In recent years, there has been a proliferation of interest in identifying the environments that alter the relationship between one’s genetic predispositions and the likelihood that they will express conduct disorder (i.e., gene-by-environment interaction effects, or G × E). Thus, even an individual who has a high genetic loading for conduct problems may never go on to develop an actual disorder. Studies of twins have shown that the genetic influences on conduct disorder related phenotypes vary as a function of urban-rural residency (Legrand et al., 2008); peer deviance (Button et al., 2007); parent-child conflict (Burt and Klump, 2014); paternal drug dependence (Haber et al., 2010); and parental monitoring (Dick et al., 2007). These twin studies of G × E demonstrate that genetic variance for conduct disorder differs across levels of the environment. And across many of these latent G × E analyses, one theme that has emerged is that genetic variance for conduct disorder is higher in less restrictive environments (e.g., those characterized by higher peer deviance, less parental monitoring, or urban residency), which is consistent with the social opportunity
