The Malleability of Iq and the Impact of Early Childhood Intervention

In their book The Bell Curve, as well as the summary article reviewed here, Charles Murray and Richard Hernstein examine the gap between the IQ scores of blacks and whites in America (Murray and Hernstein 1994). They assert that the mean IQ score of the black population is consistently around 85, while that of the white population is 100, indicating an IQ gap of approximately 15 points or 1 standard deviation. Given the substantial size of this gap, the authors set out to review arguments for the possible causes of such a difference. They examine the merits of various arguments that suggest that the gap is an artifact of the test used, but conclude that this is not a principal cause of the IQ gap. They then conclude that the 15-point gap must be due to an actual difference in ability, which may be attributable to environmental differences, genetic differences or both. The authors compare the hypothesis that the IQ gap is entirely environmentally-determined with the claim that it is somewhat environmentally-determined and somewhat genetically-based. To make this comparison, they analyze claims that IQ is malleable; from this, they conclude that it is not sufficiently malleable for the IQ gap to be entirely caused by environmental factors and that genetic differences are playing a role in the degree of malleability. This conclusion is based, in part, on the claim that even when the environment is changed for blacks (e.g. through adoption into a white family), IQ rises more for blacks that have some white ancestry (e.g. one white parent) than for blacks that are solely of African descent. The authors also base this