This study used a genetically informed design to assess the effects of friends' and nonfriends' reticent and dominant behaviors on children's observed social reticence in a competitive situation. Potential gene-environment correlations (rGE) and gene-environment interactions (GxE) in the link between (a) friends' and…

We examined whether self-restraint in early childhood predicted individual differences in 3 executive functions (EFs; inhibiting prepotent responses, updating working memory, and shifting task sets) in late adolescence in a sample of approximately 950 twins. At ages 14, 20, 24, and 36 months, the children were shown an attractive toy and told not…

Background: Despite extensive efforts, the causes of autism remain unknown. Advancing paternal age has been associated with various neurodevelopmental disorders. We aim to investigate three unresolved questions: (a) What is the association between paternal age and autism spectrum disorders (ASD)?; (b) Does paternal age moderate the genetic and…

Imitation, vocabulary, pretend play, and socially insightful behavior were investigated in 5,206 same- and opposite-sex 2-year-old twin pairs in the United Kingdom. Individual differences in imitative ability were due to modest heritability (30%), while environmental factors shared between twins (42%) and unique to each twin (28%) also made…

The present study is the first to utilize twin modeling to examine whether parent-teacher disagreement for ADHD ratings is due to parent or teacher bias, or due to raters observing different but valid ADHD behaviors. A joint analysis was conducted with 106 twin pairs, including twins selected for ADHD and control twin pairs. Total ADHD scores were…

Background: Relatively little is known about the genetic architecture of childhood behavioral disorders in very young children. Method: In this study, parents completed the Infant-Toddler Social and Emotional Assessment, a questionnaire that assesses symptoms of childhood disorders, as well as socio-emotional competencies, for 822 twin pairs…

Shorter version of this paper read at theannual meetings of the American Psychological Association, September 1965. Research supported by NIMH grant MH-16841.

Maternal ratings on internalizing (INT) and externalizing (EXT) behaviors were collected in a large, population-based longitudinal sample. The numbers of participating twin pairs at ages 3, 7, 10, and 12 were 5,602, 5,115, 2,956, and 1,481, respectively. Stability in both behaviors was accounted for by genetic and shared environmental influences.…

The genetic and environmental etiologies of sex-typed behavior were examined during the preschool years in a sample of 3,990 three- to four-year-old twin and nontwin sibling pairs. Results showed moderate genetic and significant shared environmental influence for boys and substantial genetic and moderate shared environmental influence for girls.…

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…

Task persistence, measured by a composite score of independent teacher, tester and observer reports, was examined using behavioral genetic analysis. Participants included 92 monozygotic and 137 same-sex dizygotic twin pairs in Kindergarten or 1st grade (4.3 to 7.9 years old). Task persistence was widely distributed, higher among older children,…