CONTINUITY AND CHANGE IN GENERAL COGNITIVE-ABILITY FROM 1 TO 7 YEARS OF AGE

Observed and latent sources of individual differences in cognitive development were explored in data from adopted and nonadopted siblings measured from 12 months to 7 years and identical and nonidentical twins measured from 12 to 36 months. Longitudinal path models, designed to examine the structure of observed stability and assess the genetic and environmental sources of age-to-age change and continuity, suggest that observed continuity arises from age-specific effects that persist over time and from developmental influences that are static and unchanging. Genetic influences account for the age-specific yet persistent effects, shared sibling environment effects are constant from 1 to 7 years, and nonshared environmental factors are specific to each measurement age. Thus, genetic influences are a major source of both continuity and change in mental development, whereas shared and nonshared environmental effects contribute to continuity and change, respectively.