Genes and Environment

TL;DRAbstract

A classic approach to assessing the relative contributions of genes and environment to human behavior is to interrogate identical and fraternal twins. Hughes et al. have recruited 1116 pairs of twins (56% of whom are identical) in England and Wales and measured their performance at 5 years of age on a battery of theory-of-mind tasks, which collectively probe an understanding that beliefs can be false representations of reality (see also Perner and Ruffman, Perspectives, 8 April, p. 214). They find that genetic factors account for very little of the variance in task performance, and that shared (for example, siblings and social-economic status) and nonshared environmental factors each explain about half of the variance. The nonshared influences may come either from within the home, in the form of contrasting parental care, or from without, via interactions with socially skilled peers. It will be of interest to revisit these children in order to explore the relation between their theory-

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