Hostname: page-component-586b7cd67f-t7czq Total loading time: 0 Render date: 2024-11-28T05:33:53.776Z Has data issue: false hasContentIssue false
  • English
  • Français

Twin Studies of Political Behavior: Untenable Assumptions?

Published online by Cambridge University Press:  13 November 2008

Jon Beckwith  and
Corey A. Morris
Jon Beckwith
Affiliation:
Department of Microbiology and Molecular Genetics, Harvard Medical School. E-mail: [email protected]
Corey A. Morris
Affiliation:
Program of Biological and Biomedical Sciences, Harvard Medical School. E-mail: [email protected]
Get access Rights & Permissions [Opens in a new window]

Abstract

Using the “classical twin method,” political scientists John Alford, Carolyn Funk, and John Hibbing conclude that political ideologies are significantly influenced by genetics, an assertion that has garnered considerable media attention. Researchers have long used human twins in attempts to assess the degree of genetic influence on various behavioral traits. Today, this methodology has been largely replaced in favor of contemporary molecular genetic techniques, and thus heritability studies have seen a diminishing role in behavioral genetic research of the twenty-first century. One important reason the twin method has been superseded is that it depends upon several questionable assumptions, the most significant of which is known as the equal environments assumption. Alford, Funk, and Hibbing argue that this crucial assumption, and thus their conclusion, holds up under empirical scrutiny. They point to several studies in support of this assumption. Here, we review the evidence presented and conclude that these attempts to test the equal environments assumption are weak, suffering significant methodological and inherent design flaws. Furthermore, much of the empirical evidence provided by these studies actually argues that, contrary to the interpretation, trait-relevant equal environments assumptions have been violated. We conclude that the equal environments assumption remains untenable, and as such, twin studies are an insufficient method for drawing meaningful conclusions regarding complex human behavior.

Type
Comment
Information
Perspectives on Politics , Volume 6 , Issue 4 , December 2008 , pp. 785 - 791
Copyright
Copyright © American Political Science Association 2008

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Ainslie, Ricardo C., Olmstead, Kelly M., and O'Loughlin, Daniel D.. 1987. The early developmental context of twinship: Some limitations of the equal environments hypothesis. American Journal of Orthopsychiatry 57 (1): 120–4.CrossRefGoogle ScholarPubMed
Alford, John R., Funk, Carolyn L., and Hibbing, John R.. 2005. Are political orientations genetically transmitted? American Political Science Review 99 (2): 153–68.CrossRefGoogle Scholar
Alford, John R., Funk, Carolyn L., and Hibbing, John R.. 2008. Beyond liberals and conservatives to political genotypes and phenotypes. Perspectives on Politics 6 (2): 321–28.CrossRefGoogle Scholar
Beckwith, Jon. 2006. Wither human behavioral genetics? In Wrestling with Behavioral Genetics: Science, Ethics, and Public Conversation, ed. Parens, E., Chapman, A., and Press, N.. Baltimore: Johns Hopkins University Press.Google Scholar
Beckwith, Jon, Geller, Lisa, and Sarkar, Sahotra. 1991. “IQ and Heredity.” [Letter to the Editor] Science 252 (5003): 191.Google Scholar
Bouchard, Thomas J. Jr., Lykken, David T., McGue, Matthew, Segal, Nancy L., and Tellegen, Auke. 1990. Sources of human psychological differences: The Minnesota Study of Twins Reared Apart. Science 250 (4978): 223–8.CrossRefGoogle ScholarPubMed
Cronk, Nikole J., Slutske, Wendy S., Madden, Pamela A.F., Bucholz, Kathleen K., Reich, Wendy, and Heath, Andrew. 2002. Emotional and behavioral problems among female twins: An evaluation of the equal environments assumption. Journal of the American Academy of Child and Adolescent Psychology 41 (7): 829–37.CrossRefGoogle ScholarPubMed
Ehrlich, Paul, and Feldman, Marcus W.. 2007. The fallacy of genetic reductionism. Dædalus Spring: 5–12.Google Scholar
Eriksson, Marit, Rasmussen, Finn, and Tynelius, Per. 2006. Genetic factors in physical activity and the equal environment assumption—the Swedish Young Male Twin Study. Behavior Genetics 36 (2): 238–47.Google Scholar
Flynn, James R. 2007 What Is Intelligence? Cambridge: Cambridge University Press.CrossRefGoogle Scholar
Horwitz, Allan V., Videon, Tami M., Schmitz, Mark F., and Davis, Diane. 2003a. Rethinking twins and environments: Possible sources for assumed genetic influences in twin research. Journal of Health and Social Behavior 44 (2): 111–29.Google Scholar
Horwitz, Allan V., Videon, Tami M., Schmitz, Mark F., and Davis, Diane. 2003b. Double vision: Reply to Freese and Powell. Journal of Health and Social Behavior 44 (2): 136–41.CrossRefGoogle ScholarPubMed
Joseph, Jay. 1998. The equal environment assumption of the classical twin method: A critical analysis. Journal of Mind and Behavior 19 (3): 325–58.Google Scholar
Joseph, Jay. 2004. The Gene Illusion. New York: Algora Publishing.Google Scholar
Kamin, Leon J., and Goldberger, Arthur S.. 2002. Twin studies in behavioral research: A skeptical view. Theoretical Population Biology 61 (1): 83–95.Google Scholar
Kendler, Kenneth S., Neale, Michael C., Kessler, Ronald C., Heath, Andrew C., and Eaves, Lindon J.. 1993. A test of the equal-environment assumption in twin studies of psychiatric illness. Behavior Genetics 23 (1): 21–7.CrossRefGoogle ScholarPubMed
Morris, Corey, Shen, Aimee, Pierce, Khadija, and Beckwith, Jon. 2007. Deconstructing violence. GeneWatch 20 (2): 3–9.Google Scholar
Morris-Yates, Allen, Andrews, Gavin, Howie, P., and Henderson, S.. 1990. Twins: A test of the equal environments assumption. Acta Psychiatrica Scandinavica 81 (4): 322–6.CrossRefGoogle ScholarPubMed
Pam, Alvin, Kemker, Susan S., Ross, Colin A., and Golden, R.. 1996. The “equal environments assumption” in MZ-DZ twin comparisons: An untenable premise of psychiatric genetics? Acta geneticae medicae et gemellologiae 45 (3): 349–60.Google Scholar
Plomin, Robert, Willerman, Lee, and Loehlin, John C.. 1976. Resemblance in appearance and the equal environments assumption in twin studies of personality traits. Behavior Genetics 6 (1): 43–52.Google Scholar
Prescott, Carol A., Johnson, Ronald C., and McArdle, John J.. 1999. Chorion type as a possible influence on the results and interpretation of twin study data. Twin Research 2 (4): 244–9.Google Scholar
Richardson, Ken. 1998. The Origins of Human Potential. London: Routledge.Google Scholar
Rutter, Michael. 2002. Nature, nurture, and development: From evangelism through science towards policy and practice. Child Development 73 (1): 1–21.CrossRefGoogle Scholar
Sampson, Robert J., Sharkey, Patrick, and Raudenbush, Stephen W.. 2008. Durable effects of concentrated disadvantage on verbal ability among African-American children. Proceedings of the National Academies of Sciences 105 (3): 845–52.Google Scholar
Scarr, Sandra, and Carter-Saltzman, Louise. 1979. Twin method: Defense of a critical assumption. Behavior Genetics 9 (6): 527–42.Google Scholar
Schaffner, Kenneth F. 2006. Behavior: Its nature and nurture. In Wrestling with Behavioral Genetics: Science, Ethics, and Public Conversation, ed. Parens, E., Chapman, A., and Press, N.. Baltimore: Johns Hopkins University Press.Google Scholar
Sober, Elliott. 2001. Separating nature and nurture. In Genetics and Criminal Behavior, ed. Wasserman, D.T. and Wachbroit, R.S.. Cambridge: Cambridge University Press.Google Scholar
Turkheimer, Eric. 2006. Mobiles: A gloomy view of research into complex human traits. In Wrestling with Behavioral Genetics: Science, Ethics, and Public Conversation, ed. Parens, E., Chapman, A., and Press, N.. Baltimore: Johns Hopkins University Press.Google Scholar
Turkheimer, Eric, Haley, Andreana, Waldron, Mary, D'Onofrio, Brian, and Gottesman, Irving I.. 2003. Socioeconomic status modifies heritability of IQ in young children. Psychological Science 14 (6): 623–8.CrossRefGoogle ScholarPubMed
Xian, Hong, Scherrer, Jeffrey F., Eisen, Seth A., True, William R., Heath, Andrew C., Goldberg, Jack, Lyons, Michael J., and Tsuang, Ming T.. 2000. Self-reported zygosity and the equal-environments assumption for psychiatric disorders in the Vietnam Era Twin Registry. Behavior Genetics 30 (4): 303–10.CrossRefGoogle ScholarPubMed