A parent-offspring adoption study of cognitive abilities in early childhood

Do cognitive abilities in early childhood relate genetically and/or environmentally to isomorphic abilities in adulthood? Are specific cognitive abilities diffentiated in early childhood in terms of their prediction of adult cognitive abilities? The present study, the first behavioral genetic analysis of specific cognitive abilities in early childhood, explored these questions using parent-offspring data for 186 adopted children and 151 nonadopted children tested in the longitudinal Colorado Adoption Project at 3 years of age and 162 adopted children and 138 nonadopted children tested at 4 years. The children's Stanford-Binet IQ and scores for four specific cognitive abilities (verbal, spatial, perceptual speed, and memory) were correlated with corresponding measures for their parents—the biological and adoptive parents of the adopted children and the natural parents of the nonadopted children. Significant correlations were found between biological mothers' IQ and the IQ of their adopted away offspring at 3 and 4 years of age, suggesting genetic influence for IQ. However, specific cognitive abilities yielded no significant correlations between biological mothers and their adopted-away offspring. These results suggest that substantial genetic continuity exists for IQ from early childhood to adulthood, but not for specific cognitive abilities.