The Bell Curve: Intelligence and Class Structure in American Life (50 page)

Second, we have become convinced that the topic of genes, intelligence, and race in the late twentieth century is like the topic of sex in Victorian England. Publicly, there seems to be nothing to talk about. Privately, people are fascinated by it. As the gulf widens between public discussion and private opinion, confusion and error flourish. As it was true of sex then, so it is true of ethnic differences in intelligence now: Taboos breed not only ignorance but misinformation. The dangers of the misinformation are compounded by the nature of the contemporary discussion of race. Just beneath the surface of American life, people talk about race in ways that bear little resemblance to the politically correct public discussion. Conducted in the workplace, dorm rooms, taverns, and country clubs, by people in every ethnic group, this dialogue is troubled and often accusatory. The underground conversation is not limited to a racist minority. It goes on everywhere, and we believe is increasingly shaped by privately held beliefs about the implications of genetic differences that could not stand open inspection.

The evidence about ethnic differences can be misused, as many people say to us. Some readers may feel that this danger places a moral prohibition
against examining the evidence for genetic factors in public. We disagree, in part because we see even greater dangers in the current gulf between public pronouncements and private beliefs. And so, for better or worse, here are the major strands of current thinking about the role of genes in cognitive differences between races.
⁷⁴

A good place to start is by correcting a common confusion about the role of genes in individuals and in groups. As we discussed in Chapter 4, scholars accept that IQ is substantially heritable, somewhere between 40 and 80 percent, meaning that much of the observed variation in IQ is genetic. And yet this information tells us nothing for sure about the origin of the differences between races in measured intelligence. This point is so basic, and so commonly misunderstood, that it deserves emphasis:
That a trait is genetically transmitted in individuals does not mean that group differences in that trait are also genetic in origin.
Anyone who doubts this assertion may take two handfuls of genetically identical seed corn and plant one handful in Iowa, the other in the Mojave Desert, and let nature (i.e., the environment) take its course.
⁷⁵
The seeds will grow in Iowa, not in the Mojave, and the result will have nothing to do with genetic differences.

The environment for American blacks has been closer to the Mojave and the environment for American whites has been closer to Iowa. We may apply this general observation to the available data and see where the results lead. Suppose that all the observed ethnic differences in tested intelligence originate in some mysterious environmental differenees—mysterious, because we know from material already presented that socioeconomic factors cannot be much of the explanation. We further stipulate that one standard deviation (fifteen IQ points) separates American blacks and whites and that a fifth of a standard deviation (three IQ points) separates East Asians and whites. Finally, we assume that IQ is 60 percent heritable (a middle-ground estimate). Given these parameters, how different would the environments for the three groups have to be in order to explain the observed difference in these scores?

The observed ethnic differences in IQ could be explained solely by the environment if the mean environment of whites is 1.58 standard deviations better than the mean environment of blacks and .32 standard deviation worse than the mean environment for East Asians, when
environments are measured along the continuum of their capacity to nurture intelligence.
⁷⁶
Let’s state these conclusions in percentile terms: The
average
environment of blacks would have to be at the 6th percentile of the distribution of environments among whites, and the
average
environment of East Asians would have to be at the 63rd percentile of environments among whites, for the racial differences to be entirely environmental.

Environmental differences of this magnitude and pattern are implausible. Recall further that the B/W difference (in standardized units) is smallest at the lowest socioeconomic levels. Why, if the B/W difference is entirely environmental, should the advantage of the “white” environment compared to the “black” be greater among the better-off and better-educated blacks and whites? We have not been able to think of a plausible reason. An appeal to the effects of racism to explain ethnic differences also requires explaining why environments poisoned by discrimination and racism for some other groups—against the Chinese or the Jews in some regions of America, for example—have left them with higher scores than the national average.

Environmental explanations may successfully circumvent these problems, but the explanations have to be formulated rather than simply assumed. Our initial objective is to warn readers who come to the discussion with firmly held opinions on either side. The heritability of individual differences in IQ does not necessarily mean that ethnic differences are also heritable. But those who think that ethnic differences are readily explained by environmental differences haven’t been tough-minded enough about their own argument. At this complex intersection of complex factors, the easy answers are unsatisfactory ones.

Now we turn to some of the more technical arguments, beginning with those that argue for some genetic component in group differences.

P
ROFILE
D
IFFERENCES
B
ETWEEN
W
HITES AND
E
AST
A
SIANS.
Races differ not just in average scores but in the profile of intellectual capacities. A full-scale IQ score is the aggregate of many subtests. There are thirteen of them in the Wechsler Intelligence Scale for Children (WISC-R), for example. The most basic division of the subtests is into a verbal IQ and a performance IQ. In white samples,
the verbal and performance IQ subscores tend to have about the same mean, because IQ tests have been standardized on predominantly white populations. But individuals can have imbalances between these two IQs. People with high verbal abilities are likely to do well with words and logic. In school they excel in history and literature; in choosing a career to draw on those talents, they tend to choose law or journalism or advertising or politics. In contrast, people with high performance IQs—or, using a more descriptive phrase, “visuospatial abilities”—are likely to do well in the physical and biological sciences, mathematics, engineering, or other subjects that demand mental manipulation in the three physical dimensions or the more numerous dimensions of mathematics.

East Asians living overseas score about the same or slightly lower than whites on verbal IQ and substantially higher on visuospatial IQ. Even in the rare studies that have found overall Japanese or Chinese IQs no higher than white IQs (e.g., the Stevenson study of Japanese, Taiwanese, and Minnesotans mentioned earlier),
⁷⁷
the discrepancy between verbal and visuospatial IQ persists. For Japanese living in Asia, a 1987 review of the literature demonstrated without much question that the verbal visuospatial difference persists even in examinations that have been thoroughly adapted to the Japanese language and, indeed, in tests developed by the Japanese themselves.
⁷⁸
A study of a small sample of Korean infants adopted into white families in Belgium found the familiar elevated visuospatial scores.
⁷⁹

This finding has an echo in the United States, where Asian-American students abound in engineering, in medical schools, and in graduate programs in the sciences, but are scarce in law schools and graduate programs in the humanities and social sciences. Most people reflexively assume that this can be explained by language differences. People who did not speak English as their first language or who grew up in households where English was not the language of choice choose professions that are not so dependent on fluent English, we often hear. But the explanation becomes less credible with every passing year. Philip Vernon, after reviewing the evidence on Asian-Americans, concluded that unfamiliarity with the English language and American culture is a plausible explanation only for the results of the early studies. Contemporary studies of Asian-Americans who are thoroughly acculturated also show the typical discrepancy in verbal and visuospatial abilities. American Indians and Inuit similarly score higher visuospatially than verbally;
their ancestors migrated to the Americas from East Asia hundreds of centuries ago.
⁸⁰
The verbal-visuospatial discrepancy goes deeper than linguistic background.

Vernon’s overall appraisal was that the mean Asian-American IQ is about 97 on verbal tests and about 110 on visuospatial tests.
⁸¹
Lynn’s 1987 review of the IQ literature on East Asians found a median verbal IQ of 98 and a median visuospatial IQ of 106.
⁸²
As of 1993, for Asian-American students who reported that English was the first language they learned (alone or with another language), the Asian-American SAT mean was .21 standard deviation above the national mean on the verbal test and .43 standard deviation above the national mean on the math test. Converted to an IQ metric, this amounts to a 3.3 point elevation of mathematical scores over verbal scores for the high IQ Asian-American population that takes the SAT
⁸³

Why do visuospatial abilities develop more than verbal abilities in people of East Asian ancestry in Japan, Hong Kong, Taiwan, mainland China, and other Asian countries and in the United States and elsewhere, despite the differences among the cultures and languages in all those countries? Any simple socioeconomic, cultural, or linguistic explanation is out of the question, given the diversity of living conditions, native languages, educational resources, and cultural practices experienced by Hong Kong Chinese, Japanese in Japan or the United States, Koreans in Korea or Belgium, and Inuit or American Indians. We are not so rash as to assert that the environment or the culture is
wholly
irrelevant to the development of verbal and visuospatial abilities, but the common genetic history of racial East Asians and their North American or European descendants on the one hand, and the racial Europeans and their North American descendants, on the other, cannot plausibly be dismissed as irrelevant.

P
ROFILE
D
IFFERENCES
B
ETWEEN
W
HITES AND
B
LACKS.
Turning now to blacks and whites (using these terms to refer exclusively to Americans), ability profiles have also been important in understanding the nature, and possible genetic component, of group differences. The argument has been developing around what is known as
Spearman’s hypothesis.
⁸⁴
This hypothesis says that if the B/W difference on test scores reflects a real underlying difference in the general mental ability,
g,
then the size of the B/W difference will be related to the degree to which the test is saturated with
g.
⁸⁵
In other words, the better a test measures
g,
the larger the black-white
difference will be. Arthur Jensen began to explore this possibility when he looked at the pattern of subtest scores on the WISC-R, taking advantage of the fact that the WISC-R has thirteen subtests, each measuring a somewhat different skill. Converting their statistical procedures into a more easily understood form, here is the logic of what Arthur Jensen and his coauthor, Cyril Reynolds, did.
⁸⁶

On average, low-SES whites get lower test scores than high-SES whites. But suppose you were to go through a large set of white test scores from a low-SES and a high-SES group and pull out everyone with an overall IQ score of, say, 105. Now you have identical scores but very different SES groups. The question becomes, What does the pattern of subtest scores look like? The answer is, The same. Once you equalize the overall IQ scores, low-SES and high-SES whites also had close-to-identical mean scores on the individual subtests.

Now do the same exercise with blacks and whites. Again, let us say that you pull all the tests with a full-scale IQ score of exactly 105. Again, you examine the scores on the subtests. But this time the pattern of subtest scores is
not
the same for blacks and whites, even though the subtests add up to the identical overall score.
⁸⁷
Despite identical overall scores, whites are characteristically stronger than blacks on the subtests involving spatial-perceptual ability, and blacks are characteristically stronger than whites in subtests such as arithmetic and immediate memory, both of which involve retention and retrieval of information.
⁸⁸
As Jensen and Reynolds note, the pattern of subtest differences between whites and blacks differs sharply from the “no differences” result associated with SES. This directly contradicts the hypothesis that the B/W difference reflects primarily SES differences.
⁸⁹
What accounts for the different subtest profiles? Jensen and Reynolds proceeded to demonstrate that the results are consistent with Spearman’s hypothesis. Whites and blacks differ more on the subtests most highly correlated with
g,
less on those least correlated with
g.

Since that initial study using the WISC-R, Jensen has been assembling studies that permit further tests of Spearman’s hypothesis. He concluded from over a dozen large and representative samples of blacks and whites
⁹⁰
that “Spearman’s hypothesis has been borne out significantly by every study (i.e., 13 out of 13) and no appropriate data set has yet been found that contradicts Spearman’s hypothesis.”
⁹¹
There appears to be no dispute with his summary of the facts. It should be noted that not all group differences behave similarly. For example, deaf children often
get lower test scores than hearing children, but the size of the difference is not positively correlated with the test’s loading on
g.
⁹²
The phenomenon seems peculiarly concentrated in comparisons of ethnic groups.