Estimates the extent to which heredity influences perceptions of childhood family environment in a sample of 58 monozygotic and 46 dizygotic pairs of adult twins who were reared apart. The data confirm the importance of genetic factors in some, but not all, measures of family environment. Environmental influences were more important than genetic…

The mother, father, and adolescent siblings from 675 families were observed interacting in problem-solving sessions. Siblings were monozygotic twins, dyzygotic twins, or full siblings in nondivorced families and full, half, and unrelated siblings in stepfamilies. Results suggested a greater genetic component to adolescent behavior than to parent…

A study involving 55 children with a language impairment and 76 with normal language investigated the heritability of auditory processing impairment in same-sex twins (ages 7 to 13, selected from a sample of 37 pairs). Although correlations between co-twins were high, lack of significant difference between monozygotic and dizygotic twins suggested…

Explored genetic and environmental underpinnings of temperamental differences in 3- to 16-month-old twins and their parents. Found that additive genetic and shared environmental effects best represented smiling, laughter, and duration of orienting. Shared environmental effects fully accounted for co-twin similarity for soothability. Additive…

Parents of Swedish twin pairs ages 7 to 9 years and of British twin pairs ages 8 to 16 years completed the Child Behavior Checklist. Found that genetic factors influenced aggressive antisocial behavior to a greater extent than nonaggressive antisocial behavior, which was also significantly influenced by the shared environment. There was a…

Examined the origins of high general cognitive ability (g) in twins who were participating in the MacArthur Longitudinal Twin Study. Formed high g groups from the 19th percentile and above at each age. Results suggested increasing genetic influence and increasing genetic stability from 14 to 36 months and substantial genetic influences with…

Two studies of twin, sibling, and cousin pairs among children attempted to extend a model, called DF analysis, which separates hereditary and shared environmental influences. First study supported the validity of DF analysis applied to kinship height and weight data. The second study showed that spanking, reading, and quality of home environment…

Investigated the degree to which individual differences in child-parent attachment were mediated by genetic, shared environmental, and nonshared environmental influences. Found an overall concordance rate of 67 percent at the secure/insecure level. Twin similarity on the continuous measure of attachment security was consistent with a modest role…

Reviews current research on a woman's chances of bearing twins and the genetic relationship, prenatal competition, and personality similarities between twins. In addition, the nature/nurture controversy is discussed in terms of evidence from studies of identical twins reared apart. Future studies are suggested to discover the ways twinning might…

Studied continuity and change in general cognitive ability from infancy to adolescence in adoptees (107 children), biological siblings (87 pairs), and twins (224 monozygotic and 189 dyzygotic pairs). Findings generally support previous findings about genetic and environmental factors, with the exception that in the transition to adolescence,…

"The Bell Curve" declares that studies of separated identical twins--the "purest" of "direct" methods for estimating IQ heritability--indicate a value of +.75-+.80. But, the main study cited suggests a heritability of "two-thirds" for the middle class, and Herrnstein and Murray neglect to mention numerous…

Examined infant verbal and nonverbal cognitive development for 1,937 pairs of same-sex 2-year-old twins. Found that verbal and nonverbal development correlated .42. Genetic factors were responsible for less than half of this phenotypic correlation. The genetic correlation between verbal and nonverbal abilities was only .30, suggesting that genetic…

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.…

This paper presents the results of a study which examined heritability ratios for the major ethnic and socioeconomic groups in the Los Angeles Unified School District. Scores on three measures (the Cooperative Primary Reading Test, the Comprehensive Test of Basic Skills, and a composite set of intelligence tests) were compared for twins from…

This data compared language complexity measures, birth information, and family data for twins and singletons of the same sex, age, and socio-economic status. The subjects were four pairs of male twins, four pairs of female twins, four pairs of opposite sex twins, and 24 singletons, 32-33 months of age. Samples of each child's spontaneous…