There are several limitations to the current research that warrant caution regarding the conclusions we have drawn. First, the Cloninger scales may not represent a comprehensive assessment of personality, and it remains to be seen to what extent the results generalise to other personality traits, such as the Big Five. However, results from an international consortium show that SNP-based heritability estimates for two of the Big Five traits, Extraversion and Neuroticism, very closely accord with our results for the related traits Novelty Seeking and Harm Avoidance, respectively (Vinkhuyzen et al. in press). Second, we had to rely on previous twin-sibling studies for the heritability of Cloninger's scales due to all genetic variants. Twin-sibling studies provide fairly robust estimates of broad-sense heritability (i.e. H2 in Table 3), but they do not allow separate unbiased estimates of additive and nonadditive genetic variation (Keller and Coventry 2005; Keller et al. 2010). Extended twin-family designs (which can make good estimates of these parameters) are only available for Neuroticism (closely related to Cloninger's Harm Avoidance), for which a very large (N=45,850) study including parents, aunts/uncles,
