Studied continuity and change in general cognitive ability from infancy to adolescence in adoptees (107 children), biological siblings (87 pairs), and twins (224 monozygotic and 189 dyzygotic pairs). Findings generally support previous findings about genetic and environmental factors, with the exception that in the transition to adolescence,…

The genetic and environmental etiologies of sex-typed behavior were examined during the preschool years in a sample of 3,990 three- to four-year-old twin and nontwin sibling pairs. Results showed moderate genetic and significant shared environmental influence for boys and substantial genetic and moderate shared environmental influence for girls.…

Conducted a trivariate genetic analysis of the Home Observation for Measurement of the Environment (HOME), Mental Development Index (MDI), and Task Orientation (TO). Found that for 101 nonadoptive and 92 adoptive sibling pairs at 12 and 24 months of age, TO explained the remaining genetic variance on the HOME not explained by the MDI. (MDM)

Examined genetic and environmental contribution to self-reported peer-group characteristics among adoptive and nonadoptive adolescent sibling pairs. Found that although peer preference is influenced, in large part, by nonshared environment factors, genetic influence is present. Substantial genetic influence emerged for college orientation, and…

Explored aggression and delinquency in unrelated adoptive sibling pairs and biologically-related sibling pairs in the Colorado Adoption Project at 7, 9, 10, 11, and 12 years. Found that boys and adopted children were higher in externalizing behavior problems than girls and biologically related pairs. Sex differences in delinquency were more…

This chapter argues for the value of sibling research in addressing behavioral genetic issues on the etiology of individual differences. The goal of the report is to provide a set of simple and practical examples of sibling analyses in order to highlight the importance of incorporating siblings in future research. It begins with a discussion of…

This study of 707 sibling pairs, 10- to 18-years-old, examined parent-child and sibling interactions to determine the effects of genetics on family environment. The sample included identical and fraternal twins and full siblings in nondivorced families, as well as full, half, and unrelated siblings in divorced families. Found significant genetic…

This behavioral genetic study examined perceived competence and self-worth in same-sex twins, siblings, and stepsiblings 10 to 18 years old, and again 3 years later. Findings at second assessment showed six of seven subscales heritable. Genetic contributions to stability were found for perceived scholastic competence, athletic competence, physical…

Extensive data on twins, nontwin siblings, siblings separated by adoption, and parent-child similarity indicate that the heritability of intelligence is closer to .50 than to .70. Differences could be due to environmental or genetic changes in the population, or to methodology. (Author/CP)

Used the Sibling Inventory of Differential Experience with 396 adolescent and young adult children to determine the extent to which genetic differences between siblings or sibling differences in family constellation variables were responsible for differential experiences. (HOD)

Examined the genetic and environmental contributions to the predictive association between parenting and adolescent adjustment in identical and fraternal twins, and full, half, and genetically unrelated siblings in nondivorced and stepfamilies. Found that cross-lagged associations between parental conflict-negativity and adolescent antisocial…