The activity level of 60 pairs of infant twins was measured for 2 days. Differences in activity level for monozygotic and dizygotic twins, as indicated by motion recorders and parent ratings, showed evidence of genetic influences. (BC)

Literature from the field of developmental behavior suggests that the relative effect of genetic influences on cognitive ability may increase with age, whereas the relative effect of shared environment may decrease. Implications of these findings are discussed, including the importance of studying environmental issues outside the family.…

Uses data from a sample of New Zealand twins to test the relationship between education and volunteering, holding unobservable family effects constant. Results show that education significantly reduces the probability of volunteering and the supply of volunteer hours. Volunteering may not be an external benefit of education. (Contains 18…

The authors investigated the etiology of low mathematics performance in 7-year-olds in the context of normal variation. The lowest 15% were selected from a representative U.K. sample of 2,178 same-sex twin pairs rated by their teachers according to National Curriculum criteria in 3 domains of mathematics. Model-fitting analyses of mathematics…

In this paper we test the hypothesis advanced by Weiss ("J. Economic Perspectives" 9(4)(1995)133) that under sorting models the return to schooling across identical twins would decline over time compared to the return for the population as a whole. The analyses undertaken on a relatively large sample of Australian twins are consistent…

Parental divorce is associated with problematic offspring adjustment, but the relation may be due to shared genetic or environmental factors. One way to test for these confounds is to study offspring of twins discordant for divorce. The current analyses used this design to separate the mechanisms responsible for the association between parental…

Objective: The purpose of this study was to assess heritability of activity, attention, and impulsivity by comparing young monozygotic (MZ) twins with dizygotic (DZ) twins using objective measures. Method: The OPTAx test is an infrared motion analysis to record the movement pattern during a continuous performance test. Seventeen MZ and 12 same…

Objective: To investigate children selected from a community sample for showing extreme autistic-like traits and to assess the degree to which these individual traits--social impairments (SIs), communication impairments (CIs), and restricted repetitive behaviors and interests (RRBIs)--are caused by genes and environments, whether all of them are…

We analyze the relationship between prenatal WIC participation and birth outcomes in New York City from 1988 - 2001. The analysis is unique for several reasons. First, we have over 800,000 births to women on Medicaid, the largest sample ever used to analyze prenatal participation in WIC. Second, we focus on measures of fetal growth distinct from…

The genetic and environmental etiologies of diverse aspects of language ability and disability, including articulation, phonology, grammar, vocabulary, and verbal memory, were investigated in a U.K. sample of 787 pairs of 4.5-year-old same-sex and opposite-sex twins. Moderate genetic influence was found for all aspects of language in the normal…

We conducted behavior?genetic analyses of kindergarten reading, spelling, phonological awareness, rapid naming, and spoken sentence processing in 172 pairs of monozygotic and 153 pairs of same-sex dizygotic twin kindergarten children sampled in the United States and Australia. We also modeled progress from preschool to kindergarten in…

Background: Longitudinal pediatric neuroimaging studies have demonstrated increasing volumes of white matter and regionally-specific inverted U shaped developmental trajectories of gray matter volumes during childhood and adolescence. Studies of monozygotic and dyzygotic twins during this developmental period allow exploration of genetic and…

Background: Differences in personality profiles were examined between children who differed in their co-morbidity of externalizing disorders: attention-deficit/hyperactivity disorder (ADHD) and conduct disorder (CD). Methods: 11- and 17-year-old male and female twins from a community sample were categorized as ADHD only, CD only, co-morbid…

This article presents an overview of some methods and results from our continuing studies of genetic and environmental influences on dyslexia, and on individual differences across the normal range that have been conducted over the past 25 years in the Colorado Learning Disabilities Research Center (CLDRC) and in related projects. CLDRC…

The author, herself a mother of twins, reviews research on exceptional twins. She considers reasons for fascination with twins and comments upon important advances in technology. Current research in Indianapolis to measure cognitive, perceptual, personality, and chromosome patterns of twins is described. Differences in the makeup of identical and…