Collectively, these studies provide provocative evidence that the importance of genetic influences on drinking behaviors varies under different environmental circumstances, highlighting the importance of socio-cultural factors in the expression of genetic propensities for drinking outcomes. Positive GxE findings from twin studies were all in the predicted direction of effect, such that the relative importance of genetic influences on variance in drinking behaviors was greater in more permissive socio-cultural environments with easier access to alcohol and substance using peers, and lower in more restrictive social environments (cf. Turkheimer, Haley, Waldron, D’Onofrio, & Gottesman (2003) for a similar outcome regarding cognitive abilities). Results from adoption studies provided somewhat more limited support for a diathesis-stress model of GxE in which individuals’ genotypes influenced how likely they were to use or misuse alcohol in response to environmental adversity or stressors. In particular, sensitivity to the pathogenic effects of stressors on drinking was important for a less genetically influenced form of alcoholism with a later onset (Type I) among males.
