By Pilar Ossorio

Over the past two centuries biomedical science has, at times, provided justification for white privilege.  Science has been used to support the proposition that differences in achievement reflect innate differences in ability among racial groups.  Broadly speaking, the view that differences in academic achievement, IQ scores, employment status or wealth primarily reflect innate differences is called "biological determinism."1  As the late Stephen J. Gould pointed out, at its core, biological determinism is "a theory of limits.  It takes the current status of groups as a measure of where they should and must be (even while it allows some rare individuals to rise as a consequence of their fortunate biology)."2

Biological determinism lost most of its scientific credibility by the mid-20th century, and lost much of its social and political power after World War II; however, it never entirely disappeared.  Today, some people believe that persistent racial gaps in, for instance, school achievement, family income, and wealth must reflect innate differences in ability.  One human trait that is postulated to play a role in many kinds of achievement is intelligence, and some commentators theorize that racial differences in average levels of intelligence explain achievement gaps. 

At the same time, the new molecular genetics has captured the public imagination and has provided tools for conducting large-scale genetic comparisons between individuals and between human groups.  Some people will look to modern genetics to provide scientific justifications for racial inequalities.  Genetics is particularly appealing in this role because of its apparent precision, authority, and high-tech chic.  Many people reason that if groups vary with respect to innate cognitive abilities, then the differences between groups must be attributable to differing racial patterns of genetic variation. To disentangle claims about race, genetics and intelligence, we must examine beliefs about race and intelligence, and understand what role genes reasonably could or could not play with regard to the intersection of these two concepts.

In the contemporary world, beliefs about racial difference, and racial superiority or inferiority, may be articulated in the language of molecular genetics and genomics.  Modern genetics has great authority, and beliefs about race that once relied on vague notions of innate difference can be made to sound more precise and credible by framing them as genetic explanations.  Genes can be viewed as the substrate by which God or natural selection rendered some groups superior and others inferior.  Educational achievement, wealth, and other measures of status often run in families, a fact that may increase the intuitive credibility of genetic explanations. However, societalal institutions operate to entrench groups who wield power into self-perpetuating dynasties. From the Tudor monarchical dynasty in 16th century England to the Bush and Kennedy family dynasties in the 20th and 21st centuries in the United States, families with access to power pass their positions of privilege on to succeeding generations through processes that have little to do with hereditary transmission of genetic traits.

Just as there is no unitary definition of race, there is no agreed upon or single definition of intelligence; one aphorism holds that intelligence is what intelligence tests measure. Psychometricians argue that intelligence tests measure reasoning skills, although the tests also measure knowledge. Some innovative scholars have developed theories of emotional intelligence and multiple intelligences-multiple types of cognitive function that are valuable and measurable, and that may manifest differently in different contexts.3  The typical IQ test does not measure multiple intelligences; instead, the test produces a single intelligence quotient (IQ).

Some scholars argue that one's IQ indicates one's general cognitive ability, often referred to by the letter "g". 1,2  Many other scholars argue that the notion of a single, general quality that underlies performance on all cognitive tests is incoherent.3  Stephen Jay Gould has provided a thorough explanation and critique of the concept of g in The Mismeasure of Man.2  The measure "g"  has been a useful concept for commentators who seek to create social hierarchies based on intelligence, because "...ranking requires a criterion for assigning all individuals to their proper status in a single series."2 

Alfred Binet, the developer of the first intelligence test in the early 20th century, rejected the notion that his test measured a person's inborn or fixed cognitive ability.  He also declined to use his test to rank individuals according to cognitive ability.  The purpose for which he devised the test, and the only purpose for which he thought it appropriate, was to measure the intellectual capacity of children who were performing poorly in school, to determine which children had cognitive deficits for which remedial instruction might be helpful.  Later psychologists, particularly those in the United States, took up and modified Binet's test, and were willing to embrace the view that intelligence was an inborn and fixed attribute of a person.  We can call this view the hereditarian theory of IQ.

Over the past decade, some contemporary proponents of the hereditarian theory have argued that 1) IQ is the most important determinant of academic success; 2) academic success is the most important determinant of high status and wealth-generating employment; and therefore 3) the economic elite have their positions and wealth as a matter of merit (intellectual contribution to society), and conversely, members of the economic underclass also deserve their position at the bottom of the social hierarchy.4  These commentators argue that programs aimed at raising the academic achievement of disadvantaged students are misguided because those students are, on average, biologically incapable of significant academic success.  Racial gaps in test scores, from IQ to the SAT, are interpreted by hereditarians as evidence of inherent and immutable racial or ethnic differences in underlying cognitive capacity. 

Many claims of contemporary hereditarians have been critiqued and debunked in books such as Measured Lies, Inequality by Design, Whitewashing Race, and Intelligence and How to Get It.  These books describe mistakes of fact, method and logic made by the hereditarians.

A significant problem in debates about hereditarian theories of IQ is that correlations are often treated as proof of causation.  If one observes that people in lower socioeconomic brackets, on average, score lower on IQ tests than people in higher socioeconomic brackets, this does not mean that low IQ causes poverty.  It could be that poverty causes low IQ, or that something else causes both outcomes.  If IQ test scores correlate with race (however race is defined), this does not mean that some inborn racial essence causes particular IQ test scores.  One reasonable alternative explanation is that race is correlated with other factors, such as quality of schools, exposure to lead, or malnutrition, and these other factors are causing the observed differences in test scores.

Many scholars question the entire enterprise of treating heritability statistics as though genes and environment are actually separable influences on IQ or any other trait. Genes always function within particular environments to shape the developing human organism. The developmental interaction among many genes, and numerous environmental factors, is complex, varies over time, and is susceptible to chance events.

Researchers have, in fact, found evidence that some environmental factors are strongly associated with IQ and other measures of cognition. Malnutrition and exposure to environmental toxins, such as lead from paint, are strongly correlated with IQ. The quality of a person's school significantly impacts her IQ score - children who begin their education in poor quality schools and then move to better ones show increases in their IQ scores.5

A study published in 2009 found that long-term stress is negatively associated with young adults' performance on cognitive tests.6  This study measured levels of several physiological properties associated with stress, including blood pressure, cortisol, and epinephrine levels.  The researchers collected data throughout their participants' childhood years, then administered tests of cognitive performance when the children turned 17 years old.  Young adults whose bodies exhibited the highest levels of chronic stress had the least effective working memories and poorer cognitive performance. These data only show correlations between stress and IQ scores, they do not prove causation. But, they suggest an alternative theory that is at least as plausible as the theory that genetic differences are the primary cause of group differences in IQ scores.

Research also undermines the hereditarian claim that IQ is the primary determinant of achievement. Many environmental variables predict achievement as well or better than IQ, except for people whose IQ scores are at the abnormally low end of the scale.  For instance, a person's social environment may be an important determinant of her achievement, yet variables that capture a person's social environment are often, literally, left out of the equation in work done by hereditarians. The social environment includes the expectations of one's peers, encouragement by one's parents and teachers, enrichment opportunities available in the neighborhood, etc.  A decades long study that included social environment variables found that a 15 point difference in IQ scores among high school boys only explained 6 percent of the variability in their earnings at age 35.  The greater the number of social factors taken into account, the less important IQ became.7  Social context variables were still significantly correlated with earnings by age 55. 

In a related analysis, Fisher et al. demonstrated that if all adults in the country had the same score on an IQ test, the variation in household income would only decrease by about 10%. Contrary to hereditarian claims, these data suggest that differences in IQ do not explain much about professional achievement and wage inequality, including wage inequality between racial groups.5  On the other hand, factors external to an individual can greatly influence her or his lifelong course of achievement.  

Because race comprehensively structures people's lives in the United States, it is correlated with many environmental factors that can influence IQ and achievement. People of different races tend to live in different neighborhoods, so they may be exposed to different levels of lead, different quality schools, different diets and different levels or types of stress.  They may be exposed to different attitudes about achievement.  People of minority groups may routinely experience racism, a kind of stress that can have long-term physiological consequences.  On average, people of different races receive health care at different institutions, and the care they receive is not of the same quality.  In sum, racial groups differ with respect to so many environmental factors that it is very likely that environmental differences explain current racial gaps in mean IQ scores.

The environment can be modified in ways that genes cannot.  When the environment is changed, the trait of interest (in this case intelligence) may also change even though genes also play a role in shaping that trait.  In one study, African-American children in Milwaukee who were thought to be at risk for cognitive disability,  were randomized so that half received intensive day care and early, enriched education, while the other half received ordinary day care and schooling.8  By age five, children who received the intensive intervention averaged 110 on a standard IQ test (above average), while children in the control group averaged 83 (well below average).  The effects of early, intensive education were still apparent by adolescence, when the children from the intervention group scored, on average, 10 points higher on IQ tests than the children from the control group. 

There is some evidence that differing environments have influenced the entire human population's IQ scores over time.  People's average IQ scores have risen by about 3 IQ points per decade over the last century.8 The average IQ score from 1917 would amount to about 73 on today's tests.  This effect almost certainly is not due to changes in human genetics, because there has not been enough time for new intelligence-related mutations to arise and spread throughout human populations.  The most likely explanation for the rise in IQ is that some relevant environmental factors have changed, causing people to develop in ways that are reflected in higher average IQ scores.

Another piece of evidence concerning widespread environmental influences on IQ is that the mean difference between black Americans' and white Americans' test scores has narrowed since the 1970s.  Using data from several different IQ tests that were administered in a standard manner to black and non-Hispanic white people, Dickens and Flynn showed that blacks have narrowed the IQ gap by one third to one half of what it was in the 1970s.9 If IQ were a fixed, intrinsic quality of races, then the IQ gap should be stable over time, but it is not.

The binary formulation of "genes vs. environment" is misleading. Cognitive abilities are complex and will likely be influenced by a myriad of environmental factors and genes. Given the complexity of brains and cognition, one ought not expect that a few genes will play a dominant role in shaping the normal range of human cognitive abilities; numerous genes will be involved. It is statistically implausible that variants of numerous genes relating to intelligence would be distributed among racial groups in a manner that systematically conferred cognitive advantage on one group or disadvantage on another. Furthermore, there is no evidence to support the claim that current racial differences in mean IQ scores are caused by racially distinctive patterns of genetic variation.

There is evidence that IQ scores are influenced by environmental factors that are pervasively and systematically patterned along racial lines in the U.S.  Nonetheless, mean IQ differences among racial groups have been decreasing over the past few decades, perhaps in response to improved educational opportunities for some minority individuals.  Taken together, the evidence suggests that differences in IQ scores are the result of social inequality rather than its cause.                                                        


Pilar Ossorio, PhD, is Associate Professor of Law and Bioethics at the University of Wisconsin at Madison, and Program Faculty in the Graduate Program in Population Health at the UW. Dr. Ossorio is a fellow of the American Association for the Advancement of Science, a member of the editorial board of the American Journal of Bioethics, chair of an NHGRI advisory group on ethical issues in large scale sequencing, and a member of UW's institutional review board for health sciences research.



1. Anonymous. Intelligence and Genetic Determinism. GeneWatch 19: 9 - 12 (2006).

2. Gould, S.J. The Mismeasure of Man (W.W. Norton & Company, New York, 1981).

3. Cooper, R.S. Race and IQ: Molecular Genetics as Deus ex Machina. American Psychologist 60: 42-44 (2005).

4. Hernstein, R.J. & Murray, C. The Bell Curve: The reshaping of American life by difference in intelligence (Free Press, New York, 1994).

5. Fisher, C.S. et al. (eds.) Inequality By Design: Cracking the Bell Curve Myth, (Princeton University Press, Princeton, NJ, 1996); Ceci, S.J. How much does schoolign influence general intelligence and its cognitive components? A reassessment of the evidence. Developmental Psychology 27: 703 722 (1991).

6. Evans, G.W. & Schamberg, M.A. Childhood poverty, chronic stress, and adult working memory. Proceedings of the National Academy of Sciences, Early Edition 10.1073/pnas.0811910106: 1 - 5 (2009).

7. Zax, J.S. & Rees, D.I. IQ, Academic Performance, Environment, and Earnings. The Review of Economics and Statistics 84: 600 - 616 (2002).

8. Nisbett, R. Intelligence and How to Get It: Why Schools and Cultures Count (W.W. Norton & Company, New York, 2009).

9. Dickens, W.T. & Flynn, J.R. Black Americans Reduce the Racial IQ Gap. Psychological Science 17: 913 - 920 (2006).


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