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Dan Agin

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Black and White in America IV: IQ Myths and Realities

Posted: 01/25/09 02:17 PM ET

(See previous columns in this series.)

Myths about group differences in IQ and behavior depend very much on myths about individual differences in IQ and behavior. For example, some untenable ideas about the heritability of IQ are a central component of hereditarian explanations of group differences. Because of this overlap, discussion of myths about group differences often needs to include consideration of individual differences. In this column I focus on IQ and behavior myths with a special emphasis on myths related to race or groups as a whole and to cultural factors.

Myth: Biological or genetic determinism is a nothing more than a scientific discipline that studies the biological basis of all forms of human behavior.

Reality: Biological or genetic determinism as applied to human behavior is an ideology rather than a scientific discipline. It proposes that humans differ in fundamental abilities because of innate differences, that these innate differences are biologically inherited, and that human nature guarantees the formation of a hierarchical society -- top dogs and bottom dogs.

Myth: Intelligence is a general mental capability that involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly, and learn from experience -- a broad and deep capability for comprehending our surroundings. Intelligence so defined can be measured, and intelligence tests measure it well.

Reality: The deep fallacy is the idea that any concept occurring in the human mind and expressible in language is a real measurable entity. Apart from measuring learning rates (for example, "learning quickly"), nothing in this myth can be measured quantitatively and reliably with objective measuring instruments. Intelligence is a concept, not an object or a succinct event, and no more measurable than beauty, truth, wisdom, humor, misery, and so on. What we can measure quantitatively is cognitive performance on a certain task. The only meaningful definition of cognitive performance is operational and in terms of the instruments used to measure it.

Myth: Different types of intelligence tests all measure the same intelligence.

Reality: This is a fallacy. Since cognitive performance is defined operationally, the definition must change as the test changes. The myth is based on the pair correlations between scores on one type of test with scores on another type of test. But pair correlations measure only similarities of variation and imply nothing about underlying causalities. There is no basis for the idea that pair correlations between two sets of test scores indicate the tests are measuring the same variable.

Myth: The spread of people along the IQ-test continuum, from low to high, can be represented by the bell curve (the normal curve).

Reality: The questions in the IQ test are designed to produce a bell-curve distribution of scores. It's possible to design a cognitive performance test that produces another kind of distribution. What we find as the "spread of people" in cognitive performance depends on the measuring instrument we use.

Myth: Intelligence tests are not culturally biased against American blacks or other native-born English-speaking people in the United States. Culture bias in IQ tests does not explain the difference in black-white IQ scores, a difference of approximately 15 points between the means of group distributions.

Reality: The idea that all "native-born English-speaking people in the United States" develop and live in the same culture is anthropological nonsense. Cognitive performance is never independent of culture any more than the way language is used is independent of culture. Linguistic structure, in fact, controls the way people think and learn, so that if linguistic structure is culture dependent, so also is thinking and learning. As for cultural bias in IQ tests not explaining the difference in black-white IQ scores, there is no hard scientific evidence to support any such idea -- and considerable evidence against it. The notorious black-white IQ gap of one standard deviation (about 15 points), touted by genetic determinists to be independent of culture, was in fact substantially reduced between 1972 and 2002 -- and it continues to shrink.

Myth: Heritability is the squared correlation of phenotype with genotype. Heritability estimates for IQ range from 0.4 to 0.8, most estimates thereby indicating that genetics plays a bigger role than does environment in creating IQ differences among individuals.

Reality: If heritability is the squared correlation of phenotype with genotype, the assumption is that the phenotype and genotype under discussion can be measured. The human individual genotype is not yet even defined, let alone measurable, so with or without a measurable phenotype, "heritability" cannot be calculated without restrictive assumptions. As for the range of 0.4 to 0.8 for the heritability of IQ, it's a fallacy based on an assumption of independent genetic and environmental variables in a linear relationship with heritability, which means no gene-environment interactions. The deep fallacy is that any contributions to variance due to factors acting before birth (such as prenatal impacts) are assumed to be genetic. As far as genes playing "a bigger role" than environment in creating individual differences in IQ is concerned, that's a total misreading of the meaning of a correlation coefficient.

Myth: Although the environment is important in creating IQ differences, we do not know yet how to manipulate it to raise IQ permanently.

Reality: Most evidence suggests the opposite. For example, concerning prenatal impacts, the known effects on fetal brain development and later IQ of factors such as environmental pollution, maternal stress during gestation, and poor health care for pregnant women imply that removing these stressors would ultimately mean an improvement in postnatal IQ.

Myth: To the extent that genes play a role in intelligence, IQ will vary by racial admixture.

Reality: This simplistic statement is not true. Given the complexity of gene expression prenatally and postnatally, variation by racial or ethnic admixture may or may not occur. There is certainly no scientific evidence to support the myth, and racial admixture blood group analysis does not predict IQ. Human intelligence, whatever it is, is certainly not a Mendelian trait.

Myth: IQ subtests based on abstract designs have little or no cultural content.

Reality: The fallacy here is the assumption that cultural bias means only culture-dependent content. Methods of problem solution can also be culture dependent. If the method that must be used to solve an abstract problem is common to one culture but not to another culture, the problem is culturally biased.

Myth: the Spearman g-factor (also called "global intelligence" or "general intelligence") represents a biologically grounded and highly heritable cognitive resource, which gives one reason to think that not much about black-white IQ differences will change in the years to come.

Reality: The so-called biological grounding consists of correlations with various physiological parameters such as brain evoked potentials, brain pH levels, brain glucose metabolism, peripheral nerve conduction velocity, and psychological reaction time. All of these are also correlated with nearly everything that goes on in the brain, and none of these parameters has ever been established as a determinant of cognitive performance. The g correlations are merely evidence that the brain is a part of the body involved in taking an IQ test. The correlations tell us nothing about any "biological grounding" or any causal relation between any physiological variable and IQ scores. As expected, neuroscientists are not at all excited about Spearman's g-factor. It tells them nothing about the neurological substrate of cognitive performance. Concerning the "high heritability" of g, as I have pointed out, the numerical value assumes a fallacious linear statistical model and a fallacious biological model that lumps all prenatal environmental impacts with the genotype variance. As for the idea that not much about black-white differences in IQ scores will change in the years to come, there is no scientific evidence to confirm that idea, and there are hundreds of studies that suggest otherwise. The black-white IQ score distributions are now less than one standard deviation apart, and "the years to come" may demonstrate that elimination of prenatal impacts that are damaging to the brain and often transgenerational may also eliminate black-white group differences in IQ scores. There is certainly no evidence to suggest the idea that differences are intractable. A high calculated "heritability" says nothing about the possibility of future change. It's an old reality that a trait can have a current heritability of 1.0 (which means 100 percent of total variance is due to genetic variance) in a population and be completely altered in the future by a new environment that introduces environmental contributions to variance.

Myth: Genetic cluster analysis of DNA supports the common notion of individual "races" among modern peoples.

Reality: Genetic cluster analysis of DNA supports the idea of DNA clusters -- and that's all. Relating these clusters to so-called races is problematic. For example, DNA analysis reports a non-black Hispanic-American cluster different from a "white" cluster, but Hispanic-Americans are not commonly viewed as a "race" by most Americans. In addition, there is no evidence from any cluster analysis that the DNA components related to clustering are involved with intelligence or behavior. It's possible the DNA components that produce clustering are all related to superficial phenotype traits such as skin color, eye color, and so on.

Myth: The correlation between brain size and intelligence within either race, and the average difference in brain size and intelligence between blacks and whites, are well established in the scientific literature.

Reality: This canard is a common argument of white supremacists, but the scientific literature does not support the idea. What the scientific literature does suggest is a relation between cognitive performance and the thickness (or thinness) of certain regions of the cerebral cortex, but there are no reliable data measuring cortical thickness differences between ethnic groups.

Myth: Because prenatal effects are more or less random, they are difficult to remedy or control, and their occurrence has probably been reduced in recent decades by improved maternal nutrition, advances in obstetrical techniques, and improved health in general.

Reality: First, prenatal effects are not "more or less random" but usually nonrandom effects due to environmental pollution or cultural impacts on maternal psychology or physiology. Second, the variety of prenatal effects is so broad there is no basis for the statement that they are "difficult to remedy or control" --indeed, some prenatal impacts (for example, tobacco smoking and alcohol use during pregnancy, nutrition and infection, etc.) are relatively easy to control. Third, there is no evidence at all that prenatal impacts have been reduced in recent decades to make them now of little or no importance.

So much for some myths and realities. It's unfortunate that too many people who ought to know better are so eager to promote the idea of intellectual differences between blacks and whites in America. Their eagerness continues to appear as a psychiatric puzzle, the old tribal hoax covered by transparent veils.

Humans are a complex species with plastic brains that allow rapid behavioral changes from one generation to the next through cultural evolution. Brain plasticity means our brains can be wired and rewired by experience. No other species has any comparable biological capability -- not to the degree present in humans. As for black and white in America, it would certainly help us all to focus more on our similarities than on our differences. Meanwhile, until White America stops standing on the face of Black America, let's not delude ourselves that we're free of the tribal hoax.

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Here are a few books (one to be published soon) that expand on some of the ideas presented in this series of columns:

Agin, D. Changing Destiny: How the Fetal Environment Shapes IQ and Behavior. Oxford University Press, 2009 (in press).

Gould, S. The Mismeasure of Man. W. W. Norton, 1996.

Graves, J. The Emperor's New Clothes: Biological Theories of Race at the Millennium. Rutgers University Press, 2002.

Jencks, C. and Phillips, M. (Eds.) The Black-White Test Score Gap. Brookings Institution Press, 1998.

Kevles, D. In the Name of Eugenics: Genetics and the Uses of Human Heredity. Harvard University Press, 1995.

Lewontin, R., Rose, S., and Kamin, L. Not In Our Genes: Biology, Ideology, and Human Nature. Pantheon, 1984.

Tucker, W. The Science and Politics of Racial Research. University of Illinois Press, 1994.