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Not by Twins Alone: Using the Extended Family Design to Investigate Genetic Influence on Political Beliefs

Authors


Peter K. Hatemi is Assistant Professor of Political Science, University of Iowa, Iowa City, Iowa 52242 (phatemi@gmail.com). John R. Hibbing is Foundation Regents Professor of Political Science and Psychology, University of Nebraska–Lincoln, Lincoln, NE 68588 (jhibbing@unl.edu). Sarah E. Medland is a Research Officer in the Department of Genetic Epidemiology, Queensland Institute of Medical Research, 300 Herston Rd., Brisbane, Queensland, Australia (Sarah.Medland@qimr.edu.au). Matthew C. Keller is Assistant Professor of Psychology and Fellow of the Institute of Behavior Genetics, University of Colorado, Boulder, CO 80309 (matthew.c.keller@gmail.com). John R. Alford is Associate Professor of Political Science, Rice University, 6100 Main, Houston, TX 77251 (jra@rice.edu). Kevin B. Smith is Professor of Political Science, University of Nebraska–Lincoln, Lincoln, NE 68588 (ksmith1@unl.edu). Nicholas G. Martin is Laboratory Head of Genetic Epidemiology, Queensland Institute of Medical Research, 300 Herston Rd., Brisbane, Queensland, Australia (Nick.Martin@qimr.edu.au). Lindon J. Eaves is Distinguished Professor of Human Genetics and Psychiatry, Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA 23284 (ljeaves@vcu.edu).

Abstract

Variance components estimates of political and social attitudes suggest a substantial level of genetic influence, but the results have been challenged because they rely on data from twins only. In this analysis, we include responses from parents and nontwin full siblings of twins, account for measurement error by using a panel design, and estimate genetic and environmental variance by maximum-likelihood structural equation modeling. By doing so, we address the central concerns of critics, including that the twin-only design offers no verification of either the equal environments or random mating assumptions. Moving beyond the twin-only design leads to the conclusion that for most political and social attitudes, genetic influences account for an even greater proportion of individual differences than reported by studies using more limited data and more elementary estimation techniques. These findings make it increasingly difficult to deny that—however indirectly—genetics plays a role in the formation of political and social attitudes.

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