Understanding Heritability by Explaining Heritability: Recent Developments in Behaviour Genetics Tell Us More

Johnson, Penke, and Spinath (2011) extensively discuss the limitations of heritability estimates obtained from twin studies in understanding the role of genes on behavioural traits. They plead for more advanced modeling and a focus on gene– environment interplay. We review the results from advanced modeling and molecular genetic research and argue that gene– environment interplay is not likely to be the main factor in explaining heritability. It is anticipated that future developments in these areas will provide an even more complete picture on the genetic and environmental mechanisms underlying behavioural traits. Johnson et al. (2011) extensively discuss the limitations of heritability estimates obtained from twin studies in understanding the role of genes and environment on behavioural traits. They make three important points about heritability. First, heritability depends on how the trait under interest is measured. For example, measurement error and low item endorsement frequencies tend to lower heritability. Second, when heritability is based on the classical twin design, it can be biased if the assumptions of this design are violated. These assumptions include the absence of assortative mating, gene–environment interaction and correlation. Third, heritability tells us little about the underlying biology of a trait, because biology is only one of the factors that influence the magnitude of heritability estimates. They plead for more advanced modeling and a focus on gene–environment interaction and correlation (‘interplay’). In this commentary, we introduce two types of advanced modeling that we feel remain underexposed: extended twin family designs and causal modeling. We further review some recent molecular genetic studies and theoretical developments that illustrate the progress in explaining the heritabilities of complex traits. We argue that the results from these approaches suggest that gene–environment interplay is not likely to be the main factor in explaining heritability. EXTENDED TWIN FAMILY DESIGNS Extended twin family designs test assumptions underlying the classical twin design and can address more complex questions about the influence of genetic and environmental factors than the classical twin design (Eaves et al., 1978; Keller et al., 2009). Twin‐sibling studies on personality (e.g. neuroticism, extraversion, sensation seeking) and related traits converge on the finding that the heritabilities of these traits represent both additive and non‐additive genetic influences (Keller Discussion 271 Copyright © 2011 John Wiley & Sons, Ltd. Eur. J. Pers. 25: 267–286 (2011)