on tobacco or alcohol purchases. These policies influence mean levels of use (Kandel et al., 2004) but they may also be particularly effective in reducing both the variance as well as genetic tendencies to use and develop dependence on substances. As an example, Boardman (2008) shows that the heritability of daily smoking among adolescents is significantly attenuated within states that have the highest taxes per pack of cigarettes. Social network (meso-level) control emphasizes the norms, values, and sanctions developed and maintained by actors within a particular environment, i.e., the population itself develops norms and standards, rather than government or other institutions. Two previous studies have found support for the social network control model for the heritability of substance use. Kendler, Thornton, and Pedersen (2000) compared reported tobacco use among same-sex twin pairs across three birth cohorts (1910-1924; 1925-1939; and 1940-1958). According to their results, genetic factors account for fifty to sixty percent of the variance in regular tobacco use for 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
