Much to my dismay, however, my article set off an emotional furor in the world of social science. Amplified by the popular press, the furor soon spread beyond the confines of academia. Almost overnight I became a cause celebre, at least on college campuses. I had spoken what Joseph Alsop called "the unspeakable." To many Americans I had thought the unthinkable.

Science Vs. the Fear of Racism

The civil-rights movement that gained momentum in the 1950s "required" liberal academic adherence to the theory that the environment was responsible for any individual or racial behavioral differences, and the corollary belief in genetic equality in intelligence. Thus, when I questioned such beliefs I, and my theories, quickly acquired the label "racist." I resent this label, and consider it unfair and inaccurate.

The Real Meaning of Racism

When I published my article in 1969, many critics confused the purely empirical question of the genetic role in racial differences in mental abilities with the highly charged political-ideological issue of racism. Because of their confusion, they denounced my attempt to study the possible genetic causes of such differences. At the same time, the doctrinaire environmentalists, seeing their own position threatened by my inquiry, righteously and dogmatically scorned the genetic theory of intelligence.

Thankfully, the emotional furor that greeted my article has died down enough recently to permit sober and searching consideration of the true intent and substance of what I actually tried to say. Under fresh scrutiny stimulated by the controversy, many scientists have reexamined the environmentalist explanations of the black IQ deficit and found them to be inadequate. They simply do not fully account for the known facts in the comprehensive and consistent manner we should expect of a scientific explanation.

The Black IQ Deficit

A difference of one standard deviation can hardly be called inconsequential. Intelligence tests have more than proved themselves as valid predictors of scholastic performance and occupational attainment, and they predict equally well for blacks as for whites. Unpleasant as these predictions may seem to some people, their significance cannot be wished away because of a belief in equality. Of course, an individual's success and self-fulfillment depends upon many characteristics besides intelligence, but IQ does represent an index, albeit an imperfect one, of the ability to compete in many walks of life. For example, many selective colleges require College Board test scores of 600 (equivalent to an IQ of 115) as a minimum for admission. An average IQ difference of one standard deviation between blacks and whites means that the white population will have about seven times the percentage of such potentially talented persons (i.e., IQs over 115) as the black population. At the other end of the scale, the 15-point difference in average IQ scores means that mental retardation (IQ below 70) will occur about seven times as often among blacks as among whites.

The IQ difference between blacks and whites, then, clearly has considerable social significance. Yet the environmentalists dismiss this difference as artificial and claim it does not imply any innate or genetic difference in intelligence. But as I shall show, the purely environmental explanations most commonly put forth are faulty. Examined closely in terms of the available evidence, they simply do not sustain the burden of explanation that they claim. Of course, they may be possible explanations of the IQ difference, but that does not necessarily make them the most probable. In every case for which there was sufficient relevant evidence to put to a detailed test, the environmental explanations have proven inadequate. I am not saying they have been proven 100 percent wrong, only that they do not account for all of the black IQ deficit. Of course, there may be other possible environmental explanations as yet unformulated and untested.

Arguments for the Genetic Hypothesis

Let us consider some of the genetically conditioned characteristics that we already know to vary between major racial groups: body size and proportions; cranial size and shape; pigmentation of the hair, skin and eyes; hair form and distribution; number of vertebrae; fingerprints; bone density; basic-metabolic rate; sweating; consistency of ear wax; age of eruption of the permanent teeth; fissural patterns on the surfaces of the teeth; blood groups; chronic diseases; frequency of twinning; male-female birth ratio; visual and auditory acuity; colorblindness; taste; length of gestation period; physical maturity at birth. In view of so many genetically conditioned traits that do differ between races, wouldn't it be surprising if genetically conditioned mental traits were a major exception?

The Heritability of Intelligence

No precise figure exists for the heritability of intelligence, since, like any population statistic, it varies from one study to another, depending on the particular population sampled, the IQ test used, and the method of genetic analysis. Most of the estimates for the heritability of intelligence in the populations studied indicate that genetic factors are about twice as important as environmental factors as a cause of IQ differences among individuals.

I do not know of a methodologically adequate determination of IQ heritability in a sample of the U. S. black population. The few estimates that exist, though statistically weak, give little reason to suspect that the heritability of IQ for blacks, when adequately estimated, should differ appreciably from that for whites. Of course the absence of reliable data makes this a speculative assumption.

What implication does the heritability within a population have concerning the cause of the difference between two populations? The fact that IQ is highly heritable within the white and probably the black population does not by itself constitute formal proof that the difference between the populations is genetic, either in whole or in part. However, the fact of substantial heritability of IQ within the populations does increase the a priori probability that the population difference is partly attributable to genetic factors. Biologists generally agree that, almost without exception throughout nature, any genetically conditioned characteristic that varies among individuals within a subspecies (i.e., race) also varies genetically between different subspecies. Thus, the substantial heritability of IQ within the Caucasian and probably black populations makes it likely (but does not prove) that the black population's lower average IQ is caused at least in part by a genetic difference.

What about the purely cultural and environmental explanations of the IQ difference? The most common argument claims that IQ tests have a built-in cultural bias that discriminates against blacks and other poor minority groups. Those who hold this view criticize the tests as being based unfairly on the language, knowledge and cognitive skills of the white "Anglo" middle class. They argue that blacks in the United States do not share in the same culture as whites, and therefore acquire different meanings to words, different knowledge, and a different set of intellectual skills.

Culture-Fair Vs. Culture-Biased

Surprisingly, blacks tend to perform relatively better on the more culture-loaded or verbal kinds of tests than on the culture-fair type. For example, on the widely used Wechsler Intelligence Scale, comprised of 11 different subtests, blacks do better on the culture-loaded subtests of vocabulary, general information, and verbal comprehension than on the nonverbal performance tests such as the block designs. Just the opposite is true for such minorities as Orientals, Mexican-Americans, Indians, and Puerto Ricans. It can hardly be claimed that culture-fair tests have a built-in bias in favor of white, Anglo, middle-class Americans when Arctic Eskimos taking the same tests perform on a par with white, middle-class norms. My assistants and I have tested large numbers of Chinese children who score well above white norms on such tests, despite being recent immigrants from Hong Kong and Formosa, knowing little or no English, and having parents who hold low-level socioeconomic occupations. If the tests have a bias toward the white, Anglo, middle-class, one might well wonder why Oriental children should outscore the white Anglos on whom the tests were originally standardized. Our tests of Mexican-Americans produced similar results. They do rather poorly on the culture-loaded types of tests based on verbal skills and knowledge, but they do better on the culture-fair tests. The same holds true for American Indians. All these minorities perform on the two types of tests much as one might expect from the culture-bias hypothesis. Only blacks, among the minorities we have tested, score in just the opposite manner.

Intelligence Tests Are Colorblind

We have studied culture bias in some standard IQ tests by making internal analyses to see which kinds of test items produce greater differences in scores between blacks and whites. For example, we made such an item-by-item check of the highly culture-loaded Peabody Picture Vocabulary Test, on which blacks average some 15 points lower than whites. The PPVT consists of 150 cards, each containing four pictures. The examiner names one of the pictures and the child points to the appropriate picture. The items follow the order of their difficulty, as measured by the percentage of the children in the normative sample who fail the item.

California Vs. England; Boys Vs. Girls

Yet when we made exactly the same kind of comparison between blacks and whites in the same city in California, and even in the same schools, we found virtually no difference between the two groups in the order of items when ranked for difficulty, as indexed by the percent failing each item. Both groups show the same rank order of difficulty, although on each item a smaller percentage of blacks give the correct answer. In fact, even the differences between adjacent test items in terms of percent answering correctly show great similarity in both the black and white groups.

If this kind of internal analysis reflects cultural bias between different national groups, and sexual bias within the same racial group, why does it not reflect the supposed bias between the two racial groups? If the tests discriminate against blacks, why do blacks and whites make errors on the same items? Why should the most and least common errors in one group be the same as in the other?

Another way internal analysis can be used to check for bias involves looking for different patterns of item intercorrelations. For example, if a person gets item number 20 right, he may be more likely to get, say, item 30 right than if he had missed item 20. This follows because the test items correlate with one another to varying degrees, and the amount of correlation and the pattern of intercorrelations should be sensitive to group differences in cultural background. Yet we have found no significant or appreciable differences between item intercorrelations for blacks and whites.

In summary, we have found no discriminant features of test items that can statistically separate the test records of blacks and whites any better than chance, when the records are equated for total number correct. We could do so with the London versus California groups, or for sex differences within the same racial group. Thus, even when using the PPVT, one of the most culture-loaded tests, black and white performances did not differ as one should expect if we accept the culture-bias explanation for the black IQ deficit. I consider this strong evidence against the validity of that explanation.

The Effect of the Tester

The Question of "Verbal Deprivation"

If one hypothesizes that the black IQ deficit may be due to poor motivation or uncooperative attitudes of blacks in the test situation, then one must explain why little or no difference in scores occurs between blacks and whites on tests involving rote learning and memory. Such tests are just as demanding in terms of attention, effort and persistence, but do not call upon the kinds of abstract reasoning abilities that characterize the culture-fair intelligence tests. We have devised experimental tests, which look to pupils like any other tests, that minimize the need for reasoning and abstract ability, and maximize the role of nonconceptual learning and memory. On these tests black and white children average about the same scores. Therefore, the racial difference clearly does not involve all mental abililities equally. It involves mainly conceptual and abstract reasoning, and not learning and memory.

Another factor often cited as a possible explanation for the black IQ deficit is teacher expectancy—the notion that a child's test score tends to reflect the level of performance expected by his or her teacher, with the teacher's expectation often based on prejudice or stereotypes. Yet numerous studies of teacher expectancy have failed to establish this phenomenon as a contributing factor to the lower IQ scores of blacks.

Testing the Environmental Hypothesis

The "Sociologist's Fallacy"

Those who cite the socioeconomic matching studies also fail to take account of the well-established genetic difference between social classes, which invalidates their comparison. For example, when the two races are matched for social background, the average skin color of the black group runs lighter in the higher SES groups. This difference indicates that genetic characteristics do vary with SES. Thus SES matching of blacks and whites reduces the IQ difference not only because it controls for environmental differences, but because it tends to equalize genetic factors as well.

Variables That Don't Behave

But in a nationwide survey reported in the Coleman Report, in 1966, Indians scored higher than blacks on all such tests, from the first to the 12th grade. On a nonverbal test given in the first grade, for example, before schooling could have had much impact, Indian children exceeded the mean score of blacks by the equivalent of 14 IQ points. Similar findings occur with Mexican-Americans, who rate below blacks on socioeconomic and other environmental indices, but score considerably higher on IQ tests, especially on the nonverbal type. Thus the IQ difference between Indians and blacks, and between Mexican-Americans and blacks, turns out opposite to what one would predict from purely environmental theory, which of course, assumes complete genetic equality for intelligence. No testable environmental hypothesis has as yet been offered to account for these findings.

Does Malnutrition Affect Intelligence?

Nor do I know of any evidence among humans that maternal malnutrition, by itself, can have pre- or postnatal effects on a child's mental development. The severe famine in the Netherlands during the last years of World War II provided an excellent case study of such a possibility. Thousands of men conceived, gestated, and born during the period of most severe famine, were later tested, as young adults, on Raven's Standard Progressive Matrices, a nonverbal reasoning test. Their scores did not differ significantly from the scores of other Dutch youths of the same age who had not been exposed to such maternal nutritional deprivation.

If further research should definitely establish the existence of genetically conditioned differences in intelligence between certain races, what would be the practical implications? It would take several articles to consider the question adequately, but the only morally tenable position in human relations would remain unchanged: that all persons should be treated according to their own individual characteristics, and not in terms of their group identity. Let me stress that none of the research I have discussed here allows one to conclude anything about the intelligence of any individual black or white person.

Equality of rights and opportunities is clearly the most beneficial condition for any society. Acceptance of the reality of human differences in mental abilities would simply underline the need for equality of opportunity in order to allow everyone to achieve his or her own self-fulfillment. In order to take account and advantage of the diversity of abilities in the population, and truly to serve all citizens equally, the public schools should move beyond narrow conceptions of scholastic achievement. They should offer a much greater diversity of ways for children of whatever aptitude to benefit from their education.

Environment Vs. Genetics: Still an Open Question

Politicizing a Scientific Issue

Most of the attempts to politicize the issue, I have found, come from the radical left. True liberals and humanists, on the other hand, want to learn the facts. They do not wish to expend their energies sustaining myths and illusions. They wish to face reality, whatever it may be, because only on the level of reality can real problems be effectively confronted. This means asking hard questions, and seeking the answers with as much scientific ingenuity and integrity as we can muster. It means examining all reasonable hypotheses, including unpopular ones. It means maintaining the capacity to doubt what we might most want to believe, acknowledging the uncertainties at the edge of knowledge, and viewing new findings in terms of shifting probabilities rather than as absolute conclusions.

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