Differential Inheritance of Mental Abilities in the Texas Adoption Project

Correlations on subscales of Wechsler IQ tests and the Revised Beta Examination were obtained for biologically related and unrelated individuals in 18 1 adoptive families in the Texas Adoption Project. Scores were also available for many of the birth mothers of the adopted children. In general, correlations were higher for biologically related individuals, suggesting the importance of genetic influences on intellectual abilities. To examine effects specific to subscales, an analysis of residualized subscale scores was carried out using the Revised Beta. After partialling out from each of the scales the variance predictable from the rest, a model was fit to family correlations among the residuals. Of the six Beta subscales, three showed specific genetic variance, two showed specific shared environmental variance, and one showed neither.