you're referring to the conclusion of the authors in the first 1976 study when they looked at the iq scores of the children when they were 7. they pointed out that although there was a racial gap, the black average of the adopted children was higher than that of the white general population. they deemed it inconclusive because of potential pre-adoption environmental differences that may have affected the black children more negatively than the white children. in the 1994 follow up study, the authors tested the iqs of the same children when they were 17 years old. they found that the white-black iq gap of the subjects was nearly identical to that of the white-black iq gap of the general population. they did not say that the results were inconclusive and stated that the gap between the subjects was both genetic and environmental: "we think that it is exceedingly implausible that these differences are either entirely genetically based or entirely environmentally based. the true causes of racial-group differences in iq, or in any other characteristic, are likely to be too complex to be captured by locating them on a single hereditarianism-environmentalism dimension." it has been shown in other studies that the cognitive abilities of people are more affected by environmental factors at younger ages and genetics plays an increasingly larger role as they age.
United States