Using a longitudinal, large-scale sample of British twins, we addressed the prediction of both cognitive abilities and behavioral adjustment from eight domains of environmental risk: minority status, socio-economic status, maternal medical factors, twin medical factors, maternal depression, chaos within the home environment, and parental feelings towards their children and discipline. Participants included 5765 families with twins (49.1% male) born in 1994 and 1995. Aspects of environmental risk were assessed from birth until the children's third birthdays; outcome measures were assessed at their fourth birthdays. Overall prediction of outcome (via multiple regression analysis) was moderate (R = .23 -.48). SES and chaos were the strongest predictors for the cognitive outcomes whereas for total behavior problems the more proximal parenting factors were also dominant. Future analyses will investigate these environmental risk indicators in the context of the genetically sensitive twin design.Correspondence should be sent to Alison Pike, Psychology
Obsessive-compulsive disorder is unlikely to be an etiologically homogeneous condition. There is substantial etiologic overlap across the different OC symptom dimensions, but dimension-specific genetic, and particularly nonshared environmental, factors are at least as important. Hoarding shares the least amount of genetic liability with the remaining symptom dimensions. The results have implications for the current deliberations regarding OCD and the inclusion of a putative hoarding disorder in DSM-5.
Harris argues that peer relationships are the chief determinants of personality development. Harris's thesis makes the behavioral genetic investigation of peer groups particularly timely. The present study examined genetic and environmental contribution to self-reported peer-group characteristics in two samples of adolescent siblings: 180 adoptive and nonadoptive sibling pairs from the Colorado Adoption Project, and 386 sibling pairs from the Nonshared Environment and Adolescent Development Study. Substantial genetic influence emerged for college orientation, with the remaining variance accounted for by nonshared environment. For delinquency, however, the majority of the variance was explained by nonshared environment. Although genetic influence was implicated for peer popularity in twin analyses, genetic factors were not important in explaining individual differences in nontwin siblings. These results suggest that although some dimensions of peers are somewhat mediated by genetic factors, nonshared environmental influence is substantial.
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