This research has demonstrated that first, short term memory (Jensen's Level I) has only a moderate index of heritability; second, that the general intellective factor g' (Jensen's Level II) has somewhat high heritability; and third, that no evidence of hereditary variation appeared in the Figural and Verbal Divergent Thinking measures.…

Provides a comprehensive contemporary summary of the world literature on IQ correlations between relatives. A profile of average correlations consistent with a polygenic mode of inheritence is revealed from a summary of 111 studies, although a marked degree of heterogeneity of the correlations within familial groupings is also found. (CS)

In a study of 105 twin pairs, correlations for identical pairs were significantly higher than fraternal pairs on all but one factor: tough-mindedness. Data suggested several components and the total organization of those components of personality and temperament are genetically influenced. (Author)

Twin children were videotaped hitting an inflated clown figure. Three behaviors (number of hits, intensity of hits, and number of quadrants hit) showed adequate response characteristics, rater reliability, and test-retest reliability. Twin analyses of the three behavioral ratings yielded no evidence of hereditary influence. (Author)

Hereditability of the two second order intelligence factors gc and gf was studied using the MAVA design in 470 brothers reared together, 94 identical twins reared together, 124 fraternal twins reared together, and 1543 boys (fluid intelligence) and 2579 (crystallized intelligence) unrelated. All were in the 12-18 age range. (Author)

Explores longitudinal data on sex, height and weight differences among pubescent monozygotic and dizygotic twins for theoretical implications related to heredity-environment interaction effects. (RH)

Used a genetic design to investigate association between physical aggression and language development in 19-month-old twins. Found a modest but significant correlation between aggression and expressive vocabulary. Substantial heritability was found for physical aggression. Quantitative genetic modeling suggested that the correlation could not be…

Findings from a study in which twins were given tests of onward repetition and auditory processing are discussed. Children with specific language impairments were impaired on both measures, but deficits had different origins. Auditory processing problems showed no evidence of genetic influence, whereas the nonword repetition deficit was highly…

Reviews biological bases of twinning and descriptions of 10 research designs. Summarizes findings from a selected sampling of twin studies of learning disabilities, personality and temperament, attitudes, psychopathology, and social behavior. Discusses findings with special reference to the activities of mental health practitioners and counselors.…

Explored the roles of genes and environment in masculinity and femininity during pre- and early adolescence in 70 twins of 8-14 years. Results revealed significant genetic influences in all measures. Environmental influences were specific to each individual and not shared by members of the same twin pair. (RJC)

Four samples (3,172 pairs of twins reared together, 90 pairs of twins reared apart, 87 adoptive families, 114 biological families) completed the Strong Vocational Interest Battery/Strong Interest Inventory. Results suggest that variance in vocational interests can be attributed to 12% additive genetic and 24% nonadditive genetic effects, 9% to…

The genetic and environmental causes of the phenotypic association between reading and verbal short-term memory (VSTM) were analyzed using data from the Colorado Reading Project for 446 twin pairs. Results of bivariate behavioral genetic analyses indicate that both reading ability and VSTM are highly heritable. (SLD)

This report documents phonological changes in a pair of identical twin boys diagnosed as language delayed. The boys were evaluated four times between the ages of three and four. Speech samples were analyzed for phonetic inventories, phonological process use, and syllabic shapes. Observed changes in their speech generally followed normal…