Developmental studies have focused less on discrete events of childhood than on parenting behaviors and qualities of the family environment, some dimensions of which may reflect adversities of early rearing (Plomin, 1994). Parental warmth (and by its absence, affectless, chilly, or remote parental attention) has been studied extensively and shown to have substantial genetic variance. In their review, Kendler and Baker (2007) report weighted mean heritabili-ties of 37 and 34% for child-reported maternal and paternal warmth, respectively, and 35% for parents' descriptions of their own behaviors. Genetic influences appear to be substantially weaker for other parenting dimensions, such as negativity, control, and protectiveness, and again, whether reported by child (heritabilities of 15-26%) or parent (19-23%) (Kendler and Baker, 2007).
Along with absence of the father, family environments prone to discord and lacking in close interpersonal relationships have been of interest, in part, due to their association with girls' early pubertal development, which in turn increases the likelihood of a number of adolescent health outcomes, including problems of mood and conduct, early sexual activity, and teen pregnancy (Ellis, 2004). In twin studies, measures of family conflict and family cohesion show modest to moderate genetic influence, with weighted mean heritabilities in the Kendler and Baker (2007) review of 30 and 24%, respectively (Plomin et al, 1988, 1989; Jacobson and Rowe, 1999; Jang et al, 2001). In one other twin study, Krueger et al (2003) reported on the heritability of a retrospective measure of "perceived cohesion versus conflict in the family environment" derived from multiple environmental scales. The 16% of variance in this measure that could be attributed to heritable variation, moreover, was fully explained by genetic covariance with two personality factors, Negative Emotionality and Constraint. This finding suggests that people who, for genetic reasons, readily experience negative emotions and exhibit limited inhibitory control of their affect and behavior either tend to recollect their early family environments in ways colored by their personality (i.e., biased recall) or accurately recollect a family environment in which conflict was promoted and cohesion eroded via relatives' reactions to dispositional characteristics of the respondent, as expressed within the family. Unfortunately, the typical twin design is not well suited to detecting particular forms of gene-environment correlation, but adoption studies do provide examples of reactive geneenvironment correlation. In one such study, for instance, antisocial and substance abuse disorders among biological parents predicted both adolescent antisocial behaviors in their adopted-away offspring and harsher discipline and less nurturant parenting in the adolescents' adoptive parents. Importantly, structural modeling indicated that the adoptees' conduct problems mediated the relationship between psychopathologies of the biological parent and parenting behaviors of the adoptive parents (Ge et al, 1996; see also, O'Connor et al, 1998).
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