Studied 715 twins and singletons to document heritable influences on temperament during toddler and preschool ages. Found substantial shared environmental influence on positive affect and additive genetic influence on emotion regulation. Intraclass correlations from many scales showed no evidence of "too-low" dizygotic correlations that…

Since the time of Galton, high correlations have been noted in the IQ levels of identical twins, with relationships for twins reared in different families being only slightly lower than for twins reared together. This evidence has been held to demonstrate that intellectual differences among individuals and among groups are largely determined by…

Discusses the patterns of mental development of 350 pairs of twins studied longitudinally from 11/2-6 years of age. (DP)

Hierarchical factor analyses involving Schmid-Leiman transformations were conducted on specific cognitive abilities data collected from 148 identical and 135 fraternal twin pairs from the Western Reserve Twin Project. Model fitting results reflect genetic influences on specific abilities and suggest that environmental influences are less…

Taylor (1980) claims to show that the similarity in IQ between monozygotic twins reared apart found in prior studies is due to similarity in their environments. A reanalysis using Taylor's classification of environments but an alternative IQ measure shows that his findings do not constructively replicate. (Author/RD)

Data from 236 pairs of black twins and white twins aged 13-17 years were used to examine genetic and environmental factors influencing cranial size, an indirect estimate of brain volume. Genetic factors are required to account for the phenotypic variance in cranial capacity. (SLD)

This report presents data on 9-month-old twin pairs (n[MZ]=172; n[DZ]=333) from the Early Childhood Longitudinal Study, demonstrating that the role of genetic variation among infants is trivial and the shared and nonshared environment is substantial in accounting for the observed quality of infant-caregiver relationships. In contrast, maternal…

Examines the modifiability and heritability of reflection-impulsivity as measured by Matching Familar Figures. A Cotwin control method was used to study the modifiability of reflection-impulsivity and a twin study to assess its heritability. (Author/DEP)

Ninety-two adult twin-pairs were recruited. Twin zygosity was determined by self-report inventory. Monozygotic twins resembled one another more than dizygotic twins in most measures of both level and lability of mood, which provides modest evidence for a genetic influence on subclinical levels of depression. (Author/ABB)

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)

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…

Despite the importance of learning abilities and disabilities in education and child development, little is known about their genetic and environmental origins in the early school years. We report results for English (which includes reading, writing, and speaking), mathematics, and science as well as general cognitive ability in a large and…

The genetic relationship between intelligence and components of cognition remains controversial. Conflicting results may be a function of the limited number of methods used in experimental evaluation. The current study is the first to use CANTAB (The Cambridge Neuropsychological Test Automated Battery). This is a battery of validated computerised…