Externalizing behaviors are pervasive, widespread, and disruptive across a multitude of settings and developmental contexts. While the conventional diathesis-stress model typically measures the disordered end of the spectrum, studies that span the range of behavior, from externalizing to competence behaviors, are necessary to see the full picture. To that end, this study examined the additive and nonadditive relations of a dimension of parenting (ranging from warm to rejecting), and variants in dopamine, vasopressin, and neuropeptide-y receptor genes on externalizing/competence in a large sample of predominantly Caucasian twin children in toddlerhood, middle childhood, and early adolescence. Variants within each gene were hypothesized to increase biological susceptibility to both negative and positive environments. Consistent with prediction, warmth related to lower externalizing/higher competence at all ages. Earlier levels of externalizing/competence washed out the effect of parental warmth on future externalizing/competence with the exception of father warmth in toddlerhood marginally predicting change in externalizing/competence from toddlerhood to middle childhood. Warmth was a significant moderator of the heritability of behavior in middle childhood and early adolescence such that behavior was less heritable (mother report) and more heritable (father report) in low warmth environments. Interactions with warmth and the dopamine and vasopressin genes in middle childhood and early adolescence emphasize the moderational role gene variants play in relations between the rearing environment and child behavior. For dopamine, the long variant related to increased sensitivity to parent warmth such that the children displayed more externalizing behaviors when exposed to rejection but they also displayed more competence behaviors when exposed to high warmth. Vasopressin moderation was only present under conditions of parental warmth, not rejection. Interactions with neuropeptide-y and warmth were not significant. The picture that emerges is one of gene-environment interplay, wherein the influence of both parenting and child genotype each depend on the level of the other. As genetic research moves forward, gene variants previously implicated as conferring risk for disorder should be reexamined in conjunction with salient aspects of the environment on the full range of the behavioral outcome of interest.

The interplay of genes and environment on children's development is a complex dynamic process. As behavior geneticists begin to model protective as well as risk factors, and interactive as well as main effect influences, development is elucidated. It was hypothesized that positive parenting, a quality home environment, and high family cohesion would moderate the heritability of three components of temperament: Effortful Control, Negative Affectivity, and Extraversion/Surgency. Participants were drawn from the Wisconsin Twin Project and consisted of 1573 twins (51% boys), 88.5% Caucasian, M=7.93 years (SD=0.87). Higher order composites for the parenting and family environment moderators were formed from mother and father reports of Behavior Management Self-Assessment, Child Rearing Practices Report, Family Assessment Device, and Family Conflict Scale. Measures of the home environment (LEOS Living Environment Observation Scale and CHAOS Confusion, Hubbub, and Order Scale) were not composited due to the nature of the variables. Correlational analyses showed a majority of the temperament and environmental measures to be correlated (rs = -.49-.57). For Effortful Control, Negative Affectivity, and Extraversion/Surgency, estimates for the heritability and nonshared environment were 0.60 and 0.40, 0.80 and 0.20, and 0.59 and 0.41, respectively, with no significant main effects of the shared environment. Models incorporating environmental moderation of these estimates yielded parenting as a significant moderator for Negative Affectivity, LEOS for Effortful Control and Extraversion/Surgency, and CHAOS for Effortful Control and Extraversion/Surgency. Results suggest that the quality of the family environment may act as a permissive or determinative influence on the heritability and expression of temperament. Future analyses include the examination of interactive genetic influences. These findings underscore the importance of shared environment, and support the recent literature on the benefits of positive influences on children's development.