analysis and were able to account for only about a third of the missing heritability for personality. This method is considered “assumption free” in that unrelated individuals are compared to one another on the basis of similarity among measured genes, and therefore it provides a corroborating estimate of additive heritability. According to this study, two thirds of the variance traditionally assumed to be of genetic origin is due to rare genetic variants not captured by current genotyping technology, non-additive genetic effects (i.e., dominant genes, epistasis), dependencies between genes and environments, or other factors that would raise estimates of heritability in twin and family studies. Therefore, the totality of genetic influences on personality is unlikely to be found using common molecular genetic approaches. Non-additive genetic effects on personality are real possibilities that should be considered in ongoing work (see Keller, Coventry, Heath, & Martin, 2005; Rettew, Rebollo-Mesa, Hudziak, Willemsen, & Boomsma, 2008; Verweij et al., 2010). We were, however, unable to evaluate such nonadditive effects, as many of the primary studies included in our meta-analysis only reported results from models of additive genetic variation. As more evidence of nonadditive genetic effects accumulate, the trends in heritability, genetic stability, and genetic contributions
