There is an emerging literature documenting how specific environmental factors moderate the importance of genetic effects. A growing number of variables have been shown to moderate the relative importance of genetic effects on substance use and dependence and externalizing behavior. Among the environmental moderators being studied are childhood stressors (emotional, physical, and sexual abuse), availability and access to drugs and alcohol, peer-group antisocial and prosocial behavior, religiosity, parental attitudes toward drugs and alcohol, parental monitoring, and socioregional factors. Religiosity has been shown to moderate genetic influences on alcohol use among females, with genetic factors playing a larger role among individuals without a religious upbringing.41 Social contact and cotwin dependency42 have also been shown to moderate twin similarity, with reduced genetic effects and enhanced environmental influences among more codependent pairs. Genetic influences on adolescent substance use are also enhanced in environments with lower parental monitoring.43 These analyses suggest that when adolescents receive little parental monitoring, it creates an environment that allows for greater opportunity to express genetic predispositions. The moderating effects of peer alcohol use on adolescent drinking has been shown
