Watch Origins of the human mind online: Episode 15 Genes and Environments Together

How do genes and contextual factors produce individual differences in behavior? In the additive model of behavioral genetics, the 3 core infl uences on any traits are genes, shared environments, and non-shared environments—all of which are assumed to be independent of one another. Genes account for at least half of the variation in many traits; intriguingly, non-shared environmental infl uences are stronger than shared infl uences, calling into question many classic studies of parenting infl uences. In gene-environment interaction, certain genotypes are expressed only in certain environments but not others. Thus, genes and environments are interdependent; nature and nurture work together in unexpected ways to yield both strength and pathology.

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