The genetic correlation between alcohol use and peer alcohol use (rA=0.83, Figure 2A) is effectively gene-environment correlation (rGE). However, it is not clear from these analyses whether this is active vs. evocative rGE (Jaffee and Price, 2008), or a combination thereof. In the former, one’s genotype not only affects their own phenotype, it also makes them more likely to select a particular environment (e.g., an individual’s genetically influenced impulsive behavior might result in exposure to dangerous situations). In the latter, one’s genetically influenced phenotype evokes a reaction among others (e.g., a child who exhibits problem behavior might experience high levels of physical discipline). Here, it seems plausible that individuals with a genetic liability toward high alcohol consumption might also have a genetic propensity to seek out peers who use alcohol excessively (active rGE), and previous research in this sample has identified a strong genetic component to choice of peers (Kendler et al., 2007). Evocative rGE cannot be ruled out, though how it would be operating in this context in a way that is not accounted for by other components of
