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Race and intelligence

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Bell curve showing results of studies comparing races and ethnic groups with IQ among U.S. test subjects show differences in average test scores, though the distributions overlap, as seen in this graph based on Reynolds et al. 1987 (see footnote 2 for further references). The causes and meaning of the different average scores for these groups are debated.
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Race and intelligence is a controversial area of anthropology and intelligence research studying the nature, origins, and practical consequences of racial and ethnic group differences in intelligence test scores and other measures of cognitive ability.[1]

Much of the evidence currently cited is based on IQ testing in the United States. While the distributions of IQ scores among different racial-ethnic groups overlap considerably, groups differ in where their members cluster along the IQ scale.[2] Similar clustering occurs with related variables, such as school achievement, reaction time, and brain size, and the gap shows up before age 3 on most standardized tests after matching for variables such as maternal education.[3] Most variation in IQ in the U.S. occurs within individual families, not between races. However, even small differences in average IQ at the group level might theoretically have large effects on social outcomes. For example, a randomly selected group of Americans with an average IQ of 103 had a poverty rate 25% lower than a group with an average IQ of 100. Similar substantial correlations in high school drop-out rates, crime rates, and other outcomes have been measured.[4]

Many hypotheses have been proposed to explain racial-ethnic group differences in IQ. Certain environmental factors, such as childhood nutrition, are thought to modulate IQ in children[5], and other influences have been hypothesized, including education level, richness of the early home environment, and other social, cultural, or economic factors. The primary focus of the scientific debate is whether group IQ differences also reflect a genetic component. Hereditarianism hypothesizes that a genetic contribution to intelligence could include genes linked to neuron structure or function, brain size or metabolism, or other physiological differences which could vary with biogeographic ancestry.

The findings of this field are often thought to conflict with fundamental social philosophies, and have thus engendered a large controversy. Media portrayal of the role of genetic and environmental factors in explaining individual and group differences in IQ was shown in a 1988 study to be misleading regarding mainstream expert opinion. Some critics examine the fairness and validity of cognitive testing and racial categorization, as well as the reliability of the studies and the motives of the authors, on both sides. Some critics fear the misuse of the research, question its utility, feel that comparing the intelligence of racial groups is itself unethical, whether justified or unjustified. For instance, the disparity in average IQ among racial groups is sometimes mistaken for the idea that all members of one race are more intelligent than all members of another, or that ranking group IQ averages from "high" to "low" implies a moral ranking of races from "good" to "bad" or an overall ranking of "superior" to "inferior". The conclusion that some racial groups have lower average IQ scores, and the hypothesis that a genetic component may be involved, have led to heated academic debates that have spilled over into the public sphere.

Background information

Basic concepts

This research is grounded in several controversial assumptions:


Main article: Race

Racial distinctions are generally made on the basis of skin color, facial features, ancestry, national origin and self-identification. A debate is ongoing over the merit of the concept of 'race', especially from the perspective of genetics. Many scientists argue that common racial classifications are insufficient, inaccurate, or biologically meaningless. For example, Lewontin (1972) argues that there is no biological basis for race on the basis of research indicating that more genetic variation exists within such races than between them. There are also many more recent criticisms of different aspects of the concept that have been presented in recent peer-reviewed papers.[6] However, some geneticists have claimed that many of these "well-intentioned"[7] statements are false and do not "derive from an objective scientific perspective."[8] They argue instead "that from both an objective and scientific (genetic and epidemiologic) perspective there is great validity in racial/ethnic self-categorizations, both from the research and public policy points of view."[8] Recent studies have identified some genes involved in the brain that occur in different frequencies in different races, but their roles in the brain haven't yet been studied.[9]

Scientist in their publications give operational definitions to the races that they study and describe how the samples are drawn. The races used may vary according to the purpose of the study, and there is no universally agreed upon subdivision of the races of man. For example, the very large collaboration of geneticists known as the HapMap project, which used four races for its first extensive database of SNPs, studied not "Mongoloids" but rather Japanese from Tokyo and Han Chinese. Other parallel studies are examining other races than the four mentioned, and there is no supposition that there is an exhaustive, unique list of the races of man.

Within the context of genetics, races are understood by their association with geographic ancestry. For example, the category Black refers to people who have most of their ancestry in sub-Saharan Africa, rather than to people with dark skin. The racial labels used by scientific researchers in the United States correspond to geographic regions of genetic ancestry, with only a small number of individuals showing genetic cluster membership different from their self-identified race/ethnicity[10]. People labeled Blacks have most of their ancestors from sub-Saharan Africa, Whites from Europe (and sometimes the Middle East and North Africa), and East Asians from countries on the western side of the Pacific Rim. Hispanics, more often called an ethnic group rather than a race, form a genetically diverse group that includes many recent U.S. immigrants of mixed ancestry. Similarly, worldwide studies find that "if enough markers are used... individuals can be partitioned into genetic clusters that match major geographic subdivisions of the globe".[11]

The political, social and cultural structure of the United States is still weighted by race. It was only in the 1960s that racial discrimination became illegal in many areas of public and private life, including employment and housing, and some consider discrimination to remain prevalent. The national and state governments of the United States employ racial categorization in the census, law enforcement, and innumerable other ways. Many political organizations intend to represent the interests of specific racial groups. See the articles Race and Race (U.S. Census) for further discussion.

Intelligence quotient

Main article: Intelligence quotient

Intelligence is most commonly measured using IQ tests. These tests are often geared to be good measures of the psychometric variable g, and other tests that measure g (e.g., the Armed Forces Qualifying Test (AFQT)) also serve as measures of cognitive ability.

All such tests are often called "intelligence tests," though the use of the term "intelligence" is itself controversial. It is clear, however, that performance in these tests accurately predicts performance in similar life tasks (typical college courses, for example). The correlation with real-world results and especially accumulated wealth is lower and more disputed. As commonly used, "IQ test" denotes any test of cognitive ability, and "IQ" is used as shorthand for scores on tests of cognitive ability. Some critics question the validity of all IQ testing or claim that there are aspects of "intelligence" not reflected in IQ tests. Criticisms of the validity of IQ testing focus primarily on questions of "test bias", which has many related meanings. Several conclusions about tests of cognitive ability are now largely accepted:

  • IQ scores measure many, but not all of the qualities that people mean by intelligent or smart (e.g., IQ does not measure creativity, wisdom, or personality)
  • IQ scores are fairly stable over much of a person's life
  • IQ tests are predictive of school performance, to a degree that does not significantly vary by socio-economic or racial-ethnic background
  • For people living in the prevailing conditions of the developed world, cognitive ability is substantially heritable, and while the impact of family environment on the IQ of children is substantial, after adolescence this effect becomes difficult to detect.

See the articles Intelligence, IQ, and general intelligence factor for further discussion of the validity of these tests.

The contemporary debate: results and interpretations

The contemporary scholarly debate about race and intelligence involves both the relatively uncontroversial experimental results that indicate that average IQ test scores vary among racial groups, and the relatively more controversial interpretations of these IQ differences. In general, contemporary interpretations of the "IQ gap" can be divided into three broad categories:

  1. "culture-only" or "environment-only" interpretations that posit overwhelmingly non-genetic causes (e.g., socioeconomic inequality or minority group membership) that differentially affect racial groups; and
  2. "partly genetic" interpretations that posit an IQ gap between racial groups caused by approximately the same matrix of genetic and environmental forces that cause IQ differences among individuals of the same race.
  3. "insufficient data": no meaningful interpretation can be made based on available evidence.


Francis Galton 1850s
Sir Francis Galton wrote on eugenics and psychometrics in the 19th C.
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1850s to World War II

The scientific debate on the contribution of nature versus nurture to individual and group differences in intelligence can be traced to at least the mid-19th century[12]. Charles Darwin wrote in his Descent of Man (VII, On the races of Man): "[T]he various [human] races, when carefully compared and measured, differ much from each other—as in the texture of hair, the relative proportions of all parts of the body, the capacity of the lungs, the form and capacity of the skull, and even the convolutions of the brain. But it would be an endless task to specify the numerous points of difference. The races differ also in constitution, in acclimatization and in liability to certain diseases. Their mental characteristics are likewise very distinct; chiefly as it would appear in their emotional, but partly in their intellectual faculties."

Anthropologist Franz Boas was a prominent 20th C. critic of claims that intelligence differed among races.
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The writings of Sir Francis Galton, elaborating on the work of his cousin Darwin, spurred interest in the study of mental abilities, particularly as they relate to heredity and eugenics.

The fact that there are differences in the brain sizes and brain structures of different racial and ethnic groups was well known and widely studied during the 19th century and early 20th century.[13] Average ethnic and racial group differences in IQ were first found due to the widespread use of standardized mental tests during World War I.

Beginning in the 1930s, hereditarianism — the belief that genetics contribute to differences in intelligence among humans — began to fall out of favor, in part due to the advocacy of Franz Boas, who in his 1938 edition of The Mind of Primitive Man wrote, "there is nothing at all that could be interpreted as suggesting any material difference in the mental capacity of the bulk of the Negro population as compared with the bulk of the White population." The hereditarian position was greatly weakened by Boas' finding that cranial vault size had increased significantly in the U.S. from one generation to the next, because racial differences in such characteristics had been among the strongest arguments for a genetic role. Inspired by the American eugenics movement, Nazi Germany implemented the T-4 Euthanasia Program in which roughly 200.000 mentally and physically disabled Germans were killed, and about 400.000 sterilized.

Post WWII and modern times

Due in part to the association of hereditarianism with Nazi Germany, after the conclusion of World War II until the 1994 publication of The Bell Curve, it became largely taboo to suggest that there were racial or ethnic differences in measures of intellectual or academic ability and even more taboo to suggest that they might involve a genetic component[14].

File:Charles Murray.gif
Charles Murray (pictured) and Richard Herrnstein started the contemporary debate with The Bell Curve in 1994.

In 1961, the psychologist Henry Garrett coined the term equalitarian dogma to describe the then politically fashionable view that there were no race differences in intelligence, or if there were, they were purely the result of environmental factors. Those who questioned these views often put their careers at risk[15].

Stephen Jay Gould
In The Mismeasure of Man, updated in 1996, Stephen Jay Gould criticized many aspects of IQ research.
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The contemporary scholarly debate on race and intelligence may be traced to Arthur Jensen's 1969 publication in the Harvard Educational Review of "How Much Can We Boost IQ and School Achievement?"[16] In this paper, he wrote on some of the major issues that characterize the partly genetic hypothesis of racial IQ differences, and on compensatory educational programs. Reports on Jensen's article appeared in Time, Newsweek, Life, U.S. News & World Report, and The New York Times Magazine.

Press attention returned to the issue of race and intelligence in 1994 with the publication of The Bell Curve, which included two chapters on the subject of racial difference in intelligence and related life outcomes. In response to The Bell Curve, Stephen Jay Gould updated The Mismeasure of Man in 1996.[17] Among other things, he criticized the IQ test as a measure of intelligence, citing what he perceived as inherent racial and social biases as well as systematic flaws in the testing process.

The introduction of biomedicine tailored to the genetics and disease patterns of specific racial groups is currently one of the factors adding to the complexity and controversy of debates on race and science[18]. In 2006, the scholarly debate continues on the question of "whether the cause of group differences in average IQ is purely social, economic, and cultural or whether genetic factors are also involved"[19].

Public controversy

Main article: Race and intelligence (Public controversy)

Some of it might be due to the fact that IQ is both environmental and geneticlaly influenced

Media portrayal

Main article: Race and intelligence (Media portrayal)

A 1987 study found that media portrayal of intelligence-related topics, including race and intelligence research, was then misrepresentative of opinion among academics such as psychologists, sociologists, cognitive scientists, educators, and geneticists. Among these 53% thought that the black-white gap was partially genetic and 17% thought that it was entirely environmental. Journalists and editors had the opposite opinion.[20] (Discussed below, section Expert opinion)

A 2004 study found widespread research misinterpretation regarding the study's specific focus, "stereotype threat."[21] Introducing stereotype threat to a test-taking environment has been shown to increase the existing gap between Blacks or Whites in relation to Whites or Asians respectively, and has thus been offered as a potential contributor to the gap. However, 88% of accounts in the popular media, 91% in scientific journals, and 67% in psychology textbooks misinterpreted the findings as that eliminating the introduced stereotype threat eliminated the Black-White gap, when in fact the students had already been matched according to prior scores. The authors suggest the appeal of the misinterpreted findings may have been a factor, and that such research results in general may in this way be systemically more readily accepted.

Utility of research and racism

Main article: Race and intelligence (Utility of research)

One criticism of race and intelligence research, regardless of whether racial differences are genetic or not, questions its utility. It's been argued that society might actually be better off "with an untruth: that there is no good reason for this [racial] inequality, and therefore society is at fault and we must try harder"[22] Linda Gottfredson argues that suppressing race and intelligence research is actually more harmful:

Lying about race differences in achievement is harmful because it foments mutual recrimination. Because the untruth insists that differences cannot be natural, they must be artificial, manmade, manufactured. Someone must be at fault. Someone must be refusing to do the right thing. It therefore sustains unwarranted, divisive, and ever-escalating mutual accusations of moral culpability, such as Whites are racist and Blacks are lazy.[23]

Steven Pinker argues that opposition to racism is based on moral, not scientific assumptions, and is not vulnerable to being disproved by bioscientific advances. "The case against bigotry is not a factual claim that humans are biologically indistinguishable. It is a moral stance that condemns judging an individual according to the average traits of certain groups..."[24]. Pinker suggests that intellectual life may not at present be prepared to deal with this area of inquiry[25].

Accusations of bias

Main article: Race and intelligence (Accusations of bias)

The largest source of funding for proponents of the partly genetic interpretation, the Pioneer Fund, has been criticized as having a eugenic and racist political agenda, and has been characterized by the Southern Poverty Law Center as a "hate group," using the definition "malign[ing] an entire class of people, typically for their immutable characteristics".[26] Critics, moreover, have found it significant that some of the prominent researchers advancing genetic explanations have also opposed affirmative action and school integration[27]. Grantees include the current head J. Phillipe Rushton, Arthur Jensen, and Richard Lynn.

Steven Pinker argues a fear of the implications of the science of human nature ("mind, brain, genes, and evolution") has led to the perception that these are dangerous ideas[28]. Pinker argues this has resulted in a denial of human nature in which "large swaths of the intellectual landscape have been reengineered to try to rule [...] hypotheses out a priori (race does not exist, intelligence does not exist, the mind is a blank slate inscribed by parents)." Scientists working in these areas have in the past been targets of censorship, violence, and comparisons to Nazis[29].

Average test score gaps among races

Main article: Race and intelligence (Average gaps among races)
Cumulative IQ gaps by race or ethnicity based on 1981 U.S. distributions. According to these findings, WAIS IQs for Whites (mean = 101.4, SD = 14.7) were higher than those for Blacks (mean = 86.9, SD = 13.0); distributions for Hispanics (mean = 91) and Asians (mean = 106) are less precise because of overlap and small sample size. Critics claim results like these are not grounded in scientifically derived constructs, but rather in folk beliefs about them. Based on Reynolds et al. 1987, p. 330.
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The modern controversy surrounding intelligence and race focuses on the results of IQ studies conducted during the second half of the 20th century, mainly in the United States and some other industrialized nations. In almost every testing situation where tests were administered and evaluated correctly, a difference of approximately one standard deviation was observed in the US between the mean IQ score of Blacks and Whites.

Some other psychological traits, such as behavioral inhibition, have also been found to vary significantly in distribution among ethnicities[30], but group differences in tests of cognitive ability have been the subject of more attention, as they're seen by some as one of society's most pressing problems[31].

World-wide scores

Cognitive ability scores for the ten global genetic clusters identified in previous genetic cluster analysis[32] have been surveyed by Richard Lynn[33]. Lynn regards these ten population groups as races, and extracts racial averages from 620 published studies surveying a total of 813,778 tested individuals. When taken as individual national averages, the data available, particularly regarding the developing world, is speculative due to limited sampling, year of testing, and varying type of cognitive ability test used. Lynn's previous work, including IQ and the Wealth of Nations with Tatu Vanhanen, have received widespread and strong criticism, but also praise.[34]

According to Lynn, when the studies are grouped and taken as averages for the ten racial groups, the argument for their reliability is that, though additional evidence may be required to confirm some of the more limited estimates, many have very high reliability in the sense that different studies give similar results, as well as that they correlate highly with performance in international studies of achievement in mathematics and science and with national economic development[35]. Lynn argues established environmental hypotheses can explain a substantial amount of these differences. The data set for sub-Saharan Africans around the world, the one most often criticized, is drawn from 155 different studies with a combined sample of 387,286 people. 57 of the studies are from countries in Africa, 54 from western countries, and 16 from non-western countries outside of Africa.[8] In general, Lynn lists East Asians and Europeans as highest IQ, and Africans and Australian Aborigines as lowest IQ.[36] Some Ashkenazi Jews score significantly higher than any other group.[37] An IQ of 70 is often associated with mental retardation, but deficits in adaptive behavior, such as telling the time, interacting socially, and looking after oneself, have only limited correlation with IQ, and are more important than IQ in determining whether a person is able to live an independent life.[38]

IQ scores vary greatly among different nations for related groups. Blacks in Africa score much lower than Blacks in the US. Some reports indicate that the Black–White gap is smaller in the UK than in the U.S.[39]. American Blacks average about 17-20% European admixture[9][10]; UK admixtures are not as well-studied. Many studies also show differences in IQ between different groups of Whites. In Israel, large gaps in test scores and achievement separate Ashkenazi Jews from other groups such as the Sephardi[40].

Brain size, employment tests, and school achievement

IQ has a low to moderate correlation with various measures of brain size and performance on elementary tests of response time[41]. Studies have shown similar racial differences in these variables. Cranial vault size and shape have changed greatly during the last 150 years in the US. These changes must occur by early childhood because of the early development of the vault. The explanation for these changes may be related to the Flynn effect.[42]

Gaps are seen in other tests of cognitive ability or aptitude, including university admission exams such as the SAT and GRE as well as employment tests for corporate settings and the military[43]. Measures of school achievement correlate fairly well with IQ, especially in younger children. In the United States, achievement tests find that by 12th grade Black students are performing on average only as well as White and Asian students in 8th grade; Hispanic students do only slightly better than Blacks. Whether the gaps are narrowing or not is debated.

Cultural or genetic explanation?

Main article: Race and intelligence (Culture-only or partially-genetic explanation)


The most widely accepted view among intelligence researchers is that IQ differences among individuals of the same race reflect real, functionally/socially significant, and substantially genetic differences in the general intelligence factor, g. It is likewise widely believed that average IQ differences among races reflect real and significant differences in the same g factor.[44] While these conclusions are largely beyond technical dispute, the nature of g is still an active area of research.

However, it is a matter of debate whether IQ differences among races in the U.S. are entirely environmental or partly genetic. Several published consensus statements agree that the large difference between the average IQ scores of Blacks and Whites in the U.S. cannot be attributed to biases in test construction, nor can they be explained just by simple differences in socio-economic status. Recent studies have shown some genes involved in the brain occur in different frequencies in different races, but it's unknown whether there's a significant or insignificant phenotypic effect.[9]

It should be noted that most research has been done in the US and a few other developed nations. That research cannot directly be generalized to the world as a whole. Blacks in the US do not constitute a random sample of the original African population, and environmental conditions differ among nations. IQ tests done in developing countries are likely to have been affected by conditions associated with poverty that are common in the developing world, such as nutritional deficiencies and the impact of diseases (e.g., HIV, anemia or chronic parasites) that may affect IQ test scores.

The extent to which the IQ gap is caused by genetic or environmental factors is logically independent of the ability for intervention to reduce the gap. A genetic cause is not necessarily irremediable (e.g. diabetes, myopia, and phenylketonuria) and an environmental cause may not be remediable (e.g. accidents and some diseases).

Cultural explanations

Regarding the IQ gaps in the U.S., it has also been suggested that African-American culture disfavors academic achievement and fosters an environment that is damaging to IQ[45]. Likewise, it is argued that the persistence of negative racial stereotypes reinforces this effect. John Ogbu[46] has developed a hypothesis that the condition of being a "caste-like minority" affects motivation and achievement, depressing IQ. Similarly, it's suggested reduced performance from "stereotype threat" could be a contributing factor.[47]

File:James Flynn.jpg
James R. Flynn discovered the Flynn effect, that average IQ scores are increasing worldwide.

Many anthropologists have argued that intelligence is a cultural category; some cultures emphasize speed and competition more than others, for example. Even proponents of the view that the IQ gap is caused partly by genetic differences recognize that non-genetic factors are likely to be involved. Non-genetic biological factors that affect IQ have been proposed. Increased rates of low birth weight babies and lower rates of breastfeeding in Blacks as compared to Whites are some factors of many that have been proposed to affect the IQ gap.

The poorly understood Flynn effect is often cited as evidence that average IQ scores have changed greatly and rapidly, noting that average IQ in the US may have been below 75 before the start of this effect. This means, given the same test, the mean Black American performance today would be higher than the mean White American performance in 1920, though the gains causing this appear to have only occurred predominantly in the lower half of the distribution[48]. Some argue that the IQ gap among races might change in the future or is even now changing. On the supposition that the effect started earlier for Whites, because their social and economical conditions began to improve earlier than did those of Blacks, they see even more promise in this hypothesis. However, after analyzing IQ data, one research group concluded that "It appears therefore that the nature of the Flynn effect is qualitatively different from the nature of B–W differences in the United States."[49]

A recent theory claims that fluid cognition (gF') may be separable from general intelligence. gF' may be very susceptible to environmental factors, in particular early childhood stress. Some IQ tests, especially those used with children, are poor measures of gF', which means that the effect of the environment on intelligence regarding racial differences, the Flynn effect, early childhood intervention, and life outcomes may have been underestimated in many studies. [11]

Many studies that attempt to test for heritability find results that do not support the genetic hypothesis. They include studies on IQ and skin color, self-reported European ancestry, children in postwar Germany born to Black and White American soldiers, blood groups, and mixed-race children born to either a Black or a White mother. Many intervention and adoption studies also find results that do not support the genetic hypothesis. Non-hereditarians have argued that these are direct tests of the genetic hypothesis and of more value than indirect variables, such as skull size and reaction time.[50]. Hereditarians argue that these studies are flawed, or that they do support the partly-genetic hypothesis.

Genetic explanations

The contemporary debate can be traced to psychologist Arthur Jensen in 1969.
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Arthur Jensen and others have concluded that the IQ gap is substantially genetic. Rushton and Jensen argue that while plausible environmental explanation for the lower mean IQ in Blacks in the U.S. can be offered in many cases, these explanations are less capable of explaining the higher average IQ of East Asians than Whites. Under their interpretation of Lakatos's technical concept of research programmes, Jensen and Rushton argue that the culture-only hypothesis is not "progressive" but "degenerating"[51].

To support these claims, they most often cite: (1) worldwide Black–White–East Asian differences in IQ, reaction time, and brain size, with Black-White IQ differences observable at age 3 in the U.S.; (2) race differences are most pronounced on tests that are the best measures of g, which also show the highest heritability (see Spearman's hypothesis); and (3) the rising heritability of IQ with age (within races; on average 20% heritability in infants, 40% in middle childhood, and 80% in adulthood) and the disappearance (~0.0) by adulthood of shared environmental effects on IQ (e.g., family income, education, and home environment), making adopted siblings no more similar in IQ than strangers[52]. Rushton and Jensen (2005) have concluded that the best explanation is that 50%-80% of group difference is genetic.[53]

Other evidence, such as transracial adoption, certain racial admixture studies, "life-history" traits, and evolutionary explanations have also been proposed to indicate a genetic contribution to the IQ gap. Critics of this view, such as Robert Sternberg, argue that these studies are flawed and thus inconclusive or that they support the culture-only hypothesis.

Expert opinion

In a 1987 survey of scholars in specialties related to IQ, given four choices, 52.9% of respondents supported the "partly genetic" position, 1.2% of respondents supported the "entirely genetic" position, 17.7% supported the "entirely environmental" position, and 28.2% responded that there was insufficient data "to support any reasonable opinion"[54]. Respondents on average called themselves slightly left of center politically, but political and social opinions accounted for less than 10% of the variation in responses.

According to the APA's 1995 consensus statement, in contrast:

It is sometimes suggested that the Black/White differential in psychometric intelligence is partly due to genetic differences (Jensen, 1972). There is not much direct evidence on this point, but what little there is fails to support the genetic hypothesis.

The APA journal that published the statement, American Psychologist, subsequently published eleven critical responses in January 1997, most arguing that the report failed to examine adequately the evidence for partly-genetic explanations.[55] It's been suggested that a conclusive answer may not be possible until intelligence is directly linked to specific genes.

Researchers who believe that there is no significant genetic contribution to race differences in intelligence include Flynn 1980, Brody 1992, Neisser et al. 1996, Nisbett 1998, Mackintosh 1998, Jencks and Phillips 1998, and Fish 2002. Some scientists who emphasize cultural explanations do not necessarily exclude a small genetic influence. Reynolds (2000) suggests up to 20% genetic influence be included in the cultural explanation. Researchers who believe that there are significant genetic contributions to race differences in intelligence include McGurk 1953, Garrett 1961, Shuey 1966, Shockley 1968, Eysenck 1971, Baker 1974, Loehlin et al. 1975, Vernon 1979, Lynn 1991a, Waldman et al. 1994, Scarr 1995, Levin 1997, Jensen 1998b, Rushton 2000, and Gottfredson 2005b.

Significance of group IQ differences

See also: Practical importance of IQ

Within societies

There is substantial overlap in the distribution of IQ scores among individuals of each race. Jensen (1998, p. 357) estimates that in a random sample of equal numbers of US Blacks and Whites, most of variance in IQ would be unrelated to race or social class. The average IQ difference between two randomly paired people from the U.S. population, one Black and one White, is approximately 20 points. However, by the same method of calculation, the average difference between two random people is approximately 17 points, and the average difference between two siblings is 12 points.

In essays accompanying the publication of The Bell Curve, Herrnstein and Murray argue that whether the cause of the IQ gap is partly genetic or entirely environmental does not really matter because that knowledge alone would not help to eliminate the gap and that knowledge should not impact the way that individuals treat one another. They argue that group differences in intelligence ought not to be treated as more important or threatening than individual differences, but suggest that one legacy of Black slavery has been to exacerbate race relations such that Blacks and Whites cannot be comfortable with group differences in IQ or any other traits.[56]

Moreover, although it may appear paradoxical, a goal of social egalitarianism is to raise the genetic contribution to intelligence to as high as possible, by minimizing environmental inequalities and any negatively IQ-impacting cultural differences (The Blank Slate, 106-107). Any remaining group IQ differences would then be 100% hereditary, the only remaining factor that could potentially contribute to race-based outcome differences.

The appearance of a large practical importance for intelligence makes some scholars claim that the source and meaning of the IQ gap is a pressing social concern. The IQ gap is reflected by gaps in the academic, economic, and social factors correlated with IQ[57]. However, some dispute the general importance of the role of IQ for real-world outcomes, especially for differences in accumulated wealth and general economic inequality in a nation. See the "Practical importance of IQ" link above.

Two statistical effects interact to exacerbate group IQ differences. First, there seem to be minimum statistical thresholds of IQ for many socially valued outcomes (e.g., high school graduation and college admission). Second, because of the shape of the normal distribution, only about 16% of the population is at least one standard deviation above the mean. Thus, although the IQ distributions for Blacks and Whites are largely overlapping, different IQ thresholds can have a significant impact on the proportion of Blacks and Whites above and below a particular cut-off.

Approximate IQ Distributions & Significance in the United States
IQ range Whites Blacks Black:White ratio Training prospects High school dropout Lives in poverty
<75 3.6% 18.0% ~5:1 simple, supervised work; eligible for government assistance 55% 30%
<90 21.9% 59.4% ~2:1 very explicit hands on training; IQ >80 for military training; no government assistance 35% 16%
>100 53.8% 15.7% ~1:3 written material plus experience 6% 6%
>110 27.9% 3.8% ~1:7 college format 0.4% 3%
>125 5.4% 0.2% ~1:32 independent, self-teaching 0% 2%
Based on Wechsler Adult Intelligence Scale IQs for Whites (mean = 101.4, SD = 14.7) and for Blacks (mean = 86.9, SD = 13.0) from (Reynolds, Chastain, Kaufman, & McLean, 1987, p. 330). Significance data is from Herrnstein & Murray (1994). Note that correlation is not causation. For example poverty can be both a cause and consequence of low IQ.

Small differences in IQ, while relatively unimportant at the level of an individual, would theoretically have large effects at a population level. Herrnstein and Murray (1994) calculate that a 3-point drop in average IQ would have little effect on factors like marriage, divorce, or unemployment. However, the drop from IQ 100 to 97 would increase poverty rates by 11 percent and the proportion of children living in poverty by 13 percent. All else being equal, similar rises would occur in rates of children born to single mothers, men in jail, high school drop-out, and men prevented from working due to health-related problems. In contrast, if average IQ were to increase 3-points to 103, poverty rates would fall 25 percent, children living in poverty would fall 20 percent, and high school drop-out rates would fall 28 percent.

Percentages of Blacks and Whites (Statistically Matched for IQ) in Educational and Social Outcomes
Condition (matching IQ) Blacks Whites
High school graduation (103) 91 89
College graduation (114) 68 50
High-level occupation (117) 26 10
Living in poverty (100) 14 6
Unemployed for 1 month or more (100) 15 11
Married by age 30 (100) 58 79
Unwed mother with children (100) 51 10
Has ever been on welfare (100) 30 12
Mothers in poverty receiving welfare (100) 74 56
Having a low birth-weight baby (100) 6 3
Average annual wage (100) $25,001 $25,546
from Herrnstein & Murray (1994), Chapter 14.

Studies from The Bell Curve and elsewhere indicate that controlling for IQ narrows, eliminates, or even reverses the Black-White gap in social and economic factors associated with IQ. After controlling for IQ, the probability of having a college degree or working in a high-IQ occupation is higher for Blacks than Whites. Controlling for IQ shrinks the income gap from thousands to a few hundred dollars. Controlling for IQ cuts differential poverty by about three-quarters and unemployment differences by half. However, controlling for IQ has little effect on differential marriage rates. For many other factors, controlling for IQ eliminates the differences between Whites and Hispanics, but the Black-White gap remains (albeit smaller).

Another study found that wealth, race and schooling are important to the inheritance of economic status, but IQ is not a major contributor and the genetic transmission of IQ is even less important.[58]

Whites are not a homogeneous group regarding real-world outcomes. For example, in the U.S. 33.6% of persons with self-reported Scottish ancestry has completed college, while only 16.7% of persons with self-reported French-Canadian ancestry have done so.[59]

Between nations

Differences in intelligence have been used to explain differences in economic growth between nations. One example is IQ and the Wealth of Nations. The book, which has not been peer-reviewed, is sharply criticized in the peer-reviewed paper The Impact of National IQ on Income and Growth.[60] Another peer-reviewed paper, Intelligence, Human Capital, and Economic Growth: An Extreme-Bounds Analysis, finds a strong connection between intelligence and economic growth[61]. It has been argued that East Asian nations underachieve compared to IQ scores. One suggested explanation is that verbal IQ is more important than visuospatial IQ[62].

The book Guns, Germs and Steel instead argues that historical differences in economic and technological development for different areas can be explained by differences in geography, which affects factors like population density and spread of new technology, noting for instance that current IQ scores cannot explain why the world's first civilizations appeared along the river plains in the Middle East.

For highly successful minorities

The book World on Fire notes the existence in many nations of minorities that have created and control a disproportionate share of the economy. Examples include Chinese in Southeast Asia; Whites, Indians, Lebanese and Igbo people of Western Africa; Whites in Latin America; and Jews in pre-World War II Europe, modern America, and modern Russia. These minorities are often resented and sometimes persecuted by the less successful majority.

In the United States, Jews, Japanese, and Chinese earn incomes 1.72, 1.32, and 1.12 times the American average, respectively (Sowell, 1981, p. 5). Jews and East Asians have higher rates of college attendance, greater educational attainment, and are many times overrepresented in the Ivy League and many of the United States' most prestigious schools[63],. At Harvard, for example, Asian American and Jewish students together make up 51% of the student body, though only constituting roughly 6% of the US population[64]. In various Southeast Asian nations, Chinese control a majority of the wealth despite being a minority of the population and are resented by the majority, and in some cases are the target of violence[65].

Achievement in science, a high-complexity occupation in which practitioners tend to have IQs well above average, also appears consistent with some group IQ disparity. Only 0.25% of the world population is Jewish, but Jews make up an estimated 28% of Nobel prize winners in physics, chemistry, medicine, and economics[66]. In the U.S., these numbers are 2% of the population and 40% of winners. A significant decline in the number of Nobel prizes awarded to Europeans, and a corresponding increase in the number of prizes awarded to US citizens, occurred at the same time as Nazi persecutions of Jews during the 1930s and the Holocaust during the 1940s[67].

These highly successful minorities differ significantly in IQ subtest profiles. Ashkenazi Jews, for example, demonstrate verbal and mathematical scores more than one standard deviation above average, but visuospatial scores roughly one half standard deviation lower than the White average[68], whereas East Asians demonstrate high visuospatial scores, but average or slightly below average verbal scores.[69] Concordantly, the professions in which these populations tend to be over-represented differ [70]. The Asian pattern of subtest scores is found in fully assimilated third-generation Asian Americans, as well as in Inuits and Native Americans (both of Asian origin).[71]

Policy implications

See also: Intelligence and public policy

The public policy implications of IQ and race research are possibly the greatest source of controversy surrounding this issue. For example, the conservative policy recommendations of Herrnstein and Murray in The Bell Curve were denounced by many. Indeed, even proponents of a partly genetic interpretation of the IQ gap, such as Rushton and Jensen (2005a) and Gottfredson (2005b), argue that their interpretation does not in itself demand any particular policy response: while a conservative/libertarian commentator may feel the results justify reductions in affirmative action, a liberal commentator may argue from a Rawlsian point of view (that genetic advantages are undeserved and unjust) for substantial affirmative action[23]. According to the "Mainstream Science on Intelligence"; statement published in the Wall Street Journal in 1994:

The research findings neither dictate nor preclude any particular social policy, because they can never determine our goals. They can, however, help us estimate the likely success and side-effects of pursuing those goals via different means[72].

While not specifically race-related, policies focused on geographical regions or nations may have disproportionate influences on certain racial groups and on cognitive development. Differences in healthcare, nutrition, regulation of environmental toxins, and geographic distribution of diseases and control strategies between the developing world and developed nations have all been subjects of policies or policy recommendations (see health and nutrition policies relating to intelligence).

Finally, germinal choice technology may one day be able to directly change alleles, such as those found to influence intelligence or racially identifying traits (such as skin color; see gene SLC24A5), making them susceptible to biotechnological intervention.[73]

End material


  1. Researchers contributing to this area of inquiry mostly include psychologists, psychometricians, geneticists, sociologists, and anthropologists.
  2. Reynolds et al. 1987; Roth et al. 2001; Rushton 2000; Shuey 1958; Herrnstein and Murray 1994; Lynn 1991a. For samples of individual studies showing similar results, see the National Collaborative Perinatal Project, reported by Broman et al. 1987; the Minnesota Transracial Adoption Study; also Lynn 1977a, Lynn 1977b, Lynn 1982, Lynn 1987, Lynn 1991;Lynn et al. 1991; Lynn and Hampson 1986a Lynn and Hampson 1986b; Lynn et al. 1987a, Lynn et al. 1987b; Lynn et al. 1998; Lynn and Holmshaw 1990; Lynn et al. 1988; Lynn and Shigehasa 1991; Montie and Fagan 1988; Scarr and Weinberg 1987; Rushton 1997; Rushton and Jensen 2003; Rushton et al. 2003; Notcutt 1950; Osborne 1962 Osborne 1978; Garrett 1964, Garrett 1967; Jensen 1985 Jensen 1993; Jensen and Reynolds 1982; Peoples et al. 1995. For scientific consensus statements see Gottfredson 1997a and Neisser et al. 1996.
  3. Other clustering: Thernstrom and Thernstrom 2003; Jensen 1993; Jensen and Whang 1994; Lynn and Holmshaw 1990; Lynn and Shigehasa 1991; Ho et al. 1980a, Ho et al. 1980b; Harvey_et_al. 1994; Rushton 1991. The East-Asian/White/Black difference in average IQ can be measured in very young children. For example, a one standard deviation gap is observed in Black and White 3-year olds matched for gender, birth order, and maternal education (Peoples et al. 1995). Lynn 1996 found that by age 6 the average IQ of East Asian children is 107, 103 for White children and 89 for Black children. Broman et al. (1987) found that the same trichotomy in brain size and IQ held at 4 months, 1 year, and 7 years of age.
  4. For this calculation, Herrnstein and Murray alter the mean IQ (100) of the U.S. National Longitudinal Survey of Youth's population sample by randomly deleting individuals below an IQ of 103 until the population mean reaches 103. This calculation was conducted twice and averaged together to avoid error from the random selection.(Herrnstein_and_Murray 1994, pp. 364-368) Discussed further in the section #Significance of group IQ differences #Within societies.
  5. whether or not this carries over to adulthood remains to be investigated
  6. Sternberg et al. 2005, Suzuki and Aronson 2005, Smedley and Smedley 2005, Helms et al. 2005, [1]
  7. Collins 2004
  8. 8.0 8.1 Risch et al. 2002
  9. 9.0 9.1 Mekel-Bobrov et al. 2005, Evans et al. 2005, Wang et al. 2005
  10. Tang et al. 2005
  11. Rosenberg et al. 2005
  12. Degler 1992; Loehlin et al. 1975
  13. Broca 1873, Bean 1906, Mall 1909, Morton 1839, Pearl 1934, Vint 1934
  14. Garrett 1961; Lynn 2001, pp. 45–54
  15. Lynn 2001 pp. 67–69
  16. Jensen 1969
  17. Gould 1996
  18. Kohn 2006
  19. Rushton and Jensen 2005a
  20. Snyderman and Rothman 1988; Whether this still applies today is unknown.
  21. Sackett et al. 2004
  22. Glazer 1994. The position that knowledge of what is is dependent on statements of what is good has been criticized by microbiologist Bernard Davis as the "moralistic fallacy," an implied converse of the naturalistic fallacy(Davis 1978). The latter refers to an effort to derive an ought directly from an is (e.g., war is good because it's part of human nature) and the former refers to an effort to derive an is from an ought (e.g., war is not part of human nature because it's bad).
  23. 23.0 23.1 Gottfredson 2005b
  24. The Blank Slate p. 145
  25. Pinker 2005
  27. Tucker 2002
  28. Pinker 2006
  29. Pinker 2006, Tucker 2002
  30. Moehler et al. 2006
  31. Sackett et al. 2004 p. 11
  32. Cavalli-Sforza et al. 1994
  33. Lynn 2006
  34. Sociologist Thomas Volken argues the data for national IQs is "highly deficient," citing the three reasons given above (Volken). In a review of The Bell Curve, IQ skeptic Leon Kamin writes that "Lynn's distortions and misrepresentations of the data constitute a truly venomous racism, combined with scandalous disregard for scientific objectivity."(Kamin 1995) Kamin's other positions on IQ have been criticized as "dishonest" (Jensen) and extreme to the point of not being "conceivable"(Mackintosh 1998, pp. 78-79). In contrast to Kamin's strongly worded attack on Lynn, W. D. Hamilton described Lynn in a review of another of Lynn's books as doing "an excellent job with the facts" and being "brave [and] thick-skinned ... to swim against ... popular antirealistic currents."[2] Examples of problematic national IQ figures include that the stated average IQ score of 59 for Equatorial Guinea is based on one test of 48 children aged 10-14 in 1984; the Ethiopian average is derived from a study of Ethiopians who immigrated to Israel a year prior, and whose low scores were thought by the original authors to be a reflection of temporary adjustment to a different culture and language (note that this data is not used in the averages presented below). Kamin also argued Lynn selectively excluded data showing a similar score in Whites and sub-Saharan Africans: "Lynn chose to ignore the substance of Crawford-Nutt's paper, which reported that 228 black high school students in Soweto scored an average of 45 correct responses on the Matrices--HIGHER than the mean of 44 achieved by the same-age white sample on whom the test's norms had been established and well above the mean of Owen's coloured pupils."(Kamin 1995)
  35. Rushton 2005
  36. Lynn's meta-analysis lists East Asians (105), Europeans (100), Inuit or Eskimos (91), Southeast Asians and Native Americans each (87), Pacific Islanders (85), South Asians and North Africans (84), sub-Saharan Africans (67), and Australian Aborigines (62)(Lynn 2006). Scores for the southern-African Bushmen and central-African Pygmies together come below this, but are based on the data set that is the most limited.
  37. Lynn estimates United States and British Ashkenazim IQ scores of 107-115, in contrast to average IQ of Ashkenazim in Israel at 103. He suggests this estimate may be lower due to selective migration effects in relation to the U.S. and Britain, and immigrants from the former Soviet Block countries having posed as Ashkenazim.
  38. (Mackintosh 1998, p. 177). Mercer 1973 reported that on the basis of IQ alone 10 times as many Blacks as Whites would be classified as retarded, but when adaptive behavior measures are added to the criterion, this difference completely disapears. Some ethnic differences in cognitive ability appear in some aspects of cognitive ability and not others (see below; Mackintosh 1998, p. 178). The Black-White disparity seen in IQ does not appear in some basic cognitive functions that don't involve more than minimal elaboration, transformation, or other mental manipulation (Mackintosh 1998, p. 178; Jensen 1973).
  39. Gene Expression 2003
  40. Willms and Chen 1989
  41. Neisser et al. 1996
  42. Gravlee et al. 2003a, Gravlee et al. 2003b; Jantz and Jantz 2000, Jantz 2001
  43. Roth et al. 2001
  44. Gottfredson (2005b); Snyderman and Rothman 1987; Neisser et al. 1996; Gottfredson 1997a
  45. Boykin 1994
  46. Ogbu 1978; Ogbu 2003
  47. Steele and Aronson 1995 found that making race salient when taking a test of cognitive ability negatively affected high-ability African American students. They name this phenomenon stereotype threat. Sackett et al. 2004 point out that these findings are widely misinterpreted to mean that eliminating stereotype threat eliminated the Black-White performance gap. See also Cohen and Sherman 2005, Helms 2005, Wicherts 2005 and Sackett et al. 2005 for discussion of the implications of stereotype threat for race and intelligence research.
  48. Colom et al. 2005
  49. (Wicherts et al. 2004). Note that this does not state that the cause of this difference is genetic.
  50. Nisbett 2005
  51. Rushton and Jensen 2005a
  52. Plomin et al. 2001
  53. Rushton and Jensen 2005a, cited in "Black-White-East Asian IQ differences at least 50% genetic, scientists conclude in major law journal", and Murray, Charles (2005) "The Inequality Taboo". Commentary Magazine, September 2005.
  54. Snyderman and Rothman 1987. Critics accept the results of this survey. Robert Sternberg, for example, defends the minority view, stating "science isn't done by majority rule."[3]
  55. Charles Murray responded "actually, there is no direct evidence at all, just a wide variety of indirect evidence, almost all of which the task force chose to ignore, [making no mention of] brain size, [...] the closest thing to direct evidence [...] IQ in sub-Saharan Africa, the results of transracial adoption studies, the correlation of the black-white difference with the g-loadedness of tests, regression to racial means across the range of IQ, or other relevant data."[4]
  56. "Race, genes and I.Q. - an apologia: the case for conservative multiculturalism" Herrnstein, Richard and Murray, Charles, The New Republic, Vol. 211, 10-31-1994, pp 27(11). "The Inequality Taboo". Commentary Magazine, September 2005.
  57. Gordon 1997; Gottfredson 1997b
  58. Samuel Bowles and Herbert Gintis, "The Inheritance of Inequality," Journal of Economic Perspectives 16, no. 3 (Summer 2002). Note that race, schooling and IQ are all correlated, so considering them as separate factors lessens the apparent effect of IQ.
  59. Myth: Some ethnic groups have genetically inferior IQ's, U.S. Census data reported by Andrew Hacker; "Caste, Crime and Precocity," in The Bell Curve Wars, by Steven Fraser ed. (New York: HarperCollins, 1995), 105.
  60. Thomas Volken, "The Impact of National IQ on Income and Growth."
  61. Jones and Schneider 2005
  62. La Griffe du Lion 2004
  63. Sowell 1981, pp. 7, 93
  64. Hacker 2005
  65. Sowell 1981, pp. 133-134; Purdey 2002
  66. 2004
  67. Jank et al. 2004
  68. Cochran et al. 2005, p. 4
  69. Lynn, [5] [6], Mackintosh 1998, p.178)
  70. Lynn 1991a
  71. Herrnstein and Murray.[7]
  72. Gottfredson 1997a
  73. Stock 2002, p.194

See also


Main article: Race and intelligence (References)

External links

Consensus Statement

Collective Statements

Review Papers


Race and intelligence

Research: Test data, Explanations, and Interpretations
Controversies: Utility and Potential for bias
History | Media portrayal | References

Human race and sex group differences
Race and intelligence Sex and intelligence
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