A common theme emerges across these findings of GxE interaction from the twin literature, namely that environments that exert more social control (e.g., higher parental monitoring, less migratory neighborhoods, etc.) tend to reduce genetic influences, whereas other environments allow greater opportunity to express genetic predispositions, such as those characterized by more deviant peers and greater alcohol availability. It is likely that many of the important moderating effects of the environment associated with alcohol use and related externalizing behavior reflect differences social control and/or opportunity, resulting in differential expression of individual predispositions (Shanahan & Hofer, 2005).
