Molarity not modularity: Multivariate genetic analysis of specific cognitive abilities in parents and their 16-year-old children in the colorado adoption project

Abstract

Previous multivariate genetic analyses suggest substantial genetic overlap among specific cognitive abilities, that is, molarity rather than modularity. We report the first multivariate genetic analysis of specific cognitive ability data from the Colorado Adoption Project when the 16-year-old offspring were administered the same test battery as their parents. The sample included 129 adoptees, sets of adoptive parents, and biological mothers, 24 biological fathers, and 125 nonadopted individuals and their parents. The average phenotypic correlation among verbal, spatial, and perceptual speed is .48, 76% of which is due to genetic influences on average; memory shows lower correlations with these abilities (.27 on average), about half of which are due to genes. These results support the genetic molarity hypothesis: (1) genetic effects on these specific cognitive abilities largely overlap, suggesting a common genetic factor of general cognition; and (2) genetic effects are largely responsible for the phenotypic correlations among these traits.