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Race and intelligence

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Many studies of cognitive ability have shown that racial groups differ in measured intelligence. These results have sparked public debates concerning not only the reliability of the studies and the motives of their authors, but the validity and fairness of intelligence tests in general and extent to which measured intelligence is determined by biological and social factors.

Racial distinctions are most often based on skin colour, facial features, ancestry, genetics, and national origin. Some scientists argue that common racial classifications are not meaningful, often on the basis of research claiming that more genetic variation exists within such races than between them. See the article Race for further discussion.

Intelligence is most commonly measured by IQ tests. Some question the validity of all IQ testing. See the articles Intelligence (trait) and IQ for further discussion.

IQ gap among races

The modern controversy surrounding intelligence and race focuses on the results of IQ studies conducted during the second half of the 20th century mainly in the United States and some other industrialized nations.

Many compilations of average IQ by country place East Asian countries at the top of such lists. Some argue that this is in part attributed to some IQ tests' inherent bias towards testing spatial reasoning. They argue that logographic languages like Chinese or Japanese develop spatial reasoning better than Roman languages prevalent in Europe and America. The same reasoning has been used to explain why students from Asia-Pacific countries (eg Singapore, South Korea) tend to score better than average in tests of mathematics. Some argue that the East Asian advantage can also be explained by more rigorous education programs. Opponents of these interpretations point out that people of East Asian descent who are born and educated in the United States and primarily speak English have a higher mean IQ score than their white peers.

Arthur Jensen was one of the first researchers to propose that the IQ gap between blacks and whites is best explained by a hypothesis that attributes at least some of the cause to genetic factors. His 1969 paper in "Harvard Education Review" also stated that compensatory education was not very effective and that "genetic differences were more important than cultural or socioeconomic differences in explaining individual differences in IQ within the white population."

In 1974, an English biologist named John Randal Baker presented a lengthy argument in favor of innate racial differences in intelligence in a volume entitled "Race" (Oxford University Press, 1974), in which he claimed there had been a systematic, politically motivated suppression of classical biological anthropology outside Germany since the 1930s, and went on to attempt to demonstrate a relation among five historical civilizations (Sumerian, Egyptian, Indus valley, Helladic-Minoan and Sinic) and the supposed biological dispositions of their creators.

The IQ gaps vary greatly between different countries. Blacks in Africa score much lower. The black-white gap is much smaller in the UK than in the US. [1]

IQ gap in the US

In almost every testing situation where the tests were administered and evaluated correctly, a difference of approximately one standard deviation was observed in the US between the mean IQ score of blacks and whites. In the United States, the mean IQ score among blacks is approximately 85 and the mean IQ score among whites is approximately 100; the mean IQ score of Hispanics is usually reported to be between the mean black and white scores. The mean score for people of East Asian and Jewish descent is usually higher than the mean score of whites, but the extent of that difference is not precisely known. However, several studies place the median IQ of Ashkenazi Jews (who make up the overwhelming majority of American Jews) at approximately one standard deviation above the mean for other whites. In a normal distribution, only about 16% of the population is at least one standard deviation above the mean. Similar gaps are seen in other tests of cognitive ability or aptitude, including the SAT. Likewise, the gap is reflected by gaps in the academic, economic, and social factors correlated with IQ. The practical importance of intelligence makes the source and meaning of the IQ gap a pressing social concern.

There is some evidence that the US black-white gap in reading and math scores is starting to converge.[2] Reading and math scores are correlated with, but not substitutable for, IQ, so these findings alone may not indicate convergence in the IQ gap. The size of the black-white gap on a cognitive test correlates with the test's g-loading (roughly, a measure of IQ test quality; see Intelligence (trait) and g theory) (Jensen, 1998). The less g-loaded the test, the smaller the measured gap, so it is crucial that the IQ gap be measured by a validated test of cognitive ability rather than a correlate. Still, the correlation of IQ with grades is highest in elementary school (0.6 to 0.7; Jensen 1998), so convergence in scores may, in fact, indicate that the IQ gap is narrowing.

Reaction time

In 1991, Richard Lynn tested 1,468 9-year old children consisting of Blacks from South Africa, East Asians from Hong Kong and Japan, and Whites from Britain and Ireland. The content of the tests involved flipping a switch after one or more lights came on. Lynn found that the decision times (the time taken to make a decision about what to do) had a low correlation with IQ data on Raven Progressive Matrices tests also administered during the same study, although movement times (the time taken to execute the decision) did not. He found that the Asians had the fastest decision times, followed by the Whites, and then by the Blacks. He also determined that the Black children had movement times that were substantially faster than those of Whites and Asians on certain tests. [3] [4]

Brain size

See also: Craniometry, brain size and intelligence

Group differences in average IQ tend to mirror group differences in brain size. Numerous historical and modern studies, using skull and head measurements, weighing of brains at autopsy, and more recently, magnetic resonance imaging report racial differences. These studies are usually accompanied by a great deal of controversy.

In his 1839 Crania Americana, anthropologist Samuel George Morton reported that the mean cranial capacity of the skulls of Whites was 87 in³, while that of Blacks was 78 in³. Based on the measurement of 144 skulls of Native Americans, he reported an a figure of 82in³.

In his controversial 1995 work Race, Evolution, and Behavior, J. Philippe Rushton reported an average endocranial volume of 1,415 cm³ for "Orientals [sic]", 1,362 for Whites, and 1,268 for Blacks. When adjusted for average body size, the differences become more pronounced.

Modern studies using MRI imaging show that brain size correlates with IQ by a factor of roughly .35 to .40. In 1991, Willerman et al used data from 40 white American unversity students and reported a correlation coefficient of .35. Other studies done on samples of Caucasians show similar results, with Andreasen et al (1993) determining a correlation of .38, while Raz et al (1993) obtained a figure of .43 and Wickett et al (1994) obtained a figure of .40. A study on twins (Thompson et al., 2001) showed that frontal gray matter volume was correlated with g and highly heritable. A related study has reported that the correlation between brain size (reported to have a heritability of 0.85) and g is 0.4, and that correlation is mediated entirely by genetic factors (Posthuma et al 2002).

Cranial vault size and shape have changed greatly during the last 150 years in the US. These changes must occur by early childhood because of the early development of the vault. One explanation is the Flynn effect. [5][6][7][8]

Interpretations

Test bias

It has been suggested that IQ tests may be biased against minorities, and that this accounts for part or all of the IQ gap. Some claim that there is no evidence for test bias. IQ tests are equally good predictors of IQ-related factors (such as school performance) for blacks and whites. The performance differences persist in tests and testing situations in which care has been taken to eliminate bias. It has also been suggested that IQ tests are formulated in such as way as to disadvantage minorities. Controlled studies have shown that test construction does not substantially contribute to the IQ gap.

The lack of test bias is widely accepted in the research community. From the American Psychological Association's summary of their 1996 task force report, "Intelligence: Knowns and Unknowns": "The differential between the mean intelligence test scores of Blacks and Whites does not result from any obvious biases in test construction and administration, nor does it simply reflect differences in socio-economic status." From The Wall Street Journal: Mainstream Science on Intelligence (PDF): "Intelligence tests are not culturally biased against American blacks or other native-born, English-speaking people in the U.S. Rather, IQ scores predict equally accurately for all such Americans, regardless of race or social class."

Since the U.S. Supreme Court outlawed employee selection, including testing, which is "fair in form, but discriminatory in operation" (Griggs vs. Duke Power Co., 1971; see this page on disparate impact), American companies have had a strong incentive to construct valid tests which do not produce an IQ gap between enthnic groups, called "selection bias" in employment. Despite this incentive, these efforts have generally failed. In at least one case, regarding a police selection test in Nassau County, NY, a scandal ensued when tests which showed no selection bias were found to have validity measures that were artificially inflated by the test-makers (Gottfredson, 2003, pp. 24-26).

Many anthropologists have argued that intelligence is a cultural category; some cultures emphasize speed and competition more than others, for example. Tests based on word skills cannot accurately measure learning ability. And most IQ tests ask people to solve problems most often encountered in middle class settings. Low IQ scores are often the result of the subject speaking a different language or dialect than the test questions, or being given the test by someone from another ethnic group, or simply being tired, malnourished, or ill. IQ tests do not measure mental ability, they do measure enculturation. During WWI African-Americans from the north tested higher than those from the south. This is simply because African-Americans in the north had received more formal education (see Race: Science and Politics, written by Ruth Benedict in 1940). Thousands of ethnographic studies indicate that innate capacities for cultural evolution are equal among all human populations.

See the American Anthropological Association's Statement on Race and Intelligence [[9]]

Socio-economic factors

IQ is correlated with economic factors. Blacks and Hispanics suffer poorer economic conditions than whites. It has been suggested that the effects of poverty are responsible for some or all of the IQ gap. However, economics cannot be the whole explanation. First, the gaps are slightly smaller but still persist for individuals from the same socioeconomic backgrounds. Second, except for extreme environments, factors associated with poverty account for little of the variance in IQ scores. (However, some studies claim to prove that the socioeconomic environment completely "overrides" the race factor, at least temporarily, in adopted black children -e.g. Capron and Duyme, 1989) Third, many scientists believe that IQ determines income, and not the other way around (Murray, 1998).

Other researchers have come across what they see as additional reasons for the IQ gap. The paper Poverty and Brain Development in Early Childhood holds that there is a large amount of neural damage in many American black and Hispanic children due to inadequate nutrition, substance abuse of the children's parents, a high incidence of maternal depression, exposure to environmental toxins, psychological trauma, and the neural effects of physical abuse.

Researchers have found that many American blacks and Hispanics are not given sufficient opportunity to learn language and thinking skills during the first three years of life, possibly due to economic status. The first three years are especially critical years for neural development of the brain, and previous studies have shown that when human children were deprived of most or all language skills at an early age, they never developed the ability to master language at a later age; if they only mastered a small amount of language and thinking skills at a young age, then they could only make small improvements in later years. A recent study has shown that many American blacks and Hispanics are raised in homes where their parents speak relatively few sentences, and the sentences usually show only simple grammar. As a result, their children never hear millions of words during the time when their brains are developing linguistic skills. Without this linguistic input during their developing years, many are observed to quickly fall behind, and they can never catch up. Children in poorer welfare families, which includes a higher percentage of many minority populations, apparently hear up to 30 million fewer words by age three than children in higher income, usually white, families. (Source: The Early Catastrophe: The 30 Million Word Gap by Age 3)

The recent paper Socioeconomic statues modifies heritability of IQ in young children finds that the role of the environment is more important in poorer families. "The models suggest that in impoverished families, 60% of the variance in IQ is accounted for by the shared environment, and the contribution of genes is close to zero; in affluent families, the result is almost exactly the reverse."

Minority culture

It has been suggested that black culture disfavors academic achievement and fosters an environment that is damaging to IQ (Boykin, 1994). Likewise, it is argued that a persistence of racism reinforces this negative effect. John Ogbu (1978, 1994) has developed a hypothesis that the condition of being a "castle-like minority" affects motivation and achievement, depressing IQ. Even proponents of the view that the IQ gap is caused partly by genetic differences, such as Arthur Jensen, recognize that non-genetic factors are likely invovled. Indeed, one author has compiled a list of over one hundred possible causing of the black-white IQ gap [10]. However, direct evidence associating a certain aspect of minority culture to the IQ gap has not been found.

One environmental source of the IQ gap which has been suggested is poor motivation among low scorers. This hypothesis is seemingly discredited by findings promoted by the researcher Arthur Jensen using elementary cognitive tasks to measure intelligence. For example, one such test asks the subject to lift a finger from a depressed button to strike a light when it flashes. When more than one light is offered as a target the task involves a decision of which to hit (i.e. the one which is lit). These tests measure both reaction time (from when the bulb illuminates to when the subject lifts their finger) and movement time (from when the subject lifts their finger to when the subject reaches the bulb). While movement time measurements show no difference (or an advantage to blacks), reaction time measurements negatively correlate with IQ scores and show the same performance gaps between those two races. Jensen argues that it is difficult to imagine that people could be motivated during one part of each segment of the test but not motivated during the other.

Cultural explanations for the IQ deficit among blacks and Hispanics compared to whites and Asian minorities are complemented – and sometimes challenged – by the observation that Asian minorities score well on IQ tests and on average enjoy greater economic success than other minorities. Along these lines, East Asians are sometimes referred to as "model minorities". Likewise, Jewish populations have suffered past discrimination and persecution, but do not exhibit an IQ deficit.

Black mothers are known to breastfeed infants less and for a shorter time than white mothers. Studies have shown IQ gains lasting into adulthood with increased duration of breastfeeding.

The Flynn effect

The Flynn effect is large a documented worldwide increases in IQ scores for at least several decades. Attempted explanations have included improved nutrition, a trend towards smaller families, better education, greater environmental complexity, and heterosis.

Some think that there are no genetic differences and that the Flynn effect will eliminate differences in IQ test scores in the future. They argue that the Flynn effect started and will end sooner for the more affluent parts of society and that blacks will or have started to close the gap.

However, comparing the Flynn effect (IQ differences within races over time) to contemporary IQ differences between races is contested; for example, one report concludes "that the nature of the Flynn effect is qualitatively different from the nature of B-W differences in the United States" (Wicherts et al., 2004). Others note that this is not mentioned in the abstract, refers to "measurement invariance", and is not a statement about the role of genetics in the B-W gap.

Genetics

Part of the gap may well be genetic; there is no a priori reason to believe that every ethnic group or race has precisely the same distribution of genes that affect intelligence; a small amount of random variation early in human evolution may have later crystallized into differences seen today. Also there might have been smaller evolutionary pressure towards greater intelligence in some environments.

The genetic hypothesis is often ignored or disregarded in primary research on group differences. It has been well-studied by researchers doing meta-analyses that combine multiple sources of primary materials.

Jensen has concluded that the IQ gap is at least partly genetic. Jensen and colleagues reach this conclusion based on an evaluation of some of the above evidence. While accepting that some fraction of the supporting evidence may be false, they argue that the partly-genetic hypothesis is favored over the culture-only hypothesis by a preponderance of the evidence. In this view, average intelligence differences among races are like average skin color differences: a product of different allelic frequencies within each population. Others are critical of Jensen's methods and evaluation.

Spearman's hypothesis

Intelligence as measured by g, a general factor of cognitive ability, and its various biological correlates (e.g., the volume of gray matter in the frontal cortex) are claimed to be partly genetically determined (see g theory). g has the highest measured heritability of any cognitive ability factor. The degree to which black and white cognitive test scores differ is linearly correlated with the test's degree of g-loading, with a correlation of 0.6 (Jensen, 1998); a phenomena called Spearman's hypothesis. This study combined scores on 149 psychometric tests obtained from 15 independent samples totaling 43,892 blacks and 243,009 whites (Jensen, 1998). However, reanalyzing the data from several previous studies that used the statistical method invented by Jensen (the method of correlated vectors) with a more recent and improved method (multigroup confirmatory factor analysis) failed to find evidence for Spearman's hypothesis, but also failed to refute it. [11]. This leaves the validity of Spearman's hypothesis, considered a central justification for the genetic explanation, an unresolved question.

Other evidence

Other evidence that is interpreted as indirect support for the hypothesis that the Black-White-Asian IQ gap is party due to genetic differences, rather than culture alone, includes:

  • world-wide Black-White-Asian differences in IQ, reaction time, and brain size
  • correlations between an IQ subtest's g-loading, heritability, and the magnitude of the Black-White-Asian score gap for that subtest
  • rising heritability of IQ with age, and decreasing shared-family effects (e.g., socioeconomic factors) on IQ after adolescence
  • a few studies suggest that IQ heritability and gene-environment interactions within races are the same for Blacks and Whites
  • finding that when Black and White children are matched for IQ, their siblings tend to have IQs that regress towards different means (85 for Blacks and 100 for Whites)
  • American Blacks have a lower average IQ than Hispanic and Native American groups, which are more socioeconomically deprived
  • East Asians outscore Whites worldwide, even when they are more socioeconomically deprived
  • at least one study found that even malnourished East Asian children, when adopted by Whites, eventually develop a higher average IQ than whites.

Critics note that there are arguments against all of the above. For example, the only nation-wide tests have been done in a few developed countries. See the criticism against IQ and the Wealth of Nations. Socioeconomically deprived East Asians do not always outscore whites, for example Chinese children malnourished due to the cultural revolution have low IQ in one study. That blacks are less socioeconomically deprived than Hispanics or Native Americans is controversial. g-loading and statistical tests for heritablity are criticized by other researchers. Many studies do not control for SES which has been shown to be relatively more important in the poorest families. Parents adopting children are generally wealthier than the average parent, may be better parents due to screening before adoption, and often choose a healthy child to adopt. One estimate is that the average IQ in the U.S. was below 75 before the Flynn effect started and it seems likely that the effect started earlier for whites.

Other interpretations

The two most widely-known works concerning race and intelligence are The Mismeasure of Man by Stephen Jay Gould, originally published in 1981, and The Bell Curve by Richard Herrnstein and Charles Murray, published in 1994. Media controversy surrounding The Bell Curve motivated Gould to revise and expand The Mismeasure of Man to respond to arguments from The Bell Curve, publishing the book's second edition in 1996. Many current researchers think that both books are outdated due to new research.

A recent paper in the Psychological Review, "Heritability Estimates Versus Large Environmental Effects: The IQ Paradox Resolved" by William T. Dickens of The Brookings Institution and James R. Flynn presents a mechanism by which environmental effects on IQ may be magnified by feedback effects. This work may provide a resolution of the contradiction between the viewpoint of The Bell Curve's authors and the 'nurture' effects observed by others.

Some cite research that they believe indicates that discriminated or lower-status minorities do tend to have lower IQ, without apparent genetic differences. Like blacks and Hispanics in the US, minorities in some societies show achievement gaps (such as the Maori in New Zealand, aboriginals in Australia, scheduled castes ("untouchables") in India, non-European Jews in Israel, and the Burakumin in Japan). The most prominent finding cited is that Northern Irish Catholics used to score about 15 points lower than Protestants. Similarly, Irish, Italian and Polish immigrants in the USA are reported to have all scored about 80 pts in the beginning of the 19th century, but now tend to reach 100. The same is true of persons from rural versus urban areas in general (see e.g. this article by conservative columnist and economist Thomas Sowell and this page on European and Greek IQ. More arguments of the kind are to be found here).

Comparative economic analyses are sometimes presented as evidence that environmental explanations of the IQ gap are incomplete. IQ and the Wealth of Nations, a book by Richard Lynn and Tatu Vanhanen, is the most recent prominent example of an economic analysis of the IQ and race issue. The book, which was not peer-reviewed, is sharply criticzed in the peer-reviewed paper The Impact of National IQ on Income and Growth [12].

Summary

The source of and meaning of the IQ gap is not known. Many theories have been proposed, but none are generally accepted. Most of the theories are supported by only indirect evidence. The cause may be environmental. Many attribute the difference primarily to cultural factors that disadvantage caste-like minorities. Many researchers in the field of intelligence suggest that the difference is partially genetic and partially environmental. Other observers insist that the differences may be entirely environmental. The cause of the IQ gap may be identical to the cause of IQ differences between all individuals, or it may represent a race-specific effect. This is an active area of research.

Biological differences in brain volume and reaction time, which show low to moderate correlations with IQ, are not by themselves evidence for genetic differences. Even if the IQ gap does indicate differences in intelligence, this may be due to environmental differences in factors such as nutrition during pregnancy or early childhood which may produce biological differences with no genetic component. In general, simple correlations cannot decide the role of genetics. Advanced statistical methods are instead used with hotly debated results.

Because the cause of the IQ gap is ultimately an empirical question, it should be possible to resolve this question in the future. Irrefutable direct evidence is currently lacking and may continue to be so until intelligence is mapped to specific genes.

Most research has been done in the US and a few other developed nations. That research cannot directly be generalized to the world as a whole. Blacks in the US are not random sample from Africa and environmental conditions differ between nations. IQ tests done in developing countries are likely affected by impoverished environmental conditions that are common in the developing world, such as nutritional deficiencies (e.g., iodine deficiency is known to affect intelligence) and the impact of diseases (e.g., HIV, anemia or chronic parasites that may affect IQ test scores).

See also

References

  • Gottfredson, L.S. (2003). Suppressing intelligence: hurting those we intend to help. Unpublished. PDF
  • Jensen, A.R. (1998). The g Factor. Praeger, Connecticut, USA.
  • Murray, Charles (1998). Income Inequality and IQ, AEI Press PDF
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