Skip to main content
    • Aa
    • Aa

Twin Studies of Political Behavior: Untenable Assumptions?

  • Jon Beckwith (a1) and Corey A. Morris (a2)

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 One important reason the twin method has been superseded is that it depends upon several questionable assumptions, the most significant of which is known as the equal environments assumption.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.

Linked references
Hide All

This list contains references from the content that can be linked to their source. For a full set of references and notes please see the PDF or HTML where available.

Ricardo C. Ainslie , Kelly M. Olmstead , and Daniel D. O'Loughlin . 1987. The early developmental context of twinship: Some limitations of the equal environments hypothesis. American Journal of Orthopsychiatry 57 (1): 120–4.

Thomas J. Bouchard Jr., David T. Lykken , Matthew McGue , Nancy L. Segal , and Auke Tellegen . 1990. Sources of human psychological differences: The Minnesota Study of Twins Reared Apart. Science 250 (4978): 223–8.

Nikole J. Cronk , Wendy S. Slutske , Pamela A.F. Madden , Kathleen K. Bucholz , Wendy Reich , and Andrew Heath . 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.

Marit Eriksson , Finn Rasmussen , and Per Tynelius . 2006. Genetic factors in physical activity and the equal environment assumption—the Swedish Young Male Twin Study. Behavior Genetics 36 (2): 238–47.

Allan V. Horwitz , Tami M. Videon , Mark F. Schmitz , and Diane Davis . 2003a. Rethinking twins and environments: Possible sources for assumed genetic influences in twin research. Journal of Health and Social Behavior 44 (2): 111–29.

Allan V. Horwitz , Tami M. Videon , Mark F. Schmitz , and Diane Davis . 2003b. Double vision: Reply to Freese and Powell. Journal of Health and Social Behavior 44 (2): 136–41.

Jay Joseph . 2004. The Gene Illusion. New York: Algora Publishing.

Leon J. Kamin , and Arthur S. Goldberger . 2002. Twin studies in behavioral research: A skeptical view. Theoretical Population Biology 61 (1): 8395.

Kenneth S. Kendler , Michael C. Neale , Ronald C. Kessler , Andrew C. Heath , and Lindon J. Eaves . 1993. A test of the equal-environment assumption in twin studies of psychiatric illness. Behavior Genetics 23 (1): 21–7.

Allen Morris-Yates , Gavin Andrews , P. Howie , and S. Henderson . 1990. Twins: A test of the equal environments assumption. Acta Psychiatrica Scandinavica 81 (4): 322–6.

Robert Plomin , Lee Willerman , and John C. Loehlin . 1976. Resemblance in appearance and the equal environments assumption in twin studies of personality traits. Behavior Genetics 6 (1): 4352.

Carol A. Prescott , Ronald C. Johnson , and John J. McArdle . 1999. Chorion type as a possible influence on the results and interpretation of twin study data. Twin Research 2 (4): 244–9.

Michael Rutter . 2002. Nature, nurture, and development: From evangelism through science towards policy and practice. Child Development 73 (1): 121.

Robert J. Sampson , Patrick Sharkey , and Stephen W. Raudenbush . 2008. Durable effects of concentrated disadvantage on verbal ability among African-American children. Proceedings of the National Academies of Sciences 105 (3): 845–52.

Sandra Scarr , and Louise Carter-Saltzman . 1979. Twin method: Defense of a critical assumption. Behavior Genetics 9 (6): 527–42.

Elliott Sober . 2001. Separating nature and nurture. In Genetics and Criminal Behavior, ed. D.T. Wasserman and R.S. Wachbroit . Cambridge: Cambridge University Press.

Eric Turkheimer , Andreana Haley , Mary Waldron , Brian D'Onofrio , and Irving I. Gottesman . 2003. Socioeconomic status modifies heritability of IQ in young children. Psychological Science 14 (6): 623–8.

Hong Xian , Jeffrey F. Scherrer , Seth A. Eisen , William R. True , Andrew C. Heath , Jack Goldberg , Michael J. Lyons , and Ming T. Tsuang . 2000. Self-reported zygosity and the equal-environments assumption for psychiatric disorders in the Vietnam Era Twin Registry. Behavior Genetics 30 (4): 303–10.

Recommend this journal

Email your librarian or administrator to recommend adding this journal to your organisation's collection.

Perspectives on Politics
  • ISSN: 1537-5927
  • EISSN: 1541-0986
  • URL: /core/journals/perspectives-on-politics
Please enter your name
Please enter a valid email address
Who would you like to send this to? *


Altmetric attention score

Full text views

Total number of HTML views: 5
Total number of PDF views: 23 *
Loading metrics...

Abstract views

Total abstract views: 451 *
Loading metrics...

* Views captured on Cambridge Core between September 2016 - 23rd August 2017. This data will be updated every 24 hours.