Shared environmental influences on personality: a combined twin and adoption approach.

Abstract

In the past, shared environmental influences on most personality traits have been found to be negligible in behavior genetic studies (e.g., Bouchard & McGue, 2003). However, most studies have been based on biometrical modeling of twins only. Failure to meet key assumptions of the classical twin design could lead to biased estimates of shared environmental effects. Alternative approaches to the etiology of personality are needed. In the current study we estimated the impact of shared environmental factors using both twin and adoption data. We found evidence for shared environmental influence on MPQ Alienation, Harm Avoidance, and Traditionalism scales and that with one exception, biometrical models constraining parameter estimates to be equal across study type (twins vs. adoptees) fitted no worse than models allowing these parameters to vary.