DIFFERENTIAL INHERITANCE OF MENTAL ABILITIES IN THE TEXAS ADOPTION PROJECT

Correlations on subscales of Wechsler IQ tests and the Revised Beta Ex amination were obtained for biologically related and unrelated individ uals in 181 adoptive families in the Texas Adoption Project. Scores we re also available for many of the birth mothers of the adopted childre n. In general, correlations were higher for biologically related indiv iduals, suggesting the importance of genetic influences on intellectua l abilities. To examine effects specific to subscales, an analysis of residualized subscale scores was carried out using the Revised Beta. A fter partialling out from each of the scales the variance predictable from the rest, a model was fit to family correlations among the residu als. Of the six Beta subscales, three showed specific genetic variance , two showed specific shared environmental variance, and one showed ne ither.