The Heritability of Personality Is Not Always 50%: Gene‐Environment Interactions and Correlations Between Personality and Parenting

Abstract

Twin studies of personality are consistent in attributing approximately half of the variance in personality to genetic effects, with the remaining variance attributed to environments that make people within the same families different. Such conclusions, however, are based on quantitative models of human individual differences that estimate genetic and environmental contributions as constants for entire populations. Recent advances in statistical modeling allow for the possibility of estimating genetic and environmental contributions contingent on other variables, allowing the quantification of phenomena that have traditionally been characterized as gene-environment interaction and correlation. We applied these newer models to understand how adolescents' descriptions of their relationships with their parents might change or moderate the impact of genetic and environmental factors on personality. We documented notable moderation in the domains of positive and negative emotionality, with parental relationships acting to both enhance and diminish both genetic and environmental effects. We discuss how genetic and environmental contributions to personality might be more richly conceptualized as dynamic systems of gene-environment interplay -systems that are not captured by classical concepts, such as the overall heritability of personality. KeywordsTwin study; Behavior Genetics; Interpersonal Relationships Individual differences are heritable, by which we mean that genetic influences make a substantial contribution to individual differences in peoples' observable characteristics (or "phenotypes"). Indeed, this finding is so universal that Turkheimer (2000) enshrined it as the "first law" of behavior genetics. Turkheimer (2000) went on to propose second and third laws as well. The "second law" states that being raised in the same family has a smaller effect on individual differences than genetic effects. The "third law" is that a nontrivial portion of Correspondence concerning this article should be addressed to Robert F. Krueger, Department of Psychology, University of Minnesota, N414 Elliott Hall, 75 East River Road, Minneapolis, MN 55455−0344. Electronic mail may be sent to krueg038@umn.edu. NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript individual differences can be attributed to effects unique to each individual person, beyond genetic differences, and also beyond being raised in the same family.These laws are well-supported by an extensive literature, and they clearly apply to personality as much as they apply to other individual differences (for recent reviews of the behavior genetics of personality, see, e.g., Krueger, Johnson & Kling, 2006; Krueger & Johnson, in press). Indeed, these laws have had a fundamental impact on thinking in scientific psychology. Our late colleague David Lykken described the impact of behavior genetic studies as "rearranging the furniture in psychology's house." The "furniture," or the topics of interest in psychology, was not fund...

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