Intellectual resemblance among adoptive adoptive and biological relatives: the Texas adoption project.

Intellectual and personality measures were available from unwed mothers who gave their children up for adoption at birth. The same or similar measures have been obtained from 300 sets of adoptive parents and all of their adopted and natural children in the Texas Adoption Project. The sample characteristics are discussed in detail, and the basic findings for IQ are presented. Initial analyses of the data on IQ suggest moderate heritabilities. Emphasis is placed on the preliminary nature of these findings.