With respect to the moderating influence of peers on associations between CHRM2 and development in externalizing behavior, our findings appear to fall in line with a diathesis-stress model, whereby affiliating with antisocial peers exacerbates one’s own biological predisposition to act out. It is possible, however, that this interpretation is an artifact of our use of median splits to plot the environmental effects, or of truncation at the positive end of the peer groups’ behavioral continuum. That is, CHRM2 could function more differentially, also protecting against the development of risky externalizing behavior in particularly prosocial peer environments (see Belsky et al., 2009). Future research is necessary to better characterize these effects. In addition, modeling gene-environment interactions within a regression framework does not allow us to differentiate between moderating and moderated variables. So, although our findings are presented in terms of moderating influence of peers’ behaviors on genetic susceptibility, it could also be conceived of as genetic moderation of the peer groups’ influences.
