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== Background information == |
== Background information == |
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'''Racial distinctions''' are most often based on skin color, facial features, ancestry, and national origin. Some scientists argue that common racial classifications are not meaningful, often on the basis of research indicating that more genetic variation exists within such races than between them. <!-- DEAD Link [http://www.aaanet.org/stmts/race.htm]--> To define terms, racial labels used in the [[United States]] relate to genetic ancestry (Tang et al., 2005). People labeled ''[[Blacks]]'' have most of their ancestors from sub-Saharan Africa, ''[[Whites]]'' from Europe, and ''[[East Asians]]'' from Pacific Rim countries. ''[[Hispanics]]'', more often called an [[ethnic group]] than a race, |
'''Racial distinctions''' are most often based on skin color, facial features, ancestry, and national origin. Some scientists argue that common racial classifications are not meaningful, often on the basis of research indicating that more genetic variation exists within such races than between them. <!-- DEAD Link [http://www.aaanet.org/stmts/race.htm]--> To define terms, racial labels used in the [[United States]] relate to genetic ancestry (Tang et al., 2005). People labeled ''[[Blacks]]'' have most of their ancestors from sub-Saharan Africa, ''[[Whites]]'' from Europe, and ''[[East Asians]]'' from Pacific Rim countries. ''[[Hispanics]]'', more often called an [[ethnic group]] than a race, is a genetically diverse group that includes many recent Mexican, Puerto Rican, and Cuban immigrants, with mixed Native American and European ancestry. See the articles [[Race]] and [[Race (U.S. Census)]] for further discussion. |
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'''Intelligence''' is most commonly measured by performance on IQ tests. In turn, IQ tests are generally geared to measure the [[psychometric]] variable '''''g'''''. Some question the validity of all IQ testing or claim that there are aspects of intelligence not reflected in IQ tests. See the articles [[Intelligence (trait)|Intelligence]], [[intelligence quotient|IQ]], and [[G theory|''g'' theory]] for further discussion. |
'''Intelligence''' is most commonly measured by performance on IQ tests. In turn, IQ tests are generally geared to measure the [[psychometric]] variable '''''g'''''. Some question the validity of all IQ testing or claim that there are aspects of intelligence not reflected in IQ tests. See the articles [[Intelligence (trait)|Intelligence]], [[intelligence quotient|IQ]], and [[G theory|''g'' theory]] for further discussion. |
Revision as of 19:58, 17 June 2005
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Race and intelligence refers to the controversy surrounding the findings of many studies that racial groups show differences in average intelligence quotient (IQ) test scores and other measures of intelligence such as school achievement, reaction time, or brain size.
These results have sparked public debates concerning not only the reliability of the studies and the motives of their authors, but also the validity and fairness of intelligence tests in general. The primary focus of the scholarly debate is the question of whether group differences in average intelligence are caused by environmental factors (such as nutrition, the richness of the early home environment, and other social, cultural or economic factors) or whether there is also a genetic component that follows racial classifications.
Background information
Racial distinctions are most often based on skin color, facial features, ancestry, and national origin. Some scientists argue that common racial classifications are not meaningful, often on the basis of research indicating that more genetic variation exists within such races than between them. To define terms, racial labels used in the United States relate to genetic ancestry (Tang et al., 2005). People labeled Blacks have most of their ancestors from sub-Saharan Africa, Whites from Europe, and East Asians from Pacific Rim countries. Hispanics, more often called an ethnic group than a race, is a genetically diverse group that includes many recent Mexican, Puerto Rican, and Cuban immigrants, with mixed Native American and European ancestry. See the articles Race and Race (U.S. Census) for further discussion.
Intelligence is most commonly measured by performance on IQ tests. In turn, IQ tests are generally geared to measure the psychometric variable g. Some question the validity of all IQ testing or claim that there are aspects of intelligence not reflected in IQ tests. See the articles Intelligence, IQ, and g theory for further discussion.
Some researchers have argued that race and intelligence research is fundamentally flawed. Stephen Jay Gould expressed this view in his 1981 book The Mismeasure of Man. Tate & Audette (2001) argue that issues of "race" and "intelligence" are pseudo-questions because both concepts are arbitrary social constructions. Similarly, in a 2005 review paper Sternberg and colleagues question the basis of race and intelligence research[1]:
- In this article, the authors argue that the overwhelming portion of the literature on intelligence, race, and genetics is based on folk taxonomies rather than scientific analysis. They suggest that because theorists of intelligence disagree as to what it is, any consideration of its relationships to other constructs must be tentative at best. They further argue that race is a social construction with no scientific definition. Thus, studies of the relationship between race and other constructs may serve social ends but cannot serve scientific ends.
These views can be constrasted with those expressed in "Intelligence: Knowns and Unknowns", a report from the American Psychological Association, and "Mainstream Science on Intelligence", a statement signed by 52 intelligence researchers meant to outline "conclusions regarded as mainstream among researchers on intelligence".
The debates described in the following article assume that IQ tests measure some interesting aspect of intelligence and that some interesting information may be gained by studying racial group differences. For a critique of these assumptions, please see the previously mentioned articles.
The scholarly debate about race and intelligence involves both the relatively less controversial experimental results which find that average IQ test scores vary between racial groups, and the relatively more controversial interpretation of these IQ score differences. In general, interpretations of the "IQ gap" can be divided into two categories:
- "culture-only" interpretations that posit environmental causes (e.g., socioeconomic inequality or minority culture membership) that differentially affect racial groups; and
- "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.
History
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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 (Degler, 1991; Loehlin, Lindzey, & Spuhler, 1975). The writings of Sir Francis Galton, elaborating on the work of his cousin Charles Darwin, spurred interest in the study of mental abilities, particularly 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 (Bean, 1906; Broca, 1873; Mall, 1909; Morton, 1839; Pearl, 1934; Vint, 1934).
Average ethnic and racial group differences in IQ were first found with the widespread use of standardized mental tests in 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 (Boas, 1938).
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, since racial differences in such characteristics had been among the strongest arguments for a genetic role.
Eugenics was later adopted by the Nazi party as a justification for the systematic elimination of "parasitic" races, especially the Jews: notably a group with higher average IQ than other Whites.
Due 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. (Garrett, 1961; Lynn, 2001, pp. xlv-liv).
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 (Lynn, 2001, pp. 67-69).
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?" In this paper Jensen concluded that:
- (a) IQ tests measure socially relevant general ability; (b) individual differences in IQ have a high heritability, at least for the White populations of the United States and Europe; (c) compensatory educational programs have proved generally ineffective in raising the IQs or school achievement of individuals or groups; (d) because social mobility is linked to ability, social class differences in IQ probably have an appreciable genetic component; and tentatively, but most controversially, (e) the mean Black-White group difference in IQ probably has some genetic component (from Rushton & Jensen, 2005).
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 (Herrnstein & Murray, 1994), which included two chapters on the subject of racial difference in intelligence and related life outcomes. In response to The Bell Curve, Stephen Gould updated The Mismeasure of Man, criticising many aspect of IQ research. Some IQ researchers have been accused of misrepresenting the available data, especially when trying to associate the results with various other claimed differences in personality and physical characteristics.
In 2005, 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" (Rushton & Jensen, 2005).
Moral criticism
A political motivation is frequently ascribed to researchers who work on questions of race and intelligence. Many have been described as racists. In turn, many researchers have questioned the political motivations of their critics.
Another common criticism of race and intelligence research is that society would be better off not knowing if races differ in IQ, regardless of whether the cause were genetic or not. For example, Glazer (1994, p. 16) asked of race and intelligence research in The Bell Curve, "what good will come of it?" He adds,
- Our society, our polity, our elites, according to Herrnstein and Murray, live with an untruth: that there is no good reason for this [racial] inequality, and therefore society is at fault and we must try harder. I ask myself whether the untruth is not better for American society than the truth.
More recently, Yale psychologist Robert Sternberg asked whether race and intelligence researchers Arthur Jensen and J. Philippe Rushton show "good taste" in their choice of research topics. Further, he questioned, "What good is research of the kind done by Rushton and Jensen supposed to achieve?" (Sternberg, 2005). Harvard University microbiologist Bernard Davis (1978) criticized this position as the "moralistic fallacy", implying it was the converse of the naturalistic fallacy. Some researchers in the field of race and intelligence argue that suppressing race and intelligence research is actually more harmful. For example, Gottfredson (2005) argues against the suggestion of a benevolent untruth,
- 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.
Race in the United States
- see also Race
The political, social and cultural structure of the United States is still explicitly conscious of race; legal equality of Whites and Blacks did not fully materialize until the 20th century. The national and state governments of the United States employ race in the census, law enforcement, and innumerable other ways. Many minority races have political organizations to represent their interests. Racial discrimination is illegal in many areas of public and private life, including employment.
Average intelligence gaps among races
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. IQ studies outside these nations are few and small. It is uncertain what the average IQ or subgroup IQ tests scores would be with more complete studies in the developing world. IQ test scores in the developing world may be affected by factors less important in the developed world such as nutritional deficiencies. Most of the following article refers to studies attempting to explain race differences in IQ test scores in the US and do not refer to the world as a whole.
IQ gap in the US
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. In the United States, the mean IQ score among Blacks is approximately 85 and the mean IQ score among Whites is approximately 100; the mean IQ score of Hispanics is usually reported to be between the mean Black and White scores (Herrnstein and Murray report a mean "Latino" IQ of 89 in The Bell Curve). The mean score for people of East Asian and Jewish descent is usually higher than the mean score of Whites, but the extent of that difference is not precisely known. However, several studies place the median IQ of Ashkenazi Jews (who make up the overwhelming majority of American Jews) at approximately one standard deviation above the mean for other Whites, with the primary Jewish advantage in verbal reasoning and the East Asian advantage primarily in spatial reasoning. In The Bell Curve, Herrnstein and Murray report mean IQ scores for East Asians and Jewish Americans of 106 and 113, respectively.
Similar 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 (Roth et al. 2001).
School achievement gap
Measures of school achievement, such as the National Assessment of Educational Progress in the United States, 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. Closing this achievement gap is one of the aims of the No Child Left Behind act. Examining the achievement gap, Ogbu (2003) attributes the gap to academic disengagement of Black students and parents. Similarly, Thernstrom & Thernstrom (2003) cite environmental causes. The school achievement gap can potentially be explained by many environmental factors that do not affect IQ tests to a similar degree, like bias in those giving grades or constructing tests.
Attempts to redress the acheivement gap in the U.S. include Head Start and related early intervention programs. However, neither Head Start nor more intensive programs have been able to produce lasting gains in IQ or school achievement (Jensen, 1998). Lack of sufficient funding is often cited as a reason for the failure of Head Start programs to have lasting impact.
Is the gap closing?
Richard Nisbett and others have argued that the Black-White gap on various ability tests has narrowed from the 1970s to the 1990s (Grissmer, 1994; Grissmer, Flanagan, & Williamson, 1998; Grissmer, Williamson, Kirby, & Berends, 1998; Hedges & Nowell, 1998; Nisbett, 1995, 1998, 2005). These tests include the Equality of Educational Opportunity (EEO) survey, the National Longitudinal Study, the High School and Beyond survey, the National Education Longitudinal Study, and the National Assessment of Educational Progress program (NAEP).
The Journal of Blacks in Higher Education found that although the Black-White gap on the SAT declined from 1976-1988, it has been increasing since 1988. On the other hand, some studies find that the gap has been decreasing for the most of the 20th century and that this continued during the nineties.[2]
Jensen (1998 pp. 375-376, 407-408, 494-495) has argued that the Black-White differences in g have not narrowed. In support of this claim, he presents evidence that, while there have been gains in measures of acquired competency such as scholastic achievement, these improvements do not indicate gains in g. Jensen also argues that Black-White differences in g seen in measures of reaction time have not narrowed.
A meta-analysis by Roth et al. (2001) found a mean Black-White score difference of 1.1 standard deviations (6,246,729 samples; ranging from 0.38 to 1.46 depending on the g loading of the test). As to whether the IQ gap is narrowing, they speculated that any reduction was "either small, potentially a function of sampling error ... or nonexistent for highly g loaded" tests (Roth et al. 2001).
Gottfredson (2005) agreed that the Black-White gap observed in the National Assessment of Educational Progress test has narrowed from 1.07 to 0.89 standard deviations. However, she then argues that reduction stopped by the mid-1980s and is compatible with stable group differences in g.
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, and that all of the remaining difference could be explained by a few environmental factors.[3] One possible explanation is that the Flynn effect started earlier for Whites but has now stopped while continuing for Blacks. Reading and math scores are correlated with, but not substitutable for, IQ, so these findings alone may not indicate convergence in the IQ gap. Still, the correlation of IQ with grades is highest in elementary school (0.6 to 0.7; Jensen 1998), so convergence in scores may, in fact, indicate that the IQ gap is narrowing.
IQ gaps in other nations
Attempted compilations of average IQ by race generally place Ashkenazi Jews at the top, followed by East Asians, Whites, other Asians, Arabs and Blacks. See IQ and the Wealth of Nations for an attempted compilation of average IQ for different nations and a discussion of associated measurement problems.
The IQ scores vary greatly among different nations for the same group. Blacks in Africa score much lower than Blacks in the US. The black-white gap is much smaller in the UK than in the U.S.[4] Another example is Jews who score much lower in developing nations and Koreans who score much lower in Japan.
There are many examples of IQ score differences between close neighbours in the same nation, for example between French vs. Flemish speakers in Belgium, Slovaks vs. Gypsies in Slovakia, Irish and Scottish vs. English in Great Britain, and white speakers of Afrikaans vs. white speakers of English in South Africa. The difference between the white neighbours Protestants and Catholics in Northern Ireland is as large as the differences between whites and blacks in the U.S.[5]
There has been only one comparative study on IQ scores in different European nations. The difference between the highest and lowest average national IQ scores were 8 points. Northern and southern Europeans did not differ on their average IQ scores but the southern Europeans had a larger variation. The Norwegians had less than half of the variability of the white American population while Italians and Bulgarians had about 150%.
Reaction time
In 1991, Richard Lynn tested 1,468 9-year old children consisting of Blacks from South Africa, East Asians from Hong Kong and Japan, and Whites from Britain and Ireland. The content of the tests involved flipping a switch after one or more lights came on. Lynn found that the decision times (the time taken to make a decision about what to do) had a low correlation with IQ data on Raven's Progressive Matrices tests also administered during the same study, and that movement times (the time taken to execute the decision) did not show any correlation. He found that the Asians had the fastest decision times, followed by the Whites, and then by the Blacks. He also determined that the Black children had movement times that were substantially faster than those of Whites and Asians on certain tests.[6] Studies have shown similar patterns in response time on tests of arithmetic (Jensen, 1993; Jensen and Whang, 1994). For details, see Shigehisa and Lynn (1991) for Japan; Chan and Lynn (1989) for Hong Kong and Britain; Lynn (1991) for Ireland; and Lynn and Holmshaw (1990) for South Africa.
Brain size
Group differences in average IQ tend to mirror group differences in brain size. Numerous historical and modern studies, using skull and head measurements, weighing of brains at autopsy, and more recently, magnetic resonance imaging report racial differences. These studies are usually accompanied by a great deal of controversy.
In his 1839 Crania Americana, anthropologist Samuel George Morton reported that the mean cranial capacity of the skulls of Whites was 87 in³, while that of Blacks was 78 in³. Based on the measurement of 144 skulls of Native Americans, he reported an a figure of 82in³.
Morton's work has been criticized by Stephen Jay Gould, who alleged in his 1981 book The Mismeasure of Man that Morton was guilty of fudging data and "overpacking" the skulls with filler. Despite Gould's retabulation of Morton's data, however, the differences in brain size among different races still persist, with the data still showing a difference of about four cubic inches between modern Caucasians and Africans. Gould writes that the differences are "trivial", but J. Philippe Rushton (1996) responds that a difference of only a single cubic inch equates to millions of neurons.
In 1988, J. S. Michael remeasured a random sample of Morton's skulls and concluded that Morton had made very few errors. J. Philippe Rushton (1989) additionally reanalyzed Gould's retabulation, concluding that Morton had shown a pattern of decreasing brain size proceeding from East Asians, Europeans, and Africans.
In 1873, Paul Pierre Broca found the same pattern by weighing brains at autopsy. Other historical studies showing a Black-White difference in brain size include Bean (1906), Mall, (1909), Pearl, (1934) and Vint (1934).
In his controversial 1995 work Race, Evolution, and Behavior, J. Philippe Rushton reported an average endocranial volume of 1,415 cm³ for "Orientals [sic]", 1,362 for Whites, and 1,268 for Blacks. When adjusted for average body size, the differences become more pronounced; i.e., the encephalization quotients (EQ) display greater differences than do absolute brain sizes (Jerisen, 1973, 2000; Rushton, 1991). Rushton (1991) found an EQ of 7.26 for East Asians as compared to 6.76 for Caucasians. Differences in brain size between Asians and Europeans sometimes do not appear until adjusted for body size (Rushton, 1997). In some cases Europeans averaged higher absolute brain sizes than East Asians but lower relative brain sizes when adjusted for body size (Rushton, 1994).
Other studies that have shown similar patterns in average brain size include Ho et al. (1980), who measured brains at autopsy, and Beals et al. (1984), who measured approximately 20,000 skulls, finding the same East Asian → European → African pattern. Other studies have shown the same pattern in average head size, including Rushton (1992), Rushton (1994), and the National Collaborative Perinatal Project [7] (described by Broman, Nichols, Shaugnessy, & Kennedy, 1987) which collected anthropometric data, including head measurements and IQ, on approximately 35,000 children from 1959 to 1974 (although the study began with over 50,000 subjects, some attrition occured as with many longitudinal studies). Analyses of the data found the East Asian → White → Black pattern in head size and IQ at 4 months, 1 year, and 7 years of age.
Modern studies using MRI imaging have revealed similar results (Harvey, Persaud, Ron, Baker, & Murray, 1994) and have shown that brain size correlates with IQ by a factor of roughly .35 to .40. In 1991, Willerman et al. used data from 40 White American university students and reported a correlation coefficient of .35. Other studies done on samples of Caucasians show similar results, with Andreasen et al (1993) determining a correlation of .38, while Raz et al (1993) obtained a figure of .43 and Wickett et al. (1994) obtained a figure of .40. The correlation between brain size and IQ seems to hold for comparisons between and within families (Gignac et al. 2003; Jensen 1994; Jensen & Johnson 1994). However, one study found no within family correlation (Schoenemann et al. 2000). A study on twins (Thompson et al. 2001) showed that frontal gray matter volume was correlated with g and highly heritable. A related study has reported that the correlation between brain size (reported to have a heritability of 0.85) and g is 0.4, and that correlation is mediated entirely by genetic factors (Posthuma et al 2002). Note that none of the MRI studies have studied racial differences.
East Asian brains have greater width and breadth (i.e., are more brachycephalic) and are more spherically shaped than those of Europeans, which are more so than those of Africans. Africans tend to have longer and narrower (more dolichocephalic) brains (Beals et al., 1984; McShane, 1983; Rushton & Ankney, 2000). Beals et al. proposed that the longer and narrower African brain evolved for better heat dissipation in a warmer climate, while East Asians and Europeans evolved comparatively shorter and wider brains for thermoregulatory purposes in a cooler climate. Rushton & Ankney (2000, pp. 612-613) question the thermoregulatory hypothesis, instead positing that brachycephalization and sphericalization allow for greater brain size. At the same time, Rushton and Ankney believe it is possible that the need to thermoregulate in Africa may have selected against increasing brain size.
Rushton and Ankney (2000) found a pattern of descending prognathism, glabella size, postorbital constriction, and temporal fossae in African, European, and East Asian skulls and propose that these structures shrank over the course of evolution to allow greater brain size.
Rushton has been accused by other researchers of misrepresenting the data. When they have reanalyzed the data, Zack Cernovsky et al. argue that many of Rushton's claims are incorrect. [8]
The American Psychological Association's Task Force Report on Intelligence reports that with respect to "racial differences in the mean measured sizes of skulls and brains (with East Asians having the largest, followed by Whites and then Blacks)...there is indeed a small overall trend" (Neisser, 1997, p. 80).
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.[9]
Culture-only or partially-genetic explanation?
Test bias
It has been suggested that IQ tests may be biased against minorities, and that this accounts for part or all of the IQ gap. Some claim that there is no evidence for test bias. IQ tests are equally good predictors of IQ-related factors (such as school performance) for 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.
The lack of test bias is widely accepted in the research community. From the American Psychological Association's summary of their 1996 task force report, "Intelligence: Knowns and Unknowns": "The differential between the mean intelligence test scores of Blacks and Whites does not result from any obvious biases in test construction and administration, nor does it simply reflect differences in socio-economic status" (Neisser et al., 1996). From The Wall Street Journal: Mainstream Science on Intelligence (PDF): "Intelligence tests are not culturally biased against American Blacks or other native-born, English-speaking people in the U.S. Rather, IQ scores predict equally accurately for all such Americans, regardless of race or social class."
Since the U.S. Supreme Court outlawed employee selection, including testing, which is "fair in form, but discriminatory in operation" (Griggs v. Duke Power Co., 1971; see this page on disparate impact), American companies have had a strong incentive to construct valid tests which do not produce an IQ gap between ethnic groups, called "selection bias" in employment. Despite this incentive, these efforts have generally failed. For example, in one case regarding a police selection test in Nassau County, New York, a scandal ensued when tests which showed no "selection bias" (Black-White score gap) were found to have been denuded of their ability to measure intelligence (Gottfredson, 2005, pp. 24-26 PDF).
Motivation
One environmental source of the IQ gap which has been suggested is poor motivation among low scorers. This hypothesis is seemingly discredited by findings promoted by the researcher Arthur Jensen (1998) using elementary cognitive tasks to measure intelligence. For example, one such test asks the subject to lift a finger from a depressed button to strike a light when it flashes. When more than one light is offered as a target the task involves a decision of which to hit (i.e. the one which is lit). These tests measure both reaction time (from when the bulb illuminates to when the subject lifts their finger) and movement time (from when the subject lifts their finger to when the subject reaches the bulb). While movement time measurements show no difference (or an advantage to Blacks), reaction time measurements negatively correlate with IQ scores and show the same performance gaps between races (Jensen, 1993; Jensen and Whang, 1994). Jensen argues that it is difficult to imagine that people could be motivated during one part of each segment of the test but not motivated during the other. The correlation between IQ and reaction time is low (from .20 to .40). A review by Deary (2000) that combined several studies with six measures produced a multiple correlation of reaction time to IQ of .67. This correlation is within the range of correlations between different kinds of IQ tests.
Socio-economic factors
![](https://upload.wikimedia.org/wikipedia/commons/thumb/c/c6/1995-SAT-vs-Income-Education.png/356px-1995-SAT-vs-Income-Education.png)
IQ is correlated with economic factors. Blacks and Hispanics suffer poorer economic conditions than Whites. It has been suggested that the effects of poverty are responsible for some or all of the IQ gap. However, in the American Psychological Association report Neisser et al. (1996) argue that economics cannot be the whole explanation. First, see the discussion in "Shared and nonshared environmental effects" below. Second, to the moderate extent that IQ and income are related, it appears that IQ determines income, and not the other way around (Murray, 1998). (Note there are many other potential environmental factors beside income.) Third, there are gaps in SAT scores that are slightly smaller but still persist for individuals with similar family income and parental education. This stability has suggested alternative explanations:
- Some argue that Blacks are discriminated against such that they must have a higher or at least equal intelligence in order to achieve the same socioeconomic status (SES) as Whites. One should then expect that Black children should have a higher or equal IQ compared to children from Whites with the same SES. That they score lower on SAT tests can thus be interpreted as evidence for strong adverse influence from environmental factors different from SES or from SES factors other than income and parental education, like systematic discrimination discouraging school and achievement motivation and learning or cultural differences in nutrition like duration of breastfeeding.
- It is possible that Black and Hispanic parents achieve higher SES with lower intelligence; perhaps by having (on average) greater amounts of a compensating character, or through affirmative action. However, affirmative action has lts largest effect on young people newly employed with lower income.
- Another alternative explanation is that by comparing the SES of parents to the intelligence of their children, the score gap shown here reflects regression towards different average racial scores from one generation to the next; a partly-genetic origin of intelligence differences would predict this effect.
- SAT scores correlate fairly well with IQ scores but they are not the same and may measure different things.
Work by Carneiro et al. (2005) on average Black-Hispanic-White differences in IQ, education, and income casts doubt on conventional explanations of Black-White differences:
- Hispanic children start with cognitive and noncognitive deficits similar to those of black children. They also grow up in similarly disadvantaged environments and are likely to attend schools of similar quality. Hispanics complete much less schooling than blacks. Nevertheless, the ability growth by years of schooling is much higher for Hispanics than for blacks. By the time they reach adulthood, Hispanics have significantly higher test scores than do blacks. Conditional on test scores, there is no evidence of an important Hispanic-white wage gap. Our analysis of the Hispanic data illuminates the traditional study of black-white differences and casts doubt on many conventional explanations of these differences since they do not apply to Hispanics, who also suffer from many of the same disadvantages. The failure of the Hispanic-white gap to widen with schooling or age casts doubt on the claim that poor schools and bad neighborhoods are the reasons for the slow growth rate of black test scores.
Researchers have found that many American Blacks and Hispanics are not given sufficient opportunity to learn language and thinking skills during the first three years of life, possibly due to economic status. The first three years are especially critical years for neural development of the brain, and previous studies have shown that when human children were deprived of most or all language skills at an early age, they never developed the ability to master language at a later age; if they only mastered a small amount of language and thinking skills at a young age, then they could only make small improvements in later years. A recent study has shown that many American Blacks and Hispanics are raised in homes where their parents speak relatively few sentences, and the sentences usually show only simple grammar. As a result, their children never hear millions of words during the time when their brains are developing linguistic skills. Without this linguistic input during their developing years, many are observed to quickly fall behind, and they can never catch up. Children in poorer welfare families, which includes a higher percentage of many minority populations, apparently hear up to 30 million fewer words by age three than children in higher income, usually White, families. (Source: The Early Catastrophe: The 30 Million Word Gap by Age 3)
Cultural explanations
Many anthropologists have argued that intelligence is a cultural category; some cultures emphasize speed and competition more than others, for example. During WWI African-Americans from the north tested higher than those from the south. This could be because African-Americans in the north had received more formal education (see Race: Science and Politics, written by Ruth Benedict in 1940). Thousands of ethnographic studies indicate that innate capacities for cultural evolution are equal among all human populations. The American Anthropological Association has endorsed a statement deriding all studies of race and intelligence .
It has been suggested that Black culture disfavors academic achievement and fosters an environment that is damaging to IQ (Boykin, 1994). Likewise, it is argued that a persistence of racism reinforces this negative effect. John Ogbu (1978, 1994) has developed a hypothesis that the condition of being a "caste-like minority" affects motivation and achievement, depressing IQ. Even proponents of the view that the IQ gap is caused partly by genetic differences, such as Arthur Jensen, recognize that non-genetic factors are likely involved. Indeed, one author has compiled a list of over one hundred possible causes of the Black-White IQ gap.[10] These include the following:
- lack of reading material in the home
- poor cultural amenities in the home
- weak structural integrity of the home
- foreign language in the home
- low preschool attendance
- no encyclopedia in the home
- low level of parental education
- little time spent on homework
- low parental educational desires for child
- low parental interest in school work
- negative child self-concept (self-esteem)
- low child interest in school and reading
However, such factors have not been found to have an effect on IQ that lasts to adulthood among members of the same race (see below).
Cultural explanations for the IQ deficit among Blacks and Hispanics compared to Whites and East Asian minorities are complemented – and sometimes challenged – by the observation that East Asian minorities score well on IQ tests and on average enjoy greater economic success than other minorities. Along these lines, East Asians are sometimes referred to as "model minorities". Likewise, Jewish populations have suffered past discrimination and persecution, but do not exhibit an IQ deficit. However, Jews and East Asians are today less discriminated than Blacks.
Language
Some argue that the higher IQ test scores in East Asian nations are in part attributed to some IQ tests' inherent bias towards testing spatial reasoning. They argue that logographic writing systems like those used by Chinese or Japanese develop spatial reasoning better than the alphabetic writing systems prevalent in Europe and America. The same reasoning has been used to explain why students from Asia-Pacific countries (e.g., Singapore, South Korea) tend to score better than average in tests of mathematics. Some argue that the East Asian advantage can also be explained by more rigorous education programs.
A direct comparative test between Greek and Chinese studenst showed no difference in IQ or g, contradicting earlier studies which do not take the finer architecture of mental processing into account. The Chinese did outperform the Greeks in visuo/spatial ability, but this difference was smaller at earlier ages, grew during the first years of schooling and decreased later. The authors suggest that this pattern can be explained as follows: the Chinese students train their visuo/spatial ability during their early school years, as they have to learn many logographic characters of the Chinese writing system. Later in life, the Greek students adopt compensating strategies to deal with visuo/spatial information, and therefore the difference decreases in this realm.[11]
The Flynn effect
The Flynn effect consists of large documented worldwide increases in IQ scores for at least several decades. Attempted explanations have included improved nutrition, a trend towards smaller families, better education, greater environmental complexity, and heterosis.
Some think that there are no genetic differences and that the Flynn effect will eliminate differences in IQ test scores in the future. They argue that the Flynn effect started sooner and will end sooner for the more affluent parts of society and that Blacks sooner or later will close the gap. They note that the effect is very large over time, one estimate is that the average IQ in the U.S. below 75 before the Flynn effect started.
However, comparing the Flynn effect (IQ differences within races over time) to contemporary IQ differences between races is contested; for example, one report concludes "that the nature of the Flynn effect is qualitatively different from the nature of B-W differences in the United States" (Wicherts et al. 2004). Others note that a racial component is not mentioned in the abstract, that the above statement refers to "measurement invariance", and that it is not a statement about the role of genetics in the B-W gap.
Nongenetic biological factors
Other researchers have come across what they see as additional reasons for the IQ gap. The paper Poverty and Brain Development in Early Childhood holds that there is a large amount of neural damage in many American Black and Hispanic children due to inadequate nutrition, substance abuse of the children's parents, a high incidence of maternal depression, exposure to environmental toxins, psychological trauma, and the neural effects of physical abuse. Masters (1997) has proposed a "neurotoxity hypothesis" where pre- and post-natal exposure to heavy metal poisons differentially impacts Blacks. Drug abuse during pregnancy (e.g., alcohol and phenobarbital) can negatively affect IQ.
Infant mortality may be an indicator of environmental conditions that are subletal but damaging to health. The rate of infant mortality in the U.S. Black population is twice that of the White population, which in turn is twice the rate of infant mortality among Asians.[12] The rates of low birth weight (LBW), defined as less than 5.5 pounds, are correlated with infant death. LBW is different than premature birth; LBW can occur in full-term babies. LBW babies are at risk for many developmental, behavioral and cognitive abnormalities, including mental retardation. LBW (and premature birth) affect Blacks at twice the overall rate for the U.S. population.[13] Mother's age is the strongest predictor of LBW, where teenagers are especially susceptible. Most of the Black-White differences in LBW are not account for by other environmental variables such as socioeconomic status, poverty status, mother's age, and education; but differential prenatal care explains some of the gap (Naylor & Myrianthopoulos, 1967). Thus, the cause of the Black-White gap in LBW is a mystery. Environmental intervention has strong but short-lasting effects on IQ among LBW babies (Brooks-Gunn et al., 1994). Studies of LBW Black and White babies matched for birth weight and gestational age still find a one standard deviation IQ gap (Montie & Fagan, 1998).
A study of LBW babies indicates that breastfeeding can significantly improve their IQ scores tested at 8 years old (Lucas et al., 1996). After controlling for possible confounding factors, an improvement of 8.3 IQ points was found in the brestfeed group as compared to the formula fed group. Black mothers are known to breastfeed infants less and for a shorter time than White mothers (Ryan et al., 1996; Leary, 1988). Studies have shown IQ gains lasting into adulthood with increased duration of breastfeeding. Several recent studies shows that the intake of certain micronutrients, like those present in breast milk or fish oil, affects IQ scores even in developed nations. Helland et al. (2003) have shown larger head size at birth and higher IQ scores at 4 years of age when mothers took fish oil supplements during pregnancy and lactation.[14] Jensen (1998) believes that dietary supplementation is a promising avenue of research for raising Black children's levels of g. Lynn (1990) has proposed a nutritional hypothesis for the Flynn effect.
Genetics
Part of the gap may well be genetic; there is no a priori reason to believe that every ethnic group or race has precisely the same distribution of genes that affect intelligence; a small amount of random variation early in human evolution may have later crystallized into differences seen today. Also there might have been smaller evolutionary pressure towards greater intelligence in some environments. The partly genetic hypothesis is often ignored or disregarded in primary research on group differences. It has been well-studied by researchers doing meta-analyses that combine multiple sources of primary materials.
Arthur Jensen and others have concluded that the IQ gap is partly genetic. That is, they argue that the same mix of genetic and environment factors that cause IQ differences among individuals or between families of the same race also causes the differences seen between races. Jensen and colleagues reach this conclusion based on an evaluation of some of the following evidence. While accepting that some fraction of the supporting evidence may be false, they argue that the partly-genetic hypothesis is favored over the culture-only hypothesis by a preponderance of the evidence (Rushton and Jensen 2005; Gottfredson 2005). In this view, the genetic contribution to average intelligence differences among races are like average skin color differences: a product of different allelic frequencies within each population. Others are critical of Jensen's methods and evaluation (Sternberg 2005; Suzuki & Aronson 2005; Nisbett 2005).
The results of most (indirect) analyses used to test the genetic hypothesis do not logically contradict an environmental explanation of the lower IQ of Blacks. That is, a plausible (but some argue ad hoc) environmental explanation for the lower mean IQ in Blacks can be offered in most cases. However, many argue that the higher average IQ of East Asians than Whites is anomalous for an environment-only theory of IQ differences (Rushton & Jensen, 2005).
Shared and nonshared environmental effects
- see also IQ: genetics vs environment
The heritability of intelligence within groups is high. It is widely recognized that within-group heritability does not in itself indicate that between-group differences are genetic in origin, although it is likely a necessary condition. Different kinds of evidence are needed to address the question of between-group heritability. As Herrnstein and Murray explain in The Bell Curve:
- As we discussed in Chapter 4, scholars accept that IQ is substantially heritable, somewhere between 40 and 80 percent, meaning that much of the observed variation in IQ is genetic. And yet this tells us nothing for sure about the origin of the differences between races in measured intelligence. This point is so basic, and so commonly misunderstood, that it deserves emphasis: That a trait is genetically transmitted in individuals does not mean that group differences in that trait are also genetic in origin. Anyone who doubts this assertion may take two handfuls of genetically identical seed corn and plant one handful in Iowa, the other in the Mojave Desert, and let nature (i.e., the environment) take its course. The seeds will grow in Iowa, not in the Mojave, and the result will have nothing to do with genetic differences. (Herrnstein & Murray, The Bell Curve, 1994, p. 298.)
In most studies, measured heritabilities for intelligence are the same for Blacks as for Whites. A 1975 review by Loehlin et al. found some evidence suggesting lower heritability in Blacks than Whites (e.g., Scarr-Salapatek, 1971), but a larger body of evidence suggested equal heritabilities for both races. An analysis of the Georgia Twin Study by Osborne (1980) found equal heritabilities for both Blacks and Whites.
Two kinds of environmental effects can be distinguished: shared and nonshared effects (see nature versus nurture). Twin and adoption studies, used to measure heritability, can also be used to quantify the two types of environmental effects (Plomin, DeFries, & Loehlin, 1977). Shared environmental effects are due to factors experienced in common by all children raised in the same family but that differ among families. Examples of shared environmental effects include socio-economic factors, family cultural practices, and parental influences on children. Nonshared effects are unique for each child, and thus differ among families. Examples include chance events such as accidents, illness, and childhood friends. Anything that happens to one sibling and not to the other contributes to nonshared effects.
McGue et al. (1993) found (among a population of people studied in the U.S.) that the nonshared environmental effects on IQ remain approximately constant throughout life. Shared environmental effects in their study remained approximately constant (40% to 30%) from 4 to 20 years of age but then drop to zero in adulthood. Genetic factors increase throughout development (from 40% to 50%) but especially after 20 years of age (from 50% to 80%). Plomin et al. (2001) corroborates these results. Environmental factors usually proposed to explain the Black-White gap are shared effects (e.g. social class, religion, cultural practices, father absence, and parenting styles). Jensen (1997) argues that because these effects account for little variance within a race, they are unlikely to account for the differences among races in developed nations.
However, others studies do support that shared environmental factors in developed nations can affect IQ, including IQ gains lasting into adulthood (Capron and Duyme, 1989).[15] However, many such studies measure IQ in children (those shared effects that have disappeared in studies don't disappear until adulthood) or, some critics claim, do not have the controls needed to differentiate genetic and environmental effects. Others argue that some IQ gains disappear exactly because the interventions cease, continuing interventions like Head Start have showed that the IQ gains then remain.
In a re-analysis of adoption data from Capron and Duyme (1989), Jensen (1998a) found that the IQ gains that result from being adopted into high socioeconomic-status homes do not produce gains in g, but only in non-g factors. Jensen also found that the g factor scores of the adopted children reflected the socioeconomic level of their biological parents, not their adopted parents. This is consistent with Jensen's theory that g is the predominant genetic component of IQ scores; see Spearman's hypothesis below from the relationship between g and racial difference in IQ.
The recent paper Socioeconomic status modifies heritability of IQ in young children finds that the role of the environment is more important in poorer families. "The models suggest that in impoverished families, 60% of the variance in IQ is accounted for by the shared environment, and the contribution of genes is close to zero; in affluent families, the result is almost exactly the reverse." This suggests that the role of shared environmental factors may have been underestimated in older studies which often only studied affluent middle class families.
Also, note that only the range of shared environmental effects captured in heritability studies are actually known to disappear in adulthood; more extereme environmental deprivation may likely have a lasting impact on IQ in adults. Heritability only tells us what is the contribution of genes to variation in a trait, not what it could be. Thus, heritability measures in the U.S. population cannot be extraoplated to populations in developing nations.
Spearman's hypothesis
Intelligence as measured by g as defined by the g theory, the in-contention "general factor of cognitive ability", and its various biological correlates (e.g., the volume of gray matter in the frontal cortex) are claimed to be partly genetically determined. g has the highest measured heritability of any cognitive ability factor. Jensen formulated a hypothesis now referred to as Spearman's hypothesis which states that the degree of difference between black and white cognitive test scores will be correlated with the degree of the test's g-loading. Spearman's hypothesis has a strong form, which says that all test-score differences can be traced to g, and a weak form, which claims that some but not all differences are due to g.
Jensen found that black-white cognitive test score differences and test g-loadings correlate with a correlation coefficient of 0.6 (Jensen, 1998), and concluded that the weak form of Spearman's hypothesis was thus confirmed. Jensen's study combined scores on 149 psychometric tests obtained from 15 independent samples totaling 43,892 Blacks and 243,009 Whites (Jensen, 1998). Dolan and Hamaker (2001) have reanalyzed the data from several previous studies (Jensen & Reynolds, 1982; Naglieri & Jensen, 1987) that used the statistical method invented by Jensen (the method of correlated vectors) with a more recent and improved method (multigroup confirmatory factor analysis). Their results statistically were consistent with the weak form of Spearman's hypothesis that black-white group differences were predominantly on the g factor. However, their analysis of the data set failed to "establish Spearman's hypothesis as an empirically established fact". They also speculate that "it is possible that the analysis of all available data sets ... will demonstrate that a model incorporating the weak version of Spearman's hypothesis provides the best description of the data."[16] This leaves the validity of Spearman's hypothesis, considered a central justification for the genetic explanation, an unresolved question.
Gene-environment interactions
Minority-specific effects on intelligence arising from cultural background differences between the races would be expected to affect the correlations between the measures of environmental background variables and outcome measures. Rowe et al. (1994) compared cross-sectional correlation matrices using both independent variables (e.g., home environment, peer characteristics) and developmental outcomes (e.g., achievement, delinquency). Rowe et al. (1995) compared correlations between academic achievement and family environment. They found that the covariance matrix of each group were equal. That is, they failed to find evidence for distortions in the correlations between the background variables and the outcome measures that would suggest a minority-specific developmental factor.
Similarly, Carretta (1995), Owen (1992), and Rushton et al. (2000, 2002, 2003) found nearly identical statistical structure on psychometric variables in each group. The factor structure of cognitive ability is nearly identical for Blacks and for Whites; there were no race-specific factors.
Using structural equation modeling Rowe and Cleveland (1996) estimated the genetic architecture for Black and White siblings. They found that the best-fitting model for the source of differences between and within races was the same: both genetic and environmental factors. Jensen (1998b, p. 465) reanalyzed a subset of this data. This analysis found that the Black-White IQ difference was best explained by a model of both genetic and environmental factors, and that the genetic-only and the environmental-only models were inadequate.
Nichols (1972) using differential heritabilities among Blacks and Whites and later Rushton (1989) using inbreeding depression calculated in Japan found that the Black-White gap is least on IQ subtests most affected by the environment, and greatest on subtests that are least affected by the environment. It is difficult to attribute the relationship between inbreeding depression from Japan with the Black-White IQ gap in the U.S. to an environmental (not-genetic) cause.
These results have not been thoroughly retested.
Evolutionary explanations for putative genetic differences
Two mainstream theories of the evolution of contemporary humans in exist. They are general theories and not specifically about the development of genetic differences in IQ but provide possible explanations also for this. They concern the relationship between modern humans and other hominds. The single-origin hypothesis proposes that modern humans evolved in Africa and later replaced hominds in other parts of the world. The multiregional hypothesis proposes that modern humans evolved at least in part from independent hominid populations. An emerging synthesis theory proposes that the genes of contemporary human are predomintantly decendent from a recent African origin, but that interbreeding with other hominds may have contributed genes to local populations (Templeton, 2002). Eswaran et al. (2005) speculate that "as much as 80% of the nuclear genome is significantly affected by assimilation from archaic humans (i.e., 80% of loci may have some archaic admixture, not that the human genome is 80% archaic)." Populations within continents are more closely related to one another than to populations on other continents (Mountain and Cavalli-Sforza 1997; Stephens et al. 2001; Rosenberg et al. 2002; Bamshad et al. 2003). Thus, to the extent that racial labels correspond to ancient ancestry, racial groups (especially in the U.S.) are statistically distinguishable on the basis of genetics (Tang et al., 2005).
In his controversial 1995 work Race, Evolution, and Behavior, J. Philippe Rushton argued that racial differences in IQ, as well as a number of other racial differences, could be explained by the relative success of an evolutionary "strategy" favoring reproduction potential over other strengths (r-selection) and one favoring traits that are highly adaptive in a stable environment (K-selection). The r-selection strategy was claimed to be more adaptive in the African environment than elsewhere. All humans are extremely K-selected, Rushton claims. He posits that the comparatively cold and harsh environment of Europe caused the evolution of those who migrated there slightly more to a K-selected pattern than those who remained in Africa, and the even harsher environment of Northeastern Asia forced the evolution of East Asians to an even higher level of K-selective behavior. This theory has been severely criticized.[17]
Richard Lynn has developed similar theories and argues that the ice age that took place in East Asia from about 28,000 to 12,000 years ago acted as a selection force on East Asians to increase intelligence by requiring the building of shelter, making clothes, and making fires, and selected especially strongly for spatial skills such as those needed to hunt large prey and build the tools necessary to do so. (Lynn 1991). Rushton (1996) has cited the fact that the order in Blacks, Whites, and East Asians appeared is the same as the order of their respective brain sizes as additional evidence. This theory, however, has difficulty explaining why Native Americans, who appeared even later and emigrated from the northernmost parts of Asia, do not currently have high scores on IQ tests. On the other hand, Rushton (1995) argues that lower scores of Native Americans can be attributed to the evolutionary relaxation of cognitive demands due to the more temperate environment and comparative ease with which North American fauna could be hunted. But it can be argued that life along the fertile river plains in China was not particularly harsh. It is also questionable that conditions in deserts are no less harsh but people living there do not currently score high on IQ tests.
The theory is directly contradicted by the only comparative study on IQ scores in different European nations that showed a statistically insignificant association between the average IQ and latitude of various European nations. There was a larger variation in IQ scores in southern Europe. Possible explanations for this include sample selection, larger environmental differences affecting IQ scores between urban and rural areas in southern Europe at the time of the test (1981), and/or that northern Europe gained a social stratification later in history which caused less genetic variation in IQ.[18] In contrast, Beals et al. (1984, p. 309) found a correlation of 0.62 (p=0.00001) between latitude and cranial capacity in samples worldwide and reported that each degree of latitude was associated with an increase of 2.5 cm³ in cranial volume. A more recent study finds this pattern only when including a Siberian population living in extremely cold condition. The explanation may be natural selection for a thermoregulatory capacity in extremely cold environments, resulting in brachycephalization, rather than a selection for intelligence.[19]
The Imperial examination system in China and similar systems in other East Asians nations have been proposed as an explanation for the higher average IQ, compared for example with the caste system in India which made if much more difficult for the intelligent but poor to gain SES. Celibacy for priests have been invoked as an explanation for claimed lower IQ in catholic countries, although this also seem to be contradicted by the equal IQ in northern and southern Europe.
Constant persecutions favoring a high IQ have been proposed as an explanation for the higher average Ashkenazi IQ, but other persecuted groups like the Romani do not score highly on IQ tests. Another theory suggests that there was selective breeding for Talmudic scholarship, but this seems unlikely to have been important since there weren't very many professional rabbis. A selective force that only affects a tiny fraction of the population can never be strong enough to cause important evolutionary change in tens of generations. A more plausible, but difficult to evaluate without detailed demographic information, variant of this is that achievement in Talmudic scholarship had high status and that rich families therefore preferred to marry their daughters to males who excelled in this. Yet another explanation, and according to a recent paper[20] the most likely, is that they mostly worked jobs in which increased IQ strongly favored economic success, in contrast with other populations, who were mostly peasant farmers.
Comparison of interpretations
The Black-White IQ gap in the U.S. may be explained by a variety of interpretations. In order to differentiate between alternatives, additional evidence is needed. The "partly-genetic" and "culture-only" interpretations offer contrasting points of view on this evidence.
Partly genetic | Culture only |
---|---|
Black-White-East Asian differences in IQ, reaction time, brain size and other physiological variables in the United States and a few other developed countries (e.g. UK, Japan). Larger brain size and higher IQ of East Asians than Whites is a challenge for the culture-only theory. | The gaps may be explained by many other factors except genetics (see above). Differences among some White groups are as large as the difference between Whites and Blacks in the US. Many racial groups show great variation when tested at different times and in different places, indicating large environmental influences. The IQ scores and larger brain size of East Asians have numerous possible explanations, e.g. many East Asian nations have a very high consumption of fish. One study has shown larger head size at birth and higher IQ scores at 4 years of age when the mothers took fish oil supplement during pregnancy and lactation. |
Black-White-East Asian differences in culture-fair and reaction-time IQ test scores exist world-wide despite international differences in social, cultural, and economic conditions. Higher IQ scores among East Asians (living in East and South Asia) than Whites (living in North American and Europe) is a challenge for culture-only theories because standards of living in Asia are lower than or equal to those in North America or Europe. For example, average IQ scores are higher in the People's Republic of China (Lynn & Vanhanen, 2002) than for African Americans even though per capita GDP (PPP) is lower in China ($5,000 as of 2003) than per capita African American income ($15,583 as of 2003) (DeNavas-Walt, Proctor, & Mills 2004). Jensen (1998) discusses his observation among Californa children that very low IQ Blacks are qualitatively normal in social and motor skills, but perform no better than Whites with equally low IQ on cognitive tasks except those that require rote memorization, where "mentally retarded" Blacks do significantly better than Whites. He speculates that 12.5% of cases of IQ <70 are due to organic defects in Blacks, compared to 50% in Whites, giving the impression that low IQ Whites are more handicapped than low IQ Blacks. | The only nationwide IQ tests have been done in a few developed countries, and the few studies in other nations have been severely criticized, see IQ and the Wealth of Nations. One argument of many against the reliability of the IQ scores in developing nations is that some such countries a majority of the population would be classified by the IQ scores as mentally retarded. For example, Equatorial Guinea is one of the few African nations that actually have a study and is classified as having the lowest average IQ in the world, 59, based on study of 48 persons 10-14 years old. A large proportion of the population should also be classified as moderately (<16%) and severely (<2%) mentally retarded. In the U.S., the moderately mentally retarded require moderate supervision and the severely mentally retarded often have other physical disabilities and may thus require constant supervision, be unable to provide for themselves, be unable to speak long sentences, and, in many cases, be unable to do things like getting dressed without help. |
The Black-White IQ gap in the US has remained constant at approximately one standard deviation since it was first measured in the early 1900s despite social and economic change during that time, including the civil rights movement and Brown v. Board of Education. Recent changes in skill test score gaps do not indicate changes in g. | Other studies show that the gap in the US is narrowing. For example, one large recent study found much smaller differences than earlier studies in math and reading skills in young children and found that all of the remaining differences could be explained by a few environmental factors.[21] |
The IQ gaps remains approximately constant as individuals age. Some environmenal theories would predict a growing or shrinking IQ gap during development. | Many environmental factors, like nutrition during pregnancy and lactation, can have a life long effect. Jensen (1998) reports some evidence of decreasing IQ among African American boys at adolescence. |
Correlations between an IQ subtest's heritability or inbreeding depression and the magnitude of the Black-White-East Asian score gap for that subtest. Environmental theories would predict the opposite. | What subtest are most heritable and how to measure this is debated. |
Correlations between an IQ subtest's g-loading, and the magnitude of the Black-White-East Asian score gap for that subtest. | g-loading and the method of correlated vectors, the statistical method used in many older studies, has been criticized heavily in recent research as discussed previously. |
Rising heritability of IQ with age, and decreasing shared-family effects (e.g., socioeconomic factors) on IQ after adolescence. An environmental cause of the IQ gap would necessarily be a shared family effect. Lack of shared family effects on adult IQ is a challenge to culture only theories. | High within-group heritability does not logically exclude the all environmental interpretation. |
Studies suggesting that IQ heritability and gene-environment interactions within races are the same for Blacks and Whites. That is, no race-specific statistical factors, such as an effect of White racism, have been identified in such analyses. The IQ gap exists even among middle- and upper-class Black and White families where within-race heritabilities are high and shared family effects are near zero. | Many factors that can affect IQ differ between Blacks and whites, for example duration of breastfeeding or poverty.Many older studies have only studied middle class families but SES has recently been shown to be relatively more important in poorer families. |
The finding that when Black and White children are matched for IQ, their siblings tend to have IQs that regress towards different means (85 for Blacks and 100 for Whites). For example, among Black and White children matched with an IQ of 120, the siblings of the Black children have an average IQ of 100 whereas the siblings of the White children have an average IQ of 110. This is a stronger test of the party-genetic hypothesis than regression from parents to offspring because siblings share a similar environment (Jensen, 1973). This is a novel prediction of the partly genetic hypothesis. | Regression towards the mean only shows that mean IQ scores are different which is not a new finding. That is not evidence that the cause of this difference is genetic. |
American Blacks have a lower average IQ than Hispanic and Native American groups, which are more socio-economically deprived. For example, the Inuit, who live in the Arctic, have higher average IQs than North American Blacks (Berry 1966; MacArthur 1968) despite being extremely poor (Vernon 1965, 1979). | That Blacks are less socioeconomically deprived than Hispanics or Native Americans in the US is controversial. The Inuit cannot be directly compared to the US population, for example they have substantially different nutrition from eating large amounts of fish. |
The three-way differences in the IQ and SAT scores of children persists even after controlling for parental income or education, which seems to counter arguments that the gap is due to socioeconomic conditions.[22] In addition, some researchers have argued from studies in siblings that IQ affects socioeconomic status, rather than the other way around. | Adjustments for socioeconomic conditions almost completely eliminate differences in IQ scores between black and white children. The remaining difference is statistically insignificant.[23] SAT scores are not the same as IQ scores. |
Ashkenazi Jews have often been persecuted and discriminated against, but they still display the highest average IQ of any ethnic group, as well as SAT scores higher than those of non-Jewish Caucasians. This seems to counter arguments that depressed IQ scores of African Americans are due to discrimination or prejudice. | Persecution of and discrimination against Jews was strongest in the past, while Blacks are still being discriminated against in various ways today. |
The three-way 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, Fagan, & Drotar, 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. | Environmental factors can affect very young children, for example nutrition by the mother during pregnancy and breastfeeding. More breastfeeding gives IQ gains and the duration of this is known to differ between White and Black mothers. Two studies in Chile shows that nutritional status affects IQ, scholastic achievement, and brain volume.[24] |
Three-way differences in reaction times have been demonstrated, and it is difficult to explain differences in reaction time through lack of motivation or cultural differences on the part of the subjects. | Differences in reaction time or brain volume may be caused by environmental factors. As noted, there have been large changes in cranial vault size and shape during the last century in the US for both Black and Whites, far beyond what can be explained genetically. In addition, reaction time and brain size have only a low correlation with IQ test scores and are not shown to have any real-world significance. |
Average Black-White-East Asian differences in IQ (both positive and negative) remain following transracial adoption. Three studies of East Asian children adopted by White familes reported average IQ scores in the adopted East Asian children that are as high or higher than Whites, despite the fact that some of the children in the studies had suffered some forms of preadoptive deprivation or malnutrition and associated developmental delays (Clark & Hanisee, 1982; Frydman & Lynn, 1989; Winick, et al. 1975). Burrow & Finley (2004) found Black-White-East Asian differences in cognitive and psychological variables among adolescents adopted by white families. They also found that Black-White mixed-race children fell in between the White and Black averages. The higher average IQ of adopted East Asian children is a challenge to the culture-only theory. | Existing adoption studies lack behavior genetic controls needed to distinguish between genetic and environmental effects. Several other adoption studies finds no IQ difference between Whites and East Asians.[25] |
No studies of Black-White genetic admixture have been performed with the multi-locus DNA sequencing required to make reliable conclusions. | IQ have very low positive to low negative correlation with Whiteness of skin, degree of European blood groups, or self-reported degree of European ancestry among Blacks. |
No studies that make use of proper behavior genetic techniques have been able to identify environmental factors to explain the IQ gap. | A study which showed near-disappearance of the black-white gap among children of black and white servicemen raised by German mothers after World War II. Some, like the American Psychological Association, consider this study be strong evidence against the genetic explanation.[26] |
Average IQ scores gaps within the U.S. and internationally[27] have been stable since they were first measured in the early and mid 20th century (Lynn & Vanhanen, 2002; see above), despite the Flynn effect. One statistical analysis suggests that the Flynn effect is qualitatively different than the Black-White IQ gap (Wicherts et al. 2004). | One estimate is that the average IQ in the U.S. was below 75 before the Flynn effect started and it seems likely that the effect started earlier and may end sooner for Whites. Some studies show that the IQ gaps is decreasing in the US and even if they are not this may change in the future if the Flynn effect ends first for Whites. Lynn and Vanhanen only have IQ scores from 3 developing nations before 1950, in two of these only 1 study, make any claims of knowing average continental IQ strange indeed. The Wicherts study refers to "measurement invariance", is not a statement about the role of genetics in the B-W gap, and is a relatively minor statement that not mentioned in the abstract. |
A similar dichotomy in spatial/nonspatial intelligence test scores is present in both East Asians and several Native American and Inuit populations (Connelly, 1983; Diessner & Walker, 1986; Tempest, 1987; Zarske & Moore, 1982; McShane & Plas, 1982, 1984).[28] | Dichotomy in intelligence is entirely compatible with an all environmental explanation but may not be with the g theory. East Asians may have higher spatial ability for example due to their knowledge of iconographic languages. |
Partly-genetic theory is predicated on a model that the IQ gap has (the genetic) part of its origin in human evolution. Thus, it predicts that the Black-White-East Asian differences in average IQ, reaction-time, and brain size should be accompanied by a similar pattern of differences in other inherited traits. Proponents cite three-way average differences in personality, maturation, and reproductive traits as support of this prediction. Research on racial differences in twining and testis size was the subject of a review by author and scientist Jared Diamond (1986) in the journal Nature, in which he investigated correlations between possible racial variations in testicular size and hormone levels and found one small study suggesting that dead Danish men on autopsy have larger testicles than dead Chinese men. Some studies also suggested lower hormone levels and frequency of twins among Asians than Africans. | Differences may have environmental causes and may be unrelated to one another. Many of these claims of differences have been shown to be false, for example references to scientific literature with respects to racial differences in sexual characteristics turned out to be references to a a nonscientific semipornographic book and to an article in the Penthouse Forum.[29]. Regarding Jared's study, he notes that smaller testicle size among Koreans was not associated with a lower frequency of sexual intercourse, which directly contradicts Rushton rK-theory. There is only an insignificant difference in frequency of twins between Whites and Blacks in the U.S (34.8 vs 34.7), also contradicting the theory. [30] Higher frequency of twins in certain African populations can be explained by large scale consumption of Yam which in rats produces such results. [31] |
Other interpretations
The two most widely-known works concerning race and intelligence are The Mismeasure of Man by Stephen Jay Gould, originally published in 1981, and The Bell Curve by Richard Herrnstein and Charles Murray, published in 1994. Media controversy surrounding The Bell Curve motivated Gould to revise and expand The Mismeasure of Man to respond to arguments from The Bell Curve, publishing the book's second edition in 1996. Many current researchers think that both books are outdated due to new research.
A recent paper in the Psychological Review, "Heritability Estimates Versus Large Environmental Effects: The IQ Paradox Resolved" by William T. Dickens of The Brookings Institution and James R. Flynn presents a mechanism by which environmental effects on IQ may be magnified by feedback effects. This work may provide a resolution of the contradiction between the viewpoint of The Bell Curve's authors and the 'nurture' effects observed by others. A latter paper responded to objections.[32]
Some cite research that they believe indicates that discriminated or lower-status minorities do tend to have lower IQ, some without apparent genetic differences. Like Blacks and Hispanics in the U.S., minorities in some societies show achievement gaps (such as the Maori in New Zealand, aboriginals in Australia, scheduled castes ("untouchables") in India, non-European Jews in Israel, and the Burakumin in Japan). The most prominent finding cited is that Northern Irish Catholics used to score about 15 points lower than Protestants. Similarly, Irish, Italian and Polish immigrants in the U.S. are reported to have all scored about 80 in the beginning of the 19th century, but now tend to reach 100. The same is true of persons from rural versus urban areas in general (see e.g., this article by conservative columnist and economist Thomas Sowell and this page on European and Greek IQ. More arguments of the kind are to be found here).
Opinions of scholars
A survey published in 1987 by Mark Snyderman and Stanley Rothman of a broad sample of 1,020 scholars in specialties that would give them reason to be knowledgeable about IQ asked, "Which of the following best characterizes your opinion of the heritability of the Black-White difference in I.Q.?" (emphasis original).[33] The responses were divided into five categories:
- The difference is entirely due to environmental variation: 15%.
- The difference is entirely due to genetic variation: 1% (8 respondents).
- The difference is a product of both genetic and environmental variation: 45%.
- The data are insufficient to support any reasonable opinion: 24%.
- No response: 14%.
No single response was endorsed by more than half of those surveyed, but the majority of those who replied chose the option "The difference is a product of both genetic and environmental variation".
The survey group was composed of indiviudals who are members of:
- American Education Research Association
- National Council on Measurement in Education
- American Psychological Association:
- Developmental Psychology
- Educational Psychology
- Evaluation and Measurement
- School Psychology
- Counceling Psychology
- Industrial/Organizational Psychology
- American Sociological Association: Education
- Behavior Genetics Association
- Cognitive Science Society
However, the survey is old and it is unclear what specialties are represented.
IQ, race, and public policy
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. However, 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. Two statistical effects interact to exacerbate 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. (See IQ for a discussion of its practical importance.)
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. |
Real-world outcomes
The IQ gap is reflected by gaps in the academic, economic, and social factors correlated with IQ (Gordon 1997; Gottfredson 1997). For example, Murray (1998) argues from IQ variation among siblings (full brothers/sisters who grew up in the same home, where one of the sibling pairs has a normal range IQ) that IQ has a large effect on adult life outcomes.[34] For example, Murray found that very bright siblings in the 90th+ centile of IQ earned $13,000 more in annual income (in 1993) compared to siblings in the 75–89th centile, who in turn earned $4,000 more than the normal siblings in the 25–74th centiles (Murray, 1998). Similarly. lower IQ sibling groups had lower average incomes. Rates of educational and occupational attainment were likewise stratified by IQ. The effects of IQ were nearly identical even among the "Utopian" subset of siblings that grew up in families not burdened by divorce or poverty. However, these differences are less impressive when considering that in 1993 the average family income was $61,800 while the average family income of the richest 10% was $172,400. [35] (Note these income values are larger than those from Murray's study, possibly because these values include income other than wages. Murray found average family incomes at five IQ tiers of $53,000 for the top 10 percent of IQ, $45,000 for the next 15 percent, $37,000 for the middle 50 percent, $23,400 for the next 15 percent, and $12,000 for the bottom 10 percent.)
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.
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 (albiet smaller).
However, IQ is only one of several factors that are important for economic outcomes. Personality, for example, and especially conscientiousness, may play a large role in economic outcomes. Some scholars dispute the importance of IQ test score results for real-world achievement.[36] Some argue that the role of IQ gradually becomes weaker with age and after school. They cite evidence that IQ is correlated with early school grades but other factors explain most of the variance.[37] Regarding economic inequality, one study found that if we could magically give everyone identical IQs, we would still see 90 to 95 percent of the inequality we see today.[38] 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.[39] Some argue that IQ scores are used as an excuse for not trying to reduce poverty or otherwise improve living standards for all. Claimed low intelligence has historically been used to justify the feudal system and unequal treatment of women.
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. [40]
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.[41] It has been argued that East Asian nations underachieve compared to IQ scores. One suggested explanation is that verbal IQ is more important than spatial IQ.[42] 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.
The book World on Fire notes the existence in many nations of successful minorities that have created and control a disproportionate share of the economy. Examples include Chinese in Southeast Asia; Whites, Indians, Lebanese and Ibo in Africa; Whites in Latin America; and Jews in 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, 1983). 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, [43] even though affirmative action discriminates against East Asians in the admissions process. 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 (Purdey, 2002).
Achievement in science may be more closely associated with IQ than for example income, which may be greatly influence by inherited wealth, other personality characteristics, or even physical characteristics such as athletic ability or beauty. Only 0.25% of the world population are Jews, but 20–30% of all Nobel prize winners in physics, chemistry, and medicine are Jewish.[44] A large scale decline in the number of Nobel prized awarded to Europe and similar increase in the number of prized awarded to the U.S. occurred at the same time as Nazi persecutions of Jews during the 1930s and the Holocaust during the 1940s.[45]
Policy implications
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 (2005) and Gottfredson (2005) argue that their interpretation does not in itself demand any particular policy response. They argue instead that the primary determinant of policy conclusions from race and intelligence research will be political philosophy itself.
For example, while a conservative/libertarian commentator like Charles Murray may call for reductions in affirmative action, a liberal commentator may use the same evidence to argue from a Rawlsian point of view (that genetic advantages are undeserved and unjust) for substantial and permanent affirmative action (Gottfredson, 2005). This point of view was summarized in 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.[46]
All of the most cost effective methods to improve the world, according to the Copenhagen consensus, would probably also directly or indirectly raise IQ scores, especially providing micronutrients to pregnant women and children. Reducing malaria might also have a large effect since it affects 300–500 million persons each year, mostly children under the age of 5 in Africa, causing widespread anemia during a period of rapid brain development, and also direct brain damage from cerebral malaria to which children are more vulnerable.
Summary
The source of and meaning of the average IQ differences between groups is not known. Many theories have been proposed, but none are generally accepted. Most of the theories are supported by only indirect evidence. The cause may be environmental. Many attribute the difference primarily to cultural factors that disadvantage caste-like minorities. Many researchers in the field of intelligence suggest that the difference is partially genetic and partially environmental. Other observers suggest that the differences may be entirely environmental. The cause of the IQ gap may be identical to the cause of IQ differences between all individuals, or it may represent a race-specific effect. This is an active area of research. In general, simple correlations cannot decide the role of genetics. Advanced statistical methods are instead used with hotly debated results.
Biological differences in brain volume and reaction time, which show low to moderate correlations with IQ, are not by themselves evidence for genetic differences. Even if these differences or the average IQ test score gap indicate a gap in actual intelligence, this may be due to environmental differences in factors such as nutrition during pregnancy or early childhood which may produce such differences without any genetic cause.
Because the cause of the IQ gap is ultimately an empirical question, it should be possible to resolve this question in the future. Irrefutable direct evidence is currently lacking and may continue to be so until intelligence is mapped to specific genes.
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 from Africa, 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 (for instance, iodine deficiency is known to substantially affect intelligence and iodine is usually by law added to certain food products in developed nations but is deficient in hundreds of millions in the third world) and the impact of diseases (e.g., HIV, anemia or chronic parasites that may affect IQ test scores).
Finally, genetic engineering may soon be able to directly change the genetic determinants of intelligence. This change may make genetic intelligence and other genetic characteristics a matter of voluntary parental (or enforced governmental) decision. This could theoretically, in a single generation, dramatically increase human intelligence and make the current concept and discussion of race and possible associated characteristics obsolete.
Notes
- ^ "Intelligence, Race, and Genetics," American Psychologist 60, no. 1 (January 2005): 46–51.
- ^ Min-Hsiung Huang and Robert M. Hauser, "Convergent Trends in Black-White Test-Score Differentials in the U.S.: A Correction of Richard Lynn1," University of Wisconsin–Madison, July 31, 2000.
- ^ Roland G. Fryer Jr. and Steven D. Levitt, "Understanding the Black-White Test Score Gap in the First Two Years of School," The Review of Economics and Statistics 86, no. 2 (2004).
- ^ IQ comments, Gene Expression, September 23, 2003.
- ^ Myth: Some ethnic groups have genetically inferior IQ's.
- ^ Richard Lynn, "Race Differences in Intelligence: A Global Perspective ," The Mankind Quarterly 31, no. 3 (1991): 255–96; Means for Progressive Matrices and 12 reaction time measures for 9-year-old children from five countries.
- ^ National Collaborative Perinatal Project, 1959-1974
- ^ Joseph L Graves, "What a tangled web he weaves: Race, reproductive strategies and Rushton's life history theory," Anthropological Theory 2, no. 2 (2002): 131–54; Leonard Lieberman et al., "How 'Caucasoids' Got Such Big Crania and Why They Shrank," Current Anthropology 42 (2001): 69–95; Zack Cernovsky, "On the similarities of American blacks and whites: A reply to J.P. Rushton," Journal of Black Studies 25 (1995): 672.
- ^ Clarence C. Gravlee, H. Russell Bernard, and William R. Leonard, "Heredity, Environment, and Cranial Form: A Reanalysis of Boas’s Immigrant Data," American Anthropologist 105, no. 1 (2003); Clarence C. Gravlee, H. Russell Bernard, and William R. Leonard, "Boas’s Changes in Bodily Form: The Immigrant Study, Cranial Plasticity, and Boas’s Physical Anthropology," American Anthropologist 105, no. 2 (June 2003); R.L. Jantz and Lee Meadows Jantz, "Secular change in craniofacial morphology," American Journal of Human Biology 12, no. 3 (April 1999): 327–38; R.L. Jantz, "Cranial change in Americans: 1850–1975," Journal of Forensic Sciences 46, no. 4 (July 2001): 784–87.
- ^ Joel Wiesen, "An Annotated List of Many Possible Reasons for the Black-White Mean Score Differences Seen With Many Cognitive Ability Tests: Notes to File," Applied Personnel Research, March 18, 2005.
- ^ Greek IQ
- ^ National Center for Health Statistics: Vital Statistics of the United States (1988).
- ^ Scientific American, April 1996, p.25.
- ^ "Fat, Fitness And Performance," Peak Performance; I.B. Helland et al., "Maternal supplementation with very-long-chain n-3 fatty acids during pregnancy and lactation augments children's IQ at 4 years of age," Pediatrics 111, no. 1 (January 2003): 39–44.
- ^ "Myth: Social intervention cannot raise IQ; Intelligence Quotient, The Encyclopedia of Adoption.
- ^ Papers relating to group difference in IQ test scores & Spearman's hypothesis.
- ^ Joseph L. Graves, "What a tangled web he weaves: Race, reproductive strategies and Rushton's life history theory," Anthropological Theory 2, no. 2 (2002): 131–54; Leonard Lieberman et al., "How 'Caucasoids' Got Such Big Crania and Why They Shrank,"; Current Anthropology 42 (2001): 69–95; Zack Cernovsky, "On the similarities of American blacks and whites: A reply to J.P. Rushton," Journal of Black Studies 25 (1995): 672.
- ^ Greek IQ
- ^ Charles C. Roseman, "Detecting interregionally diversifying natural selection on modern human cranial form by using matched molecular and morphometric data" Proceedings of the national Academy of Sciences of the United States vol. 101 no. 35 (August 31, 2004):12824-12829.
- ^ Gregory Cochran, Jason Hardy, Henry Harpending, "Natural History of Ashkenazi Intelligence," Journal of Biosocial Science (June 2005).
- ^ See note 3 above.
- ^ Arthur Hu's Index of Diversity, Scholastic Aptitude Test.
- ^ "Myth: The black/white IQ gap is largely genetically caused.
- ^ D.M. Ivanovic et al., "Nutritional status, brain development and scholastic achievement of Chilean high-school graduates from high and low intellectual quotient and socio-economic status," British Journal of Nutrition 87, no. 1 (January 2002): 81–92; D.M. Ivanovic et al., "Head size and intelligence, learning, nutritional status and brain development. Head, IQ, learning, nutrition and brain," Neuropsychologia 42, no. 8 (2004): 1118–31.
- ^ Marinus H. van IJzendoorn, Femmie Juffer, and Caroline W. Klein Poelhuis, "Adoption and Cognitive Development: A Meta-Analytic Comparison of Adopted and Nonadopted Children’s IQ and School Performance," Psychological Bulletin 131, no. 2 (2005): 301–316.
- ^ William T. Dickens, "Behavioral Genetics and School Readiness," The Future of Children 15, no. 1 (Spring 2005): 55–69; "Intelligence: Knowns and Unknowns," Report of a Task Force established by the Board of Scientific Affairs of the APA.
- ^ IQ studies by year from IQ and the Wealth of Nations by Lynn & Vanhanen
- ^ Abstracts from the Journal of American Indian Education 1987; Rhett Diessner and Jacqueline L. Walker, "A Cognitive Pattern of the Yakima Indian Students," Journal of American Indian Education 25, no. 2 (January 1986); "Smart Fraction Theory II: Why Asians Lag," La Griffe du Lion 6, no. 2 (May 2004).
- ^ Zack Cernovsky, "On the similarities of American blacks and whites: A reply to J.P. Rushton," Journal of Black Studies 25 (July 1995): 672.
- ^ Table 50 National Vital Statistics Reports Vol. 52, No. 10, December 17, 2003. CDC.
- ^ "What's in a yam? Clues to fertility, a student discovers," Yale Medicin Summer 99
- ^ William T. Dickens and James R. Flynn, "The IQ Paradox: Still Resolved," Psychological Review 109, no. 4 (2002).
- ^ Richard Herrnstein and Charles Murray, "Race, genes and I.Q.—an apologia: the case for conservative multiculturalism," The New Republic 211, no. 11 (October 1994): 27.
- ^ Charles Murray, Income Inequality and IQ (Washington, DC: American Enterprise Institute Press, 1998)
- ^ Effective Federal Tax Rates: 1979-2001 Congressional Budget Office.
- ^ Cary Cherniss, "Emotional Intelligence: What it is and Why it Matters" (Paper presented at the Annual Meeting of the Society for Industrial and Organizational Psychology, New Orleans, La., April 15, 2000).
- ^ "What Can You Predict from an IQ Test Score?," Lefton Learning Community.
- ^ Myth: IQ best predicts if you will succeed or fail in life.
- ^ Samuel Bowles and Herbert Gintis, "The Inheritance of Inequality," Journal of Economic Perspectives 16, no. 3 (Summer 2002).
- ^ Myth: Some ethnic groups have genetically inferior IQ's.
- ^ Thomas Volken, "The Impact of National IQ on Income and Growth."
- ^ "Smart Fraction Theory II: Why Asians Lag," La Griffe du Lion 6, no. 2 (May 2004).
- ^ Falk, Gerhard. "American Jews"
- ^ Jewish Nobel Prize Winners, JINFO.ORG.
- Old World vs. New World: Evolution of Nobel Prize Shares," University of Maryland (December 2004). Wolfgang Jank, Bruce L. Golden, and Paul F. Zantek, "
- ^ "Mainstream Science on Intelligence," Wall Street Journal, December 13, 1994.
See also
- Brain size and intelligence
- Brain to body mass ratio
- Craniometry
- Cyril Burt
- Race and crime
- Stanley Porteus
- Sex and intelligence
- William Shockley
References
- Template:Journal reference
- Bamshad MJ, Wooding S, Watkins WS, Ostler CT, Batzer MA, Jorde LB (2003) Human population genetic structure and inference of group membership. Am J Hum Genet 72:578–589
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Boas, F. (1938). The mind of primitive man. New York, NY: Appleton, Century, Crofts.
- Template:Journal reference
- Broca, P. (1873). Sur les crânes de la caverne de l’Homme Mort (Loere). Revue d’Anthropologie, 2, 1–53.
- Template:Journal reference
- Broman, S. H., Nichols, P. L., Shaughnessy, P. & Kennedy, W. (1987). Retardation in young children. Hillsdale, NJ: Erlbaum.
- Template:Journal reference
- Capron, C. & Duyme,M. (1989). Assessment of effects of socioeconomic status on IQ in a full cross-fostering design. Nature, 340, 552-553.
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Connelly, J. B. (1983). Recategorized WISC-R score patterns of older and younger referred Tlingit Indian children. Psychology in the Schools, 20, 271-275.
- Template:Journal reference
- . ISBN 019852417X.
{{cite book}}
: Missing or empty|title=
(help); Unknown parameter|Author=
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suggested) (help); Unknown parameter|Publisher=
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suggested) (help); Unknown parameter|Title=
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suggested) (help); Unknown parameter|Year=
ignored (|year=
suggested) (help) - Degler, C. N. (1991). In search of human nature. New York: Oxford University Press.
- DeNavas-Walt, C., Proctor, B.D., & Mills, R.J. (2004). Income, poverty, and health insurance coverage in the United States: 2003 (U.S. Census Bureau). Retrieved June 7, 2005 from http://www.census.gov/prod/2004pubs/p60-226.pdf
- Template:Journal reference
- Template:Journal reference
- Diessner, R. & Walker, Jacqueline L. (1986). A cognitive pattern of the Yakima Indian students [Electronic version]. Journal of American Indian Education, 25 (2). Retrieved June 6, 2005 from http://jaie.asu.edu/v25/V25S2cog.html
- Template:Journal reference
- Template:Journal reference
- 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: Frank Columbus, Editor, Advances in Psychological Research vol. VI, pp. 31-60. Huntington, NY: Nova Science Publishers, Inc. [47]
- . ISBN 0710006519.
{{cite book}}
: Missing or empty|title=
(help); Unknown parameter|Author=
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suggested) (help); Unknown parameter|Publisher=
ignored (|publisher=
suggested) (help); Unknown parameter|Title=
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ignored (|year=
suggested) (help) - Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Gignac, G. E., Vernon, P. A., & Wickett, J. C. (2003). "Factors influencing the relationship between brain size and intelligence". In H. Nyborg (Ed.), The scientific study of general intelligence: Tribute to Arthur R. Jensen (pp. 93–106). London: Elsevier.
- Glazer, N. (1994, October 31). "The lying game." The New Republic, 15–16.
- Template:Journal reference
- Template:Journal reference Retrieved from http://www.udel.edu/educ/gottfredson/reprints/1997whygmatters.pdf
- Gottfredson, L. S. (2005). "Suppressing intelligence research: Hurting those we intend to help". In R. H. Wright & N. A. Cummings (Eds.), Destructive trends in mental health: The well-intentioned path to harm (pp. 155-186). New York: Taylor and Francis. Pre-print PDF PDF
- Template:Journal reference
- Gottfredson, L. S. (in press). "Social consequences of group differences in cognitive ability (Consequencias sociais das diferencas de grupo em habilidade cognitiva)". In C. E. Flores-Mendoza & R. Colom (Eds.), Introducau a psicologia das diferncas individuais. Porto Allegre, Brazil: ArtMed Publishers. PDF
- . ISBN 0833016164.
{{cite book}}
: Missing or empty|title=
(help); Unknown parameter|Author=
ignored (|author=
suggested) (help); Unknown parameter|Publisher=
ignored (|publisher=
suggested) (help); Unknown parameter|Title=
ignored (|title=
suggested) (help); Unknown parameter|Year=
ignored (|year=
suggested) (help) - Grissmer, D., Flanagan, A., & Williamson, S. (1998). "Why did the Black-White score gap narrow in the 1970s and 1980s?" In M. Phillips (Ed.), The Black-White test score gap (pp. 182–226). Washington, DC: Brookings Institution.
- Grissmer, D., Williamson, S., Kirby, S. N., & Berends, M. (1998). "Exploring the rapid rise in Black achievement scores in the United States" (1970–1990). In U. Neisser (Ed.), The rising curve: Long-term changes in IQ and related measures (pp. 251–286). Washington, DC: American Psychological Association.
- Template:Journal reference
- Harvey, I., Persaud, R., Ron, M. A., Baker, G., & Murray, R. M. (1994). Volumetric MRI measurements in bipolars compared with schizophrenics and healthy controls. Psychological Medicine, 24, 689–699.
- Hedges, L., & Nowell, A. (1998). "Black-White test score convergence since 1965". In A. Phillips (Ed.), The Black-White test score gap (pp. 149–181). Washington, DC: Brookings Institution.
- . ISBN 0029146739.
{{cite book}}
: Missing or empty|title=
(help); Unknown parameter|Author=
ignored (|author=
suggested) (help); Unknown parameter|Publisher=
ignored (|publisher=
suggested) (help); Unknown parameter|Title=
ignored (|title=
suggested) (help); Unknown parameter|Year=
ignored (|year=
suggested) (help) - Template:Journal reference
- Template:Journal reference
- . ISBN 0060121947.
{{cite book}}
: Missing or empty|title=
(help); Unknown parameter|Author=
ignored (|author=
suggested) (help); Unknown parameter|Publisher=
ignored (|publisher=
suggested) (help); Unknown parameter|Title=
ignored (|title=
suggested) (help); Unknown parameter|Year=
ignored (|year=
suggested) (help) - . ISBN 0029164303.
{{cite book}}
: Missing or empty|title=
(help); Unknown parameter|Author=
ignored (|author=
suggested) (help); Unknown parameter|Publisher=
ignored (|publisher=
suggested) (help); Unknown parameter|Title=
ignored (|title=
suggested) (help); Unknown parameter|Year=
ignored (|year=
suggested) (help) - Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Jensen, A. R. (1997). "The puzzle of nongenetic variance". In R. J. Sternberg & E. L. Grigorenko (Eds.), Intelligence, heredity, and environment (pp. 42–88). Cambridge, England: Cambridge University Press.
- Template:Journal reference
- . ISBN 0275961036.
{{cite book}}
: Missing or empty|title=
(help); Unknown parameter|Author=
ignored (|author=
suggested) (help); Unknown parameter|Publisher=
ignored (|publisher=
suggested) (help); Unknown parameter|Title=
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ignored (|year=
suggested) (help) - Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Jerison, H. J. (1973). Evolution of the brain and intelligence. New York: Academic Press.
- Jerison, H. J. (2000). The evolution of intelligence. In R. J. Sternberg (Ed.), Handbook of intelligence (pp. 216–244). Cambridge: Cambridge University.
- Leary, W.E. "Why fewer blacks choose to breast-feed than do whites" New York Times, April 7, 1988 (p. B6)
- Loehlin, J. C., Lindzey, G., & Spuhler, J. N. (1975). Race differences in intelligence. San Francisco: Freeman.
- Template:Journal reference
- Template:Journal reference
- Lynn, R. (1978). "Ethnic and racial differences in intelligence: International comparisons". In R. T. Osborne, C. E. Noble, & N. Weyl (Eds.), Human variation: The biopsychology of age, race, and sex (pp. 261–286). New York: Academic Press.
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Lynn, R. (2001). The science of human diversity: A history of the Pioneer Fund. Lanham, MD: University Press of America.
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- . ISBN 027597510X.
{{cite book}}
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suggested) (help) - Template:Journal reference
- Masters, R. (1997). Brain biochemistry and social status: The neurotoxity hypothesis. In E. White (Ed.), Intelligence, political inequality, and public policy (pp. 141-183). Westport, CT: Praeger.
- Template:Journal reference
- McShane, D. A. & Plas, J. M. (1982). Wechsler scale performance patterns of American Indian children. Psychology in the Schools, 19, 8-17.
- McShane, D. A., & Plas, J. M. (1984). The cognitive functioning of American Indian children: Moving from the WISC to the WISC-R. The School Psychology Review, 13, 61-73.
- Template:Journal reference
- McGue, M., Bouchard, T. J., Jr., Iacono, W. G., & Lykken, D. T. (1993). "Behavioral genetics of cognitive ability: A life-span perspective". In R. Plomin & G. E. McClearn (Eds.), Nature, nurture, and psychology (pp. 59–76). Washington, DC: American Psychological Association.
- Template:Journal reference
- Mountain JL, Cavalli-Sforza LL (1997) Multilocus genotypes, a tree of individuals, and human evolutionary history. Am J Hum Genet 61:705–718
- Murray, Charles (1998). Income Inequality and IQ, AEI Press PDF
- Template:Journal reference
- Template:Journal reference
- Neisser, U. (1997). Never a dull moment. American Psychologist, 52, 79-81.
- Neisser, U., Boodoo, G., Bouchard, T. J. Jr., Boykin, A. W., Brody, N., Ceci, S. J. et al. (1996). Intelligence: Knowns and unknowns. American Psychologist, 51, 77-101. [48]
- Nisbett, R. E. (1995). "Race, IQ and scientism". In S. Fraser (Ed.), The bell curve wars (pp. 36–57). New York: HarperCollins.
- Nisbett, R. E. (1998). "Race, genetics, and IQ". In A. Phillips (Ed.), The Black-White test score gap (pp. 86–102). Washington, DC: Brookings Institution.
- Template:Journal reference
- Ogbu, J. U. (2002). "Cultural amplifiers of intelligence: IQ and minority status in crosscultural perspective". In J. M. Fish (Ed.), Race and intelligence: Separating science from myth (pp. 241–278). Mahwah, NJ: Erlbaum.
- Ogbu, J. U. (2003). Black American students in an affluent suburb: A study of academic disengagement. Mahwah, NJ: Erlbaum.
- . ISBN 0936396008.
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- Template:Journal reference
- Template:Journal reference
- . ISBN 0716751593.
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- Purdey, J.E. Anti-Chinese Violence in Indonesia, 1996-1999 [Electronic version]. Doctoral dissertation, University of Melbourne. Retrieved June 16, 2005 from http://eprints.unimelb.edu.au/archive/00000840/
- Template:Journal reference
- Template:Journal reference
- Rosenberg NA, Pritchard JK, Weber JL, Cann HM, Kidd KK, Zhivotovsky LA, Feldman MW (2002) Genetic structure of human populations. Science 298:2381–2385
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference Retrieved from http://www.ssc.uwo.ca/psychology/faculty/rushtonpdfs/Gould.pdf
- Template:Journal reference
- Template:Journal reference
- . ISBN 0965683613.
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- Template:Journal reference
- Rushton, J. P., & Ankney, C. D. (2000). Size matters: a review and new analyses of racial differences in cranial capacity and intelligence that refute Kamin and Omari. Personality and Individual Differences, 29, 591–620.
- Template:Journal reference
- Template:Journal reference Retrieved from http://www.ssc.uwo.ca/psychology/faculty/rushtonpdfs/PPPL1.pdf
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- . ISBN 0465020755.
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ignored (|year=
suggested) (help) - Stephens JC, Schneider JA, Tanguay DA, Choi J, Acharya T, Stanley SE, Jiang R, et al (2001) Haplotype variation and linkage disequilibrium in 313 human genes. Science 293:489–493
- Template:Journal reference
- Template:Journal reference
- Template:Journal reference
- . ISBN 0887388396.
{{cite book}}
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suggested) (help) - Tang H, Quertermous T, Rodriguez B, Kardia SL, Zhu X, Brown A, Pankow JS, Province MA, Hunt SC, Boerwinkle E, Schork NJ, Risch NJ (2005). Genetic structure, self-identified race/ethnicity, and confounding in case-control association studies. Am J Hum Genet 76, 268-75.
- Tate, C., & Audette, D. (2001). Theory and research on "race" as a natural kind variable in psychology. Theory and Psychology, 11, 495-520.
- Template:Journal reference Retrieved on June 6, 2005, from http://jaie.asu.edu/v26/V26S3phy.htm
- The Persistent Racial Scoring Gap on the SAT (in Special Report: The SAT as a Major Roadblock to Black Students' Aspirations to Higher Education) The Journal of Blacks in Higher Education, 29. (Autumn, 2000), 85–88.
- Thernstrom, A., & Thernstrom, S. (2003). No excuses: Closing the racial gap in learning. New York: Simon & Schuster.
- Template:Journal reference
- Template:Journal reference
- . ISBN 0716707373.
{{cite book}}
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- Wickett, J.C., Vernon, P.A., & Lee, D.H. (1994). In vivo brain size, head perimeter, and intelligence in a sample of healthy adult females. Personality and Individual Differences, 16, 831-838.
- Willerman, L., Schultz, R., Rutledge, J. N., and Bigler, E. (1991). In vivo brain size and intelligence. Intelligence, 15, 223-228.
- Template:Journal reference
- Zarske, J. A., & Moore, C. L. (1982). Recategorized WISC-R scores of learning disabled Navajo Indian children. Psychology in the Schools, 19: 156-159.
External links
- The Wall Street Journal: Mainstream Science on IntelligencePDF
- American Psychological Association Task Force Report, "Intelligence: Knowns and Unknowns"
- Legal scholar and microbiologist Pilar Ossorio answers questions from viewers about science, medicine, racial classification, and more.
- Prof. Evelynn Hammonds on the history of race in science and medicine in the United States
- "Heritability Estimates Versus Large Environmental Effects: The IQ Paradox Resolved"; Psychological Review, 2001, Vol. 108, No. 2, 346-369
- "We're All Related To Kevin Bacon" – Steve Olson on popular misconceptions about genetics in the Washington Post
- The Skeptic's Dictionary entry on IQ and race
- Poverty and Brain Development in Early Childhood 1999 report
- The Early Catastrophe: The 30 Million Word Gap by Age, American Educator, Spring 2003
- Race and Intelligence
- The Black-White Test Score Gap (1998) online (page-image) version of ISBN 0815746091
- Race, Genetics and IQ – Professor Richard E. Nisbett examines the evidence and different arguments. (PDF)
- Miscellaneous articles by Richard Lynn et al.
- Thirty Years of Research on Race Differences in Cognitive Ability by J. Philippe Rushton and Arthur R. Jensen in Psychology, Public Policy, and Law 2005, Vol. 11, No. 2, 235–294
- Crippled by Their Culture - Race doesn't hold back America's black rednecks. Nor does racism by Thomas Sowell
- Cultural Bias in Intelligence Testing
- Cultural Bias in IQ Testing
- Are IQ Tests Biased?
- Psychological Testing (Powerpoint)
- Culturally Inane
- Scholars Provide an Overview of Explanations for Black-White Test Score Gap
- What if the Heriditarian Hypothesis is true? by Linda Gottredson