Race and intelligence

This article also discusses issues regarding ethnicity and intelligence.

While each is individually contentious, the topics of race and intelligence when considered together have led to ongoing and heated debate. This debate focuses on the nature, causes, and rectifications of ethnic differences in intelligence test scores. Fundamental to understanding the debate is the question, "What are the relative roles of nature and nurture in causing individual and group differences in cognitive ability?" Despite almost unanimous agreement among researchers that differences in IQ scores are to some degree heritable in individuals, there is no agreement on whether these genetic differences exist between any populations of humans, whether it's possible for them to exist, whether it would be possible to meaningfully measure them, and whether it would be ethical to study them if they did exist. While research and debate on race and intelligence encompasses a variety of topics, the nature-nurture question attracts the most public attention. Various explanations for racial group differences have been proposed, but none is generally accepted. While these differences are of a size that could be accounted for by environmental factors, no specific environmental factors have been identified as definitive causes, and genetic factors cannot be ruled out.

Controversy centers on the results of intelligence testing studies conducted both in the industrialized nations such as United States and Western Europe as well as developing nations. Controversies endure, too, over the nature of race, the purpose of intelligence, whether it can be quantified, whether the intelligence quotient (IQ) is a culturally biased measure, and whether intelligence is culturally malleable.

History

The idea that there are differences in the brain structures or sizes of different racial and ethnic groups was widely held and studied during the 19th and early 20th centuries. During this time period, research on race and intelligence was often used to claim that one race was superior to another, justifying the poor status and treatment of the "inferior" race.

Sir Francis Galton, a psychometrician and polymath (1822–1911), spurred interest in the study of mental abilities, particularly as they relate to heredity and eugenics. Galton claimed from his field observations in Africa that the African people were significantly below Anglo-Saxons' position in the normal frequency distribution of general mental ability; these claims continue to spark controversy in academia.

The scientific debate on the contribution of nature versus nurture to individual and group differences in intelligence can be traced back to at least the mid-19th century. Beginning in the 1930s, race difference research and hereditarianism — the belief that genetics are the primary cause of differences in intelligence among human groups — began to fall out of favor in psychology and anthropology after major internal debates. By 1961, the mainstream view was that there were no race differences in intelligence, or if there were, they were solely the result of environmental factors.

Contemporary issues

The most controversial and most publicized part of the 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 1970s debates

See also: Arthur Jensen

Publication in 1969 of psychology psychologist Arthur Jensen's controversial article, "How Much Can We Boost IQ and School Achievement?" triggered the modern debate. In it, he wrote, "All we are left with are various lines of evidence, no one of which is definitive alone, but which, viewed together, make it a not unreasonable hypothesis that genetic factors are strongly implicated in the average negro-white intelligence difference. The preponderance of evidence is, in my opinion, less consistent with a strictly environmental hypothesis than with a genetic hypothesis, which, of course, does not exclude the influence of environment or its interaction with genetic factors." Philosopher Peter Singer wrote that Jensen's article was widely reported in the popular press "as an attempt to defend racism on scientific grounds".

An advocate of population control, physicist William Shockley focused on questions of race, intelligence, and eugenics and published several controversial papers arguing that intelligence is primarily hereditary. He postulated that the higher reproduction rate of those with lower intelligence has a dysgenic effect on society and proposed that individuals with IQs below 100 be paid to undergo voluntary sterilization. Biologists and geneticists criticized his theories, comparing them to rationale used by the Nazis in carrying out their genocidal policies. Criticism of Shockley's racial ideas appeared in scientific journals and was reflected in the popular press.

Arguing that environmental factors could explain the black-white IQ gap, population geneticist Luigi Luca Cavalli-Sforza debated Jensen and Shockley.

The 1990s debates

See also: The Bell Curve

Discussion centers on whether group differences in average IQ are purely social, economic, and cultural or are hard-wired in genetics. The American Anthropological Association has declared that "differentiating species into biologically defined 'races' has proven meaningless and unscientific as a way of explaining variation," while the American Psychological Association acknowledged inter-group IQ differences that can be influenced by environmental factors.

Individuals such as Michael Levin and J. Philippe Rushton differ from the American Anthropological Association and American Psychological Association in their claims that IQ score differences are traceable to genetics. Stephen Jay Gould, Richard Levin, Richard Lewontin and Joseph L. Graves contend that the proponents of the genetics explanation are wrong.

The The Bell Curve by psychologist Richard Herrnstein and American Enterprise Institute political scientist Charles Murray wrote: "The debate about whether and how much genes and environment have to do with ethnic differences remains unresolved. The universality of the contrast in nonverbal and verbal skills between East Asians and European whites suggests, without quite proving, genetic roots." Herrnstein and Murray said intelligence is a better predictor of many factors including financial income, job performance, unwed pregnancy, and crime than parents' socioeconomic status or education level.

The Bell Curve attracted attention, both critical of and in defense of the book. Critics called it scientific racism. Several books were written in response, including The Bell Curve Debate and The Mismeasure of Man (second edition) and scholarly associations released statements of opinion.

The American Psychological Association's Board of Scientific Affairs in 1995 established a task force which produced a report, "Intelligence: Knowns and Unknowns" The psychology association report authors wrote that IQ scores have high predictive validity for individual differences in school achievement, for adult occupational status, even when variables such as education and family background have been statistically controlled, and they said individual differences in intelligence are substantially influenced by genetics (75% in adults). Contrary to Herrnstein and Murray's findings, they wrote that prolonged malnutrition during childhood does have long-term intellectual effects. The APA report writers took issue with The Bell Curve's genetic implications:

The differential between the mean intelligence test scores of Blacks and Whites (about one standard deviation, although it may be diminishing) does not result from any obvious biases in test construction and administration, nor does it simply reflect differences in socio-economic status. Explanations based on factors of caste and culture may be appropriate, but so far have little direct empirical support. There is certainly no such support for a genetic interpretation. At present, no one knows what causes this differential.

The APA report concluded with a call for more reflection in debates on intelligence and for a "shared and sustained effort" for more research to answer the many unanswered questions that remain.

Eleven critical responses appeared in the January 1997 issue of American Psychologist, suggesting ways in which the APA report could have been improved. Only Lynn and Rushton "dispute[d] the task force's conclusion that there is no direct evidence for a genetic interpretation of the Black—White IQ difference."

On December 13, 1994, psychologist Linda Gottfredson and 51 specialists in intelligence and related fields asserted on the opinion page of the Wall Street Journal that IQ bell curves differ across racial and ethnic groups for varying reasons. They maintained that, "Most experts believe that environment is important in pushing the bell curves apart, but that genetics could be involved too.

In 1994, the American Anthropological Association declared itself "deeply concerned by recent public discussions which imply that intelligence is biologically determined by race. Repeatedly challenged by scientists, nevertheless these ideas continue to be advanced. Such discussions distract public and scholarly attention from and diminish support for the collective challenge to ensure equal opportunities for all people, regardless of ethnicity or phenotypic variation."

In August 1995, at the National Bureau of Economic Research economist Sanders Korenman and Harvard University sociologist Christopher Winship found certain errors in Herrnstein's methodology. Korenman and Winship concluded: "... there is evidence of substantial bias due to measurement error in their estimates of the effects of parents` socioeconomic status. In addition, Herrnstein and Murray`s measure of parental socioeconomic status (SES) fails to capture the effects of important elements of family background (such as single-parent family structure at age 14). As a result, their analysis gives an exaggerated impression of the importance of IQ relative to parents` SES, and relative to family background more generally. Estimates based on a variety of methods, including analyses of siblings, suggest that parental family background is at least as important, and may be more important than IQ in determining socioeconomic success in adulthood."

Policy debates

See also: Intelligence and public policy

Public policy implications of IQ and race research are one of the greatest sources of controversy surrounding this issue. Regardless of the source of the IQ gap, most educators agree that it must be addressed; they often advocate equitable funding for education. An achievement gap refers to the observed disparity on a number of educational measures between the performance of groups of students, including groups defined by race or ethnicity.

Some proponents of a genetic interpretation of the IQ gap, such as Rushton and Jensen (2005a) and Gottfredson (2005b), have sometimes argued that their interpretation does not in itself demand any particular policy response: while a conservative/libertarian commentator may feel the results justify, for example, 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. Since all races have representatives at all levels of the IQ curve, this means any policy based on low IQ affects members of all races.

In the book Practical Ethics, philosopher Peter Singer wrote that:

Let us suppose that the genetic hypothesis turns out to be correct... I believe that the implications of this supposition are less drastic than they are often supposed to be...

First, the genetic hypothesis does not imply that we should reduce our efforts to overcome other causes of inequality between people... Perhaps we should put special efforts into helping those who start from a position of disadvantage, so that we end with a more egalitarian result. Second, the fact that the average IQ of one racial group is a few points higher than that of another does not allow anyone to say that all members of the higher IQ group have higher IQs... The point is that these figures are averages and say nothing about individuals... The third reason... is simply that, as we saw earlier, the principle of equality is not based on any actual equality that all people share. I have argued that the only defensible basis for the principle of equality is equal consideration of interests... Equal status does not depend on intelligence. Racists who maintain the contrary are in peril of being forced to kneel before the next genius they encounter.

Policies focused on geographical regions or nations may have disproportionate influences on certain racial groups and on cognitive development. Differences in health care, 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 intelligence).

Test score difference

United States

The observed differences in average test score achievement between ethnic groups varies depending on the populations studied and the type of tests used. Self defined black and white United States citizens have been the subjects of the greatest number of studies. Black-White average IQ differences appear to increase with age, averaging nearly 17 points by age 24. According to James Flynn, the overall average Black-White gap has reduced by one third over the last 30 years. A large (21,260 children) and probably the most recent (1998) study found that the Black-White gap for young children in reading and math scores was much smaller than in earlier studies. Black-White differences on school achievement tests shrunk over the last 30 years, but some of the improvements did not continue through the 1990s. The average black-white IQ difference also varies depending on test content. For example, two subsections of the WISC IQ test, known as forward and reverse digit-span, ask children to repeat a long series of numbers either forwards or backwards. The black-white difference on forward digit span is relatively small, while the difference on reverse digit span is relatively large. Across a battery of tests, the size of the Black-White gap is correlated with the extent to which the tests measure the psychometric factor g, which also accounts for most of the variation in interindividual differences in IQ test performance. Using a variety of statistical techniques, Dolan and colleagues have found that the black-white IQ gap can be accounted for by differences in g and the other interindividual ability factors measured by IQ tests, and also that IQ tests measure roughly the same mix of abilities in both black and white populations. 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.

The IQ distributions of other racial and ethnic groups in the United States are less well studied. Hispanic and Native American populations, including Arctic Natives, tend to score worse on average than White populations but better on average than Black populations. East Asian populations may score higher on average than White populations in the United States as they do elsewhere. A 1960 study of 1236 American teenagers calculated six IQ measures for Jews relative to white gentiles. The results found that the relative IQ of American Jews varied from a low of 91.3 (visual reasoning) to a high of 109.7 (Mathematics). A recent review by Lynn (2004) used a 10 word vocabulary test to estimate the IQ of American Jews. The population of 150 Jews scored half a standard deviation above the 5300 white gentiles in verbal IQ.

For each of these populations, there is some evidence that the mixture of ability factors that distinguish individuals are differentially distributed between groups. For example, East Asian populations tend to outscore White populations in performance IQ, whereas the test score differences skew towards higher verbal IQ for Ashkenazi-White differences. However, the mixture of abilities within groups appears to be nearly identical across many ethnic groups. The stability of these differences is also less well studied than Black-White differences.

Worldwide

According to Richard Lynn, J. Philippe Rushton, and others, IQ test score differences are observed cross-culturally and around the world. Lynn has published three books summarizing IQ test scores from around the world. The inaccuracy of the cross cultural IQ scores is well documented, but many scholars use the results as an estimate of worldwide IQ scores. Lynn's meta-analysis lists East Asians (105), Europeans (99), Inuit (91), Southeast Asians and Amerindians (87 each), Pacific Islanders (85), Middle Easterners (including South Asians and North Africans) (84), sub-Saharan Africans (67), and Australian Aborigines (62). International achievement test scores, including TIMSS and PISA, have also been used to estimate average IQ worldwide with similar results where data is available. The very low IQ scores reported for sub-Saharan African populations is especially controversial. For example, Wicherts argues that the average IQ of sub-Saharan Africans is poorly measured and is more likely 78. Sternberg, a critic of Rushton and Lynn, reported an average IQ of 70 for "young adolescents" in Kenya. There is a paradox from IQ studies in Africa that has yet to be resolved. Europeans with an IQ of 70 are considered mentally retarded. However, the Africans found to have an IQ of 70 were perfectly normal with the apparent ability to function normally in their social environment. This has led to questions of the validity of these IQ tests A 1995 study published in the Journal of Nutrition concluded that IQ scores of children in the West Indies are depressed to some extent by environmental conditions, such as macronutrient and micronutrient deficiencies and even blood lead levels. The study suggested the existence of broader links between malnutrition and IQ levels across the developing world as a whole.

Southern Italian immigrants in the US scored below 80 on IQ tests in the early 20th century but had improved their average scores in later decades, bringing the validity of theories of genetically fixed and racially based IQ into further question.

Genetic and environmental factors

The cause(s) of group average IQ test score differences are not known but hypotheses have been proposed. Many scholars have offered descriptions of the variety of hypotheses that have been proposed. These descriptions usually distinguish between those hypotheses which invoke a contribution of genetic factors and those which solely invoke environmental (i.e., non-genetic) factors. Some descriptions of the positions are themselves controversial. In a review published in 2007, Hunt and Carlson listed four positions. The first position, attributed to Jensen and Rushton, is that group differences in IQ reflect differences in intelligence that are "due in substantial part to genetically determined differences in brain structure and/or function" The second position, attributed to Ogbu and Sowell, is that the differences in intelligence test scores are due to social factors. The third view, attributed to Sternberg and colleagues, is that the use of IQ scores to argue for differences in intelligence is an inappropriate use of tests in different groups. The fourth position, attributed to Fish and others, is that there is no such thing as race: "a term motivated by social concerns and not a scientific concept".

Prominent proponents of the genetic hypothesis are predominately psychologists or experts in intelligence testing, such as Charles Spearman, Hans Eysenck, Arthur Jensen, J. Philippe Rushton, Linda Gottfredson, Richard Herrnstein, and David C. Rowe. A few prominent proponents have come from other fields, such as political scientist Charles Murray, evolutionary psychologist Satoshi Kanazawa, and philosophers Michael Levin and Neven Sesardic. Not all proponents share the same views, nor have all of their views been constant throughout their careers. Prominent critics come from many backgrounds, and hold a diversity of views. They include psychologists and experts in intelligence testing such as James Flynn (prior to his work on IQ Flynn was a political scientist), Ulric Neisser, Robert Sternberg, and a number of less well known psychometricians who criticize the underlying IQ test data. Other critics include economists Thomas Sowell and Roland G. Fryer Jr. Anthropologists such as Ashley Montagu, Leonard Lieberman, and Jonathan Marks argue that "race" is a social and not a biological concept. For example Marks (1996) argues that the eugenics movement of the 1920s identified Ashkenazi Jews from Europe as intellectually inferior due to their genetics, but that Murray and Herrnstein claim this group as a "cognitive elite" in The Bell Curve, concluding that "race" is a social construct that does not reflect underlying biology. Sociologists John Ogbu, Claude S. Fischer and Troy Duster, paleontologist Stephen Jay Gould, geneticist Richard C. Lewontin and evolutionary biologist and physiologist Jared Diamond also oppose the genetic hypothesis.

The genetic hypothesis has been characterized as inherently racist. Eric Turkheimer, a professor of clinical psychology at the University of Virginia, argues that proponents of a genetic contribution, whom he calls "racialists", deserve "vigorous disapprobation" and do not deserve "respect". Turkheimer writes that he disagrees with his colleagues, such as Flynn and Ceci, who "agree that the question is a legitimate matter for scientific inquiry, to be settled by cool-headed evaluation of the empirical evidence". Flynn does not accept Turkheimer's arguments. Rushton and Jensen argue that the policy issues should be regarded as separate from the academic inquiry.

What is heritability?

See also: Heritability of IQ

An environmental factor that varies between groups but not within groups can cause group differences in a trait that is otherwise 100% heritable. The height of this "ordinary genetically varied corn" is 100% heritable, but the difference between the groups is totally environmental. This is because the nutrient solution varies between populations, but not within populations.

The consensus among intelligence researchers is that IQ differences between individuals of the same racial-ethnic group reflect real, functionally and socially significant, and substantially heritable differences in intelligence.

Concordance rates for IQ from twin studies and other study designs consistently fall in the range of 50% to 80%, with the estimated heritability in young (preschool) children in the lower range and adults in the higher range.

Critics have also questioned the interpretation of heritability as a whole. Lewontin suggests that some genotypes are more influenced by environments than others, leading to the possibility that populations that have similar genetic variance in the same environment can have different heritabilities because of their different genotypes. David Layzer (1974) contends that the development of a trait can be influenced by genetic differences qualitatively and that heritability estimates cannot measure such qualitative differences, as such it is possible that even with a heritability of close to 100% it is possibly for phenotypic variance to be due largely to environment.

As a comparison, schizophrenia is estimated to be at least 70% heritable, of which 30% of the actual genes have been accounted for.

Genetic hypothesis

File:TBC-BW-IQ-SES-withDiff.png

Socioeconomic status (SES) varies both between and within populations, but Black-White differences in IQ persist among the children of parents matched for SES, and the gap is largest among the children of wealthiest and best educated parents.

Much of the research on explaining group differences stems from an observation promoted first by Arthur Jensen and later James Flynn and others regarding an environmental explanation for group differences. According to Jensen the very high within-group heritability of IQ (within both white and black populations) presents a problem for environmental explanations of group differences in IQ. They consider two general classes of environmental factors: common environmental factors and X-factors. Common environmental factors vary within and between populations. X-factors vary between populations, but do not vary substantially within populations. They first consider common environmental factors. To account for a 1 SD B-W IQ gap only in terms of common environmental factors would require very large environmental differences. For example, if the within-group heritability of IQ is 80%, then a B-W IQ difference of 2.24 SD in common environmental factors is required. For a heritability of 40%, a difference of 1.29 SD is required. Jensen and Flynn agree that it is an empirical question whether common environmental factors that influence IQ differ between whites and blacks to such an extent, and both agree that most commonly suggested environmental factors do not. Jensen believes that empirical evidence supports the view that the B-W IQ gap is caused by both common environmental factors and genetic factors. Flynn disagrees and believes that empirical evidence supports the view that the B-W IQ gap is caused by yet unrecognized environmental factors.

The alternative to common environmental factors is to hypothesize that X-factors account for the B-W IQ gap. A frequently-cited example from Lewontin describes the effect of a hypothetical X-factor. Imagine that the height of "ordinary genetically varied corn" is 100% heritable when grown in a uniform environment. Further imagine that two populations of corn are grown: one in a normal nutrient environment and the other in a deficient nutrient environment. Consequently, the average height of the corn grown in the deficient nutrient environment is less than the average height of the corn grown in the normal environment. In such a scenario, the within-group heritability of height is 100% in both populations, but the substantial difference between groups are due entirely to environmental factors. The quality of the nutrient is an "X-factor" in the language of Jensen and Flynn. With respect to the B-W IQ gap, Jensen suggests that effects associated with racism (both overt and institutionalized racism) might be X-factors. Flynn believes that attributing the B-W gap to the effects of racism is incorrect, because the most plausible ways in which discrimination could affect IQ are themselves common environmental factors. These may include psychological effects such as stereotype threat; biological effects such as poor nutrition, health care and living close to toxic environments; and educational effects such as a lack of good schools. Instead, Flynn and his colleague William Dickens have developed more complicated models to explain the black-white gap in terms of environmental factors. One initial motivation of the Dickens-Flynn theory was Flynn's observation that IQ test scores have been rising over time in countries around the world – termed the Flynn effect. Flynn and others believe an explanation for the Flynn effect may elucidate the cause of the B-W gap. Jensen and others disagree.

A few of the notable proponents of the partly genetic hypothesis are Raymond B. Cattell, Arthur Jensen and Hans Eysenck.

Rushton and Jensen examined 10 categories of research evidence from around the world to contrast "a hereditarian model" (50% genetic-50% cultural) and a culture-only model (0% genetic-100% cultural). Their article "Thirty Years of Research on Race Differences in Cognitive Ability" was published in the APA journal Psychology, Public Policy and Law showing evidence that they believe supports the hereditarian model. Rushton and Jensen (2005a) believe that the best explanation for the gap is that 50%-80% of the group differences in average US IQ is genetic.

Other evidence, such as the Minnesota Transracial Adoption Study, certain racial admixture studies, behavior genetic modeling of group differences, "life-history" traits, and evolutionary explanations have also been proposed to indicate a genetic contribution to the IQ gaps and explain how these arose.

The decoding of the human genome has enabled scientists to search for sections of the genome that contribute to cognitive abilities. Current studies using Quantitative trait loci have yielded little success in the search for genes influencing intelligence. Robert Plomin is confident that QTLs responsible for the variation in IQ scores exist, but that more powerful tools of analysis will be required to detect them. Some researchers have expressed reluctance to investigate possible links between genes and intelligence, due to the controversy it can produce.

A 2005 literature review article on the links between race and intelligence in American Psychologist stated that no gene has been shown to be linked to intelligence, "so attempts to provide a compelling genetic link of race to intelligence are not feasible at this time". Another 2007 study in the journal Behavioral and Brain Functions found that a gene which influences risk for schizophrenia also appears to influence intelligence, depending on which allele of it a person carries. The New York Times has reported on an analysis of this study performed by a non-scientist blogger, which compared its results to an online database of allele frequencies in various ethnic groups, and claimed that the alleles of this gene which influence IQ are distributed unequally between races. The New York Times emphasized the speculative nature of these results, because the relationship between these alleles and IQ is unconfirmed.]

Environmental effects

Main article: Environment and intelligence

Critics of the significantly genetic view, such as Robert Sternberg, argue that these studies are either flawed and thus inconclusive, or else that they support a primarily environment (<20% genetic) hypothesis. For example, Dolan and Hamaker (2001) argue that the statistical methods linking the Black-White gap to g are insufficient. They reanalyzed the data from several earlier studies and concluded that Spearman's hypothesis is not an "empirically established fact" (i.e., that Black-White IQ differences may be due to differences in common factors other than g) due to insufficient power in the data to choose between alternative models. "This leaves the validity of Spearman's hypothesis, considered a central justification for the genetic explanation, an unresolved question." However, they did confirm that the Black-White IQ gap is not due to measurement artifacts, and is instead due to some measured factor that varies both within and between groups.

Nisbett (2005) argues that many studies find results that do not support the genetic hypothesis. They include studies on IQ and skin color that reported that the average correlation between skin color and IQ is .1 (the average correlation between IQ and judged “Negroidness” of features is even lower); IQ and self-reported European ancestry; IQ and blood groups showing degree of European Ancestry; IQ among children in post WWII Germany born to black and white American soldiers; and IQ among mixed-race children born to either a black or a white mother. He argues that these are direct tests of the genetic hypothesis and of more value than indirect variables, such as skull size and reaction time. He argues that "There is not a shred of evidence in this literature, which draws on studies having a total of five very different designs, that the gap has a genetic basis." He argues further that many intervention and adoption studies also find results that do not support the genetic hypothesis. He also argues "that the Black-White IQ gap has lessened considerably in recent decades." Hunt and Carlson argue that Nisbett's interpretations are far too strong in light of problems with these studies that have been recognized for decades. Gottfredson writes that the studies Nisbett cites "actually lack the ability to rule out any hypothesis at all, genetic or not".

Dickens (2005) states that "Although the direct evidence on the role of environment is not definitive, it mostly suggests that genetic differences are not necessary to explain racial differences. Advocates of the hereditarian position have therefore turned to indirect evidence...The indirect evidence on the role of genes in explaining the black-white gap does not tell us how much of the gap genes explain and may be of no value at all in deciding whether genes do play a role. Because the direct evidence on ancestry, adoption, and cross-fostering is most consistent with little or no role for genes, it is unlikely that the black-white gap has a large genetic component."

Fryer and Levitt (2006), with data from "the first large, nationally representative sample" of its kind, report finding only a very small racial difference when measuring mental function for children aged eight to twelve months, and that even these differences disappear when including a "limited set of controls". "On tests of intelligence, Blacks systematically score worse than Whites, whereas Asians frequently outperform Whites. Some have argued that genetic differences across races account for the gap. Using a newly available nationally representative data set that includes a test of mental function for children aged eight to twelve months, we find only minor racial differences in test outcomes (0.06 standard deviation units in the raw data) between Blacks and Whites that disappear with the inclusion of a limited set of controls. The only statistically significant racial difference is that Asian children score slightly worse than those of other races." They argue that their report poses "a substantial challenge to the simplest, most direct, and most often articulated genetic stories regarding racial differences in mental function." They conclude that "to the extent that there are any genetically-driven racial differences in intelligence, these gaps must either emerge after the age of one, or operate along dimensions not captured by this early test of mental cognition."

The Flynn effect

Main article: Flynn effect

The secular, international increase in test scores, commonly called the Flynn effect, is seen by Flynn and others as reason to expect the eventual convergence of average black and white IQ scores. Flynn argues that the average IQ scores in several countries have increased about 3 points per decade during the 20th century, which he and others attribute predominantly to environmental causes. This means, given the same test, the mean performance of African Americans today could be higher than the mean for white Americans in 1920, though the gains causing this appear to have occurred predominantly in the lower half of the IQ distribution. If an unknown environmental factor can cause changes in IQ over time, they argue, then contemporary differences between groups could also be due to an unknown environmental factor. One unresolved question is whether the secular IQ gains can be predominantly a real change in cognitive ability. Flynn's face-value answer to this question is "No", and some other researchers have found reason to concur. In terms of the mixture of ability factors that IQ tests were designed to measure, such as g and verbal and mathematical ability, changes in IQ scores over time are different than either within-group individual differences and between group differences. For example, there has been little increase over time in performance on either the forward digit-span or reverse digit-span subtests, and tests of school achievement have been less affected than tests of abstract reasoning. Other recent studies have found that g has improved substantially. Cranial vault size has increased and the shape changed during the last 150 years in the US; these changes must occur by early childhood because of the early development of the vault. It also estimated that the average white IQ in past decades was lower than current average black IQs, a fact which shows the change of IQ over time. But while black Americans in the early 21st century may score higher than white Americans in the early 19th century, the fact remains that the roughly 1 standard deviation IQ gap between black and white Americans living at the same time has held constant since the earliest days of intelligence testing, convincing some observers like Richard Lynn that the black-white gap in the U.S. is not only genetic, but 100% genetic. Indeed Arthur Jensen is struck by how consistent the gap has been, despite the enormous rise in the scores of both races.

Health

Percentage of children aged 1-5 with blood lead levels at least 10 µg/dL. Black and Hispanic children have measurably higher levels than white children. High levels of lead at an early age may affect intelligence.

Main article: Health and intelligence

Main article: Race and health

Numerous explanations beside genetics have been proposed to account for the IQ gaps in the U.S. High rates of low birth-weight babies, lower rates of breastfeeding, and exposure to toxins are some factors. The Flynn effect is often cited as evidence that average IQ scores have changed greatly and rapidly, for reasons poorly understood, thus the IQ gap between races could change in the future or is changing, especially if the Flynn effect started earlier for Whites.

High levels of lead at an early age may affect intelligence; studies indicate that black and Hispanic children have measurably higher levels than white children. A 10 µg/dL increase in blood lead at 24 months of age is associated with a 5.8-point lower IQ later in life. In 1976 77.8% of all children had at least this much lead in their blood.

Exposure to lead is frequently attributed to housing conditions including lead based paint, which is no longer used but has accumulated in older buildings; people of lower economic means are more frequently exposed to lead from housing.

Stereotype threat

Main article: Stereotype threat

Stereotype threat is the fear that one's behavior will confirm an existing stereotype of a group with which one identifies; this fear may in turn lead to an impairment of performance. Testing situations that highlight the fact that intelligence is being measured tend to lower the scores of individuals from racial-ethnic groups that already score lower on average. Stereotype threat conditions cause larger than expected IQ differences among groups but do not fully explain the gaps found in non-threatening test conditions.

Quality of education

Some researchers have written that studies that find test performance gaps between races even after adjusting for education level, such as the analysis found in The Bell Curve, fail to adjust for the quality of education. Not all high school graduates or college graduates have received the same quality of education. A 2006 study reported that years of education is an inadequate measure of the educational experience among multicultural elders, and that adjusting for quality of education greatly reduced the overall effect of racial differences on the tests. A 2004 study reported that quality of education and cultural experience influence how older African Americans approach neuropsychological tasks and concluded that adjustment for these variables may improve specificity of neuropsychological measures. Yet another study reported that, although significant differences were observed between the ethnic groups when matched for years of education, equating for literacy level eliminated all performance differences between African Americans and European Americans on both cancellation tasks which assess visual scanning (like reaction time tests, cancellation task tests are sometimes regarded as "culture free" tests of intelligence). Eric A. Hanushek and Steven G. Rivkin wrote in their 2006 book that unequal distributions of inexperienced teachers and of racial concentrations in schools can explain all of the increased achievement gap between grades 3 and 8. In recent years there have also been studies into the degrees in which many minorities, especially blacks, have internalized pathologies about their supposed lack of intelligence and the effects it has in their self-confidence, quality of learning and achievement. Additionally, Jensen's studies (Jensen, 1974b) show that 7% of black children of black professionals have mean IQs below that of white children from low-income families, yet this seems to have little to no detriment on the black children's success.

A 2004 study in South Africa found highly significant effects for both level and quality of education within the black African first language groups taking the Wechsler IQ tests. The scores of black African first language groups with advantaged education were comparable with the US standardization, whereas scores for black African first language participants with disadvantaged education were significantly lower than this. The study cautioned that faulty conclusions may be drawn about the effects of ethnicity and the potential for neuropsychological misdiagnosis.

Racial discrimination in education

Roslyn Arlin Mickelson writes that racial discrimination in education arises from actions of institutions or individual state actors, their attitudes and ideologies, or processes that systematically treat students from different racial/ethnic groups disparately or inequitably. Despite advancement in education reform efforts, to this day African American students continue to experience inequities within the educational system. Hala Elhoweris, Kagendo Mutua, Negmeldin Alsheikh and Pauline Holloway conducted a study of the effect of students' ethnicity on teachers' educational decision making. The results of this study indicated that the student's ethnicity did make a difference in the teachers' referral decisions for gifted and talented educational programs. Recently, a number of scholars have examined the issue of disproportionate representation of minority students in special education programs

Teachers' perceptions of a students cultural background may affect school achievement. African American students with African American cultural backgrounds, for example, have been found to benefit from culturally responsive teaching. In a 2003 study researchers found that teachers perceived students with African American culture-related movement styles as lower in achievement, higher in aggression, and more likely to need special education services than students with standard movement styles irrespective of race or other academic indicators.

Ellis Cose writes that low expectations may have a negative impact on the achievement of minorities. He writes that black people did not need to read The Bell Curve to be aware of the low expectations held for them by the majority culture. He recalls examples of low expectations from his teachers in school who regarded his use of AAVE as "laziness" and teachers who did not feel it was important to purchase new text books because they did not expect the students to be able to read anything complex. He contrasts these low expectations with the high expectations philosophy of Xavier University where, using the ideas Whimbey articulated in his book Intelligence can be Taught teachers created a program called SOAR. SOAR raised the performance of black students and lead Xavier to become the university that sends the greatest number of black students to medical school in the United States. The SOAR program produced gains equivalent to 120 points on an SAT test. Cose writes that "..we must treat people, whatever their color, as if they have unlimited intellectual capacity."

Structural equation models have been used to test for possible uncommon factors in the development of children belonging to different ethnic groups, which would include the results of racial discrimination. However, these tests have concluded that black, white, Hispanic and Asian children follow developmental processes which are "nearly identical."

Caste-like minorities

The book Inequality by Design: Cracking the Bell Curve Myth claims that it is not lower average intelligence that leads to the lower status of ethnic minorities, it is instead their lower status that leads to their lower average intelligence test scores. The following table from the same book compares social status or caste position to test scores and school success in countries around the world.

Group Differences Around the World

	Status or Caste Position		Test Scores, School Success
Country	High	Low	High	Low
United States	Whites	Blacks	Whites	Blacks
	Asians	Latinos	Asians	Latinos
	East Asians	Southeast Asians	East Asians	Southeast Asians
	Whites	American Indians	Whites	American Indians
Northern Ireland	Protestants	Catholics	Protestants	Catholics
Australia	Whites	Aborigines	Whites	Aborigines
New Zealand	Whites	Maori	Whites	Maori
South Africa	English	Afrikaners	English	Afrikaners
Belgium	Flemish	French	Flemish	French
Israel	Jews	Arabs	Jews	Arabs
	Western Jews	Eastern Jews	Western Jews	Eastern Jews
India	Nontribals	Tribal people	Nontribals	Tribal people
	Brahmin	Dalit	Brahmin	Dalit
	High caste	Low caste	High caste	Low caste
Czechoslovakia	Slovaks	Gypsies	Slovaks	Gypsies
Notes: Czechoslovakia split into the Czech Republic and Slovakia in 1993. The Flemish are not a minority in Belgium. The PISA 2006 results for schoolchildren 15 years of age showed that the Flemish outperformed the Walloons (French). Afrikaans speakers make up the majority of the white population; most South Africans, however, identified themselves in the census as black, and speak one of the Bantu languages as their home language

Viewpoints

Given the observed differences in IQ scores between certain groups, a great deal of debate revolves around the significance of these observations. Various interpretations of test data lead to a multitude of conflicting conclusions as to which specific explanations the data support.

The range of views among contemporary scholars include:

• James Flynn argues that differences in cognitive abilities between races exist and are of social/environmental origin.
• Arthur Jensen argues that differences in cognitive abilities between races exist and are caused by both social/environmental disparities and also genetic differences between races.
• Ashley Montagu and Joseph L. Graves, amongst others, argue that race is not a biological concept, but rather is socially constructed, and hence measurements of IQ differences between races cannot reflect an underlying intrinsic biological cause.
• Robert Sternberg argues that the use of differences in test scores to argue for race differences in intelligence is a case of the inappropriate use of tests in different groups.

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).

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).

Coming advances in genetics and genomics are expected to soon provide the ability to test hypotheses about group differences more rigorously than has as yet been possible.

Jared Diamond's Guns, Germs and Steel instead argues that historical differences in economic and technological development for different geographic areas can be explained by differences in geography (which affects factors like population density and spread of new technology) and differences in available crops and domesticatable animals. Richard Nisbett argues in his 2004 The Geography of Thought that some of these regional differences shaped lasting cultural traits, such as the collectivism required by East Asian rice irrigation, compared with the individualism of ancient Greek herding, maritime mercantilism, and money crops wine and olive oil However, it has been suggested that these environmental differences may operate in part by selecting for higher levels of IQ.

J. Philippe Rushton, psychology professor at the University of Western Ontario and head of the Pioneer Fund, has written a controversial book called Race, Evolution, and Behavior: A Life History Perspective. Rushton claims in the book that race is a valid biological concept and that racial differences frequently arrange in a continuum of Mongoloids (Orientals, East Asians) at one extreme, Negroids (blacks, Africans) at the opposite extreme, and Caucasoids (whites, Europeans) in the middle. It has been heavily criticized.

Differing rates of economic growth have also been attributed to numerous factors other than racial IQ gaps such as local availability of resources, climate, and sociopolitical factors. See for example the Global Competitiveness Report, the Ease of Doing Business Index, and the Index of Economic Freedom or works by Kenneth Pomeranz, Eric Jones, Joel Mokyr, and Douglass C. North.

Criticisms

Outdated methodology

A 2006 paper by Professor Denny Borsboom argues that mainstream contemporary test analysis does not reflect substantial recent developments in the field and "bears an uncanny resemblance to the psychometric state of the art as it existed in the 1950s." It also claims that some of the most influential recent studies on group differences in intelligence, in order to show that the tests are unbiased, use outdated methodology. In particular the reliance on classical test theory rather than more sophisticated measurement models as found in item response theory. In response to criticism proponents of the genetic hypothesis claim they use a standard for intelligence known as g. g is measured by performance on test items without the influence of language or math.

Utility of research

Theories of race and intelligence have been challenged on grounds of their utility. Critics want to know what purpose such research could serve and why it has been an intense an area of focus for a few researchers. Some defend the research, saying it has egalitarian aims. IQ is, after all, a predictor of educational achievement and special needs. Accordingly, as a matter of public policy, resources can be better allocated by reducing the data to better understand the challenges; it is considered a pure science. Still others say that the true motivation for the research is the same as that of the eugenics movement and other forms of scientific racism. Even supporters of intelligence research have described such research as analogous to "working with dynamite" or "dangerous play" in sports.

Jensen and Rushton have justified their research in this area as being necessary to answer the question of how much white racism should be held responsible for ethnic groups’ unequal performance in certain areas. They maintain that when racism is blamed for disparities which are the result of biological differences, the result is mutual resentment, and unjustified punishment of the more successful group. They state:

[T]he view that one segment of the population is largely to blame for the problems of another segment can be even more harmful to racial harmony, by first producing demands for compensation and thereby inviting a backlash. Equating group disparities in success with racism on the part of the more successful group guarantees mutual resentment. As overt discrimination fades, still large racial disparities in success lead Blacks to conclude that White racism is not only pervasive but also insidious because it is so unobservable and “unconscious.” Whites resent that nonfalsifiable accusation and the demands to compensate Blacks for harm they do not believe they caused.

Regarding whether research in this area is desirable, John C. Loehlin wrote in 1992, "Research on racial differences in intelligence is desirable if the research is appropriately motivated, honestly done, and adequately communicated." [emphasis original] Defenders of the research suggest that both scientific curiosity and a desire to draw benefits from the research are appropriate motivations. Researchers such as Richard Lynn have suggested that conclusions from the research can help make political decisions, such as the type of educational opportunities and expectations of achievement policy makers should have for people of different races. Charles Murray, a political scientist of the American Enterprise Institute has used their conclusions to criticize social programs based on racial equality that fail, he claims, to recognize the realities of racial differences.

Test construction

While the existence of average IQ test score differences has been a matter of accepted fact for decades, a great deal of controversy exists among scholars over the question of whether these score differences reflected real differences in cognitive ability. Some claim that there is no evidence for test bias since IQ tests are equally good predictors of IQ-related factors (such as school performance) for U.S. Blacks and Whites. The performance differences persist in tests and testing situations in which care has been taken to eliminate bias. It has also been suggested that IQ tests are formulated in such a way as to disadvantage minorities. Controlled studies have shown that test construction does not substantially contribute to the IQ gap. However, some psychometricians are not satisfied that the question of test bias is fully answered by these results.

The preponderance of evidence indicates that IQ tests measuring general intelligence are crossculturally valid. There is little or no evidence of population-specific cultural effects apart from the obvious example of language bias. For example, Robert Sternberg et al. found that the IQ of 12- to 15-year-old Kenyans predicted school grades at about the same level as they do in the West. IQ also predicted university performance equally well in African and non-African engineering students in South Africa in a 2004 study. Salgado et al. (2003) demonstrated the international generalizability of general mental ability across 10 member countries of the European Community and differences in a nation’s culture, religion, language, socioeconomic level or employment legislation did not affect the predictive validity of IQ tests.

However, other studies have found evidence for bias. A 2005 study finds some evidence that the WAIS-R is not culture-fair for Mexican Americans. Other recent studies have questioned the culture-fairness of IQ tests when used in South Africa.

Source of funding

Proponents of genetic explanations of race/IQ correlation, such as Rushton, Lynn, and Jensen, have often been criticized for receiving funding from the Pioneer Fund, a group that had ties to Nazis and the eugenics of the early 20th century. The Southern Poverty Law Center considers the Pioneer Fund to be a hate group. Rushton is the current head of the Pioneer Fund and has spoken at conferences of the American Renaissance magazine, in which he has also published articles. Anti-racist Searchlight Magazine described one of these articles as a "veritable 'who’s who' of American white supremacy.".

Proponents of genetic explanations of race-IQ correlation have in turn accused their critics of suppressing scientific debate in the name of political correctness. They claim harassment and interference with both their work and funding. The Pioneer Fund, whose stated purpose is "to advance the scientific study of heredity and human differences", makes "no grants to individuals but only to research institutions, mainly universities, mostly for specialized 'niche' projects, which have difficulty attracting funds from government sources or from larger foundations".

See also

• Sex and intelligence
• Neuroscience and intelligence
• Height and intelligence
• Hominid intelligence
• The Mismeasure of Man
• IQ and Global Inequality
• Race Differences in Intelligence

Other medical:

• Population groups in biomedicine
• Ancestry and health

References

• Akey, J. M., Eberle, M. A., Rieder, M. J., Carlson, C. S., Shriver, M. D., Nickerson, D. A. and Kruglyak, L. (2004). "Population History and Natural Selection Shape Patterns of Genetic Variation in 132 Genes". PLoS Biology. 2 (10): e286. doi:10.1371/journal.pbio.0020286. PMID 15361935.{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: unflagged free DOI (link)
• Bean, R. B. (1906). "Some Racial Peculiarities of the Negro Brain". American Journal of Anatomy. 5: 353–432. doi:10.1002/aja.1000050402.
• Berry, J. W. (1966). "Temne and Eskimo Perceptual Skills". International Journal of Psychology. 1: 207–222. doi:10.1080/00207596608247156.
• Broca, P. (1873). "Sur Les Crânes De La Caverne De 'Homme Mort (Loere)". Revue d’Anthropologie. 2: 1–53.
• Brody, N. (1992). Intelligence. San Diego, CA: Academic.
• Carlson CS, Thomas DJ, Eberle MA, Swanson JE, Livingston RJ, et al. (2005). Genomic regions exhibiting positive selection identified from dense genotype data. Genome Res 15: 1553–1565. PMID 16251465
• Carretta, T. R. and Ree, M. J. (1995). "Near Identity of Cognitive Structure in Sex and Ethnic Groups". Personality and Individual Differences. 19 (2): 149–155. doi:10.1016/0191-8869(95)00031-Z. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
• Chan, J. and Lynn, R. (1989). "The Intelligence of Six-Year-Olds in Hong Kong". Journal of Biosocial Science. 21: 461–464. doi:10.1017/S0021932000018198. PMID 2808473. {{cite journal}}: Cite has empty unknown parameter: |month= (help)CS1 maint: multiple names: authors list (link)
• Cochran, G., Hardy, J., and Harpending, H. (2005). "Natural History of Ashkenazi Intelligence" (PDF). Journal of Biosocial Science. 38 (5): 659. doi:10.1017/S0021932005027069.{{cite journal}}: CS1 maint: multiple names: authors list (link)
• Colom, R., Lluis-Font, J.M., and Andrés-Pueyo, A. (2005). "The generational intelligence gains are caused by decreasing variance in the lower half of the distribution: Supporting evidence for the nutrition hypothesis". Intelligence. 33: 83–91. doi:10.1016/j.intell.2004.07.010.{{cite journal}}: CS1 maint: multiple names: authors list (link)
• Degler, C. N. (1992). In Search of Human Nature:The Decline and Revival of Darwinism in American Social Thought. New York: Oxford University Press. ISBN 0-415-28659-X.
• Dickens, W. T. (2005). "Genetic Differences and School Readiness" (PDF). Future of Children. 15 (1): 55–69. PMID 2005-04825-005. {{cite journal}}: Check |pmid= value (help); Unknown parameter |month= ignored (help)
• Dickens, W.T., and J.R. Flynn (In press). "Black Americans reduce the racial IQ gap: Evidence from standardized samples" (PDF). Psychological Science. {{cite journal}}: Check date values in: |year= (help)CS1 maint: multiple names: authors list (link)
• Dolan, C. V. (1997). "A Note on Schönemann's Refutation of Spearman's Hypothesis". Multivariate Behavioral Research. 32: 319–325. doi:10.1207/s15327906mbr3203_4.
• Dolan, C. V. (2000). "Investigating Spearman's Hypothesis by Means of Multi-Group Confirmatory Factor Analysis". Multivariate Behavioral Research. 35: 21–50. doi:10.1207/S15327906MBR3501_2.
• Dolan, C. V. and Hamaker, E. L. (2001). "Investigating Black-White Differences in Psychometric IQ: Multi-Group Confirmatory Factor Analyses of the WISC-R and K-Abc, and a Critique of the Method of Correlated Vectors". In F. Columbus (ed.). Advances in Psychological Research (PDF). Huntington, NY: Nova Science Publishers, Inc. ISBN 1-56072-897-3. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)CS1 maint: multiple names: authors list (link)
• Espanshade, T. J., Chung, C. Y. (2005). "The Opportunity Cost of Admission Preferences at Elite Universities" (PDF). Social Science Quarterly. 86 (2): 293–305. doi:10.1111/j.0038-4941.2005.00303.x. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
• Flynn, J. R. (1980). Race, IQ and Jensen. London: Routledge & Kegan Paul. ISBN 0-7100-0651-9. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)
• Flynn, J. R. (1987). "Massive IQ Gains in 14 Nations: What IQ Tests Really Measure". Psychological Bulletin. 101: 171–191. doi:10.1037/0033-2909.101.2.171.
• Flynn, J. R. (1987b). Race and IQ: Jensen's case refuted. In S. Modgil & C. Modgil (Eds.), Arthur Jensen: Consensus and controversy (pp. 221–232). Lewes, England: Falmer Press.
• Flynn, J. R. (1999). "Searching for Justice: The Discovery of IQ Gains over Time". American Psychologist. 54: 5–20. doi:10.1037/0003-066X.54.1.5.
• Flynn, J. R. (1999b). Reply to Rushton: A gang of gs overpowers factor analysis. Personality and Individual Differences, 26, 391–393.
• Gottfredson, L. S. (1997). "Mainstream Science on Intelligence: An Editorial with 52 Signatories, History, and Bibliography (Reprinted from the Wall Street Journal, 1994)" (PDF). Intelligence. 24 (1): 13–23. doi:10.1016/S0160-2896(97)90011-8. {{cite journal}}: Unknown parameter |month= ignored (help) appeared originally as "Mainstream Science on Intelligence" in Wall Street Journal, December 13, 1994.
• Gottfredson, L. S. (2005b). "What If the Hereditarian Hypothesis Is True" (PDF). Psychology, Public Policy, and Law. 11: 311–319. doi:10.1037/1076-8971.11.2.311.
• Hacker, Andrew (2005). "The Truth About the Colleges". The New York Review of Books. 52 (17). {{cite journal}}: Unknown parameter |month= ignored (help)
• Herrnstein, R. J. and Murray, C. (1994). The Bell Curve: Intelligence and Class Structure in American Life. New York: Free Press. ISBN 0-02-914673-9. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)CS1 maint: multiple names: authors list (link)
• Jank, Wolfgang (2004). Old World vs. New World: Evolution of Nobel Prize Shares (PDF). Department of Decision & Information Technologies, University of Maryland. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
• Jensen, A. R. (1969). "How Much Can We Boost IQ and Scholastic Achievement". Harvard Educational Review. 39: 1–123.
• Jensen, A. R. (1973). Educability and Group Differences. London: Methuen. ISBN 0-06-012194-7.
• Jensen, A. R. (1993). "Spearman's Hypothesis Tested with Chronometric Information-Processing Tasks". Intelligence. 17 (1): 47–77. doi:10.1016/0160-2896(93)90039-8. {{cite journal}}: Unknown parameter |month= ignored (help)
• Jensen, A. R. (1998b). The g Factor: The Science of Mental Ability. Westport, CT: Praeger Publishers. ISBN 0-275-96103-6.
• Jensen, A. R. and Whang, P. A. (1994). "Speed of Accessing Arithmetic Facts in Long-Term Memory: A Comparison of Chinese-American and Anglo-American Children". Contemporary Educational Psychology. 19: 1–12. doi:10.1006/ceps.1994.1001.{{cite journal}}: CS1 maint: multiple names: authors list (link)
• jinfo.org (2004). "Jewish Nobel Prize Winners," Accessed 9 June 2005.
• Jones, Garett, and Schneider, Joel W (2005). "Intelligence, Human Capital, and Economic Growth: a Bayesian Averaging of Classical Estimates (BACE) Approach" ( – ^{Scholar search}). {{cite journal}}: Cite journal requires |journal= (help); External link in |format= (help); Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
• Kayser, M., Brauer, S. and Stoneking, M. (2003). "A genome scan to detect candidate regions influenced by local natural selection in human populations". Mol Biol Evol. 20 (6): 893–900. doi:10.1093/molbev/msg092. PMID 12717000. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
• Litwack, Leon How Free is Free? Harvard University Press: 2009 ISBN 9780674031524
• Loehlin, J. C., Lindzey, G. and Spuhler, J. N. (1975). Race Differences in Intelligence. San Francisco: W. H. Freeman. ISBN 0-7167-0754-3. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)CS1 maint: multiple names: authors list (link)
• Lynn, R. (1991a). "Race Differences in Intelligence: A Global Perspective". Mankind Quarterly. 31: 255–296.
• Lynn, R. (1991b). "The Evolution of Racial Differences in Intelligence". Mankind Quarterly. 32: 99–173. {{cite journal}}: Cite has empty unknown parameter: |month= (help)
• Lynn, R. (2001). The Science of Human Diversity: A History of the Pioneer Fund. Lanham, MD: University Press of America. ISBN 0-7618-2041-8.
• Lynn, R. (2006). Race Differences in Intelligence: An Evolutionary Analysis. Washington Summit Books. 1593680201. {{cite book}}: Unknown parameter |month= ignored (help)
• Lynn, R., Hampson, S., and Magee, M. (1984). "Home Background, Intelligence, Personality and Education as Predictors of Unemployment in Young People". Personality and Individual Differences. 5: 549–57. doi:10.1016/0191-8869(84)90029-1. {{cite journal}}: Cite has empty unknown parameter: |month= (help)CS1 maint: multiple names: authors list (link)
• Lynn, R. and Holmshaw, M. (1990). "Black-White Differences in Reaction Times and Intelligence". Social Behavior and Personality. 18: 299–308. doi:10.2224/sbp.1990.18.2.299. {{cite journal}}: Cite has empty unknown parameter: |month= (help)CS1 maint: multiple names: authors list (link)
• Lynn, R. and Shigehasa, T. (1991). "Reaction Times and Intelligence: A Comparison of Japanese and British Children". Journal of Biosocial Science. 23: 409–416. doi:10.1017/S0021932000019519. PMID 1939289. {{cite journal}}: Cite has empty unknown parameter: |month= (help)CS1 maint: multiple names: authors list (link)
• Lynn, R. and Vanhanen, T. (2002). IQ and the Wealth of Nations. Westport, CT: Praeger. ISBN 0-275-97510-X. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)CS1 maint: multiple names: authors list (link)
• MacArthur, R. S. (1968). "Some Differential Abilities of Northern Canadian Native Youth". International Journal of Psychology. 3: 43–51. doi:10.1080/00207596808246642.
• Mackintosh, N. J. (1998). IQ and human intelligence. Oxford; New York: Oxford University Press. ISBN 0-19-852368-8.
• Mall, F. P. (1909). "On Several Anatomical Characters of the Human Brain, Said to Vary According to Race and Sex, with Special Reference to the Weight of the Frontal Lobe". American Journal of Anatomy. 9: 1–32. doi:10.1002/aja.1000090102.
• "Innately Inferior or Equal?" in The Struggle for Equality by Princeton University historian James M. McPherson

(Princeton University Press: 1964)

• Morton, S. G. (1839). Crania Americana; or, a Comparative View of the Skulls of Various Aboriginal Nations of North and South America. To Which Is Prefixed an Essay on the Varieties of the Human Species. Philadelphia: Simpkin Marshall & Co.
• Murray, C. (2005). "The Inequality Taboo" ( – ^{Scholar search}). Commentary Magazine. 120 (2): 13–22. {{cite journal}}: External link in |format= (help); Unknown parameter |month= ignored (help)
• Murray, C. and Herrnstein, R. J. (1994). "Race, Genes and IQ - an Apologia". New Republic. 211 (18): 27–37. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
• Neisser, U. (1997). "Never a Dull Moment". American Psychologist. 52: 79–81. doi:10.1037/0003-066X.52.1.79.
• Neisser, U., Boodoo, G., Bouchard, T. J., Boykin, A. W., Brody, N., Ceci, S. J., Halpern, D. F., Loehlin, J. C., Perloff, R., Sternberg, R. J. and Urbina, S. (1996). "Intelligence: Knowns and Unknowns" (PDF). American Psychologist. 51 (2): 77–101. doi:10.1037/0003-066X.51.2.77. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
• Nisbett, R. E. (2005). "Heredity, Environment, and Race Differences in IQ: A Commentary on Rushton and Jensen (2005)". Psychology, Public Policy, and Law. 11: 302–310. doi:10.1037/1076-8971.11.2.302.
• Ogbu, J. U. (1978). Minority Education and Caste: The American System in Cross-Cultural Perspective. San Diego, CA: Academic Press.
• Pearl, R. (1934). "The Weight of the Negro Brain". Science. 80: 431–434. doi:10.1126/science.80.2080.431. PMID 17816046.
• Pinker, Steven (2006). "The Edge Annual Question — 2006: What is Your Dangerous Idea?". The Edge. {{cite journal}}: Unknown parameter |month= ignored (help)
• Plomin, R., DeFries, J. C., McClearn, G. E. and McGuffin, P. (2001). Behavioral Genetics (4th Ed.). New York: Freeman. ISBN 0-7167-5159-3. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)CS1 maint: multiple names: authors list (link)
• Purdey, J. E., University of Melbourne (2002). http://eprints.unimelb.edu.au/archive/00000840/
• Reynolds, C. R., Chastain, R. L., Kaufman, A. S., & McLean, J. E. (1987). "Demographic characteristics and IQ among adults: Analysis of the WAIS-R standardization sample as a function of the stratification variables". Journal of School Psychology. 25: 323–342. doi:10.1016/0022-4405(87)90035-5.{{cite journal}}: CS1 maint: multiple names: authors list (link)
• Roth, P. L., Bevier, C. A., Bobko, P., Switzer, F. S. and Tyler, P. (2001). "Ethnic Group Differences in Cognitive Ability in Employment and Educational Settings: A Meta-Analysis". Personnel Psychology. 54 (2): 297–330. doi:10.1111/j.1744-6570.2001.tb00094.x. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
• Rowe, D. C. (2005). "Under the Skin: On the Impartial Treatment of Genetic and Environmental Hypotheses of Racial Differences". American Psychologist. 60 (1): 60–70. doi:10.1037/0003-066X.60.1.60. PMID 15641922. {{cite journal}}: Unknown parameter |month= ignored (help)
• Rushton, J. P. (1989a). "Japanese Inbreeding Depression Scores: Predictors of Cognitive Differences between Blacks and Whites". Intelligence. 13: 43–51. doi:10.1016/0160-2896(89)90005-6.
• Rushton, J. P. (2000). Race, Evolution, and Behavior: A Life History Perspective (3rd ed.). Port Huron, MI: Charles Darwin Research Institute. ISBN 0-9656836-1-3.
• Rushton, J. P. (2005). "(Book review) Lynn Richard, Race Differences in Intelligence: An Evolutionary Analysis" (PDF). Personality and Individual Differences: In press.
• Rushton, J. P. and Jensen, A. R. (2003). "African-White IQ Differences from Zimbabwe on the Wechsler Intelligence Scale for Children—Revised Are Mainly on the g Factor" (PDF). Personality and Individual Differences. 34: 177–183. doi:10.1016/S0191-8869(02)00192-7.{{cite journal}}: CS1 maint: multiple names: authors list (link)
• Rushton, J. P. and Jensen, A. R. (2005a). "Thirty Years of Research on Race Differences in Cognitive Ability". Psychology, Public Policy, and Law. 11: 235–294. doi:10.1037/1076-8971.11.2.235. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
• Smedley, A. and Smedley, B. D. (2005). "Race as Biology Is Fiction, Racism as a Social Problem Is Real: Anthropological and Historical Perspectives on the Social Construction of Race" (PDF). American Psychologist. 60 (1): 16–26. doi:10.1037/0003-066x.60.1.16. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
• Snyderman, M. and Rothman, S. (1988). The IQ Controversy, the Media, and Public Policy. New Brunswick, NJ: Transaction Books. ISBN 0-88738-839-6. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)CS1 maint: multiple names: authors list (link)
• Sowell, T. (1981). Ethnic America: A History. New York: Basic Books. ISBN 0-465-02075-5. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)
• Stajich, J. E. and Hahn, M. W. (2005). "Disentangling the effects of demography and selection in human history". Molecular Biology and Evolution. 22 (1): 63–73. doi:10.1093/molbev/msh252. PMID 15356276. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
• Sternberg, R. J. (2005). "There Are No Public-Policy Implications: A Reply to Rushton and Jensen (2005)". Psychology, Public Policy, and Law. 11: e72. doi:10.1037/1076-8971.11.2.295. {{cite journal}}: Cite has empty unknown parameter: |month= (help)
• Stock, Gregory (2002). Redesigning Humans: Our Inevitable Genetic Future. Boston: Houghton Mifflin. p. 194. ISBN 0-618-06026-X.
• Storz, J. F., Payseur, B. A. and Nachman, M. W. (2004). "Genome Scans of DNA Variability in Humans Reveal Evidence for Selective Sweeps Outside of Africa". Molecular Biology and Evolution. 21 (9): 1800–1811. doi:10.1093/molbev/msh192. PMID 15201398.{{cite journal}}: CS1 maint: multiple names: authors list (link)
• Suzuki, L. and Aronson, J. (2005). "The Cultural Malleability of Intelligence and Its Impact on the Racial/Ethnic Hierarchy". Psychology, Public Policy, and Law. 11 (2): 320–327. doi:10.1037/1076-8971.11.2.320. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
• Vint, F. W. (1934). "The Brain of the Kenya Native". Journal of Anatomy. 48: 216–223.
• Voight, B. F., Kudaravalli, S., Wen, X., Pritchard, J. K. (2006). "A Map of Recent Positive Selection in the Human Genome". PLoS Biology. 4 (3): e72. doi:10.1371/journal.pbio.0040072. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link) CS1 maint: unflagged free DOI (link)
• Wade, Nicholas (2006). Before the Dawn: Recovering the Lost History of Our Ancestors. New York: Penguin Press. ISBN 1-59420-079-3.
• Wicherts, J. M., Dolan, C. V., Hessen, D. J., Oosterveld, P., van Baal, G. C. M., Boomsma, D. I. and Span, M. M. (2004). "Are intelligence tests measurement invariant over time? Investigating the nature of the Flynn effect". Intelligence. 32 (5): 509–537. doi:10.1016/j.intell.2004.07.002.{{cite journal}}: CS1 maint: multiple names: authors list (link)
• Wright, W. D. (2007). Crisis of the Black Intellectual. ISBN 0–88378–251–0. {{cite book}}: Unknown parameter |nopp= ignored (|no-pp= suggested) (help)

External links

Collective statements

• APA Task Force Examines the Knowns and Unknowns of Intelligence
• Statement on "Race" and Intelligence. American Anthropological Association. Adopted December 1994.
• Mainstream Science on Intelligence. Intelligence, v24 n1 p. 13–23 January–February 1997

Review papers

• James Flynn and Charles Murray debate – news summary
• June 2005 issue of Psychology, Public Policy, and Law, Vol. 11, No. 2.
  • Thirty Years of Research on Race Differences in Cognitive Ability J. Philippe Rushton & Arthur R. Jensen
  • There Are No Public-Policy Implications Robert J. Sternberg
  • What if the Hereditarian Hypothesis is True? Linda S. Gottfredson
  • Heredity, Environment, and Race Differences in IQ Richard E. Nisbett
  • The Cultural Malleability of Intelligence and Its Impact on the Racial/Ethnic Hierarchy Lisa Suzuki & Joshua Aronson
  • Wanted: More Race Realism, Less Moralistic Fallacy J. Philippe Rushton & Arthur R. Jensen
• Race, Genetics and IQ Richard E. Nisbett (PDF)
• The Inequality Taboo Charles Murray archived version
• The Black-White Test Score Gap (1998) online (page-image) version of ISBN 0-8157-4609-1

Others

• Crippled by Their Culture - Race doesn't hold back America's black rednecks. Nor does racism by Thomas Sowell
• Race and IQ: Part 1, Part 2, by Thomas Sowell
• The Skeptic's Dictionary entry on IQ and race
• (Skeptic Magazine): Two book reviews, by Paul R. Gross and Alondra Oubre, of Sarich’s and Miele’s book, Race: The Reality of Human Differences
• Criticism on source material of Bell Curve book
• Poverty and Brain Development in Early Childhood 1999 report
• Miscellaneous articles by Richard Lynn et al.
• Are IQ Tests Biased?
• Scholars Provide an Overview of Explanations for Black-White Test Score Gap
• School Readiness: Closing Racial and Ethnic Gaps
• A review of the field (January 2006) Kohn, Marek, "This racist undercurrent in the tide of genetic research: As taboos fall away, there's a danger that denial of racial difference will be replaced with uncritical acceptance," The Guardian.
• The Lessons of the Ashkenazim: Groups and Genes, Steven Pinker, June 2006, The New Republic.