Feeling inhibited and socially not at ease is reflected in the trait social inhibition (SI). SI is associated with psychopathology that arises in young adulthood, such as anxiety. We aim for a better insight into the genetic and environmental contributions to SI across the life span, and as such examine their contributions to SI stability and…

In the present study, we investigated genetic and environmental effects on motor impulsivity from childhood to late adolescence using a longitudinal sample of twins from ages 9 to 18 years. Motor impulsivity was assessed using errors of commission (no-go errors) in a visual go/no-go task at 4 time points: ages 9-10, 11-13, 14-15, and 16-18 years.…

Despite implications that stranger fear is an important aspect of developing behavioral inhibition, a known risk factor for anxiety, normative and atypical developmental trajectories of stranger fear across infancy and toddlerhood remain understudied. We used a large, longitudinal data set (N = 1285) including multi-trait, multi-method assessments…

This study investigated the mean-level and individual-level trends as well as the genetic and environmental sources of rank-order continuity and change in temperament traits ("Briskness, Perseveration, Sensory Sensitivity, Emotional Reactivity, Endurance, and Activity"). We analyzed self-reports and peer ratings from 2 adult age groups…

During childhood and adolescence, increases in heritability and decreases in shared environmental influences have typically been found for cognitive abilities. A sample of more than 2,500 pairs of twins from the Twins Early Development Study was used to investigate whether a similar pattern would be found for science performance from 9 to 12…

The relation between intelligence and birth order was shown in a recent publication [Bjerkedal, T., Kristensen, P., Skjeret, G. A. & Brevik, J. I. (2007). Intelligence test scores and birth order among young Norwegian men (conscripts) analyzed within and between families. "Intelligence," 35, 503-514] to be negative. Subjects in this…

Observational measures of monozygotic and dizygotic twins' reactions to simulations of distress in others were obtained when the twins were 14 and 20 months old. Components of concern for others increased with age. Girls scored higher than boys on most measures. There was modest evidence for heritability of empathy. (BC)

Examines genetic influences on language by assessing 158 preschool twins on vocabulary comprehension, semantic knowledge, morphology, syntax, and articulation. Vocabulary comprehension was significantly influenced by heredity, whereas performance skills were influenced by between-family environmental factors. (Author/AS)

Influences of heredity and environment on educational and occupational choice in mid-life and elderly cohorts were studied using longitudinal twin data (413 pairs). For both education and occupation there is a trend toward increasing genetic variance for females in comparison to males in the younger cohort. (SLD)

This study was designed to assess genetic influence on behavioral inhibition and its varying expression in 92 monozygotic and 86 dizygotic twin pairs. Infant behavior and mother-child interaction were observed and videotaped during structured play sessions at age 14, 20, 24, and 36 months. Analysis of the results suggests that most of the overlap…

Etiology of high and low cognitive ability in adulthood was explored through multiple regression analysis of data from 302 pairs of Swedish twins (median age=65.6 years). Both high and low cognitive ability groups demonstrate significant group heritability, with shared rearing environment of relatively low importance. (SLD)

Collected data on twins' performance on 13 cognitive variables measured three times at three-year intervals. Twins were monozygotic or dizygotic pairs reared together or apart and were in six cohorts ranging in age from 41 through 84 years. Found stable mean cognitive performance across time on eight measures for the younger cohorts, and…

This study of 640 twins with reading disability and 436 controls (mean age 12) examined external validity of the distinction between specific reading retardation and reading backwardness, in 3 domains: genetic etiology, sex ratio and clinical correlates, and neuropsychological profiles. There was no evidence of differential genetic etiology of the…

Factor analysis of 25 rating scales from Bayley's infant behavior record were performed for a sample of about 300-400 infant twins tested one or more times between 3 and 24 months of age. The analyses provided five major and two minor factors that were considerably consistent at all ages. (Author/DB)