men, regardless of birth cohort. Among women, however, they show that none of the variance is due to genetic factors in the early cohort but there is a consistent convergence in these estimates such that by the later cohort, there is no significant gender difference in the heritability of regular tobacco use. They argue that this is due to changes in the social restrictions on women’s tobacco use across these periods. As society became more permissive, it appears women were able to act in accordance with their own genetic predisposition, thereby increasing heritability. Timberlake et al. (2006) show that self-rated religiosity mutes the additive genetic component for smoking onset; they show an average heritability estimate of roughly sixty percent but this estimate drops to nearly zero among adolescents who report that religion is “more important than anything else” to them. In both cases, the heritability estimates are the smallest among those who are socialized in more controlled social environments with clearly established norms and corresponding sanctions against using substances. Low levels of PPD may also characterize environments with greater levels of social control because they are more stable, integrated, and supportive environments with greater resources to monitor adolescents’ behaviors effectively.
