Racial-group differences in IQ in the Minnesota Transracial Adoption Study: A reply to Levin and Lynn

Abstract

The etiology of racial differences in intelligence and achievement is one of the most heated areas of social science research. In this article, we respond to criticisms by Levin and Lynn of our 1992 follow-up study of IQ and achievement in a simple of transracial adoptees and their families, in particular to their assertion that our results provide strong support for a genetic etiology underlying racial differences in measured intelligence. In that follow-up, as well as in publications from the original study (Scarr & Weinberg, 1976, 1977), we argued for beneficial effects on transracial adoptees' IQs and achievements due to being raised in white, upper-middle-class homes. In this article, we address a number of issues raised in Levin's and Lynn's critiques, including the magnitude of adoptee racial-group differences in IQ and achievement, the inclusion of white and Asian/Indian adoptee groups in such analyses, the confounding of important early environmental influences with race differences, the confusion of within-group and between-group influences on IQ, the regional U.S. differences in African-American norms for IQ and achievement, the effects of renormed IQ tests on adoptee group differences, and the nature of the available evidence regarding a genetic hypothesis for racial differences in intelligence. We argue that, contrary to Levin's and Lynn's assertions, results from the Minnesota Transracial Adoption Study provide little or no conclusive evidence for genetic influences underlying racial differences in intelligence and achievement.