- Race and intelligence
Human intelligence Abilities and Traits Models and Theories Fields of study Race Classification Genetics Group differences Social Related
The connection between race and intelligence has been a subject of debate in both popular science and academic research since the inception of intelligence testing in the early 20th century. There are no universally accepted definitions of either race or intelligence in academia, and any discussion of their connection involves studies from multiple disciplines, including psychology, anthropology, biology, and sociology.
The official position of the American Anthropological Association is that intelligence cannot be biologically determined by race. The American Psychological Association has said that while there are differences in average IQ between racial groups, and there is no conclusive evidence for environmental explanations, there is even less empirical support for a genetic interpretation, and no adequate explanation for the racial IQ gap is presently available. According to a 1996 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, and all peoples "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."
Intelligence quotient (IQ) tests performed in the United States have consistently demonstrated a significant degree of variation between different racial groups, with the average score of the African American population being lower— and that of the Asian American population being higher— than that of the European-American population. At the same time, there is a considerable overlap between these group scores, and individuals of each group can be found at all points on the IQ spectrum. Similar findings have been reported for related populations around the world, although these studies are generally considered less reliable due to the relative paucity of test data and the difficulties inherent in the cross-cultural comparison of intelligence test scores. While the existence of racial IQ gaps is well-documented and not subject to much dispute, there is no consensus among researchers as to their cause.
Four contemporary classifications of position regarding study of differences in IQ based on race/ethnicity are seen. The first is that these gaps reflect a real difference in average group intelligence, which is caused by a combination of environmental factors and heritable differences in brain function. A second position is that differences in average cognitive ability between races exist and 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 the differences 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 History of the debate
- 2 Ethics of research
- 3 The validity of "race" and "IQ"
- 4 Group differences
- 5 Potential environmental causes
- 6 Genetic arguments
- 7 Significance of group differences
- 8 Policy relevance
- 9 External links
- 10 References
History of the debate
The history of the race and intelligence controversy concerns the historical development of a debate, primarily in the United States, concerning possible explanations of group differences in scores on intelligence tests. Historically there have been differences among average scores in IQ tests of different population groups; these have sometimes been called "racial IQ gaps". Researchers believe that environmental (socioeconomic and cultural) factors contribute to this, but have not agreed on whether the gaps are due only to environmental factors, or whether there is any genetic contribution that can be substantiated.
Claims of races having different intelligence were used to justify colonialism, slavery, social darwinism, and racial eugenics. In the late 19th and early 20th centuries, group differences in intelligence were assumed to be due to race and, apart from intelligence tests, research relied on measurements such as brain size or reaction times. The first IQ test was created between 1905 and 1908 and revised in 1916 (the Stanford–Binet Intelligence Scales). Alfred Binet, the developer of these tests, warned that these should not be used to measure innate intelligence or to label individuals. However, at the time there was great concern in the United States about the abilities and skills of recent immigrants. Different nationalities were sometimes thought to comprise different races, such as Slavs. The tests were used to evaluate draftees for World War I, and researchers found that people of southern and eastern Europe scored lower than native-born Americans. At the time, such data was used to construct an ethnically based social hierarchy, one in which immigrants were rejected as unfit 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.
In the 1920s, some scientists reacted to eugenicist claims linking abilities and moral character to racial or genetic ancestry. Despite that, states such as Virginia enacted laws based in eugenics, such as its 1924 Racial Integrity 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). By the mid-1930s most US psychologists had adopted the view that environmental and cultural factors played a dominant role. In addition, psychologists were reluctant to risk being associated with the German Nazi claims of a "master race".
In 1969 Arthur Jensen revived the hereditarian point of view in the article, "How Much Can We Boost IQ and School Achievement?":82 It followed changes in public programs introduced to try to correct decades of discrimination against poor African Americans. In 1954 the US Supreme Court ruled in Brown v. Board of Education that public school segregation was unconstitutional. As part of the Great Society programs under President Lyndon Johnson, the Head Start Program was started with the goal of early intervention to help socially disadvantaged children succeed by providing remedial education. Given the effects of segregation and discrimination into the 1960s, many Head Start programs served African-American children.
Jensen's article questioned remedial education for African-American children; he suggested their poor educational performance reflected an underlying genetic cause rather than lack of stimulation at home. Jensen's work, publicized by the Nobel laureate physicist William Shockley, sparked controversy amongst the academic community and student protests.
In their 1988 book The IQ Controversy, the Media, and Public Policy, Mark Snyderman and Stanley Rothman claimed to document a liberal bias in the media coverage of scientific findings regarding IQ. The book builds on the results of a survey of more than 600 psychologists, sociologists and educationalists. 45 percent of those surveyed thought that black-white differences in IQ were the product of both genetic and environmental variation, while 15 percent believed that 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.
Another debate followed The Bell Curve (1994), a book by Richard Herrnstein and Charles Murray, who argued in favor of the hereditarian viewpoint. It provoked the publication of several interdisciplinary books representing the environmental point of view, as well as some in popular science. They include The Bell Curve Debate (1995), Inequality by Design: Cracking the Bell Curve Myth (1996) and a second edition of The Mismeasure of Man (1996) by Steven J. Gould. One book written from the hereditarian point of view at this time was The g Factor: The science of mental ability (1998) by Jensen. In 1994 a group of 52 scientists, including leading hereditarians, signed the statement "Mainstream Science on Intelligence". The Bell Curve also led to a 1995 report from the American Psychological Association, "Intelligence: Knowns and Unknowns", acknowledging a gap between average 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. The article was followed by a series of responses, some in support, some critical. Richard Nisbett, another psychologist who had also commented at the time, later included an amplified version of his critique as part of the book Intelligence and How to Get It: Why Schools and Cultures Count (2009). Rushton and Jensen in 2010 made a point-for-point reply to this and again summarized the hereditarian position.
Two public figures claimed in interviews that one of the main causes for poverty in Africa is a low average intelligence which caused great controversy. Following an interview in the monthly supplement of Helsingin Sanomat, Lynn's coauthor Tatu Vanhanen, a political scientist and father of the Prime Minister of Finland Matti Vanhanen, was investigated by the Finnish police between 2002 and 2004. In 2007 James D. Watson, Nobel laureate in biology, gave a controversial interview to the Sunday Times Magazine during a book tour in the United Kingdom. This resulted in the cancellation of a Royal Society lecture, along with other public engagements, and his suspension from his administrative position at Cold Spring Harbor Laboratory. He subsequently cancelled the tour and resigned from his position.
Many of the leading hereditarians, mostly psychologists, have received funding from the Pioneer Fund with Rushton as its current head. The Southern Poverty Law Center lists the Pioneer Fund as a hate group, citing the fund's history, its funding of race and intelligence research, and its connections with racist individuals. On the other hand, Ulrich Neisser writes that "Pioneer has sometimes sponsored useful research—research that otherwise might not have been done at all." Other sources and researches have criticized the Pioneer Fund for promoting scientific racism, eugenics and white supremacy. Similarly, Ullica Segerstråle points out that a number of critics of the hereditarian point of view have been self-admittedly motivated by a Marxist ideology, and supported by organizations such as Science for the People whose goals are political as well as scientific.
Ethics of research
The 1996 report of the APA had comments on the ethics of research on race and intelligence. Gray and Thompson (2004) as well as Hunt and Carlson (2007) have also discussed different possible ethical guidelines. Nature in 2009 invited two editorials on the ethics of research in race and intelligence by Steven Rose (against) and Stephen J. Ceci and Wendy M. Williams (for).
According to critics, research will run the risk of simply reproducing the horrendous effects of the social ideologies (such as Nazism or Social Darwinism) justified in part on claimed hereditary racial differences. Stephen Rose maintain that the history of eugenics makes this field of research difficult to reconcile with current ethical standards for science.
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. Flynn, a non-hereditarian, has argued 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.
The validity of "race" and "IQ"
The concept of intelligence and the degree to which it is measurable is and has been a matter of discussion. Psychology, a psychology textbook by Schacter et al., argue that while there 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 universally accepted. A recurring criticism is that different societies value and promote different kinds of skills and that the concept of intelligence is therefore culturally variable and cannot be measured the same in different societies. Consequently, some critics argue, that proposed relationships to other variables are necessarily tentative.
In fields such as psychology, medicine, economics, political science, criminology, and other research on group differences, intelligence is commonly measured using intelligence quotient (IQ) tests. The statement "Mainstream Science on Intelligence" argued that "IQ is strongly related, probably more so than any other single measurable human trait, to many important educational, occupational, economic, and social outcomes ... Whatever IQ tests measure, it is of great practical and social importance". Most of the research on intelligence differences between racial groups is based on IQ testing. These tests are highly correlated with the psychometric variable g (for general intelligence factor). Other tests that are also highly correlated with g are also seen as measures of cognitive ability and have sometimes been used in the research. US examples include the Armed Forces Qualifying Test, SAT, GRE, GMAT and LSAT. International student assessment tests that have been used include the Trends in International Mathematics and Science Study, Programme for International Student Assessment, and Progress in International Reading Literacy Study. Other variables with much lower correlations such as brain size and reaction time have also been used.
Also the concept of race as a meaningful category of analysis is hotly contested. The authors of two articles in two encyclopedias, the Encyclopedia Britannica and the Encyclopedia of Race, Ethnicity and Society, argue that today the mainstream view is that race is a social construction that is not mainly based in actual biological differences but on folk ideologies that construct groups based on social disparities and superficial physical characteristics. Sternberg. et all (2005) argue that the overwhelming portion of the literature correlating race with identity has tacitly adopted folk definitions of race. The American Anthropological Association in 1998 published a "Statement on 'Race'" which rejected the existence of "races" as unambiguous, clearly demarcated, biologically distinct groups. Others argue that this view is restricted to certain fields, while in other fields, including anthropology in some other nations, race is still seen as a valid biological category.
Race in the studies is almost always determined using self-reports, rather than based on analyses of the genetic history of the tested individuals. According to psychologist David Rowe, self-report is the preferred method for racial classification in studies of racial differences because classification based on genetic markers alone ignore the "cultural, behavioral, sociological, psychological, and epidemiological variables" that distinguish racial groups. Hunt and Carlson write that "Nevertheless, self-identification is a surprisingly reliable guide to genetic composition. Tang et al. (2005) applied mathematical clustering techniques to sort genomic markers for over 3,600 people in the United States and Taiwan 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."
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 most anthropologists. For example C. Loring Brace and Jonathan Kaplan and geneticist Joseph Graves, have argued that while there it is certainly possible to find biological and genetic variation that corresponds roughly to the groupings normally defined as races, this is true for almost all geographically distinct populations. The cluster structure of the genetic data is therefore dependent on the initial hypotheses of the researcher and the populations sampled. When one samples continental groups the clusters become continental, if one had chosen other sampling patterns the clusters would be different. Weiss and Fullerton have noted that if one sampled only Icelanders, Mayans and Maoris, three distinct clusters would form and all other populations could be described as being composed of admixtures of Maori, Icelandic and Mayan genetic materials. Kaplan therefore concludes that while racial groups are characterized by different allele frequencies, this does not mean that racial classification is a natural taxonomy of the human species, because multiple other genetic patterns can be found in human populations that crosscut racial distinctions. In this view racial groupings are social constructions that also have biological reality which is largely an artifact of how the category has been constructed.
Earl Hunt agrees that racial categories are defined by social conventions, though he points out that they also correlate with clusters of both genetic traits and cultural traits. Hunt explains that due to this, racial IQ gaps 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 and the many factors correlated with race which could potentially affect performance. These factors include health and wealth, biological differences, and education.
US test scores
Rushton and Jensen (2005 and 2010) write that in the United States, self-identified blacks and whites have been the subjects 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). 15% to 20% of the black IQ distribution exceeds the white median IQ, so many blacks obtain scores above the white average. The black-white IQ difference is largest on those tests that best represent the general intelligence factor g. The 1996 APA report "Intelligence: Knowns and Unknowns" and the 1994 statement "Mainstream Science on Intelligence" gave more or less similar estimates. Roth et al. (2001) in a review of the results of a total of 6,246,729 participants on other tests of cognitive ability or aptitude found a black-white gap of 1.1 SD. Consistent results were found for college and university application tests such as the Scholastic Aptitude Test (N = 2.4 million) and Graduate Record Examination (N = 2.3 million), as well as for tests of job applicants in corporate sections (N = 0.5 million) and in the military (N = 0.4 million).
A 2006 study by Dickens and Flynn estimated that the black-white gap closed by about 5 or 6 IQ points between 1972 and 2002, which would be a reduction by about one-third. However this was challenged by Rushton & Jensen who claim the gap remains stable. Murray in a 2006 study agree with Dickens and Flynn that there has been a narrowing of the gap, "Dickens' and Flynn's estimate of 3–6 IQ points from a base of about 16–18 points is a useful, though provisional, starting point". But he argues that this has stalled and that there has been no further narrowing for people born after the late 1970s. He found similar results in a 2007 study.
The IQ distributions of other racial and ethnic groups in the United States are less well-studied. The Bell Curve (1994) stated that the average IQ of African Americans was 85, Latino 89, White 103, Asian 106, and Jews 113. Asians score relatively higher on visuospatial than on verbal subtests. The few Amerindian populations that have been systematically tested, including Arctic Natives, tend to score worse on average than white populations but better on average than black populations.
According to several studies, Ashkenazi Jews score 0.75 to 1.0 standard deviation above the general European average. This corresponds to an IQ of 112–115. Other studies have found somewhat lower values. During the 20th century, they made up about 3% of the US population but won 27% of the US science Nobel Prizes and 25% of the Turing Awards. They have high verbal and mathematical scores, while their visuospatial abilities are typically somewhat lower, by about one half standard deviation, than the European average. See also Ashkenazi intelligence.
The racial groups studied in the United States and Europe are not necessarily a random sample of the populations in other parts of the world. Therefore, results from data in the US and Europe do not necessarily apply to the rest of the world.
The validity and reliability of IQ scores obtained from outside of the United States and Europe have been questioned due to the possibility of test bias as discussed in a later section. Nevertheless, some researchers have attempted to measure IQ variation in a global context.
Raw scores on IQ tests have been rising. This score increase, primarily in the lower end of the distribution, is known as the "Flynn effect," named for James R. Flynn, who did much to document it and promote awareness of its implications. In the United States the increase has been continuous and approximately linear from the earliest years of testing to the present. 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.
Potential environmental causes
The following environmental factors are some of those suggested as explaining a portion of the differences in average IQ between races. These factors are not mutually exclusive with one another, and some may in fact directly contribute 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, and the differences in average brain size between races could be the result of nutritional factors.
A 1996 report by the American Psychological Association states that controlled studies show that the black-white IQ gaps are not substantially due to bias in the content or administration of the IQ tests. Furthermore, the tests are equally valid predictors of future achievement for black and white Americans. This view is reinforced by Nicholas Mackintosh in his 1998 book IQ and Human Intelligence, and by a 1999 literature review by Robert Brown et al.
Studies on other groups and in other nations have argued that IQ tests may be biased against certain groups. The validity and reliability of IQ scores obtained from outside of the United States and Europe have been questioned, in part because of the inherent difficulty of comparing IQ scores between cultures. Several researchers have argued that cultural differences limit the appropriateness of standard IQ tests in non-industrialized communities. In the mid-1970s, for example, the Soviet psychologist Alexander Luria 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.
Stereotype threat is the fear that one's behavior will confirm an existing stereotype of a group with which one identifies; this fear may in turn lead to an impairment of performance. Testing situations that highlight the fact that intelligence is being measured tend to lower the scores of individuals from racial-ethnic groups that already score lower on average. Stereotype threat conditions cause larger than expected IQ differences among groups but do not explain the gaps found in non-threatening test conditions.
A 2009 meta-analysis by Jelte Wicherts found evidence of significant publication bias in 55 studies of stereotype threat and its effect on IQ, in which those that found a strong effect were more likely to be published than those that did not. Reviewing both published and unpublished studies, Wicherts found that stereotype threat did not have an effect on all test-taking settings in which a difference in average scores is observed between races, and therefore was not an adequate explanation for the racial IQ gap.[verification needed]
According to the report of a 1996 APA task force regarding the US gaps, socioeconomic status (SES) cannot account for all of the observed racial-ethnic group differences in IQ. Their first reason for this conclusion is that the black-white test score gap is not eliminated when individuals and groups are matched on SES. Second, excluding extreme conditions, nutritional and biological factors that may vary with SES have shown little effect on IQ. Third, the relationship between IQ and SES is not simply one in which SES determines IQ, but differences in intelligence, particularly parental intelligence, also cause differences in SES, making separating the two factors difficult.
Rushton and Jensen argue that controlling for SES only reduces the black-white gap by a third or 5 points. If there are racial genetic differences, then this figure is overstated since part of the differences in parental SES are due to differences in parental IQ. Furthermore, they argue, an environment-only explanation predicts that the IQ gap would be smaller at higher levels of parental SES since these children would be less exposed to the environmental factors lowering IQ. However, the gap is actually larger at higher parental SES levels. They also point to studies finding higher average IQ for East Asians, American Indians, and Inuit with similar or worse SES than blacks. Comparing black and white children in terms of socioeconomic indicators found that the black children from the best areas and schools (those producing the highest average scores) still average slightly lower on IQ than the white children with the worst socioeconomic factors.
Health and nutrition
Environmental factors including lead exposure, breast feeding, and nutrition can significantly affect cognitive development and functioning. For example, iodine deficiency causes a fall, in average, of 12 IQ points. Such impairments may sometimes be permanent, sometimes be partially or wholly compensated for by later growth. The first two years of life is the critical time for malnutrition, the consequences of which are often irreversible and include poor cognitive development, educability, and future economic productivity. The African American population of the United States is statistically more likely to be exposed to many of the possible prenatal and perinatal detrimental environmental factors.
The Copenhagen consensus in 2004 stated that lack of both iodine and iron has been implicated in impaired brain development, and this can affect enormous numbers of people: it is estimated that one-third of the total global population are affected by iodine deficiency. In developing countries, it is estimated that 40% of children aged four and under suffer from anaemia because of insufficient iron in their diets.
Eppig, Fincher, and Thornhill (2009) argue that "From an energetics standpoint, a developing human will have difficulty building a brain and fighting off infectious diseases at the same time, as both are very metabolically costly tasks" and that differences in prevalence of infectious diseases (such as malaria) may be an important explanation for differences in IQ between different regions of the world. They also tested other hypotheses as well, including genetic explanations, concluding that infectious disease was "the best predictor". Christopher Hassall and Thomas Sherratt repeated the analysis, and concluded "that infectious disease may be the only really important predictor of average national IQ".
In order to mitigate the effects of education on IQ, Eppig, Fincher, and Thornhill (2011) repeated their analysis across the United States where standardized and compulsory education exists. The correlation between infectious 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".
Several studies have proposed that a large part of the gap can be attributed to differences in quality of education. Racial discrimination in education has been proposed as one possible cause of differences in educational quality between races. According to a paper by Hala Elhoweris, Kagendo Mutua, Negmeldin Alsheikh and Pauline Holloway, teachers' referral decisions for students to participate in gifted and talented educational programs was influenced in part by the students' ethnicity.
The Abecedarian Early Intervention Project, an intensive early childhood education project, was also able to cause an average IQ gain of 4.4 points at age 21 in the black children who participated in it compared to controls. Arthur Jensen agreed that the Abecedarian project demonstrates that education can have a significant 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.
Rushton and Jensen argue that long-term follow-up of the Head Start Program found large immediate gains for 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. Nisbett argues that they ignore studies such as a study by Ramey and colleagues, which found that at the age 12, 87% black of infants exposed to an intervention had IQs in the normal range (above 85) compared to 56% of controls, and none of the intervention-exposed children were mildly retarded compared to 7% of controls. Other early intervention programs have shown IQ effects in the range of 4–5 points, which are sustained until at least age 8–15. Effects on academic achievement can also be substantial. Nisbett also argues that not only early age intervention can be effective, citing other successful intervention studies from infancy to college.:304-5
Logographic writing system
Complex logographic writing systems have been proposed as an explanation for the higher visuospatial IQ scores of East Asians. Critics argue that the causation may be reversed with higher visuospatial ability causing the development of pictorial symbols in writing rather than alphabetic ones. Another argument is that East Asians adopted at birth also score high on IQ tests. Similar relatively higher visuospatial abilities are also found among Inuit and American Indians whose ancestors migrated from East Asia to the Americas.
A large number of studies have shown that systemically disadvantaged minorities, such as the African American minority of the United States generally perform worse in the educational system and in intelligence tests than the majority groups or less disadvantaged minorities such as immigrant or "voluntary" minorities. The explanation of these findings may be that children of caste-like minorities, due to the systemic limitations of their prospects of social advancement, do not have "effort optimism", i.e. they do not have 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".
This argument is also explored in the book Inequality 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 minorities, it is instead their lower status that leads to their lower average intelligence test scores. One example being Jews in the early 20th century in the US who, the authors argue, scored low on IQ tests. To substantiate this claim, the book presents a table comparing social status or caste position with test scores and measures of school success in several countries around the world. Examples include Koreans, Peruvians and 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, people from Northeast in Brasília, São Paulo and Rio de Janeiro metropolitan areas, and including a minority of poors of European descent) in Brazil, Afrikaners in South Africa, Catholics in North Ireland, Irish and Scottish in Great Britain, Flemish in Belgium, Arabs and Sephardi Jews in Israel, and Dalit, low caste, and tribal people in India. The authors note, 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 from study to study, and that there is no simple way to compare the size of group differences. The statement regarding 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. Jay Gould in the The Mismeasure of Man also argued that Jews in the early 20th century scored low on IQ tests. Rushton as well as Cochran et al. have argued that this is a misrepresentation of the studies and that also the early testing support a high average Jewish IQ.
Hereditarians reply that purely sociocultural factors like this cannot explain the gap, because the size of the gap on any test is dependent on that test's degree of g-loading. As an example, Charles Murray notes that the test of reciting a string of digits backwards is much more g-loaded than reciting it forwards, and the black-white gap is around twice as large on the first test as on the second. According to Murray, there is no way that culture or 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.
Cultural traditions valuing education
Flynn has argued for importance of continued intellectual stimulation in order to sustain IQ. He writes, citing other authors, that "many black people have not signed up for the 'great mission' of the white middle class – the constant quest to stimulate intellectual growth and get their child into Harvard or Oxbridge. Rather than a 'hothouse' approach', they favour a 'natural growth' view: give a child food and love, and all will be well." There is a black teenage subculture of "Dressing sharply, sexual conquests, hanging out, drugs, hip-hop and atypical speech all crowd out more cognitively demanding pursuits."
JR Harris suggested in The Nurture Assumption that different peer group cultures may contribute to the black-white IQ gap. She cites the work of Thomas Kindermann, whose longitudinal studies find that peer groups significantly affect scholastic achievement.
Hereditarians argue that there is a substantial (50–80% in the US according to Rushton and Jensen) genetic contribution to the IQ gaps. Non-hereditarians argue that the genetic contribution to the gaps (not to individual IQ) is nil.
One explanation for racial IQ gaps advanced by some researchers is that they are partly the result of evolutionary pressures that varied between geographic regions. C. Loring Brace has argued that such a clinal distribution in the trait is not possible, because the evolution of human intelligence is founded on the development of human linguistic behavior, and intelligence is therefore of equal survival value to all human groups. On the other hand, cultural psychologist Richard Nisbett has argued that "(t)here are a hundred ways that a genetic difference in intelligence could have arisen – either in favor of whites or in favor of blacks."
Arthur Jensen explains in The g Factor how evolutionary factors could have potentially contributed to racial IQ gaps. Jensen points out that larger and more complex brains are very metabolically expensive, so they evolve only when they provide a strong selective advantage. According to Jensen, as early humans migrated out of Africa, the need to adapt to colder climates created a stronger selective pressure for intelligence in Europe and Asia than existed in Africa. J. Philippe Rushton carries this idea a step further in Race, Evolution, and Behavior, proposing that human groups differ in intelligence due to r/K selection theory, with Africans being more r-selected and Asians more K-selected.
C. Loring Brace regards evolutionary explanations for racial IQ gaps as unfounded speculation. Regarding Rushton’s application of r/K selection to human groups, Joseph L. Graves argues that not only is r/K selection theory considered to be virtually useless when applied to human life history evolution, but Rushton himself does not apply the theory correctly, and displays a lack of understanding evolution in general.
Race and genetics
The decoding of the human genome has enabled scientists to search for sections of the genome that contribute to cognitive abilities, and there are also ways to study whether the differences in frequency of particular genetic variants between populations contribute to differences in average cognitive abilities. However the geneticist, Alan R. Templeton has argued that this question is muddled by the general focus on "race" rather than on populations defined by gene frequency or by geographical proximity, and by the general insistence on phrasing the question in terms of heritability of intelligence. Templeton argues 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. He also argues that phrasing the question in terms of heritability is useless since heritability applies only within groups, but cannot be used to compare traits across groups. Templeton argues that the 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 argues that this would require a Mendelian "common garden" design where specimens with different hybrid compositions are subjected to the same environmental influences, and he further argues 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.
Intelligence is both a quantitative and polygenic trait. This means that intelligence is under the influence of several genes, possibly several 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 in the search for genes influencing intelligence. Robert Plomin is confident that QTLs responsible for the variation in IQ scores exist, but due to their small effect sizes, more powerful tools of analysis will be required to detect them. Others assert that no useful answers can be reasonably expected from such research before an understanding of the relation between DNA and human phenotypes emerges. Some researchers have expressed reluctance to investigate possible links between genes and intelligence, due to the controversy it can produce.
A 2005 literature review article on the links between race and intelligence in American Psychologist stated that no gene has been shown to be linked to intelligence, "so attempts to provide a compelling genetic link of race to intelligence are not feasible at this time". Several candidate genes have been proposed to have a relationship with intelligence. However, a review of candidate genes for intelligence published in 2009 by Deary et al. failed to find evidence of an association between these genes and general intelligence, stating "there is still almost no replicated evidence concerning the individual genes, which have variants that contribute to intelligence differences".
Heritability within and between groups
Heritability is defined as the proportion of interindividual variance in a trait which is attributable to genotype within a defined population in a specific environment. A heritability of 1 indicates that variation correlates fully with genetic variation and a heritability of 0 indicates that there is no correlation between the trait and genes at all. There is broad agreement that individual variation in intelligence is neither fully genetic nor fully environmental, but there is little agreement on the relative contribution of genes and environment on individual intelligence.
It has been argued that intelligence is substantially heritable within populations, with 30–50% of variance in IQ scores in early childhood being attributable to genetic factors in analyzed US populations, increasing to 75–80% by late adolescence. High heritability does not imply that a trait is genetic or unchangeable, however, as environmental factors that affect all group members equally will not be measured by heritability (see the figure) and the heritability of a trait may also change over time in response to changes in the distribution of genes and environmental factors. High heritability also doesn't imply that all of the heritability is genetically determined, but can also be due to environmental differences that affect only a certain genetically defined group (indirect heritability).
Hereditarians have argued that there may be environmental factors ("X factors") that are not measured by the heritability figure, but such factors must have the properties of not affecting whites while at the same time affecting all blacks equally, but, the hereditarians argue, no such plausible factors have been found and other statistical tests for the presence of such an influence in the US are negative.
This argument has been criticized by other researchers using several different arguments. Firstly, as noted earlier, Templeton argues that heritability is relevant only for explaining within group variance, cannot be used to explain variation between groups. Secondly the heritability figure of .8 for White American populations have been frequently been criticized as being highly inflated. Another is arguing that there are many environmental factors, sometimes small and subtle, that together add up to a large difference between blacks and whites. 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 stimulating environments which will gradually greatly increase their advantage, which, as one consequence in their alternative model, would mean that the "heritability" figure is only in part due to direct effects of genotype on IQ.
Hereditarians argue that the same group differences are repeated worldwide, both when comparing regions and when comparing the different groups in the same region, and that non-hereditarians have particular difficulty explaining the higher results for East Asians compared to whites.
Spearman's hypothesis states that the magnitude of the black-white difference in tests of cognitive ability is entirely or mainly a function of the extent to which a test measures general mental ability, or g. The hypothesis, first formalized by Arthur Jensen in the 1980s based on Charles Spearman's earlier comments on the topic, argues that differences in g are the sole or major source of differences between blacks and whites observed in many studies of race and intelligence. Various criticisms have been advanced and the validity of the arguments remain unresolved.
Regression toward the mean
Jensen argues that if the average racial IQs are different, then due to regression toward the mean the average IQs of relatives to blacks and whites with the same IQ should be different. He argues that studies confirm this. Nisbett (2009) agrees that this seems to be the case but he sees this as a weak argument since this effect would also be expected from environmental factors depressing average black IQ more than average white IQ. Rushton and Jensen have replied that the results are seen for siblings who should have a very similar environment, that relatives of those scoring low regress upwards, and that, when looking at the magnitude of regression, the results are as predicted by a partial genetic hypothesis. Rushton agrees that these results could also be explained without a genetic contribution, but he argues that such an explanation would be contrived.
Gradual gap appearance
Fryer and Levitt (2006) found in test of children aged eight to twelve months only minor differences (0.06 SD) between blacks and whites that disappeared with the inclusion of a limited set of controls including social-economic status. Flynn has argued that the U.S. black-white gap appear gradually which suggests environmental causes. "At just 10 months old, the average score is only one point behind; by the age 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, but the 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 certain age."
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. Murray, also a hereditarian, argues that the heritability of IQ increases with age which is reflected in the racial IQ gaps gradually increasing.
Uniform rearing conditions
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 and 143 nonadopted children reared by advantaged white families. The children were restudied ten years later. Nisbett has criticized the study for a number of weaknesses that are acknowledged by the authors. Rushton and Jensen have criticized this and argued for the significance of this study.
Minnesota Transracial Adoption Study Tested at age 7 and follow-up at age 17 Biological parents Number of children Age 7, average IQ Age 17, average IQ Black-black 21 95 89 Black-white 55 110 99 White-white 16 118 106 Asian or indigenous American 12 101 96 Biological children 104 116 109
Three other studies found opposing evidence with none finding higher intelligence in white children than in black children. Rushton and Jensen have criticized some of them for being small and all of them for, unlike the Minnesota Transracial Adoption Study, not measuring IQ after puberty since, they argued, the importance of the family environment is shown to decline with age. Nisbett has argued that there is significant heritability at age seven which makes the absence of differences quite telling.
Moore (1986) compared black and mixed-race children adopted by either black or white middle-class families in the US. There was no difference in IQ between black and mixed-race children, whether raised by black or white families. Moore also observed that 23 black and interracial children raised by white parents had a significantly higher mean score than 23 age-matched children raised by black parents (117 vs 104), and argued that differences 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 white German mothers and found no significant differences. The study was criticized by Rushton and Jensen for 20-25% of the "blacks" being North Africans and that the African Americans were an elite group because the Army General Classification Test excluded 30% of African Americans tested compared to 3% of whites. Nisbett writes that Flynn has argued that the army testing could not have produced more than a 3 IQ point advantage for the African Americans soldiers compared to the general African Americans population and that the North Africans would change the results only by a small amount.
Tizard et al. (1972) studied black (African and West Indian), 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.
The data is summarized below:
Biological parents Number of children Average IQ Moore (1986) Tested at age 7-10 Black-black, interracial adoption 17 102.9 Black-white, interracial adoption 6 105.7 Black-black, transracial adoption 9 118.0 Black-white, transracial adoption 14 116.5 Eyferth (1961) 1/3 tested at age 5–10, 2/3 at age 10-13 Black-white 98 96.5 White-white 83 97.2 Tizard et al. (1972) Tested at age 2–5, results for the only test out of four finding significant differences Black-black 15 105.7 Black-white 15 109.8 White-white 25 101.3
Rushton and Jensen point to 3 adoption studies of East Asian children which in all cases scored significantly above the national averages in the US and Belgium although none had control groups from other races.
Racial admixture studies
Many people have an ancestry from different geographic regions. For example, African Americans typically have ancestors from both Africa and Europe, with, on average, 20% of their genome inherited from European ancestors. If racial IQ gaps have a partially genetic basis, blacks with a higher degree of European 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.
John C. Loehlin describes several studies that have examined the relationship between ancestry levels and IQ. A 1936 study by Witty and Jenkins examined ancestry among African-Americans with very high IQ, and found that they did not have a higher degree of European ancestry than unselected African-Americans. This study based its estimates of ancestry on self-reporting by the subjects in interviews. Mackenzie (1984) has criticized this study for comparing its sample group to a group that was not representative of the national average. More recent studies have compared IQ to ancestry estimates based on skin color, and found a correlation of 0.1-0.15 between lighter skin color and higher IQ. Nisbett considers this correlation too low to be significant, while Arthur Jensen has argued that because skin color is a highly imprecise measure of ancestry, no correlation higher than 0.2 could be expected if the hereditarian hypothesis is correct. According to Loehlin, other studies comparing the IQs of mixed-race children to those two black parents or two white parents have produced similarly inconclusive results.
The frequency of different blood types vary with ancestry. Correlations between degree of European blood types 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. T. Edward Reed, an expert on blood groups, argues that the methodology used in these studies would have been unable to detect any difference, regardless of whether or not the hereditarian hypothesis is correct.
Some authors have suggested that new studies of the relationship ancestry and IQ should be performed using modern DNA-based ancestry estimations, which would provide a more reliable measure of ancestry than is possible based on skin tone or blood groups. Such experiments have never been published, although the requirements for such a study have been discussed in the academic literature.
In a study of the head growth of 633 term-born children, it was shown that prenatal growth and growth during infancy were associated with subsequent IQ. The study's conclusion was that the brain volume a child achieves by the age of 1 year helps determine later intelligence. Within human populations, Magnetic Resonance Imaging (MRI) studies conducted to determine whether there is a relationship between brain size and a number of cognitive measures have "yielded inconsistent findings with correlations from 0 to 0.6, with most correlations 0.3 or 0.4.". For postmortem studies the correlation is about 0.15. A study on twins showed that frontal gray matter volume also was correlated with g and highly heritable. A related MRI 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.
Several studies have reported that races overlap significantly in brain size but differ in average brain size. The magnitude of these differences varies depending on the particular study and the methods used. In general, these studies have reported that East Asians have on average a larger brain size than whites who have on average a larger brain size than blacks. Other researchers have also found variation in average brain size between human groups, but concluded that this variation should be viewed as being based on biogeographic ancestry and independently of "race".
Proponents of both the environmental and hereditarian perspective believe that this variation is relevant to the racial IQ gap, although they disagree as to its cause. Ulric Neisser, The Chair of the APA's Task Force on intelligence, acknowledges the brain size difference, but points out that brain size is known to be influenced by environmental factors such as nutrition, and that this fact has been demonstrated experimentally in rats. He thus believes that data on brain size cannot be considered strong evidence for a genetic component to the IQ difference. Rushton and Jensen disagree, citing several studies of malnourished East Asians showing that they have larger brains than whites, and studies demonstrating the brain size difference at birth and prenatally just a few weeks after conception. They argue that correcting for brain size between blacks and whites does not eliminate the IQ gap, which means that factors other than brain size contribute to intelligence differences; however, matching blacks and whites for IQ eliminates the difference in average brain size, suggesting that brain size is still a contributing factor.
According to an analysis by Jelte Wicherts, the material cited by Rushton is in the form of external or postmortem cranial measurements with none using more modern MRI techniques. Such material only have a correlation of 0.2 with IQ. Furthermore, even using Rushton's data the black-white difference in brain size are small (0.6 SD units) compared to the IQ differences. Wicherts also writes that there is no reason to suppose that brain size is environmentally insensitive. Even if race differences in brain size are assumed to be entirely genetic in origin, they still leave 91–95% of racial IQ gap unaccounted for, the lower number assuming that MRI would show the same results as Rushton's data collection. Rushton argues that a 1994 MRI study in the UK on Africans and West Indians compared to Caucasians support his view although he acknowledges that the study provided no details on how, or if, the samples had been matched for age, sex, or body size.
Mental chronometry is an area of research which measures the elapsed time between the presentation of a sensory stimulus and the subsequent behavioral response by the participant. This time is known as reaction time (RT), and is considered a measure of the speed and efficiency with which the brain processes information. Scores on most types of RT tasks tend to 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 of g. The strength of the correlation with IQ varies from one RT test to another, but Hans Eysenck gives 0.40 as a typical correlation under favorable conditions. 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. Nisbett argues that some studies have found correlations closer to 0.2, and that the correlation is not always found.
Several studies have found differences between races in average reaction times. These studies have generally found that reaction times among black, Asian and white children follow the same pattern as IQ scores. A 2007 study found Statistical mediation between reaction time tests and a traditional IQ test, in that controlling for race differences on the RT tasks resulted in the race difference on the IQ test no longer being significant. Jensen has argued that since the black-white difference in RT tasks has a rank-order correlation with the tasks' g-loadings, this is evidence for the validity of Spearman's hypothesis.
Rushton and Jensen have argued that reaction time is independent of culture and that the existence of race differences in average reaction time is evidence that the cause of racial IQ gaps is partially genetic instead of entirely cultural. Responding to this argument in Intelligence and How to Get It, Nisbett has pointed to a 1993 study by Jensen and Whang in which a group of Chinese Americans had longer reaction times than a group of European Americans, despite having higher IQs. Nisbett also mentions a pair of studies by Flynn and Deary suggesting that movement time (the measure of how long it takes a person to move a finger after making the decision to do so) correlates with IQ just as strongly as reaction time does, and that average movement time is faster for blacks than for whites. In a 2010 review of Nisbett's book, Rushton and Jensen argue that Nisbett has underestimated the strength of reaction time's correlation with IQ, and the degree to which differences in reaction time are due to g.
Significance of group differences
A significant part of the debate following The Bell Curve concerned the significance of the group differences in IQ for the future achievements of the groups in the US. The book argued for the importance of IQ for factors such as future educational achievements, employment, income, divorce rates, and crime. The book's critics argued that it overstated the importance of IQ.
Earl Hunt discusses the relationship between cognitive ability, job performance and income in his 2011 book Human Intelligence. According to Hunt, cognitive test scores have a predictive validity of 0.3 to 0.6 for job performance, and also influence income. Hunt states that racial gaps exist in job performance and income, and that the gaps in job performance are about what would be predicted based on the correlation between cognitive test scores and performance. However, he also mentions that according to a 1997 study, the variation in income associated with test scores is less than the authors of The Bell Curve claimed it was.
Lynn in the 2008 book The Global Bell Curve, aiming to build on The Bell Curve, argues that group differences in IQ are an important explanation for different achievements for different groups worldwide. One example being that when East Asians arrived in Latin America as indentured plantation workers as replacement for slaves, their descendents quickly became elite groups. Lynn argues that also environmental explanations are important, as well as non-IQ genetic group differences, such as average genetic group differences on personality variables.
The mainstream explanations of social scientists and historians for international inequality, including the North-South divide, is as the result of historical and political factors such as the heritage of colonialism including conflicts and violence, discrimination, economic exploitation by developed nations, and cultural factors such as work ethics, corruption, and human capital theories where groups receive different education.
Jensen and Rushton argue that the existence of biological group differences does not rule out, but removes part of the justification for, policies such as affirmative action or redistribution in favor of the less successful group. They also argue for the importance of teaching not to stereotype from average differences, because of the significant overlap of people with varying intelligence between different races. Rushton, writing on the North African/South Asian average IQ, has argued that "Immigration policy too, must be adjusted. Mass immigration from the region is very likely to lower the average IQ of the receiving Western countries, and consequently be dysfunctional."
The environmentalist viewpoint argues for increased interventions in order to close the gaps. Nisbett argues that schools can be greatly improved and that many interventions at every age level are possible. Flynn, arguing for the importance of the black subculture, write that "America will have to address all the aspects of black experience that are disadvantageous, beginning with the regeneration of inner city neighbourhoods and their schools. A resident police office and teacher in every apartment block would be a good start." Researchers from both sides agree that interventions should be better researched.
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 such as meningitis, parasites, and cerebral malaria, in utero drug and alcohol exposure, newborn asphyxia, low birth weight, head injuries, and endocrine disorders.
Gregory Stock argues that modern biotechnology will allow parents to select desired genes in their children meaning "current debates about whether some of the differences among ethnic and racial groups are cultural or biological will soon become irrelevant, given the coming [malleability of biological traits]" He writes that such technology may allow parents to select intelligence or racially identifying traits (such as human skin color; see gene SLC24A5).
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