, 2008b, 2010; Suhay, Kalmoe, & McDermott, 2007; for responses to these critics, see Alford et al., 2008a, 2008b; Hannagan & Hatemi, 2008).
What concerns us here is the possible role of genetic influences on individual differences in political attitudes and behavior, not the undisputed fact that human beings are the product of both their genes and their environments. Political scientists Hannagan and Hatemi (2008) stated the obvious when they wrote, mistakenly implying that critics of genetic research disagree, "The scientific community recognizes that genes are very much a part of what it means to be human" (p. 332). We might as well say that the scientific community recognizes that Barack Obama won the 2008 U.S. presidential election. Human behavioral genetic researchers, however, are concerned with trait variation in the population and usually conclude that heredity plays an important role in explaining this variation.
In their twin study, Alford et al. (2005) concluded that "genetics plays an important role in shaping political attitudes and ideologies" (p. 153). They reached this conclusion on the basis of finding a significantly higher correlation of MZ (monozygotic, identical) versus same-sex DZ (dizygotic, fraternal) twin pairs on Wilson-Patterson Attitude Inventory scores. They used the "classical twin method" (hereafter the "twin method"; political science twin researchers sometimes refer to the twin method as the "classical twin design"). …