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J. Bradford Delong takes aim at an article by William Saletan at Slate, "Race, genes, and intelligence", with the work of Thomas Sowell on race, genes, and IQ. A portion of Sowell's essay is quoted below.

[T]he greatest black-white differences are not on the questions which presuppose middle-class vocabulary or experiences, but on abstract questions such as spatial perceptual ability.... [the] conclusion that this "phenomenon seems peculiarly concentrated in comparisons of ethnic groups" is simply wrong. When European immigrant groups in the United States scored below the national average on mental tests, they scored lowest on the abstract parts of those tests. So did white mountaineer children in the United States tested back in the early 1930s. So did canal boat children in Britain, and so did rural British children compared to their urban counterparts, at a time before Britain had any significant non-white population. So did Gaelic-speaking children as compared to English-speaking children in the Hebrides Islands. This is neither a racial nor an ethnic peculiarity. It is a characteristic found among low-scoring groups of European as well as African ancestry.

In short, groups outside the cultural mainstream of contemporary Western society tend to do their worst on abstract questions, whatever their race might be....

Perhaps the strongest evidence against a genetic basis for intergroup differences in IQ is that the average level of mental test performance has changed very significantly for whole populations over time and, moreover, particular ethnic groups within the population have changed their relative positions during a period when there was very little intermarriage to change the genetic makeup of these groups.

While [Herrnstein and Murray's] The Bell Curve cites the work of James R. Flynn, who found substantial increases in mental test performances from one generation to the next in a number of countries around the world, the authors seem not to acknowledge the devastating implications of that finding for the genetic theory of intergroup differences, or for their own reiteration of long-standing claims that the higher fertility of low-IQ groups implies a declining national IQ level. This latter claim is indeed logically consistent with the assumption that genetics is a major factor in interracial differences in IQ scores. But ultimately this too is an empirical issue--and empirical evidence has likewise refuted the claim that IQ test performance would decline over time.

Even before Professor Flynn's studies, mental test results from American soldiers tested in World War II showed that their performances on these tests were higher than the performances of American soldiers in World War I by the equivalent of about 12 IQ points. Perhaps the most dramatic changes were those in the mental test performances of Jews in the United States. The results of World War I mental tests conducted among American soldiers born in Russia--the great majority of whom were Jews--showed such low scores as to cause Carl Brigham, creator of the Scholastic Aptitude Test, to declare that these results "disprove the popular belief that the Jew is highly intelligent." Within a decade, however, Jews in the United States were scoring above the national average on mental tests, and the data in The Bell Curve indicate that they are now far above the national average in IQ.

Strangely, Herrnstein and Murray refer to "folklore" that "Jews and other immigrant groups were thought to be below average in intelligence. " It was neither folklore nor anything as subjective as thoughts. It was based on hard data, as hard as any data in The Bell Curve. These groups repeatedly tested below average on the mental tests of the World War I era, both in the army and in civilian life. For Jews, it is clear that later tests showed radically different results--during an era when there was very little intermarriage to change the genetic makeup of American Jews.


Sowell goes on in the same vein, pointing to comparable improvements in measured IQs among Italian-Americans and Polish-Americans, and pointing out that 15-point differences in IQ exist not only between contemporary blacks and whites in the United States, but between contemporary whites and their grandparents' generation. Whatever IQ measures, in other words, it isn't intrinsic differences between groups.
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