From specialist to generalist: Developmental transformations in the genetic structure of early child abilities.

The heritability of abilities increases substantially over development, and much of heritable variation in abilities is shared with other abilities. No study, however, has formally tested the extent to which developmental increases in heritability occur on shared versus unique variation in child abilities. A transactional perspective predicts that the relative proportion of shared to total genetic variance will increase with age, whereas an endogenous perspective predicts that such proportion will be invariant with age. We tested these competing predictions using data from a sample of 292 twins providing a total of 578 cross-sectional and longitudinal observations between ages 0 and 6 years on measures of Communication, Gross Motor, Fine Motor, Problem-Solving, and Personal-Social abilities. Consistent with predictions of the transactional perspective, developmental increases in heritability were localized to variance shared across abilities.