Genetic predisposition and environmental influences are both important factors in the development of problematic behavior (e.g., externalizing, substance use) (Rhee et al. 2003). Since the risk originates in adolescence, there may be multiplicative influences of genes and social environment unique to this developmental stage. Externalizing behaviors in adolescence such as aggression and rule breaking (e.g., defiance, theft, and vandalism) are actions that harm others. While aggression decreases, rule breaking increases during adolescence from early through mid-to-late adolescence (Bongers et al. 2004; Pepler et al. 2010). These traits are genetically influenced (Hicks et al. 2004). One salient environmental predictor of problem behavior and subsequent substance use at this developmental stage is the influence of delinquent peers (Rubin et al. 2006) which appears to be more pronounced during early adolescence (before 15-year-old) (Kendler et al. 2011) and have a strong influence on the trajectory of externalizing behaviors (Steinberg et al. 1994; Kendler et al. 2008). A twin study in adolescence suggests that genetic influences on delinquent behavior increase with age (Burt and Neiderhiser 2009).
