The effect of parental SUD liability phenotype on the child's peers’ deviance, growing over time (due to both contemporaneous and lagged effects), is consistent with both growing disconnection from parents (which is likely to be contributed by the higher level of maltreatment from drug-using parents) and the increasingly active homophilic choice of deviant peers (Kirillova et al., 2008). Inasmuch as homophily results from the individual's selection into, and/or his choice of, a behaviorally similar peer group, its genetic effects are similar to the effects of phenotypic assortative mating (Guo, 2006; Vanyukov, 2004). The phenotypic correlation between peers can induce higher genetic (in proportion to heritability) and environmental similarity between the unrelated members of the group, such as a gang. This would further augment the active genotype–environment correlation (Scarr and McCartney, 1983), insofar as the choice of environment (peer behavior) will be in part genetically mediated. Indeed, the choice of delinquent peers is significantly heritable (Button et al., 2007; Walden et al., 2004) and genetically correlated with conduct problems, reflecting active genotype–environment correlation compounded with the reciprocal influence of peers on
