Mothers were interviewed periodically over the first six years of their same-sex twins' lives and were asked to contrast them on specific behaviors. Intrapair contrasts were moderately stable across age spans for as long as 18 through 36 months. Genotypic similarity was apparently associated with intrapair similarity in emotionality and…

This paper presents further evidence to demonstrate the existence of intra-uterine effects within the normal range of intelligence. The argument is then extended further to estimate the effects of organic factors in the environment that are also pathogenic for intelligence. Various implications of these factors are discussed. (Author/KC)

Assesses etiology of reading disability as a function of mathematics performance by subjecting data from 168 same-sex twin pairs where at least one member was reading disabled to quantitative genetic analysis. Suggests that genetic factors may be especially salient as a cause of reading disability in children with borderline deficits in…

Two cohorts of same-sex twin pairs were assessed on grammar and vocabulary. Findings indicated that vocabulary and grammar correlated strongly at 2 and 3 years in both cohorts, with a consistently high genetic correlation between vocabulary and grammar at both ages. Findings suggest that the same genetic influences operate for vocabulary and…

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,…

Finds that parent-offspring resemblance in families of reading-disabled probands does not differ substantially from that in families of controls; and correlations and regressions for monozygotic twins are greater than those for dizygotic twins, suggesting that individual differences in reading achievement are due in part to heritable influences.…

"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…

Examines consequences of using alternative definitions for prevalence, sex ratio and heritability. Demonstrates that the characteristics of reading-disabled children vary with the way disability is defined. Concludes that the use of regression-based procedures for identifying reading disability is desirable. Suggests insufficient evidence exists…

Examined 114 pairs of same-sex infant twins and their parents to investigate infant predictors of adult IQ. Found that some measures of infants' information processing, language ability, and temperament predicted the average IQ of infants' parents. Results support the view that some stability in certain types of intellectual functioning from…

Subjects measures of word recognition, phonological coding, and orthographic coding obtained from analyses of identical and fraternal twins to multivariate genetic analysis. Finds that genetic influences on individual differences in word recognition were more strongly related to genetic variance in phonological coding than in orthographic coding.…

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…

Established normative data on the Pubertal Development Scale (PDS) (A. Petersen and others, 1988) of two population-based birth cohorts of Finnish twin boys and girls assessed at ages 11-12 and 14 years (complete data for 664 boys and 681 girls). Also reports longitudinal analyses of the associations between pubertal development and substance use.…

A study assessed genetic and environmental etiologies of reading, rapid naming (RN), and their covariation using data from 587 twin pairs (ages 7-20) in which one student had reading difficulties and from 360 control pairs. Correlation between reading and RN performances for subjects was significantly higher than that of controls. (Contains…

If maternal expressed emotion is an environmental risk factor for children's antisocial behavior problems, it should account for behavioral differences between siblings growing up in the same family even after genetic influences on children's behavior problems are taken into account. This hypothesis was tested in the Environmental Risk…

Background: We investigated the aetiology of language impairment in 579 four-year-old twins with low language performance and their co-twins, members of 160 MZ twin pairs, 131 same-sex DZ pairs and 102 opposite-sex DZ pairs. Methods: Language impairment in 4-year-olds was defined by scores below the 15th percentile on a general factor derived from…