Prosocial peer affiliation suppresses genetic influences on non-aggressive antisocial behaviors during childhood.

Affiliation with prosocial peers is thought to provide a critical buffer against the development of youth antisocial behavior (Deater-Deckard, 2001, Hektner et al., 2000, Kendler et al., 2008, Simonoff et al., 2004). It is thus not surprising to learn that a number of antisocial behavior interventions target peer affiliations (Feldman et al., 1983, Huey et al., 2000, Kazdin, 1987, Tremblay et al., 1995). Multisystemic Therapy, for example, is a well-regarded and highly disseminated treatment (Curtis et al., 2004) that, among other things, seeks to increase association with prosocial peers and decrease association with antisocial peers, thereby removing sources of reinforcement for antisocial behaviors and replacing them with reinforcement for prosocial activities. Given this relationship, it would be important to identify the processes underlying their association. The above treatment studies clearly point to an effect of socialization, such that prosocial peers can positively influence children’s behavior. In day-to-day life, however, children both select, and are selected by, each other as friends. Indeed, there is ample empirical evidence that children with antisocial behavior seek out and/or attract peers who are similarly inclined to engage in antisocial behaviors (Granic and Patterson, 2006, Kendler et al., 2008, Quinton et al., 1993). Although partially a function of their shared interests, there is also evidence that the affiliation of antisocial children with delinquent peers is the result of their rejection by prosocial peers because of their disruptive behaviors (Deater-Deckard, 2001, Hektner et al., 2000). Put together, the above results indicate that both socialization and selection (or more specifically, rejection) contribute to the negative association between prosocial peer affiliation and child antisocial behavior. Critically, however, we still know virtually nothing about the etiologic mechanisms through which these processes influence child antisocial behavior. One interesting possibility is that prosocial peer affiliation may exert its influence via a gene-environment interaction (GxE) process, whereby prosocial peer affiliation suppresses or deactivates the expression of genetic influences on antisocial behavior. Although researchers have discussed the notion that protective experiences might promote resilience to genetic risk (Lahey and Waldman, 2003, Rutter et al., 2006, Shanahan and Hofer, 2005), these discussions have been largely theoretical to date (for an exception, see Feinberg et al., 2007). We thus have little empirical insight into the pervasiveness of ‘GxE protection’ or the moderators that are most crucial. Importantly, the ability to identify GxE, including ‘GxE protection’, with any certainty hinges in part on a meaningful consideration of the gene-environment correlation (rGE), or genetically-influenced exposure to particular “environmental” experiences (Plomin et al., 1977, Scarr and McCartney, 1983). It may well be the case, for example, that what appears to be the suppression of genetic risk for antisocial behavior in the presence of prosocial peer affiliation may in fact reflect the rejection of children at genetic risk for antisocial behavior by their prosocial peers. In other words, what appears to be the moderation of genetic risk by environmental experience in fact reflects rGE processes. Researchers studying these processes should thus employ analytic techniques that circumvent possible rGE confounds. The current study sought to clarify whether prosocial peer affiliation reduces genetic influences on antisocial behavior, while controlling for the effects of selection (i.e., rGE). We specifically examined whether prosocial peer affiliation moderated the etiology of childhood antisocial behavior in a sample of 500 twin pairs, and conducted a series of analytic checks of those results to ensure that any positive GxE findings were indeed reflective of moderation by prosocial peer affiliation per se.