Explored genetic and environmental etiologies of individual differences in printed word recognition and related skills in identical and fraternal twin 8- to 18-year-olds. Found evidence for moderate genetic influences common between IQ, phoneme awareness, and word-reading skills and for stronger IQ-independent genetic influences that were common…

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…

Used data from sibling pairs from the National Longitudinal Study of Adolescent Health to examine how parental education moderated the genetic and environmental contributions to variation in verbal IQ. Found that the variance estimate for heritability was greater than that for shared environment for the whole sample. Both estimates were moderated…

The present study combined parallel data from the Northeast-Northwest Collaborative Adoption Projects (N2CAP) and the Western Reserve Reading Project (WRRP) to examine sibling similarity and quantitative genetic model estimates for measures of reading skills in 272 school-age sibling pairs from three family types (monozygotic twins, dizygotic…

Determinants of Schaefer's (1965) three dimensions of perceived parenting (Acceptance vs. Rejection, Psychological Control vs. Psychological Autonomy, and Firm vs. Lax Control) were investigated by administering a shortened Children's Reports of Parental Behavior Inventory to adolescent twins. The sample consisted of 46 pairs of identical twins…

This paper describes a study which examined the performance of 48 pairs of 18-month-old twins on the Mental Development Scale of the Bayley Scales of Infant Development to determine whether score differences would be found for the three subgroups of identical, fraternal same-sexed, and fraternal opposite-sexed twins. Of the 96 subjects, 46 (23…

Standardized mathematics test results of a twin sample during grades 3 and 6 were interpreted according to an interactional heredity x environment model. Results indicated that similar school instruction made monozygotic twins more alike but dizygotic twins less alike in mathematics knowledge. Social background effects were also studied. (SJL)

A computer scan of ACT Assessment records identified 3,427 sets of twins. The Hardy-Weinberg rule was used to estimate the proportion of monozygotic twins in the sample. Matrices of genetic and environmental influences were produced. The heaviest loadings were clearly in the genetic matrix. (SJL)

Critically examines the portions of Arthur Jensen's books that concern Barbara Burks' 1928 study of adoptive families. Findings are that Burks' sample was highly selective, that her environmental measures were limited, and that Jensen has misrepresented the content and implications of her study. It is also shown that Jensen's estimates of…

Examined data from 408 pairs of identical, same-sex fraternal twins at 14, 20, and 24 months to assess cognitive development and to identify genetic and environmental influences on phenotypic similarity. Found various patterns of development for separate constructs, for females versus males on each construct, and for individuals across constructs.…

Genetic effects on specific cognitive abilities as distinct from those on general cognitive ability were studied in 302 pairs of twins (some reared together, some apart) from the Swedish Adoption/Twin Study of Aging. Overall, results showed significant genetic influence on specific abilities independent of influence on general ability. (SLD)

Used behavioral genetic methods and environmental assessment techniques to assess maladaptive behavior in 6- to 11-year-old twin pairs. Found that genetic variation accounts for majority of variance in parent-reported child maladaptive behavior; in contrast, observational coding and global impressions of parent-twin interactive behavior suggest…

IQ scores from five kinship categories of 7- to 12-year-olds were analyzed into genetic and environmental components. The common environmental effects were larger for older children than younger children. Overall, the Genetic and Common Environment Sources each accounted for approximately 40% of the IQ variability in the data. (Author/LMO)

The Infant Behavior Record (IBR) assessed the temperament of 95 nonadoptive and 80 adoptive sibling pairs at 1 and 2 years of age. Data from this and an earlier similar study of identical and fraternal twins yielded evidence for genetic influence for IBR factors of extraversion, activity, and task orientation. (BC)

Examined the etiology of individual differences in literacy, phonological awareness, and language ability in monozygotic and dizygotic twins. Found that there was no genetic link between phonological awareness and literacy independent of general language ability. Individual differences in literacy ability were substantially influenced by genetics…