If books challenging religious belief are judged to ruffle feathers, than those investigating differences in IQ across human populations–whatever conclusions these draw or invite–can fairly be said to bite the heads off live chicken in one powerful Ozzy Osbourne-style jaw snap. They are never uncontroversial.
In his review of a book by University of Michigan psychologist Richard E. Nisbett, “Intelligence and How to Get It,” Jim Holt states that the author “offers a meticulous and eye-opening critique of hereditarianism.” He refers to Nisbett’s “forceful marshaling of the evidence, much of it recent … which stresses the importance of nonhereditary factors in determining I.Q.” and elaborates on Nisbett’s central claim, in which he breaks ranks from his predecessors in the field:
Nisbett bridles at the hereditarian claim that I.Q. is 75 to 85 percent heritable; the real figure, he thinks, is less than 50 percent. Estimates come from comparing the I.Q.’s of blood relatives — identical twins, fraternal twins, siblings — growing up in different adoptive families. But there is a snare here. As Nisbett observes, “adoptive families, like Tolstoy’s happy families, are all alike.” Not only are they more affluent than average, they also tend to give children lots of cognitive stimulation. Thus data from them yield erroneously high estimates of I.Q. heritability. (Think: if we all grew up in exactly the same environment, I.Q. differences would appear to be 100 percent genetic.) This underscores an important point: there is no fixed value for heritability. The notion makes sense only relative to a population. Heritability of I.Q. is higher for upper-class families than for lower-class families, because lower-class families provide a wider range of cognitive environments, from terrible to pretty good.
Holt notes that Nisbett uses basic statistics to take apart long-held notions that, for example, measured differences in IQ between U.S. blacks and Americans of predominantly European descent (a gap which has shrunk from 15 point to 9.5 in just 30 years), differences between East Asians and “white” Americans, and the superiority of Ashkenazi Jews are rooted in genetics.
Holt offers his own editorial comments at the end of his review:
Even if I.Q. inequality is inevitable, it may eventually become irrelevant. Over the last century, for reasons that aren’t entirely clear, I.Q. scores around the world have been rising by three points a decade. Some of this rise, Nisbett argues, represents a real gain in intelligence. But beyond a certain threshold — an I.Q. of 115, say — there is no correlation between intelligence and creativity or genius. As more of us are propelled above this threshold — and, if Nisbett is right, nearly all of us can be — the role of intelligence in determining success will come to be infinitesimal by comparison with such “moral” traits as conscientiousness and perseverance. Then we can start arguing about whether those are genetic.