to both the genotype and the environment of their children. Thus, for example, genetic factors influence parent–child relations [46] and parent–child relations influence peer selection (with poor parent–child relationships quality is associated with affiliation with deviant peers; [47]). Given that the relationship between peer and own alcohol use is potentially reciprocal [6], it is plausible that genetic factors create a risk environment which influences adolescent alcohol use. Given the cross-sectional nature of the present study, it was not possible to further distinguish between these processes. Peer influences are one of the strongest risk factors for adolescent alcohol involvement [3] and therefore a powerful potential domain for intervention. These results suggest individual differences in interactions with peers, which are influenced by genetic as well as environmental influences. It appears that to be most efficacious, peer-based interventions need to take into account these individual differences in addressing the relationship between peer influences and adolescent alcohol use.
