The Right Coast

August 31, 2005
More from Murray on IQ
By Mike Rappaport

Two other provacative claims by Charles Murray. First, not only is g (general intelligence) heritable, it has a physiological basis:

By the 1980’s, the robustness and value of g as an explanatory construct were broadly accepted among pyschometricians, but little was known about its physiological basis. As of 2005, we know much more. It is now established that g is by far the most heritable component of IQ.67 A variety of studies have found correlations between g and physiological phenomena such as brain-evoked potentials, brain pH levels, brain glucose metabolism, nerve-conduction velocity, and reaction time. Most recently, it has been determined that a highly significant relationship exists between g and the volume of gray matter in specific areas of the frontal cortex, and that the magnitude of the volume is under tight genetic control. In short, we now know that g captures something in the biology of the brain.
Second, the black white difference in IQ is greatest in areas without cultural content:

When you compare black and white mean scores on a battery of subtests, you do not find a uniform set of differences; nor do you find a random assortment. The size of the difference varies systematically by type of subtest. Asked to predict which subtests show the largest difference, most people will think first of ones that have the most cultural content and are the most sensitive to good schooling. But this natural expectation is wrong. Some of the largest differences are found on subtests that have little or no cultural content, such as ones based on abstract designs.