What Can an Adoption Study Tell Us About the Effect of Prenatal Environment on a Trait?

Adoption studies provide possibilities for estimating the extent to which prenatal environmental events account for individual differences on a trait. Correlations with birth mothers but not adoptive mothers suggest the presence of genetic or prenatal environmental effects; higher correlations with birth mothers than with birth fathers suggest the presence of the latter. Changes over time may also be relevant. The concepts involved are illustrated with parent-child IQ correlations from the Texas and Colorado Adoption Projects.