In 2008, Kendler and colleagues30 examined these relative changes in the importance of genes and environment in substance use from early adolescence to middle adulthood. The study provides more support for an etiologic model in which initiation and early patterns of use are more strongly influenced by social and familial environmental factors, while later levels of use are more heavily influenced by genetic factors. The importance of environment has been theorized to reflect the important influence of social and familial structure that characterizes development across adolescence. Early on, there is usually less opportunity for adolescents to express their genetic predisposition, as more of their activities and decisions are influenced by figures of authority. As adolescents move into adulthood, and usually out of the social structure of their youth, emerging adults have more opportunity to express their genetic predispositions, choosing more freely their friends and activities. In some studies, it has been observed that some of the environmental influences are still evident after individuals moves out of their parents’ homes. This is believed to reflect personal values that one’s family or community has instilled in the individual, such as religious beliefs.
