The Left and the Right, Part II: Eleven Genetic Studies

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My recent post, entitled “The Left and the Right: Physiology, Brain Structure and Function, and Attentional Differences,” is the most highly trafficked on this blog since it came to its new home here in September. But as I said then, it is just the beginning of the body of research on liberals and conservatives.

Here, then, is the second post listing such studies. It is in a different genre: Genetics.

The idea that our political preferences may be at least partly traceable to genetic influences is, it is fair to say, wildly controversial. However, the growing body of science makes it pretty hard to deny. That’s not to say that environmental influences don’t matter–but genetic influences at this point appear undeniable.

I want to underscore this: Whatever the chattering classes may say, whatever knee jerk reactions may come from ideologues, there is a large body of peer-reviewed research demonstrating the genetic transmission of political attitudes. This research has been done with vast subject pools (of twins; read here on how twin studies work and why they are so important) and it has been funded by leading government agencies. It has been conducted in multiple countries. It goes back decades.

Herewith, then, are eleven published scientific papers on the matter, arranged in chronological order so you can see how knowledge has developed and how new methodologies are now coming online. A number of the earlier findings are also summarized here, which is where I got some of the heritability estimates below (sometimes these things are tough to find in the original papers themselves):

Martin, N. G., L. J. Eaves, A. C. Heath, et al. 1986. ‘‘Transmission of Social Attitudes.’’ Proceedings of the National Academy of Sciences 15: 4364–68. Summary: Study of monozygotic (“identical”) and dizygotic (“fraternal”) twin pairs in Australia and the UK shows the heritability of numerous socio-political attitudes, such as views on the death penalty. Heritability of responses to the Wilson-Patterson conservatism scale is estimated at .62 (or 62 %). Note: None other than E.O. Wilson communicated this study to PNAS.

Eaves LJ, Martin NG, Heath AC, Schieken R, Meyer J, Silberg J, Neale M, Corey L. 1997. “Age changes in the causes of individual differences in conservatism,” Behavioral Genetics, 27:121–124. Summary: Relationship between genes and conservatism grows stronger with age in another sample of “identical” and “fraternal” twins.

Eaves, L. J., A. C. Heath, N. G. Martin, et al. 1999. ‘‘Comparing the Biological and Cultural Inheritance of Personality and Social Attitudes in the Virginia 30,000 Study of Twins and their Relatives.’’ Twin Research 2: 62–80. Summary: A large study of twin pairs in Virginia, and their family members, once again finds strong genetic influences on political attitudes and notes, “The significant contribution of genetic factors to social attitudes means that virtually no measurable aspect of human behavioral variation is so far removed from the impact of events at the genetic level as to be considered in complete isolation from the emerging theory and knowledge in genetics and sociobiology.” Estimated heritability of responses to the same Wilson-Patterson scale is .55 (that is averaged across genders; actual results were .65 for males, .45 for females).

McGue, Matt, T.J. Bouchard, N.L. Segal, A. Tellegen, M. Keyes & R. Krueger, 2003. “Evidence for the construct validity and heritability of the Wilson-Patterson conservatism scale: A Reared-apart twins study of social attitudes,” Personality and Individual Differences, Vol 34(6), 959-969. Summary: In a smaller study of Minnesota twins, the estimated heritability of conservatism is once again in the same range: .56.

Thomas J. Bouchard and Matt McGue, 2003. “Genetic and Environmental Influences on Human Psychological Differences,” Journal of Neurobiology, vol. 54, No. 1, p. 4-45. Summary: A helpful review article summarizing the papers above and finding that “there is now strong evidence that virtually all individual psychological differences, when reliably measured, are moderately to substantially heritable.” That includes political ideology.

Alford JR, Funk CL, Hibbing JR. 2005. “Are political orientations genetically transmitted?” American Political Science Review, Vol. 99, No. 2, May 2005:153–67. Summary: Important paper bringing the twins research cited above into mainstream political science thinking. The paper presents more data on a large sample U.S. and Australian twins, and once again captures the heritability of ideological attitudes (but the effect of genes on political party affiliation is much weaker).

Peter K. Hatemi et al, 2009. “Genetic and Environmental Transmission of Political Attitudes Over a Life Time,” Journal of Politics, Vol. 71, No. 3, p. 1141-1156. Summary: The influence of genetics on one’s political outlook appears to manifest itself in early adulthood for those who “leave the nest,” and are not in the family home where they grew up. Before that, in the family home, “environmental” influences appear dominant.

Peter K. Hatemi et al, 2009. “Is There a Party in Your Genes?” Political Research Quarterly 62(3):584-600. Summary: Genes appear to have little effect on political party affiliation–suggesting that unlike ideology, it is largely culturally transmitted–but do seem to affect the strength or intensity of partisan attachment.

Jaime E. Settle et al, “Friendships Moderate an Association Between a Dopamine Gene Variant and Political Ideology,” Journal of Politics, Vol. 72, No. 4, October 2010, p. 1189-1198. Summary: The famous “liberal gene” study, finding a direct relationship between a gene variant associated with novelty seeking and political liberalism–but only in a certain “environmental” context, namely, when you had a lot of friends growing up.

Peter K Hatemi et al, “A Genome-Wide Analysis of Liberal and Conservative Political Attitudes,” The Journal of Politics, Vol. 73, No. 1, January 2011, pp. 1-15. Summary: This is the scientific cutting edge–13,000 people are given political questionnaires and genome scans to try to find actual regions of the genome correlated with their political opinions. Some tantalizing results emerge.

Kevin B. Smith et al, 2011. “Linking Genetics and Political Attitudes: Reconceptualizing Political Ideology,” Political Psychology, Volume 32, Issue 3, pages 369–397. Summary: It is suggested that the way in which genes influence politics is through differing preferences for rules, order, and social stability. Note: This is the paper you really need to read if you want to make sense of how genes could ultimately be influencing political views (even if not directly; there are clearly many intermediate stages in the process), and why political ideology seems to be so strongly heritable. To quote one key sentence: “In this paper, we present the individual steps by which genetics connect to neurotransmitter systems which connect to cognitive and emotional processing tendencies which connect to values and personality traits which connect to orientations to bedrock principles which finally connect to preferences on specific political issues of the day.”

This is, again, just a sample of the research that is out there; I suspect there is a great deal more in the hopper. This is a rapidly growing field, not a shrinking one. This is the future.

So to summarize: I’ve already shown that multiple studies suggest physiological, attentional, and brain structure and function differences between liberals and conservatives. Now, I’ve also shown that multiple studies suggest genetic influences on political ideology. In neither case are these the only influences, but they appear substantial and measurable.

The evidence is pretty hard to argue with, no? How to interpret it, of course, is a very different matter–and one we can get into–but ignoring it does not seem to be an option.

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