Critically, however, nearly all of these studies examined externalizing behavior in adolescence and emerging adulthood. The single largest exception examined antisocial behavior in 975 boys and found only trend-level evidence (p = 0.16) of a diathesis–stress G × E in childhood (Kim-Cohen et al. 2006). We thus know very little about G × E in childhood conduct problems, a surprising gap in the literature given that child-onset conduct problems are typically conceptualized as more severe and chronic than those beginning later in life (Moffitt, 1993, 2003). Although one could argue that studies conducted on adult antisocial behavior generalize to child conduct problems (as the former is often a consequence of the latter), this conclusion would be premature. Indeed, recent work has suggested that the etiological processes linking particular risk experiences to conduct problems may change over the course of development (Kendler et al. 2008). For example, although studies have uniformly indicated that deviant peer affiliation exacerbates genetic influences on conduct problems/externalizing behaviors during adolescence (Cleveland et al. 2005; Button et al. 2007; Harden et al. 2008; Beaver et al. 2009;
