Minnesota Transracial Adoption Study

The Minnesota Transracial Adoption Study examined the IQ test scores of 130 black/interracial children adopted by advantaged white families. The aim of the study was to determine the contribution of genetic or cultural/environmental factors to the poorer performance of black children on IQ tests and in school as compared to white children. The initial study was published in 1976 by Sandra Scarr and Richard A. Weinberg. A follow up study was published in 1992 by Richard Weinberg, Sandra Scarr and Irwin D. Waldman.

Background and study design

 * see also: race and intelligence

On measures of cognitive ability (IQ tests) and school performance, Black children in the U.S. perform more poorly than White children. The gap in average performance between the two groups of children is approximately one standard deviation, which is equivalent to approximately 15 IQ points or 4 grade levels at high school graduation. Thus, the average IQ score of Black children in the U.S. is approximately 85, compared to the average score of White children of 100. The score gap is not due to any detectable bias, and thus it is a real ability difference. The gap is also functionally important, which makes it a socially important area of study. An unresolved question that the Minnesota Transracial Adoption Study study aimed to answer was whether the gap is partially caused by genetic factors or whether it is entirely caused by environmental/cultural factors.

By examining the cognitive ability and school performance of both Black and White children adopted into White families, the study was specifically designed to separate genetic factors from rearing conditions as causal influences in the gap. "Transracial adoption is the human analog of the cross-fostering design, commonly used in animal behavior genetics research.... There is no question that adoption constitutes a massive intervention" (Scarr & Weinberg, 1976, p. 726).

Scarr and Weinberg studied Black, White, and mixed-race Black/White children adopted by upper-middle-class White families in Minnesota. The average IQ of the adopting parents was more than 1 standard deviation above the population mean of 100. The biological children of these parents were also tested.

As Scarr & Weinberg (1976) note, transracial adoption studies only control for family environment, not social environment. For example, children who are socially identified as Black may still be subject to racial discrimination despite being raised by White parents. Yet, it was previously known that adoption into upper-middle class White families has a positive influence on the IQ and school performance of White children.

Results
The children were first tested in 1975 at age 7. In 1986, 196 of the original 265 children were retested at age 17.

The average difference in IQ scores between the testing at age 7 and testing at age 17, seen in all groups, is due to the use of different IQ tests. This difference does not bear on the interpretation of the data.

The difference in IQ scores between the adopting parents and their biological children would generally be explained in genetics by regression toward the mean.

The adopting parents of 12 of the interracial children wrongly believed that their adopted children had two Black parents. The average IQ of these 12 children was not significantly different from the scores of the 56 interracial children correctly classified by their adoptive parents as having one Black and one White parent.

Interpretations
Scarr & Weinberg (1976) interpreted the results from age 7 as support for the view that racial group differences in IQ are due to environment only. In support of this interpretation, they drew special attention to the finding that the average IQ of "socially classified" Black children was greater than the U.S. White mean. While the follow up was in 1986 it wasn't till 1992 that Weinberg et al. published their findings and interpreted their results as further support for the environment only view.

Both Levin (1994) and Lynn (1994) disputed the environment only interpretation. Each argued that the data clearly supports a hereditarian alternative: that the mean IQ scores and school achievement of each group reflected their degree of African ancestry. For all measures, the children with two Black parents scored lower than the children with one Black and White parent, who in turn scored lower than the adopted children with two White parents.

Waldman, Weinberg, and Scarr (1994) responded to Levin (1994) and Lynn (1994). They argued that preadoption factors confounded racial ancestry, preventing an unambiguous interpretation of the results. Subsequently, Jensen (1998) examined these studies and reviewed the evidence that adoption does not affect children's IQ scores after age 7.