Twins: Mental development in the preschool years

• Published in: Developmental psychology 1974-07, Vol.10 (4), p.580-588
• Main Author: Wilson, Ronald S
• Format: Article
• Language: English
• Subjects: Human; Intellectual Development; Twins
• ISSN: 0012-1649; 1939-0599
• DOI: 10.1037/h0036596

Obtained measures of mental development (Wechsler Preschool and Primary Scale of Intelligence, Bayley Scales of Infant Development, and the Stanford-Binet Intelligence Scale) for a large sample of over 350 pairs of twins from 11/2 to 6 yrs of age. Initially the twins were somewhat depressed in developmental status, but they ultimately reached parity with singletons by age 6. The age-to-age predictive correlations followed the typical simplex pattern of declining as the age span increased but still remained higher for the Bayley Scales than had previously been reported. Sex differences were also noted for the pattern of age-to-age correlations. Monozygotic twins were significantly more concordant than dizygotic twins for the measures of mental development at each age and for the changes in relative precocity between ages to age 5. By that age, the measures of intelligence had stabilized to the point where year-to-year changes were no longer a significant source of variance. Parental education and socioeconomic status gave modest positive correlations with the twins' IQ scores at age 6. Results point to the genetic blueprint as the principal determinant of childhood mental development for the broad range of home environments represented in this study.