Naturalistic observation of a set of identical twins revealed many differences in personality and motor development. (MS)

Describes a methodology of behavior genetics in the context of twin and sibling/adoption design. This model was applied to cross-sectional data on cognitive development throughout the lifespan. Results from a twin and adoption study of general intelligence are presented to illustrate the use of the basic behavior genetic model in studying causes…

Data from 148 identical and 111 fraternal twin pairs in which at least 1 member had a reading disability were statistically analyzed. Results suggest that genetic and shared-environment influences both contribute to the observed covariance between reading and mathematical deficits. (Author/DB)

A research study of identical twins, by Thomas J. Bouchard Jr., discloses that genetics exert a stronger influence over personality than we thought. Parents and teachers are advised to be active and alert observers of children's interests and talents to provide appropriate tools and resources to develop these propensities. (MLF)

Investigated the etiology of several measures of cognitive delay in over 3,000 pairs of 2-year-old twins, focusing on group-differences heritability for general and specific cognitive delays. Concluded that because the genetic and environmental origins of verbal and performance delays in infancy differ, they are better considered separately rather…

Examined the effects of gender on academic achievement for 138 mono- and 125 dizygotic twin pairs, ranging in age from 6 to 12 years. Results suggested that individual differences in academic achievement may be more influenced by genetic than environmental variance in females, and by environmental than genetic variance in males. (BC)

Virtual twins are unrelated siblings of the same age who are reared together from early infancy (UST-SA). Study uses a sample of 90 UST-SA pairs to comparatively assess the similarity of IQ subtest profile correlations for UST-SAs and twin pairs. Findings support explanatory models of intelligence that include genetic factors, demonstrating that…

In this article, the authors examined the genetic and environmental factors influencing expressive language development in a sample of 386 toddler twin pairs participating in the Wisconsin Twin Project. Expressive language was assessed using 2 measures from the MacArthur Communicative Development Inventories-Short Form: Total Vocabulary and…

Prosocial behavior is important for the functioning of society. This study investigates the extent to which environment shared by family members, nonshared environment, and genetics account for children's prosocial behavior. The prosocial behavior of twins (9,424 pairs) was rated by their parents at the ages of 2, 3, 4, and 7 and by their teachers…

Multivariate genetic analysis was used to examine the genetic and environmental aetiology of the interrelationships of diverse linguistic skills. This study used data from a large sample of 4 1/2-year-old twins who were tested on measures assessing articulation, phonology, grammar, vocabulary, and verbal memory. Phenotypic analysis suggested two…

Appraised cognitive patterning and development for 142 pairs of twins at 4, 5, and 6 years of age. From the results it was inferred that within a broad range of home environments, the genotype exerts a significant influence on the child's cognitive development. (Author/SDH)

Analyzed 20 test items for evidence of concordance for samples that included at least 120 pairs of identical twins and 85 pairs of same-sex fraternal twins at ages 3, 6, 9 and 12 months. Also computed within-pair correlations for the total number of Piagetian-equivalent items passed. (Author/SDH)

Scores were obtained on 31 item-clusters from the California Psychological Inventory for 490 identical and 317 same-sex fraternal twin pairs from the National Merit twin sample. Ordinary and cross-pair correlations were calculated and used to derive three matrices hypothesized to reflect the influence of genes, shared environment, and unshared…

Holtzman Inkblot Technique (HIT) responses of 36 same sex and 29 opposite sex college student twin pairs are analyzed. The results are discussed in terms of comparable genetic determination studies with Rorschach responses and the necessity for separate male and female norms on several HIT score response scales. (Author/DEP)

Obtained objective measures of activity, fidgeting, vigilance, selective attention, and aggression for a sample of 87 twin pairs in late childhood. Little evidence for genetic influence on behavior was found. Between-family environmental sources of variance were far more important than within-family factors. (Author/RH)