This likely suggests that they are also the most sensitive to environmental changes, which undermines Jensen's argument that the black–white gap is most likely caused by genetic factors. Mackintosh also argues that Spearman's hypothesis, which he considers to be likely to be correct, simply shows that the test score gap is based on whatever cognitive faculty is central to intelligence, but does not show what this factor is. make the same point, noting also that the increase in the IQ scores of black test takers necessarily indicates an increase in g. Flynn has criticized Jensen's basic assumption that confirmation of Spearman's hypothesis would support a partially genetic explanation for IQ differences. He argues that, no matter what the causes are of average group IQ differences, one would expect the differences to be greater for more complex tasks. Flynn thus sees the correlation between g-loading and the test score gap to offer no clue to the cause of the gap. Adoption studies A number of IQ studies have been done on the effect of similar rearing conditions on children from different races. The hypothesis is that this can be determined by investigating whether black children adopted into white families demonstrated gains in IQ test scores relative to black children reared in black families. Depending on whether their test scores are more similar to their biological or adoptive families, that could be interpreted as supporting either a genetic or an environmental hypothesis. Critiques of such studies question whether the environment of black children—even when raised in white families—is truly comparable to the environment of white children. Several reviews of the adoption study literature have suggested that it is probably impossible to avoid confounding biological and environmental factors in this type of study. Another criticism by is that adoption studies on the whole tend to be carried out in a restricted set of environments, mostly in the medium-high SES range, where heritability is higher than in the low-SES range. The Minnesota Transracial Adoption Study (1976) examined the IQ test scores of 122 adopted children and 143 nonadopted children reared by advantaged white families. The children were restudied ten years later. The study found higher IQ for white people compared to black people, both at age 7 and age 17. Acknowledging the existence of confounding factors, Scarr and Weinberg, the authors of the original study, did not consider that it provided support for either