Double Vision: Reply to Freese and Powell

Horwitz, Allan V.; Videon, Tami M.; E, Schmitz, Mark; Davis, Diane

doi:10.2307/1519804

Cited by 6 publications

(5 citation statements)

References 11 publications

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“… 4 I.e., Pam et al 1996, Joseph 1998, Kamin and Goldberger 2002, Rutter 2002, Horwitz et al 2003a and 2003b, Beckwith 2006, and Ehrlich and Feldman 2007.…”

Section: Notesmentioning

confidence: 99%

“… 11 Three notable exceptions include 1) a study looking at the environments of twins' first year of life, finding that twins disproportionately experience a number of developmental circumstances that raise questions about generalizing twins studies to the population at large (Ainslie et al 1987); 2) a study indicating that intrauterine environment may bias psychological and behavioral estimates of heritability (Prescott et al 1999); and 3) a study demonstrating social sources of shared twin behavior previously attributed largely to genetic influences (Horwitz et al 2003a and 2003b). …”

Section: Notesmentioning

confidence: 99%

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Twin Studies of Political Behavior: Untenable Assumptions?

Beckwith

Morris

2008

Perspect. polit.

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 One important reason the twin method has been superseded is that it depends upon several questionable assumptions, the most significant of which is known as the equal environments assumption.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

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“… 4 I.e., Pam et al 1996, Joseph 1998, Kamin and Goldberger 2002, Rutter 2002, Horwitz et al 2003a and 2003b, Beckwith 2006, and Ehrlich and Feldman 2007.…”

Section: Notesmentioning

confidence: 99%

Section: Notesmentioning

confidence: 99%

Twin Studies of Political Behavior: Untenable Assumptions?

Beckwith

Morris

2008

Perspect. polit.

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“…This would occur, for instance, if family members, teachers, and friends tended to treat identical twins more similarly than fraternal twins — which is what studies of twins have found. 38,39,40 This may be the source of the “mystery of missing heritability” arising from high estimates of heritability from twin studies, on the one hand, and, on the other, studies of the genome itself, which have turned up relatively few genes associated with various traits and explain only a fraction of the estimated heritability. Additionally, twin studies may likely produce inflated estimates for heredity by confounding purely genetic effects with gene-environment, and a host of potential genetic and epigenetic, interactions.…”

Section: Interpreting the Resultsmentioning

confidence: 99%

The “chicken-and-egg” development of political opinions

Beattie

2017

Polit. life sci.

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Twin studies have revealed political ideology to be partially heritable. Neurological research has shown that ideological differences are reflected in brain structure and response, suggesting a direct genotype-phenotype link. Social and informational environments, however, also demonstrably affect brain structure and response. This leads to a "chicken-and-egg" question: do genes produce brains with ideological predispositions, causing the preferential absorption of consonant information and thereby forming an ideology, or do social and informational environments do most of the heavy lifting, with genetic evidence the spurious artifact of outdated methodology? Or are both inextricably intertwined contributors? This article investigates the relative contributions of genetic and environmental factors to ideological development using a role-play experiment investigating the development of opinions on a novel political issue. The results support the view that the process is bidirectional, suggesting that, like most traits, political ideology is produced by the complex interplay of genetic and (social/informational) environmental influences.

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“…The EEA received an exorbitant amount of attention by scholars uncomfortable with physiological predictors that have been infiltrating the social science literature. Such criticisms emerged in sociology (Horwitz, Videon, Schmitz, & Davis, 2003), education psychology (Richardson & Norgate, 2005), and also in political science (Beckwith & Morris, 2008;Charney, 2008).…”

mentioning

confidence: 99%

“…From this perspective, Horwitz et al (2003) was most on track with their criticism of the EEA. Their article included an actual test that highlighted that MZ twins tend to share friends more often than DZ twins, and a specific mechanism on how this could influence their alcohol consumption heritability estimates.…”

mentioning

confidence: 99%

Do Heritability Estimates of Political Phenotypes Suffer From an Equal Environment Assumption Violation? Evidence From an Empirical Study

Littvay¹

2012

Twin Res Hum Genet

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Using data from the Minnesota Twins Political Survey, this paper tests for the presence of unequal environments (EEA) by zygosity in political attitudes. Equal environment measures used include shared bedroom, friends, classes, and dressing alike. Results show an EEA violation at p < .05 in 5% of the models tested. The violations' impact on heritability estimates and their confidence levels appear random in magnitude and direction. No reasonable post hoc explanation emerged for understanding the presence of the violation in some items but not others. This article establishes reasonable priors for the absence of EEA violations in political phenotypes based on the tested environmental components. The findings place the burden on critics to present theoretical work on the specific mechanisms of EEA violations based on which additional empirical assessments could (and should) be conducted.

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Double Vision: Reply to Freese and Powell

Cited by 6 publications

References 11 publications

Twin Studies of Political Behavior: Untenable Assumptions?

Twin Studies of Political Behavior: Untenable Assumptions?

The “chicken-and-egg” development of political opinions

Do Heritability Estimates of Political Phenotypes Suffer From an Equal Environment Assumption Violation? Evidence From an Empirical Study

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