race and intelligence - wikipedia, the free encyclopedia

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From Wikipedia, the free encyclopedia

The connection between race and intelligence has been a subject of debate in both popular science and

academic research since the inception of IQ testing in the early 20th century.[1] There is no widely acceptedformal definition of either race or intelligence in academia, nor is there agreement on IQ's validity as a gauge

of intelligence.[2]

Historically, claims that races differed in intelligence were used to justify colonialism,slavery, Social Darwinism, and eugenics. After losing favor in the post-war period, the idea of racialdifferences in intelligence was revived by Arthur Jensen in 1969 and drew public attention following the

publication ofThe Bell Curve in 1994. Any discussion of a connection between race and intelligenceinvolves studies from multiple disciplines, including psychology, anthropology, biology and sociology.

Differences in mean IQ scores between racial groups in the United States are well-documented and notsubject to much dispute. The average IQ scores of Asian Americans are higher than those of White

Americans, and the average IQ scores of White Americans are higher than those of African Americans.[3]

Both environmental and genetic explanations have been advanced to account for these differences in IQscores and group differences in educational achievement. Systemically disadvantaged minorities performworse in education and on intelligence tests. Other environmental arguments include differences in healthand nutrition (including lead exposure and iodine deficiency), educational quality, and test bias.

The American Psychological Association has said that while there are differences in average IQ betweenracial groups, there is no conclusive evidence for either environmental or genetic explanations for those

differences.[4][5] The position of the American Anthropological Association is that variation in intelligence

cannot be meaningfully explained by dividing a species into biologically defined races.[6] According to a1996 statement from the American Association of Physical Anthropologists, although heredity influences

behavior in individuals, it does not affect the ability of a population to function in any social setting, allpeoples "possess equal biological ability to assimilate any human culture," and "racist political doctrines find

no foundation in scientific knowledge concerning modern or past human populations." [7]

1 History of the debate2 Ethics of research3 Validity of "race" and "IQ"4 Group differences

4.1 United States test scores4.2 Flynn effect5 Potential environmental causes

5.1 Test bias5.2 Stereotype threat5.3 Socioeconomic environment5.4 Health and nutrition5.5 Education5.6 Logographic writing system5.7 Caste-like minorities5.8 Cultural traditions valuing education5.9 Group subculture

6 Genetic arguments6.1 Genetics of race and intelligence6.2 Heritability within and between groups

e and intelligence - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Race_and_intelligence

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Alfred Binet (18571911),

inventor of the first

intelligence test.

6.3 Spearman's hypothesis6.4 Gradual gap appearance6.5 Adoption studies6.6 Racial admixture studies6.7 Mental chronometry6.8 Brain size

7 Policy relevance

8 See also9 References10 Bibliography11 External links

Main article: History of the race and intelligence controversy

See also: Scientific racism

Claims of races having different intelligence were used to justify colonialism,slavery, social Darwinism, and racial eugenics. In the late 19th and early 20thcenturies, group differences in intelligence were assumed to be due to raceand, apart from intelligence tests, research relied on measurements such as

brain size or reaction times to demonstrate such differences. The first IQ testwas created between 1905 and 1908 and revised in 1916 (the StanfordBinetIntelligence Scales). Alfred Binet, the developer of these tests, warned thatthese should not be used to measure innate intelligence or to label

individuals.[8] However, at the time there was great concern in the UnitedStates about the abilities and skills of recent immigrants. Different immigrantnationalities were sometimes thought to belong to different races, such asSlavs. The tests were used to evaluate draftees for World War I, andresearchers found that people of southern and eastern Europe scored lowerthan native-born Americans. At the time, such data were used to construct anethnically based social hierarchy, one in which immigrants were rejected asunfit for service and mentally defective. It was not until later that researchers

realized that lower language skills by new English speakers affected their scores on the tests.[9]

In the 1920s, many scientists reacted to eugenicist claims linking abilities and moral character to racial or

genetic ancestry. Despite that, states like Virginia enacted laws based in eugenics, such as its 1924 RacialIntegrity Act, which established the one-drop rule as law. Generally, understanding grew about the

contribution of environment to test-taking and results (such as having English as a second language).[10] Bythe mid-1930s most US psychologists had adopted the view that environmental and cultural factors played adominant role. In addition, psychologists were reluctant to risk being associated with the German Nazi claims

of a "master race".[11]

In 1969, Arthur Jensen revived the hereditarian point of view in the article, "How Much Can We Boost IQ

and Scholastic Achievement?"[12][13][14] It followed changes in public programs introduced to try to correctdecades of discrimination against poor African Americans. Jensen's article questioned remedial education for

African-American children; he suggested their poor educational performance reflected an underlying geneticcause rather than lack of stimulation at home.[15] Jensen's work, publicized by the Nobel laureate physicistWilliam Shockley, sparked controversy amongst the academic community and student protests.


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In their 1988 bookThe IQ Controversy, the Media, and Public Policy, Mark Snyderman and StanleyRothman claimed to document inaccurate media coverage of scientific findings regarding IQ. The book

builds on the results of a survey conducted in 1984. The survey was sent to 1020 scholars within fields thatdeal with the issue of IQ and had 661 respondents. 45 percent of the respondents thought that black-whitedifferences in IQ were the product of both genetic and environmental variation, while 15 percent believedthat the differences were entirely due to environmental factors; the rest either declined to answer the

question, or thought that there was insufficient evidence to give an answer.[16]

Another debate followed the appearance ofThe Bell Curve (1994), a book by Richard Herrnstein andCharles Murray, who argued in favor of the hereditarian viewpoint. It provoked the publication of severalinterdisciplinary books representing the environmental point of view, as well as some in popular science.[17][18] They include The Bell Curve Debate (1995),Inequality by Design: Cracking the Bell Curve Myth

(1996) and a second edition ofThe Mismeasure of Man (1996) by Steven J. Gould.[18] One book writtenfrom the hereditarian point of view at this time was The g Factor: The Science of Mental Ability (1998) byJensen. In 1994 a group of 52 scientists, including leading hereditarians, signed the statement "MainstreamScience on Intelligence". The Bell Curve also led to a 1995 report from the American PsychologicalAssociation, "Intelligence: Knowns and Unknowns", acknowledging a difference between mean IQ scores of

whites and blacks as well as the absence of any adequate explanation of it, either environmental or genetic.The review article "Thirty Years of Research on Race Differences in Cognitive Ability" by Rushton and

Jensen was published in 2005.[19] The article was followed by a series of responses, some in support, some

critical.[11][20] Richard Nisbett, another psychologist who had also commented at the time, later included anamplified version of his critique as part of the bookIntelligence and How to Get It: Why Schools and

Cultures Count(2009).[21] Rushton and Jensen in 2010 made a point-by-point reply to this thereafter.[22]

Some of the authors proposing hereditarians explanations for group differences have received funding from

the Pioneer Fund which was headed by Rushton until his death in 2012.[13][18][23][24] The Southern Poverty

Law Center lists the Pioneer Fund as a hate group, citing the fund's history, its funding of race andintelligence research, and its connections with racist individuals.[25] On the other hand, Ulrich Neisser writesthat "Pioneer has sometimes sponsored useful researchresearch that otherwise might not have been done

at all."[26] Other sources and researches have criticized the Pioneer Fund for promoting scientific racism,

eugenics and white supremacy.[13][27][28][29]

The 1996 report of the APA had comments on the ethics of research on race and intelligence.[1] Gray &

Thompson (2004) as well as Hunt & Carlson (2007) have also discussed different possible ethical guidelines.[1][30]Nature in 2009 featured two editorials on the ethics of research in race and intelligence by Steven

Rose (against) and Stephen J. Ceci and Wendy M. Williams (for).[31][32]

According to critics, research on group differences in IQ will run the risk of reproducing the negative effectsof social ideologies (such as Nazism or social Darwinism) that were justified in part on claimed hereditary

racial differences.[6][33] Steven Rose maintains that the history of eugenics makes this field of research

difficult to reconcile with current ethical standards for science.[32]

Linda Gottfredson argues that suggestion of higher ethical standards for research into group differences in

intelligence is a double standard applied in order to undermine disliked results.[34]

James R. Flynn hasargued that had there been a ban on research on possibly poorly conceived ideas, much valuable research on

intelligence testing (including his own discovery of the Flynn effect) would not have occurred.[35]


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Main articles: Race (classification of humans), Race and genetics, Intelligence quotient, and

Intelligence

The concept of intelligence and the degree to which intelligence is measurable is a matter of debate. Whilethere is a general consensus within Western science about how to define intelligence, the concept of

intelligence as something that can be unequivocally measured by a single figure is not universallyaccepted.[36] A recurring criticism is that different societies value and promote different kinds of skills andthat the concept of intelligence is therefore culturally variable and cannot be measured by the same criteria

in different societies.[36] Consequently, some critics argue that proposed relationships to other variables are

necessarily tentative.[37]

The concept of race as a biologically meaningful category of analysis is also hotly contested.[38] Articles intheEncyclopdia Britannica and theEncyclopedia of Race, Ethnicity and Society state that the currentmainstream view is that race is a social construction mainly based not in actual biological differences butrather in folk ideologies that construct groups based on social disparities and superficial physical

characteristics.[39][40] Sternberg, Grigorenko & Kidd (2005) state, "Race is a socially constructed concept,not a biological one. It derives from people's desire to classify."[37] The concept of human "races" as naturaland separate divisions within the human species has also been rejected by the American AnthropologicalAssociation. The official position of the AAA, adopted in 1998, finds that advances in scientific knowledgehave made it "clear that human populations are not unambiguous, clearly demarcated, biologically distinctgroups" and that "any attempt to establish lines of division among biological populations [is] both arbitrary

and subjective."[33] Others argue that this view is restricted to certain fields, while in other fields, race is still

seen as a valid biological category.[41]

Race in studies of human intelligence is almost always determined using self-reports, rather than based onanalyses of the genetic characteristics of the tested individuals. According to psychologist David Rowe,self-report is the preferred method for racial classification in studies of racial differences becauseclassification based on genetic markers alone ignore the "cultural, behavioral, sociological, psychological,

and epidemiological variables" that distinguish racial groups.[42] Hunt and Carlson write that "Nevertheless,self-identification is a surprisingly reliable guide to genetic composition. Tang et al. (2005) appliedmathematical clustering techniques to sort genomic markers for over 3,600 people in the United States andTaiwan into four groups. There was almost perfect agreement between cluster assignment and individuals'

self-reports of racial/ethnic identification as white, black, East Asian, or Latino."[1] Sternberg andGrigorenko disagree with Hunt and Carlson's interpretation of Tang, "Tang et al.'s point was that ancientgeographic ancestry rather than current residence is associated with self-identification and not that such

self-identification provides evidence for the existence of biological race."[43]

The notions that cluster analysis and the correlation between self-reported race and genetic ancestry

supports a view of race as primarily based in biology is contradicted by C. Loring Brace [44] and geneticist

Joseph Graves.[45] They argue that while it is possible to find biological and genetic variation correspondingroughly to the groupings normally defined as races, this is true for almost all geographically distinct

populations. The cluster structure of the genetic data is dependent on the initial hypotheses of the researcherand the populations sampled. When one samples continental groups, the clusters become continental; if onehad chosen other sampling patterns, the clusters would be different. Kaplan 2011 therefore concludes that,while differences in particular allele frequencies can be used to identify populations that loosely correspondto the racial categories common in Western social discourse, the differences are of no more biologicalsignificance than the differences found between any human populations (e.g., the Spanish and Portuguese).

Earl B. Hunt agrees that racial categories are defined by social conventions, though he points out that they


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also correlate with clusters of both genetic traits and cultural traits. Hunt explains that, due to this, racial IQdifferences are caused by these variables that correlate with race, and race itself is rarely a causal variable.Researchers who study racial disparities in test scores are studying the relationship between the scores andthe many race-related factors which could potentially affect performance. These factors include health,

wealth, biological differences, and education.[46]

Hunt and Carlson outlined four contemporary positions on differences in IQ based on race or ethnicity. Thefirst is that these reflect real differences in average group intelligence, which is caused by a combination ofenvironmental factors and heritable differences in brain function. A second position is that differences inaverage cognitive ability between races are caused entirely by social and/or environmental factors. A third

position holds that differences in average cognitive ability between races do not exist, and that thedifferences in average test scores are the result of inappropriate use of the tests themselves. Finally, a fourth

position is that either or both of the concepts of race and general intelligence are poorly constructed and

therefore any comparisons between races are meaningless.[1]

United States test scores

Main article: Achievement gap in the United States

Rushton & Jensen (2005) write that, in the United States, self-identified blacks and whites have been thesubjects of the greatest number of studies. They state that the black-white IQ difference is about 15 to 18

points or 1 to 1.1 standard deviations (SDs), which implies that between 11 and 16 percent of the blackpopulation have an IQ above 100 (the general population median). The black-white IQ difference is largest

on those components of IQ tests that best represent the general intelligence factorg.[19] The 1996 APAreport "Intelligence: Knowns and Unknowns" and the 1994 editorial statement "Mainstream Science on

Intelligence" gave more or less similar estimates.[5][47] Roth et al. (2001), in a review of the results of a totalof 6,246,729 participants on other tests of cognitive ability or aptitude, found a difference in mean IQ scores

between blacks and whites of 1.1 SD. Consistent results were found for college and university applicationtests such as the Scholastic Aptitude Test (N = 2.4 million) and Graduate Record Examination (N = 2.3million), as well as for tests of job applicants in corporate sections (N = 0.5 million) and in the military (N =

0.4 million).[48]

A 2006 study by Dickens and Flynn estimated that the difference between mean scores of blacks and whites

closed by about 5 or 6 IQ points between 1972 and 2002,[49] which would be a reduction of about one-third.

However this was challenged by Rushton & Jensen who claim the difference remains stable.[50] In a 2006

study, Murray agreed with Dickens and Flynn that there has been a narrowing of the difference; "Dickens'and Flynn's estimate of 36 IQ points from a base of about 1618 points is a useful, though provisional,starting point". But he argued that this has stalled and that there has been no further narrowing for people

born after the late 1970s.[51] Murray found similar results in a 2007 study.[52]

The IQ distributions of other racial and ethnic groups in the United States are less well-studied. The BellCurve (1994) stated that the average IQ of African Americans was 85, Latinos 89, whites 103, East Asians106, and Jews 113. Asians score relatively higher on visuospatial than on verbal subtests. The fewAmerindian populations who have been systematically tested, including Arctic Natives, tend to score worse

on average than white populations but better on average than black populations.[48]

According to several studies, Ashkenazi Jews score 0.75 to 1.0 standard deviations above the generalEuropean average. This corresponds to an IQ of 112115. Other studies have found somewhat lower values.During the 20th century, this population made up about 3 percent of the total US population, but won 27


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percent of the US science Nobel Prizes and 25 percent of the Turing Awards. Jews have high verbal andmathematical scores, while their visuospatial abilities are typically somewhat lower, by about one half

standard deviation, than the European average.[53]

The racial groups studied in the United States and Europe are not necessarily representative samples forpopulations in other parts of the world. Cultural differences may also factor in IQ test performance andoutcomes. Therefore, results in the United States and Europe do not necessarily correlate to results in other

populations.[54]

Flynn effect

Main article: Flynn effect

Raw scores on IQ tests had until recently been rising throughout the world for a century. This score increaseis known as the "Flynn effect," named for James R. Flynn, who did much to document it and promoteawareness of its implications. In the United States, the increase had been continuous and approximatelylinear from the earliest years of testing to about 1998. For example, in the United States the average scores

of blacks on some IQ tests in 1995 were the same as the scores of whites in 1945.

[55]

The following environmental factors are some of those suggested as explaining a portion of the differences inaverage IQ between races. These factors are not mutually exclusive with one another, and some may in factcontribute directly to others. Furthermore, the relationship between genetics and environmental factors may

be complicated. For example, the differences in socioeconomic environment for a child may be due to

differences in genetic IQ for the parents,[5] and the differences in average brain size between races could be

the result of nutritional factors.[56]

Test bias

A number of studies have reached the conclusion that IQ tests may be biased against certain groups.[57][58]

[59][60] The validity and reliability of IQ scores obtained from outside the United States and Europe have

been questioned, in part because of the inherent difficulty of comparing IQ scores between cultures.[61][62]

Several researchers have argued that cultural differences limit the appropriateness of standard IQ tests in

non-industrialized communities.[63][64] In the mid-1970s, for example, the Soviet psychologist AlexanderLuria concluded that it was impossible to devise an IQ test to assess peasant communities in Russia because

taxonomy was alien to their way of reasoning.[65]

A 1996 report by the American Psychological Association states that controlled studies show thatdifferences in mean IQ scores were not substantially due to bias in the content or administration of the IQtests. Furthermore, the tests are equally valid predictors of future achievement for black and white

Americans.[5] This view is reinforced by Nicholas Mackintosh in his 1998 bookIQ and Human

Intelligence,[66] and by a 1999 literature review by Brown, Reynolds & Whitaker (1999).[67]

Stereotype threat

Main article: Stereotype threat

Stereotype threat is the fear that one's behavior will confirm an existing stereotype of a group with which

one identifies or by which one is defined; this fear may in turn lead to an impairment of performance.[68]

Testing situations that highlight the fact that intelligence is being measured tend to lower the scores of


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Percentage of children aged 1-5 with

blood lead levels at least10 g/dL.

Black and Hispanic children have

much higher levels than white children.

A 10 g/dL increase in blood lead at

24 months is associated with a5.8-point decline in IQ.[70] Although

the Geometric Mean Blood Lead

Levels (GM BLL) are declining, a

CDC report (2002) states that:

"However, the GM BLL for

non-Hispanic black children remains

higher than that for Mexican-American

and non-Hispanic white children,

indicating that differences in risk for

exposure still persist."[71]

individuals from racial-ethnic groups who already score lower on average or are expected to score lower.

Stereotype threat conditions cause larger than expected IQ differences among groups.[69]

Socioeconomic environment

According to the report of a 1996 APA task force, socioeconomic status (SES) cannot account for all theobserved racial-ethnic group differences in IQ in the US. Their first reason for this conclusion is that the

difference between mean test scores of blacks and whites is not eliminated when individuals and groups arematched on SES. Second, excluding extreme conditions, nutritional and biological factors that may vary withSES have shown little effect on IQ. Third, the relationship between IQ and SES is not simply one in whichSES determines IQ, but differences in intelligence, particularly parental intelligence, also cause differences in

SES, making separating the two factors difficult.[5]

Health and nutrition

Main article: Impact of health on intelligence

Environmental factors including lead exposure,[70]

breast feeding,[72]

and nutrition[73][74] can significantly affect cognitive developmentand functioning. For example, iodine deficiency causes a fall, on

average, of 12 IQ points.[75] Such impairments may sometimes bepermanent, sometimes be partially or wholly compensated for bylater growth. The first two years of life is the critical time formalnutrition, the consequences of which are often irreversible andinclude poor cognitive development, educability, and future

economic productivity.[76] The African American population of theUnited States is statistically more likely to be exposed to many

detrimental environmental factors such as poorer neighborhoods,schools, nutrition, and prenatal and postnatal health care.[77][78]

The Copenhagen consensus in 2004 stated that lack of both iodineand iron has been implicated in impaired brain development, and thiscan affect enormous numbers of people: it is estimated that one-thirdof the total global population are affected by iodine deficiency. Indeveloping countries, it is estimated that 40% of children aged fourand under suffer from anaemia because of insufficient iron in their

diets.[79]

Eppig, Fincher & Thornhill (2010) argue that "From an energeticsstandpoint, a developing human will have difficulty building a brainand fighting off infectious diseases at the same time, as both are verymetabolically costly tasks" and that differences in prevalence ofinfectious diseases (such as malaria) may be an importantexplanation for differences in IQ between different regions of the

world.[80] They tested other hypotheses as well, including geneticexplanations, concluding that infectious disease was "the best

predictor".[81] Christopher Hassall and Thomas Sherratt repeated the

analysis, and concluded "that infectious disease may be the onlyreally important predictor of average national IQ".[81]

In order to mitigate the effects of education on IQ, Eppig, Fincher & Thornhill (2010) repeated their analysis


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across the United States where standardized and compulsory education exists.[81] The correlation betweeninfectious disease and average IQ was confirmed, and they concluded that the "evidence suggests that

infectious disease is a primary cause of the global variation in human intelligence".[81]

Education

Several studies have proposed that a large part of the gap can be attributed to differences in quality of

education.[82] Racial discrimination in education has been proposed as one possible cause of differences ineducational quality between races.[83] According to a paper by Hala Elhoweris, Kagendo Mutua, NegmeldinAlsheikh and Pauline Holloway, teachers' referral decisions for students to participate in gifted and talented

educational programs were influenced in part by the students' ethnicity.[84]

The Abecedarian Early Intervention Project, an intensive early childhood education project, was also able tobring about an average IQ gain of 4.4 points at age 21 in the black children who participated in it compared

to controls.[72] Arthur Jensen agreed that the Abecedarian project demonstrates that education can have asignificant effect on IQ, but also said that no educational program thus far has been able to reduce the

black-white IQ gap by more than a third, and that differences in education are thus unlikely to be its only

cause.[85]

Rushton and Jensen argue that long-term follow-up of the Head Start Program found large immediate gainsfor blacks and whites but that these were quickly lost for the blacks although some remained for whites.They argue that also other more intensive and prolonged educational interventions have not produced lasting

effects on IQ or scholastic performance.[19] Nisbett argues that they ignore studies such as Campbell &Ramey (1994) which found that at the age 12, 87% black of infants exposed to an intervention had IQs inthe normal range (above 85) compared to 56% of controls, and none of the intervention-exposed childrenwere mildly retarded compared to 7% of controls. Other early intervention programs have shown IQ effectsin the range of 45 points, which are sustained until at least age 815. Effects on academic achievement can

also be substantial. Nisbett also argues that not only early age intervention can be effective, citing othersuccessful intervention studies from infancy to college.[86]

Logographic writing system

Complex logographic writing systems have been proposed as an explanation for the higher visuospatial IQscores of East Asians. Critics argue that the causation may be reversed with higher visuospatial abilitycausing the development of pictorial symbols in writing rather than alphabetic ones. Another argument isthat East Asians adopted at birth also score high on IQ tests. Similar relatively higher visuospatial abilitiesare also found among Inuit and Native Americans, whose ancestors migrated from East Asia to the

Americas.[87][88]

Caste-like minorities

A large number of studies have shown that systemically disadvantaged minorities, such as the AfricanAmerican minority of the United States generally perform worse in the educational system and in intelligencetests than the majority groups or less disadvantaged minorities such as immigrant or "voluntary"

minorities.[5] The explanation of these findings may be that children of caste-like minorities, due to thesystemic limitations of their prospects of social advancement, do not have "effort optimism", i.e. they do nothave the confidence that acquiring the skills valued by majority society, such as those skills measured by IQ

tests, is worthwhile. They may even deliberately reject certain behaviors seen as "acting white".[5][89][90][91]

This argument is also explored in the bookInequality by Design: Cracking the Bell Curve Myth (1996)which argues that it is not lower average intelligence that leads to the lower status of racial and ethnic


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minorities, it is instead their lower status that leads to their lower average intelligence test scores. Oneexample being Jews in the early 20th century in the US who, the authors argue, scored low on IQ tests. Tosubstantiate this claim, the book presents a table comparing social status or caste position with test scoresand measures of school success in several countries around the world. Examples include Koreans, Peruviansand Brazilians in Japan, Burakumin in Japan, Australian Aborigines, Romani in Czechoslovakia, Maori in

New Zealand, Afro-Brazilians, Indigenous Brazilians, Pardos and Rural Exiles (as, but not limited to, peoplefrom Northeast in Braslia, So Paulo and Rio de Janeiro metropolitan areas, and including a minority of

European descent) in Brazil, Afrikaners in South Africa, Catholics in North Ireland, Irish and Scottish inGreat Britain, Arabs and Sephardi Jews in Israel, and Dalit, low caste, and tribal people in India. The authorsnote, however, that the comparisons made in the table do not represent the results of all relevant findings,that sometimes studies have shown more mixed findings, that the tests and procedures varied greatly fromstudy to study, and that there is no simple way to compare the size of group differences. The statementregarding Arabs in Israel, for example, is based on a news report that, in 1992, 26% of Jewish high school,

predominantly Ashkenazim, students passed their matriculation exam as opposed to 15% of Arab

students.[92] Stephen Jay Gould in the The Mismeasure of Man also argued that Jews in the early 20thcentury scored low on IQ tests. Rushton as well as Cochran, Hardy & Harpending have argued that this is a

misrepresentation of the studies and that also the early testing support a high average Jewish IQ.[53][93]

Murray replies that purely sociocultural factors like this cannot explain the gap, because the size of the gapon any test is dependent on that test's degree of g-loading. As an example, Murray notes that the test ofreciting a string of digits backwards is much more g-loaded than reciting it forwards, and the black-white gapis around twice as large on the first test as on the second. According to Murray, there is no way that cultureor motivation could systematically encourage black performance on one test while decreasing it on another,

when both tests are provided by the same examiner in the same setting.[94]

Cultural traditions valuing education

Nisbett argues cultural traditions valuing education can explain the high results in the US for Ashkenazi Jews

(Talmud scholarship) and East Asians (Confucianism and the Imperial examination system).[95]

Group subculture

JR Harris suggested in The Nurture Assumption that different peer group cultures may contribute to theblack-white IQ gap. She cites the work of Thomas Kindermann, whose longitudinal studies find that peer

groups significantly affect scholastic achievement.[96]

The American Anthropological Association in 1994 stated that intelligence is not biologically determined by

race.[6] The American Psychological Association in 1994 stated that there is little evidence to supportenvironmental explanations, certainly no support for genetic interpretations, and that presently the cause of

the black-white IQ gap is unknown.[97] Some scientists, however, have concluded sufficient evidence exists

to support substantial genetic contribution to explain the black-white IQ gap.[19][22][34][98][99]

Genetics of race and intelligence

Main article: Race and genetics

The decoding of the human genome has enabled scientists to search for sections of the genome that maycontribute to cognitive abilities. However the geneticist, Alan R. Templeton suggests this question is muddled

by the general focus on "race" rather than on populations defined by gene frequency or by geographical


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An environmental factor that varies

between groups but not within groupscan cause group differences in a trait

that is otherwise 100 percent heritable.

The height of this "ordinary genetically

varied corn" is 100 percent heritable,

but the difference between the groups

is totally environmental. This is

because the nutrient solution varies

between populations, but not within

populations.[106]

proximity, and by the general insistence on phrasing the question in terms of heritability.[100] Templetonpoints out that racial groups neither represent sub-species or distinct evolutionary lineages, and that

therefore there is no basis for making claims about the general intelligence of races.[100] He also finds thatphrasing the question in terms of heritability not helpful because heritability "by definition is not applicableto between-population phenotypic differences" and is therefore "completely irrelevant to the question ofgenetic differentiation for any trait, including intelligence, among human populations." Templeton says thatthe only way to design a study of the genetic contribution to intelligence is to the correlation between degree

of geographic ancestry and cognitive abilities. He states that this would require a Mendelian "commongarden" design where specimens with different hybrid compositions are subjected to the same environmentalinfluences, and that when this design has been carried out, it has shown no significant correlation between

any cognitive and the degree of African or European ancestry.[100]

Intelligence is a polygenic trait. This means that intelligence is under the influence of several genes, possiblyseveral thousand. The effect of most individual genetic variants on intelligence is thought to be very small,well below 1% of the variance in g. Current studies using quantitative trait loci have yielded little success inthe search for genes influencing intelligence. Robert Plomin is confident that QTLs responsible for thevariation in IQ scores exist, but due to their small effect sizes, more powerful tools of analysis will be

required to detect them.[101]

Others assert that no useful answers can be reasonably expected from suchresearch before an understanding of the relation between DNA and human phenotypes emerges.[78]

A 2005 literature review article on the links between race and intelligence inAmerican Psychologiststatedthat no gene has been shown to be linked to intelligence, "so attempts to provide a compelling genetic link of

race to intelligence are not feasible at this time".[102] Several candidate genes have been proposed to have a

relationship with intelligence.[103][104] However, a review of candidate genes for intelligence published inDeary, Johnson & Houlihan (2009) failed to find evidence of an association between these genes and generalintelligence, stating "there is still almost no replicated evidence concerning the individual genes, which have

variants that contribute to intelligence differences".[105]

Heritability within and between groups

Heritability is defined as the ratio of variation attributable to geneticdifferences in an observable trait to the trait's total observablevariation. The heritability of a trait describes the proportion ofvariation in the trait that is attributable to genetic factors within a

particular population. Heritability is not the proportion of a trait thatis genetic and it does not describe what role, if any, genes play in

producing the trait itself. A heritability of 1 indicates that variation

correlates fully with genetic variation and a heritability of 0 indicatesthat there is no correlation between the trait and genes at all. There isbroad agreement that individual variation in intelligence is neitherfully genetic nor fully environmental, but there is little agreement onthe relative contribution of genes and environment on individualintelligence.

It has been argued that intelligence is substantially heritable withinpopulations, with 3050% of variance in IQ scores in early childhoodbeing attributable to genetic factors in analyzed US populations,

increasing to 7580% by late adolescence.[5][105] High heritabilitydoes not imply that a trait is genetic or unchangeable, however, asenvironmental factors that affect all group members equally will not be measured by heritability (see thefigure) and the heritability of a trait may also change over time in response to changes in the distribution of

genes and environmental factors.[5] High heritability also doesn't imply that all of the heritability is


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genetically determined, but can also be due to environmental differences that affect only a certain

genetically defined group (indirect heritability).[106]

Jensen and Rushton have argued that there may be environmental factors ("X factors") that are notmeasured by the heritability figure, but such factors must have the properties of not affecting whites while atthe same time affecting all blacks equally, but, the hereditarians argue, no such plausible factors have beenfound and other statistical tests for the presence of such an influence in the United States are negative.[22][107]

Dickens and Flynn argue that the conventional interpretation ignores the role of feedback between factors,such as those with a small initial IQ advantage, genetic or environmental, seeking out more stimulatingenvironments which will gradually greatly increase their advantage, which, as one consequence in theiralternative model, would mean that the "heritability" figure is only in part due to direct effects of genotype

on IQ.[1][108][109]

Spearman's hypothesis

Main article: Spearman's hypothesis

Spearman's hypothesis states that the magnitude of the black-white difference in tests of cognitive ability isentirely or mainly a function of the extent to which a test measures general mental ability, or g. Thehypothesis, first formalized by Arthur Jensen in the 1980s based on Charles Spearman's earlier comments onthe topic, argues that differences in g are the sole or major source of differences between blacks and whitesobserved in many studies of race and intelligence.

Studies on Spearman's hypothesis have often confirmed that racial IQ differences between Blacks and

Whites are in line with Spearman's hypothesis.[110] Some have criticized these results. Hunt and Carlsonargues Spearman's hypothesis is just one of several models that could explain the observed distributions in

test scores.[1]

Gradual gap appearance

Fryer & Levitt (2006) found in tests of children aged eight to twelve months only minor differences (0.06SD) between blacks and whites that disappeared with the inclusion of a limited set of controls including

social-economic status.[111] Flynn has argued that the United States black-white gap appears gradually whichsuggests environmental causes. "At just 10 months old, the average score is only one point behind; by theage of 4, it is 4.6 points behind, and by the age of 24, the gap is 16.6 points. This could be due to genes, butthe steady rate after the age of 4 (about 0.6 IQ points lost every year) suggests otherwise, since genetically

driven differences such as height differences between males and females tend to kick in at a certainage."[112]

Rushton and Jensen argue that the black-white IQ difference of one standard deviation is present at the age

of 3 and does not change significantly afterward.[19] Murray argues that the heritability of IQ increases with

age which is reflected in the racial IQ gaps gradually increasing.[94]

Adoption studies

Several studies have been done on the effect of similar rearing conditions on children from different races.

The Minnesota Transracial Adoption Study (1976) examined the IQ test scores of 122 adopted children and143 nonadopted children reared by advantaged white families. The children were restudied ten years later.[113][114][115] The study found higher IQ for whites compared to blacks, both at age 7 and age 17. [113][116]


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Three other studies found opposing evidence with none finding higher intelligence in white children than inblack children. However, unlike the Minnesota Transracial Adoption Study, these studies did not retest the

children post-adolescence when heritability of IQ would be much higher.[19][22][117] Moore (1986)compared black and mixed-race children adopted by either black or white middle-class families in the UnitedStates. Moore observed that 23 black and interracial children raised by white parents had a significantlyhigher mean score than 23 age-matched children raised by black parents (117 vs 104), and argued thatdifferences in early socialization explained these differences. Eyferth (1961) studied the out-of-wedlock

children of black and white soldiers stationed in Germany after World War 2 and then raised by whiteGerman mothers and found no significant differences. Tizard et al. (1972) studied black (African and WestIndian), white, and mixed-race children raised in British long-stay residential nurseries. Three out of four

tests found no significant differences. One test found higher scores for non-whites.[118]

Studies on Korean infants adopted by European families have consistently shown a higher IQ than the

European average.[19][99][119] Frydman and Lynn (1989) showed a mean IQ of 119 for Korean infantsadopted by Belgium families. After correcting for the Flynn effect, the IQ of the adopted Korean children

was still 10 points higher than the indigenous Belgian children.[19][99][119] Lynn and Rushton claim that aStams et al. (2000) dataset shows a mean IQ of 115 for Korean infants adopted in the Netherlands.

[99][120][121]

Racial admixture studies

Many people have an ancestry from different geographic regions. For example, African Americans typicallyhave ancestors from both Africa and Europe, with, on average, 20% of their genome inherited from

European ancestors.[122] If racial IQ gaps have a partially genetic basis, blacks with a higher degree ofEuropean ancestry should on average have higher IQ, because the genes inherited from European ancestors

would likely include some genes with a positive effect on IQ.[123]

Witty and Jenkins (1936) compared a group of 63 black students all with an IQ of 125 and above andcompared their white ancestry level to Herskovits (1930) national sample of blacks and concluded nosignificant difference in the level of white ancestry between their sample of gifted students and the national

sample of Herskovits (1930).[124][125]

This study has been criticized as the study's control sample of Herskovitz (1930) was not consideredrepresentative. 50 percent of the Herskovitz (1930) sample were composed of Howard University

undergraduates and well to do professions with higher than average SES.[126] Blacks in both the controlsample of Herskovitz (1930) and the test sample by Witty and Jenkins (1936) had higher percentage of white

ancestry (approximately 30%) than the national average.[127]

Shuey (1966) summarized 18 black-white admixture studies and concluded 16 out of 18 studies showed a

positive correlation between lighter skin color and higher IQ with correlation ranging from 0.12 to 0.30.[128]

[129][130] Nisbett and Jensen have both argued that skin color is a highly imprecise measure of racial

ancestry.[131]

The frequency of different blood types vary with ancestry. Correlations between degree of European bloodtypes and IQ have varied between 0.05 and -0.38 in two studies from 1973 and 1977. Nisbett writes that one

problem with these studies is that white blood genes are very weakly associated with one another in the

black population, so they are not a reliable method of estimating ancestry.[132] T. Edward Reed, an expert on

blood groups, argues that the methodology used in these studies would have been unable to detect anydifference, regardless of whether or not the hereditarian hypothesis is correct.[133]

Some authors have suggested that new studies of the relationship ancestry and IQ should be performed using


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modern DNA-based ancestry estimations, which would provide a more reliable measure of ancestry than is

possible based on skin tone or blood groups.[42][134]

Mental chronometry

Main article: Mental chronometry

Mental chronometry measures the elapsed time between the presentation of a sensory stimulus and thesubsequent behavioral response by the participant. This reaction time (RT) is considered a measure of the

speed and efficiency with which the brain processes information.[135] Scores on most types of RT tasks tendto correlate with scores on standard IQ tests as well as with g, and no relationship has been found between

RT and any other psychometric factors independent ofg.[135] The strength of the correlation with IQ variesfrom one RT test to another, but Hans Eysenck gives 0.40 as a typical correlation under favorable

conditions.[136] According to Jensen individual differences in RT have a substantial genetic component, and

heritability is higher for performance on tests that correlate more strongly with IQ.[107] Nisbett argues that

some studies have found correlations closer to 0.2, and that the correlation is not always found.[137]

Several studies have found differences between races in average reaction times. These studies have generallyfound that reaction times among black, Asian and white children follow the same pattern as IQ scores.[138][139][140] Rushton and Jensen have argued that reaction time is independent of culture and that theexistence of race differences in average reaction time is evidence that the cause of racial IQ gaps is partially

genetic instead of entirely cultural.[19] Responding to this argument inIntelligence and How to Get It,Nisbett has pointed to the Jensen & Whang (1993) study in which a group of Chinese Americans had longerreaction times than a group of European Americans, despite having higher IQs. Nisbett also mentionsfindings in Flynn (1991) and Deary (2001) suggesting that movement time (the measure of how long it takesa person to move a finger after making the decision to do so) correlates with IQ just as strongly as reaction

time, and that average movement time is faster for blacks than for whites.[141]

Brain size

Harry Jerison writes that there are real race differences in brain size, if races are defined sociologically ratherthan genetically, but it is difficult to know what to make of these differences. Within a race, sex, or agegroup, brain size has about a 0.4 correlation with IQ. He also writes that because of politics, it is almost

impossible to discuss these differences in any scientific forum.[142]

Earl Hunt states that because brain size is found to have a correlation of about .35 with intelligence amongwhites and is almost entirely genetically determined, race differences in average brain size are therefore an

important argument for a possible genetic contribution to racial IQ gaps. However as brain images areexpensive to obtain, much of the research in this area is based on external measures of head size, which onlymeasures brain size indirectly and thus makes the data less reliable. Hunt notes that Rushton's head size datawould account for a difference of .09 standard deviations between Black and White average test scores, only

a portion of the 1.0 standard deviation gap in average scores that is observed.[143]

Hunt and Carlson write that whether there is a relationship between race, genetics, brain size, and IQ is atpresent unknown. However, they say that it is an area both feasible and reasonable to study. SummarisingRushton's hypothesis that the black-white IQ gap can be explained by larger average brain size amongwhites, they say that because this argument presents a biological mechanism known to influence intelligence

that could potentially help explain racial IQ gaps, discussing ideas like this is more likely to be informativethan arguing about heritability statistics.[1]


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Main article: Intelligence and public policy

Jensen and Rushton argued that the existence of biological group differences does not rule out, but raisesquestions about the worthiness of policies such as affirmative action or placing a premium on diversity. Theyalso argued for the importance of teaching people not to overgeneralize or stereotype individuals based onaverage group differences, because of the significant overlap of people with varying intelligence between

different races.[19]

The environmentalist viewpoint argues for increased interventions in order to close the gaps.[citation needed]

Nisbett argues that schools can be greatly improved and that many interventions at every age level are

possible.[144] Flynn, arguing for the importance of the black subculture, writes that "America will have toaddress all the aspects of black experience that are disadvantageous, beginning with the regeneration ofinner city neighbourhoods and their schools. A resident police office and teacher in every apartment block

would be a good start."[112] Researchers from both sides agree that interventions should be better

researched.[137][22]

Especially in developing nations, society has been urged to take on the prevention of cognitive impairment in

children as of the highest priority. Possible preventable causes include malnutrition, infectious diseases suchas meningitis, parasites, and cerebral malaria, in utero drug and alcohol exposure, newborn asphyxia, low

birth weight, head injuries, and endocrine disorders.[145]

Ashkenazi Jewish intelligence

^ abcdefgh Hunt & Carlson 20071.^ Sternberg, Robert J.; Kaufman, Scott Barry, eds. (2011). The Cambridge Handbook of Intelligence(http://books.google.ie/books?id=FtYeTcNwzQ4C&pg=PA295&lpg=PA295&dq=%22As+with+race,+there+is+no+universally+accepted+definition+of+intelligence.%22#v=onepage&q=%22As%20with%20race%2C%20there%20is%20no%20universally%20accepted%20definition%20of%20intelligence.%22&f=false).Cambridge University Press. p. 295. ISBN 9780521518062.

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^ Rushton, J. Philippe; Jensen, Arthur R. (2005). "Thirty years of research on race differences in cognitiveability." (http://wnlibrary.com/Portabel%20Documents/R/Rushton%20Materials/Thirty%20Years%20Of%20Research%20On%20Race%20Differences%20In%20Cognitive%20Ability%20-%2

0J%20Philippe%20Rushton%20And%20Arthur%20R%20Jensen.pdf). Psychology, Public Policy, and Law11(2): 235294. doi:10.1037/1076-8971.11.2.235 (http://dx.doi.org/10.1037%2F1076-8971.11.2.235).

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^ Schacter, Gilbert & Wegner 20074.^ abcdefghi Neisser et al. 1996 "The differential between the mean intelligence test scores of blacks andwhites (about one standard deviation, although it may be diminishing) does not result from any obvious biases intest construction and administration, nor does it simply reflect differences in socio-economic status.Explanations based on factors of caste and culture may be appropriate, but so far have little direct empiricalsupport. There is certainly no such support for a genetic interpretation. At present, no one knows what causesthis differential."

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^ Falk 2008, p. 1828.^ Wroe 2008, p. 8129.^ Gray & Thompson 200430.^ Ceci & Williams 200931.^ ab Rose 2009, pp. 7868832.^ ab AAA 199833.^ ab Gottfredson 200734.^ Flynn 200935.^ ab Schacter, Gilbert & Wegner 2007, pp. 350136.^ ab Sternberg, Grigorenko & Kidd 200537.^ Daley & Onwuegbuzie 201138.^ Britannica 201239.^ Schaefer 200840.^ Kaszycka, trkalj & Strzako 200941.^ ab Rowe 200542.^ Sternberg & Grigorenko 200743.^ Brace 200544.^ Graves 200145.^ Hunt 2010, pp. 4081046.^ Gottfredson 199747.^ ab Roth et al. 200148.^ Dickens & Flynn 200649.

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^ Richardson 200461. ^ Hunt & Wittmann 200862.^ Irvine 198363.^ Irvine & Berry 1988 a collection of articles by several authors discussing the limits of assessment byintelligence tests in different communities in the world. In particular, Reuning (1988) describes the difficulties in

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