Race and intelligence (Explanations)
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| Race and intelligence |
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| Public controversy |
| Accusations of bias |
| Media portrayal |
| Utility of research |
| Average test score gaps among races |
| Explanations |
| References |
According to Linda Gottfredson, a controversial researcher at the University of Delaware IQ differences among individuals of the same race reflect (1) real, (2) functionally/socially significant, and (3) substantially genetic differences in the general intelligence factor (Gottfredson 2005b, p. 311). Also, again according to Dr Gottfredson, average IQ differences among races reflect (1) real and (2) significant differences in the same g factor (Gottfredson 2005b, p. 311). However, it is a matter of debate whether IQ differences among races in a given country are primarily environmental, primarily genetic or simply an artifact of an inaccurate use of social racial identification as a proxy for genetics.[1]
A recent review summarizing the arguments for a "primarily-genetic" explanation can be found here.[2] A critique can be found here.[3]
Contents |
[edit] 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 U.S. Blacks and Whites.[4] The performance differences persist in tests and testing situations in which care has been taken to eliminate bias.[4] It has also been suggested that IQ tests are formulated in such a way as to disadvantage minorities.[4] Controlled studies have shown that test construction does not substantially contribute to the IQ gap.[4] Studies have shown that the race of the test administrator does not have an effect on the U.S. Black-White gap (Caldwell and Knight 1970).
The lack of test bias due to test construction or methodology is widely accepted in the research community. From the American Psychological Association's summary of their 1996 task force report, "Intelligence: Knowns and Unknowns": "The differential between the mean intelligence test scores of Blacks and Whites does not result from any obvious biases in test construction and administration, nor does it simply reflect differences in socio-economic status" (Neisser et al. 1996). From The Wall Street Journal: Mainstream Science on Intelligence (PDF): "Intelligence tests are not culturally biased against American Blacks or other native-born, English-speaking people in the U.S. Rather, IQ scores predict equally accurately for all such Americans, regardless of race or social class."
This does not mean that anyone is claiming that there is no bias in the tests whatsoever.[citation needed] Somewhat but not directly related to the idea of cultural bias, is the concept of "labeling bias", described by Jencks and Phillips (1998). They insist that there exists a labeling bias in the tests, stating that most psychologists agree that IQ tests measure developed ability rather than innate ability—although the tests supposedly measure innate ability.[5] Their assertion is that non-cultural environmental factors cause gaps measured by the tests, rather than any possible innate difference based on genetics, and to use these tests as a measure of innate difference is misleading and improper. In a PBS interview, Jencks states, "If we change the names of the tests, they still measure the same thing but it wouldn't convey this idea that somehow you've gotten the potential of somebody when you measured their IQ. And I think that creates a big bias, because the people who do badly on the tests are labeled as people with low potential in many people's minds and they sometimes even believe that about themselves."
Since the U.S. Supreme Court outlawed employee selection, including testing, which is "fair in form, but discriminatory in operation" (Griggs v. Duke Power Co., 1971; see this page on disparate impact), American companies have had a strong incentive to construct valid tests which do not produce an IQ gap between ethnic groups, called "selection bias" in employment. Despite this incentive, these efforts have generally failed. For example, in one case regarding a police selection test in Nassau County, New York, a scandal ensued when tests which showed no "selection bias" (Black-White score gap) were found to have been denuded of their ability to measure intelligence (Gottfredson 2005a, pp. 24-26 PDF).
While the existence of average IQ test score differences has been a matter of accepted fact for decades, during the 1960s and 1970s a great deal of controversy existed among scholars over the question of whether these score differences reflected real differences in cognitive ability. The critics of testing argued that IQ tests are predominantly measures of cultural variables, and that these variables have nothing to do with intelligence, but they do differ between racial-ethnic and socio-economic groups. If the culture of one group prevents them from developing the skills and abilities that IQ tests measure, then that group is culturally disadvantaged. In contrast, if people from different cultures score differently despite possessing the relevant skills and abilities to the same extent, then the IQ test is culturally biased.
Cultural bias can be distinguished from cultural disadvantage. To do this, a precise definition of bias is required. Bias as mean differences merely begs the question. IQ tests must be standardized against a representative sample of people, and so one suggestion was bias as improper standardization. This has been ruled out in part because re-standardization does not affect the IQ gap. Bias as content could exist if test items presuppose knowledge that is more common in one group. This has been ruled out in part because test item difficulty levels are nearly identical for Blacks and Whites. Arguably the most important condition is bias as differential predictive validity. If test scores predict performance on some other criteria (e.g., school grades) less well for one group than another, then the test shows differential validity. IQ tests have equivalent predictive validity for Blacks and Whites across a range of criteria (Gottfredson 1997a). Other kinds of bias have been proposed, but none have been found. Of these, bias as motivation is the most difficult to resolve because empirical tests are difficult. It is argued that Blacks are less motivated than Whites to perform well on IQ tests, but if equally motivated the IQ score gap would disappear. At least two views exist on the question of motivation. One view is that intelligence is an abstract concept related to potential, and the possibility of motivation affecting IQ scores is a problem. The second and more common view is that intelligence is a behavior, and performance is more relevant than potential. Under this view, the equal predictive validity of IQ for Blacks and Whites implies that IQ tests are right to be sensitive to motivation if motivation affects performance in important life outcomes.
[edit] Motivation
One environmental source of the IQ gap which has been suggested is poor motivation among low scorers. This hypothesis has been disputed by the researcher Arthur Jensen (1998). 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, reaction time measurements negatively correlate with IQ scores and show the same performance gaps between races (Jensen 1993; Jensen and Whang 1994). Jensen argues that it is difficult to imagine that people could be motivated during one part of each segment of the test but not motivated during the other, although no correlation between movement speed and intelligence is claimed. The correlation between IQ and reaction time is low (from .20 to .40).
[edit] 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, in the American Psychological Association report Neisser et al. (1996) argue that economics cannot be the whole explanation. First, see the discussion in "Shared and nonshared environmental effects" below. Second, to the moderate extent that IQ and income are related, it appears that IQ determines income, and not the other way around (Murray 1998). (Note there are many other potential environmental factors beside income.) Third, there are gaps in IQ scores that are slightly smaller but still persist for individuals with similar family income and parental education.
Work by Carneiro et al. (2005) on average Black-Hispanic-White differences in IQ, education, and income casts doubt on conventional explanations of Black-White differences:
Hispanic children start with cognitive and noncognitive deficits similar to those of black children. They also grow up in similarly disadvantaged environments and are likely to attend schools of similar quality. Hispanics complete much less schooling than blacks. Nevertheless, the ability growth by years of schooling is much higher for Hispanics than for blacks. By the time they reach adulthood, Hispanics have significantly higher test scores than do blacks. Conditional on test scores, there is no evidence of an important Hispanic-white wage gap. Our analysis of the Hispanic data illuminates the traditional study of black-white differences and casts doubt on many conventional explanations of these differences because they do not apply to Hispanics, who also suffer from many of the same disadvantages. The failure of the Hispanic-white gap to widen with schooling or age casts doubt on the claim that poor schools and bad neighborhoods are the reasons for the slow growth rate of black test scores.
Researchers have found that many American Blacks and Hispanics are not given sufficient opportunity to learn language and thinking skills during the first three years of life, possibly due to economic status. The first three years are especially critical years for neural development of the brain, and previous studies have shown that when human children were deprived of most or all language skills at an early age, they never developed the ability to master language at a later age; if they only mastered a small amount of language and thinking skills at a young age, then they could only make small improvements in later years. A recent study has shown that many American Blacks and Hispanics are raised in homes where their parents speak relatively few sentences, and the sentences usually show only simple grammar. As a result, their children never hear millions of words during the time when their brains are developing linguistic skills. Without this linguistic input during their developing years, many are observed to quickly fall behind, and they can never catch up. Children in poorer welfare families, which includes a higher percentage of many minority populations, apparently hear up to 30 million fewer words by age three than children in higher income, usually White, families. (Source: The Early Catastrophe: The 30 Million Word Gap by Age 3)
[edit] Cultural explanations
Many anthropologists have argued that intelligence is a cultural category; some cultures emphasize speed and competition more than others, for example. During WWI African-Americans from the north tested higher than those from the south. This could be because African-Americans in the north had received more formal education (see Race: Science and Politics, written by Ruth Benedict in 1940). Thousands of ethnographic studies indicate that innate capacities for cultural evolution are equal among all human populations. The American Anthropological Association has endorsed a statement deriding all studies of race and intelligence .
Speculations about innate differences in intelligence between ethnic groups have occurred throughout history. Aristotle in the 4th century B.C. and Cicero in the 1rst. century B.C. disparaged the intelligence of the northern Europeans of the time, as did the Moors in Iberia in the 11th century. [6]
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[7] has developed a hypothesis that the condition of being a "caste-like minority" affects motivation and achievement, depressing IQ. However, Arthur Jensen has criticized these arguments on the grounds that they cannot explain the higher scores of East Indians and East Asians.[8] Even proponents of the view that the IQ gap is caused partly by genetic differences, such as Arthur Jensen, recognize that non-genetic factors are likely involved. Indeed, one author has compiled a list of over one hundred possible causes of the Black-White IQ gap.[9] These include the following:
- lack of reading material in the home
- poor cultural amenities in the home
- weak structural integrity of the home
- foreign language in the home
- low preschool attendance
- no encyclopedia in the home
- low level of parental education
- little time spent on homework
- low parental educational desires for child
- low parental interest in school work
- negative child self-concept (self-esteem)
- low child interest in school and reading
However, such factors have not been found to have an effect on IQ that lasts to adulthood among members of the same race (see below).
Cultural explanations for the IQ deficit among Blacks and Hispanics compared to Whites and East Asian minorities are complemented – and sometimes challenged – by the observation that East Asian minorities score well on IQ tests and on average enjoy greater economic success than other minorities. Along these lines, East Asians are sometimes referred to as "model minorities". East Asian and Jewish populations have suffered past discrimination and persecution which some argue is evidence against the importance of discrimination for IQ differences.[10] While the severe discrimination against Jews and East Asians have today diminished, many argue that discrimination continue against blacks and that this is impacting the IQ scores of Blacks.
[edit] Language
Some argue that the higher IQ test scores in East Asian nations are in part attributed to some IQ tests' inherent bias towards testing spatial reasoning.[citation needed] They argue that logographic writing systems, like those used by Chinese and Japanese, develop spatial reasoning better than the alphabetic writing systems prevalent in Europe and America, though there are no studies that support this hypothesis. The same reasoning has been used to explain why students from some Asian countries (e.g., Singapore) 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. [citation needed] However, even though few native-born Asian Americans learn to read and write Chinese characters, their performance is above-average on IQ tests.
A direct comparative test between Greek and Chinese students showed no difference in IQ or g, contradicting earlier studies which do not take the finer architecture of mental processing into account. The Chinese did outperform the Greeks in visuo/spatial ability, but this difference was smaller at earlier ages, grew during the first years of schooling and decreased later. The authors suggest that this pattern can be explained as follows: the Chinese students train their visuo/spatial ability during their early school years, as they have to learn many characters of the Chinese writing system. Later in life, the Greek students adopt compensating strategies to deal with visuo/spatial information, and therefore the difference decreases in this realm.[11]
[edit] The Flynn effect
The Flynn effect consists of large documented worldwide increases in IQ scores for at least several decades. Attempted explanations have included improved nutrition, a trend towards smaller families, better education, greater environmental complexity, and heterosis.
The secular, international increase in test scores, commonly called the Flynn effect, is seen by Flynn and others as reason to expect the eventual convergence of average Black and White IQ scores. As demonstrated by Flynn, the average IQ scores in several countries have increased about 3 points per decade during the 20th century, which he and others attribute predominately to environmental causes.[12] This means, given the same test, the mean Black American performance today could be higher than the mean White American performance in 1920, though the gains causing this appear to have occurred predominantly in the lower half of the IQ distribution.[13] If changes in environment can cause such large changes in IQ over time, they argue, then contemporary differences between groups could also be due to an unknown environmental factor. On the supposition that the effect started earlier for Whites, because their social and economical conditions began to improve earlier than did those of Blacks, they anticipate that the IQ gap among races might change in the future or is even now changing. An added complication to this hypothesis is the question of whether the secular IQ gains can be predominately a change in real intelligence. Flynn's face-value answer to this question is "No",[14] and other researchers have found reason to concur.[15] Responding to such concerns, Dickens and Flynn 2001 have proposed a solution which rests on genotype-environment correlation, hypothesizing that small initial differences in environment cause feedback effects which magnify into large IQ differences.[16] Such differences would need to develop before age 3, when the Black-White IQ gap can be first detected.
Comparing the Flynn effect (IQ differences within races over time) to contemporary IQ differences between races is contested; for example, one report concludes "the nature of the Flynn effect is qualitatively different from the nature of black-white differences in the United States," and that "the implications of the Flynn effect for black-white differences appear small" (Wicherts et al. 2004).
A recent theory hypothesizes that fluid cognition (gF') may be separable from general intelligence, and that gF' may be very susceptible to environmental factors, in particular early childhood stress. Some IQ tests, especially those used with children, are poor measures of gF', which means that the effect of the environment on intelligence regarding racial differences, the Flynn effect, early childhood intervention, and life outcomes may have been underestimated in many studies. The article has received numerous peer commentaries for and against.[17]
A recent, newly available, large, and nationally representative data set find only very small (0.06 SD between whites and blacks) racial differences on measures for mental funtion for children aged eight to twelve months. These differences disappear when controlling for a limited set of factors such as differences in SES. "These findings pose a substantial challenge to the simplest, most direct, and most often articulated genetic stories regarding racial differences in mental function." "To the extent that there are any genetically-driven racial differences in intelligence, these gaps must either emerge after the age of one, or operate along dimensions not captured by this early test of mental cognition."[18]
[edit] Nongenetic biological factors
Other researchers have come across what they see as additional reasons for the IQ gap. The paper Poverty and Brain Development in Early Childhood holds that there is a large amount of neural damage in many American Black and Hispanic children due to inadequate nutrition, substance abuse of the children's parents, a high incidence of maternal depression, exposure to environmental toxins, psychological trauma, and the neural effects of physical abuse. Masters (1997) has proposed a "neurotoxity hypothesis" where pre- and post-natal exposure to heavy metal poisons differentially impacts Blacks. Drug abuse during pregnancy (e.g., alcohol and phenobarbital) can negatively affect IQ.
Infant mortality may be an indicator of environmental conditions that are sublethal but damaging to health. The rate of infant mortality in the U.S. Black population is twice that of the White population, which in turn is twice the rate of infant mortality among Asians.[19] The rates of low birth weight (LBW), defined as less than 5.5 pounds, are correlated with infant death. LBW is different than premature birth; LBW can occur in full-term babies. LBW babies are at risk for many developmental, behavioral and cognitive abnormalities, including mental retardation. LBW (and premature birth) affect Blacks at twice the overall rate for the U.S. population.[20] Mother's age is the strongest predictor of LBW, where teenagers are especially susceptible. Most of the Black-White differences in LBW are not account for by other environmental variables such as socioeconomic status, poverty status, mother's age, and education; but differential prenatal care explains some of the gap (Naylor and Myrianthopoulos 1967). Thus, the cause of the Black-White gap in LBW is a mystery. Environmental intervention has strong but short-lasting effects on IQ among LBW babies (Brooks-Gunn et al. 1994). Studies of LBW Black and White babies matched for birth weight and gestational age still find a one standard deviation IQ gap (Montie and Fagan 1998).
A study of LBW babies indicates that breastfeeding can significantly improve their IQ scores tested at 8 years old (Lucas et al. 1996). After controlling for possible confounding factors, an improvement of 8.3 IQ points was found in the breastfed group as compared to the formula fed group. Black mothers are known to breastfeed infants less and for a shorter time than White mothers (Ryan et al. 1996; Leary 1988). Studies have shown IQ gains lasting into adulthood with increased duration of breastfeeding. Several recent studies shows that the intake of certain micronutrients, like those present in breast milk or fish oil, affects IQ scores even in developed nations. Helland et al (2003) have shown larger head size at birth and higher IQ scores at 4 years of age when mothers took fish oil supplements during pregnancy and lactation.[21] Jensen (1998) believes that dietary supplementation is a promising avenue of research for raising Black children's levels of g. Lynn (1990) has proposed a nutritional hypothesis for the Flynn effect.
[edit] 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 primarily genetic hypothesis is often ignored or disregarded in primary research on group differences. It has been studied by researchers doing meta-analyses that combine multiple sources of primary materials, although such meta-analyses have been harshly criticized..
Arthur Jensen and others have concluded that the Black-White IQ gap is primarily genetic. That is, they argue that the same mix of genetic and environment factors that cause IQ differences among individuals or between families of the same race also causes the differences seen between races. In this view, the genetic contribution to average intelligence differences among races are like average skin color differences: a product of different allelic frequencies within each population. Others are critical of Jensen's methods and evaluation (Sternberg 2005; Suzuki and Aronson 2005; Nisbett 2005).
The results of most (indirect) analyses used to test the genetic hypothesis do not logically contradict a primarily environmental explanation of the lower IQ of Blacks. That is, a plausible (but some argue ad hoc) environmental explanation for the lower mean IQ in Blacks can be offered in most cases.
[edit] Shared and nonshared environmental effects
- see also IQ: genetics vs environment
The heritability of intelligence within groups is high. It is widely recognized that within-group heritability does not in itself indicate that between-group differences are genetic in origin, although it is likely a necessary condition. Different kinds of evidence are needed to address the question of between-group heritability. As Herrnstein and Murray explain in The Bell Curve:
As we discussed in Chapter 4, scholars accept that IQ is substantially heritable, somewhere between 40 and 80 percent, meaning that much of the observed variation in IQ is genetic. And yet this tells us nothing for sure about the origin of the differences between races in measured intelligence. This point is so basic, and so commonly misunderstood, that it deserves emphasis: That a trait is genetically transmitted in individuals does not mean that group differences in that trait are also genetic in origin. Anyone who doubts this assertion may take two handfuls of genetically identical seed corn and plant one handful in Iowa, the other in the Mojave Desert, and let nature (i.e., the environment) take its course. The seeds will grow in Iowa, not in the Mojave, and the result will have nothing to do with genetic differences. (Herrnstein and Murray 1994, p. 298.)
In most studies, measured heritabilities for intelligence are the same for Blacks as for Whites. A review by Loehlin et al. 1975 found some evidence suggesting lower heritability in Blacks than Whites (e.g., Scarr-Salapatek 1971), but a larger body of evidence suggested equal heritabilities for both races. An analysis of the Georgia Twin Study by Osborne 1980 found equal heritabilities for both Blacks and Whites.
Two kinds of environmental effects can be distinguished: shared and nonshared effects (see nature versus nurture). Twin and adoption studies, used to measure heritability, can also be used to quantify the two types of environmental effects (Plomin et al. 1977). Shared environmental effects are due to factors experienced in common by all children raised in the same family but that differ among families. Examples of shared environmental effects include socio-economic factors, family cultural practices, and parental influences on children. Nonshared effects are unique for each child, and thus differ among families. Examples include chance events such as accidents, illness, and childhood friends. Anything that happens to one sibling and not to the other contributes to nonshared effects.
McGue et al. (1993) found (among a population of people studied in the U.S.) that the nonshared environmental effects on IQ remain approximately constant throughout life. Shared environmental effects in their study remained approximately constant (40% to 30%) from 4 to 20 years of age but then drop to zero in adulthood. Genetic factors increase throughout development (from 40% to 50%) but especially after 20 years of age (from 50% to 80%). Plomin et al. (2001) corroborates these results. Environmental factors usually proposed to explain the Black-White gap are shared effects (e.g. social class, religion, cultural practices, father absence, and parenting styles). Jensen (1997) argues that because these effects account for little variance within a race, they are unlikely to account for the differences among races in developed nations.
However, others studies do support that shared environmental factors in developed nations can affect IQ, including IQ gains lasting into adulthood (Capron and Duyme, 1989).[22] However, many such studies measure IQ in children (those shared effects that have disappeared in studies don't disappear until adulthood) or, some critics claim, do not have the controls needed to differentiate genetic and environmental effects. Others argue that some IQ gains disappear exactly because the interventions cease, continuing interventions like Head Start have showed that the IQ gains then remain.
In a re-analysis of adoption data from Capron and Duyme 1989, Jensen 1998a found that the IQ gains that result from being adopted into high socioeconomic-status homes do not produce gains in g, but only in non-g factors. Jensen also found that the g factor scores of the adopted children reflected the socioeconomic level of their biological parents, not their adopted parents. This is consistent with Jensen's theory that g is the predominant genetic component of IQ scores; see Spearman's hypothesis below from the relationship between g and racial difference in IQ.
The recent paper Socioeconomic status modifies heritability of IQ in young children finds that the role of the environment is more important in poorer families. "The models suggest that in impoverished families, 60% of the variance in IQ is accounted for by the shared environment, and the contribution of genes is close to zero; in affluent families, the result is almost exactly the reverse." This suggests that the role of shared environmental factors may have been underestimated in older studies which often only studied affluent middle class families.
Only shared environmental effects captured in heritability studies disappear in adulthood; more extreme environmental deprivation may likely have a lasting impact on IQ in adults. Heritability only tells us what is the contribution of genes to variation in a trait, not what it could be (Rushton and Jensen 2005). Thus, heritability measures in the U.S. population cannot be extrapolated to populations in developing nations.
[edit] Spearman's hypothesis
Individual differences in the general intelligence factor, g, and its various biological correlates (e.g., the volume of gray matter in the frontal cortex) are partly caused by genetic differences between individuals. g has the highest measured heritability of any cognitive ability factor. Jensen formulated a hypothesis now referred to as Spearman's hypothesis which states that the degree of difference between black and white cognitive test scores will be correlated with the degree to which the test measures g (called the test's g-loading). Spearman's hypothesis has a strong form, which says that all test-score differences can be traced to g, and a weak form, which claims that some but not all differences are due to g.
Jensen found that black-white cognitive test score differences and test g-loadings correlate with a correlation coefficient of 0.6 (Jensen 1998b), and concluded that the weak form of Spearman's hypothesis was thus confirmed. Jensen's study combined scores on 149 psychometric tests obtained from 15 independent samples totaling 43,892 Blacks and 243,009 Whites (Jensen 1998b). Dolan and Hamaker 2001 have reanalyzed the data from several previous studies (Jensen and Reynolds 1982; Naglieri and Jensen 1987) that used the statistical method invented by Jensen (the method of correlated vectors) with a more recent and improved method (multigroup confirmatory factor analysis). "On the basis of the present, as well as other results (Dolan, 2000), we are convinced that the Spearman correlation cannot be used to demonstrate the importance of g in b-w differences with any confidence." and "It is possible that the analysis of all available data sets (perhaps using an appropriate meta-analytic procedure) will demonstrate that a model incorporating the weak version of Spearman's hypothesis provides the best description of the data. However, until this work is undertaken, we cannot accept Spearman's hypothesis as an "empirically established fact"[23] This leaves the validity of Spearman's hypothesis, considered a central justification for the genetic explanation, an unresolved question.
[edit] Gene-environment interactions
Minority-specific effects on intelligence arising from cultural background differences between the races would be expected to affect the correlations between the measures of environmental background variables and outcome measures. Rowe et al. (1994) compared cross-sectional correlation matrices using both independent variables (e.g., home environment, peer characteristics) and developmental outcomes (e.g., achievement, delinquency). Rowe et al. (1995) compared correlations between academic achievement and family environment. They found that the covariance matrix of each group were equal. That is, they failed to find evidence for distortions in the correlations between the background variables and the outcome measures that would suggest a minority-specific developmental factor. Similarly, Carretta (1995), Owen (1992), and Rushton et al. (2000), Rushton et al. (2002), Rushton et al. (2003)) found nearly identical statistical structure on psychometric variables in each group. The factor structure of cognitive ability is nearly identical for Blacks and for Whites; there were no race-specific factors.
Using structural equation modeling Rowe and Cleveland (1996) estimated the genetic architecture for Black and White siblings. They found that the best-fitting model for the source of differences between and within races was the same: both genetic and environmental factors. Jensen 1998b (p. 465) reanalyzed a subset of this data. This analysis found that the Black-White IQ difference was best explained by a model of both genetic and environmental factors, and that the genetic-only and the environmental-only models were inadequate.
Nichols (1972) using differential heritabilities among Blacks and Whites and later Rushton (1989) using inbreeding depression calculated in Japan found that the Black-White gap is least on IQ subtests most affected by the environment, and greatest on subtests that are least affected by the environment. It is difficult to attribute the relationship between inbreeding depression from Japan with the Black-White IQ gap in the U.S. to an environmental (not-genetic) cause.
[edit] Rushton's application of r-K theory
In his controversial 1995 work Race, Evolution and Behavior, J. Philippe Rushton argued that racial differences in IQ, as well as a number of other racial differences, could be explained by r/K selection theory, where one evolutionary strategy favors reproduction potential over other strengths (r-selection) and one favors traits that are highly adaptive in a stable environment (K-selection). Rushton claims that humans are extremely K-selected, and that it was less extreme (there was more r-selection) in the African environment than elsewhere. He posits that the comparatively cold and harsh environment of Europe caused the evolution of those who migrated there slightly more to a K-selected pattern than those who remained in Africa, and the even harsher environment of Northeastern Asia forced the evolution of East Asians to an even higher level of K-selective behavior. This theory has been severely criticized.[24]
Richard Lynn has developed similar theories and argues that the ice age that took place in East Asia from about 28,000 to 12,000 years ago acted as a selection force on East Asians to increase intelligence by requiring the building of shelter, making clothes, and making fires, and selected especially strongly for spatial skills such as those needed to hunt large prey and build the tools necessary to do so. (Lynn 1991). Rushton (1996) has cited the fact that the order in Blacks, Whites, and East Asians appeared is the same as the order of their respective brain sizes as additional evidence. This theory, however, has difficulty explaining why Native Americans, who appeared even later and emigrated from the northernmost parts of Asia, do not currently have high scores on IQ tests. [citation needed] On the other hand, Rushton (1995) argues that lower scores of Native Americans can be attributed to the evolutionary relaxation of cognitive demands due to the more temperate environment and comparative ease with which North American fauna could be hunted. But it can be argued that life along the fertile river plains in China was not particularly harsh.[citation needed] It is also questionable that conditions in deserts are no less harsh but people living there do not currently score high on IQ tests.
The theory is directly contradicted by the only comparative study on IQ scores in different European nations that showed a statistically insignificant association between the average IQ and latitude of various European nations.[25] In contrast, Beals et al. 1984 (p. 309) found a correlation of 0.62 (p=0.00001) between latitude and cranial capacity in samples worldwide and reported that each degree of latitude was associated with an increase of 2.5 cm³ in cranial volume. A more recent study finds this pattern only when including a Siberian population living in extremely cold condition. The explanation may be natural selection for a thermoregulatory capacity in extremely cold environments, resulting in brachycephalization, rather than a selection for intelligence.[26]
Rushton sources, such as s "semi-pornographic book" and the Penthouse magazine, have been dismissed by other researchers, or have been criticized as extremely biased and inadequate reviews of the literature, as misreporting the results, or as simply false.[27] There have also been many other criticisms of the theory[28][29][30][31][32].[33][34] More recent studies contradicts Rushton's claims. A meta-analysis shows that blacks are not more psychopathic,[35] nor do they differ in from whites when testing for the big five personality traits,[36] differences in sex hormones between whites and East Asians are best explained by environmental differences,[37] and the fundamental prediction of the theory that blacks have a higher frequency of twins is incorrect.[38] However, the rate of twin births in the US has doubled since 1971, the time of the study Rushton cited, due to older moms (for which twin births are naturally more common) and fertility treatments,[39] both demographic characteristics that are more common among Whites.[40]
[edit] Other evolutionary explanations for putative genetic differences
There are two mainstream theories of the evolution of contemporary humans. The single-origin hypothesis proposes that modern humans evolved in Africa and later replaced hominids in other parts of the world. The multiregional hypothesis proposes that modern humans evolved to some degree from independent hominid populations. An emerging synthesis theory proposes that the genes of contemporary human are predominantly descended from a recent African origin, but that interbreeding with other hominids may have contributed genes to local populations (Templeton 2002). Eswaran et al. (2005) speculate that "as much as 80% of the nuclear genome is significantly affected by assimilation from archaic humans (i.e., 80% of loci may have some archaic admixture, not that the human genome is 80% archaic)."
Populations within continents are more closely related to one another than to populations on other continents (Mountain and Cavalli-Sforza 1997; Stephens et al. 2001; Rosenberg et al. 2002; Bamshad et al. 2003). Thus, to the extent that racial labels correspond to ancient ancestry, racial groups (especially in the U.S.) are statistically distinguishable on the basis of genetics (Tang et al. 2005).
The Imperial examination system in China and similar systems in other East Asians nations have been proposed as an explanation for the higher average IQ, compared for example with the caste system in India which made if much more difficult for the intelligent but poor to gain SES. Celibacy for priests have been invoked as an explanation for claimed lower IQ in Catholic countries, although this also seems to be contradicted by the equal IQ in northern and southern Europe. The earlier mentioned comparative European IQ study found that there was a larger variation in IQ scores in southern Europe. Possible explanations for the earlier mentioned difference for this include sample selection, larger environmental differences affecting IQ scores between urban and rural areas in southern Europe at the time of the test (1981), and/or that northern Europe became socially stratified later in history, causing less genetic variation in IQ.
Constant persecutions favoring a high IQ have been proposed as an explanation for the higher average Ashkenazi IQ, but other persecuted groups like the Romani do not score highly on IQ tests. Another theory suggests that there was selective breeding for Talmudic scholarship, but this seems unlikely to have been important because there weren't very many professional rabbis. A selective force that only affects a tiny fraction of the population can never be strong enough to cause important evolutionary change in tens of generations. A more plausible, but difficult to evaluate without detailed demographic information, variant of this is that achievement in Talmudic scholarship had high status and that rich families therefore preferred to marry their daughters to males who excelled in this. Yet another explanation, according to a 2005 study,[41] the most likely, is that they mostly worked jobs in which increased IQ strongly favored economic success, in contrast with other populations, who were mostly peasant farmers. (See "Natural History of Ashkenazi Intelligence")
[edit] Comparison of explanations
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The factual accuracy of this article or section is disputed. Please see the relevant discussion on the talk page. |
The possible explanations for observed differences in intelligence between racial groups generally occur along two axes - how valid a proxy race is for most genes that control intelligence, and primarily-genetic/primarily-environmental.
| Race valid proxy | Race invalid proxy | |
| Primarily-genetic |
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| Primarily-environmental |
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[edit] Detailed arguments
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The factual accuracy of this article or section is disputed. Please see the relevant discussion on the talk page. |
The Black-White IQ gap in the U.S. may be explained by a variety of explanations. In order to differentiate between alternatives, additional evidence is needed. The "primarily-genetic" and "primarily-environmental" interpretations offer contrasting points of view on this evidence.[dubious — see talk page] Typically, however, the argument is over the amount of genetic contribution. "Hereditarian" scientists typically assert anywhere from 50% - 80% genetic determinism, whereas "environmental" scientists generally accept 20% or less genetic determinism in intelligence[citation needed].
| Primarily Genetic/Race valid proxy | Primarily Environmental and/or Race invalid proxy |
|---|---|
| Methodology of determining racial gaps | |
| this refers to Rushton's life history matrix — should be discussed below, not here | The poor quality of data cited by racialist-hereditarians is strongly criticized, and all of their citations of persistent patterns are seen as unsupportable once proper controls are added and obviously invalid data is filtered out.[43] |
| Utility of racial categories | |
| Some geneticists argue categories of self-identified race/ethnicity or biogeographic ancestry are both valid and useful.[44] They emphasize the continental origin of major races: “namely, African, Caucasian (Europe and Middle East), Asian, Pacific Islander”. For other groups "a decision to split or lump smaller populations into racial groups will depend on the focus of a research question."[45] They find that these categories correspond with clusters inferred from multilocus genetic data..[46] Moreover, they conclude that this correspondence implies that genetic factors might contribute to unexplained phenotypic variation between groups.[47] In the 1985 survey reported by Leiberman and colleagues, only 16% of biologists reject the concept of race. In response to claims such as "there are no human races," Ernst Mayr, one of the 20th century's leading evolutionary biologists, said "Those who subscribe to this opinion are obviously ignorant of modern biology."[48] Risch and colleagues (2002) argue that "much of this discussion does not derive from an objective scientific perspective."[49] In response to claims that race does not exist, geneticst A.W.F. Edwards quotes Fischer: "that the best causes tend to attract to their support the worst arguments, which seems to be equally true in the intellectual and in the moral sense."[50] | Modern anthropologists use clines as an alternative to "races", with variation occurring gradually across geographic areas, instead of social constructs of "race". "By 1985 anthropology's core concept of "race" had been rejected by 41% of physical anthropologists and 55% of cultural anthropologists [Lieberman 1968; Lieberman, Stevenson, and Reynolds 1989:69]. A similar survey in 1999 found that the concept of race was rejected by 69% of physical anthropologists and 80% of cultural anthropologists (Lieberman and Kirk n.d.)"[43]
"As the 20th century reached its end, a paradox emerged in which, while most anthropologists had come to reject concepts of biological races and racism (Lieberman and Kirk n.d., Lieberman, Stevenson, and Reynolds 1989), a number of psychologists persisted in the “race” idea and the “scientific” racism that had prevailed in the 19th and much of the 20th century (Herrnstein and Murray 1994; Lynn 1977a, b; Rushton 1988b)."[43] "During the last hundred years, the debate over the meaning of race has retained a highly consistent core, despite evolution of the technical details...Each time the technical facade of these racialist arguments is destroyed, the latest jargon and half-truths from the margins of science are used to rebuild them around the same core belief in Black inferiority. No technology—even the awe-inspiring tools now available to DNA science—can overcome the handicap of fundamental conceptual errors. Race is not a concept that emerged from within modern genetics; rather, it was imposed by history, and its meaning is inseparable from that cultural origin."[1] "Race, a quantitative distinction within a species, has no equivalent defining criterion—that is, genetic variability is not restricted to discrete packages (American Anthropological Association [AAA], 1998). This aversion to distinctions without meaning is what has led most geneticists and anthropologists to the conclusion that race in its common usage has no biological basis (AAA, 1998; Darwin, 1871/1981; Gould, 1996; Graves, 2001; Kittles & Weiss, 2003; Lewontin, 2000; Mayr, 1996; Montagu, 1964; Templeton, 1998)."[1] "This point bears restating: To cluster individual members of a species into groups is not the same as creating a natural biological category. One could cluster humans into an infinite number of fractal units based on size (family, clan, deme, continent, etc.) or on a physical trait (height), and the meaning of those groupings would vary in an infinite number of ways."[1] |
| "This assertion is both counter-intuitive and factually incorrect.... If it were true, it would be impossible to create discrete clusters of humans (that end up corresponding to the major races).... Two Caucasians are more similar to each other genetically than a Caucasian and an Asian."[51] | "Genetic data ... show that any two individuals within a particular population are as different genetically as any two people selected from any two populations in the world."[52]
"From the hereditarian perspective, why then would IQ not be expected to vary between, say, Sicilians and Swedes as much as between Europeans and Africans?"[1] |
| IQ differences | |
| Black-White-East Asian differences in culture-fair and reaction-time IQ test scores exist world-wide despite international differences in social, cultural, and economic conditions.[53] Lynn 1987, among others, argues that higher IQ scores among East Asians (living in East and South Asia) than Whites (living in North American and Europe) is seen as a challenge for primarily environmental theories because standards of living in Asia are lower than or equal to those in North America or Europe. For example, average IQ scores are higher in the People's Republic of China (Lynn and Vanhanen 2002) than for African Americans even though per capita GDP (PPP) is lower in China ($5,000 as of 2003) than per capita African American income ($15,583 as of 2003) (DeNavas-Walt et al. 2004). | Assertions of Black-White-East Asian differences are based on invalid "aggregation" of data.[43][dubious — see talk page] The only nationwide IQ tests have been done in a few developed countries, and the few studies in other nations have been severely criticized, see IQ and the Wealth of Nations. editor note: make mention of the Flynn effect on so called "culture-fair" tests as Raven. |
| Sub-Saharan Africans have an average IQ of 70 (Rushton 1996a), supported by data using Raven's Progressive Matrices. Jensen (1998b) discusses his observation among California children that very low IQ Blacks are qualitatively normal in social and motor skills, but perform no better than Whites with equally low IQ on cognitive tasks except those that require rote memorization, where "mentally retarded" Blacks do significantly better than Whites. He speculates that 12.5% of cases of IQ <70 are due to organic defects in Blacks, compared to 50% in Whites, giving the impression that low IQ Whites are more handicapped than low IQ Blacks. | Such findings imply that half of all sub-Saharan Africans are mentally retarded, incapable of carrying out even simple daily tasks. One argument of many against the reliability of the IQ scores in developing nations is that some such countries a majority of the population would be classified by the IQ scores as mentally retarded. For example, Equatorial Guinea is one of the few African nations that actually have a study and is classified as having the lowest average IQ in the world, 59, based on study of 48 persons 10-14 years old. A large proportion of the population should also be classified as moderately (<16%) and severely (<2%) mentally retarded. In the U.S., the moderately mentally retarded require moderate supervision and the severely mentally retarded often have other physical disabilities and may thus require constant supervision, be unable to provide for themselves, be unable to speak long sentences, and, in many cases, be unable to do things like getting dressed without help. |
| Average IQ scores gaps within the U.S. and internationally[54] have been stable since they were first measured in the early and mid 20th century[dubious — see talk page] (Lynn and Vanhanen 2002; see above), despite the Flynn effect. One statistical analysis suggests that the Flynn effect is qualitatively different than the Black-White IQ gap (Wicherts et al. 2004). | Ulric Neisser (1997) has shown significant gains in scores on Raven's Progressive Matrices, suggesting as per the Flynn effect, substantial environmental influences are at work, not genes. One estimate is that the average IQ in the U.S. was below 75 before the Flynn effect started and it seems likely that the effect started earlier and may end sooner for Whites. Some studies show that the IQ gaps is decreasing in the US and even if they are not this may change in the future if the Flynn effect ends first for Whites. Lynn and Vanhanen only have IQ scores from 3 developing nations before 1950, in two of these only 1 study, make any claims of knowing average continental IQ strange indeed. The Wicherts study refers to "measurement invariance", is not a statement about the role of genetics in the B-W gap, and is a relatively minor statement that not mentioned in the abstract. |
| The Black-White IQ gap in the US has remained constant at approximately one standard deviation since it was first measured in the early 1900s despite social and economic change during that time, including the civil rights movement and Brown v. Board of Education.[dubious — see talk page] "A difference [of] at least [12 points] is found in virtually every comparison ever published of reasonable sized [White] and [Black] samples, at every age above 3 years, within every level of education, socioeconomic status, and occupation, in every region of the country, and at every time in history since mental ability tests were invented."[55] Narrowing of the gaps in skill test scores does not indicate changes in g. | flynn 2006 Other studies show that the gap in the US is narrowing. For example, one large recent study found much smaller differences than earlier studies in math and reading skills in young children and found that all of the remaining differences could be explained by a few environmental factors.[56] Moreover, the extent of concrete social and economic change is debatable; for example, Jonathan Kozol, in his 2005 book Shame of the Nation, found that public schools are more racially segregated today than they were in 1969. editor note: make clear the selective qualifications of comparisons avoid data sets that contradict Jensen |
| American Blacks have a lower average IQ than Hispanic and Native American groups, which are more socio-economically deprived. For example, the Inuit, who live in the Arctic, have higher average IQs than North American Blacks (Berry 1966; MacArthur 1968) despite being extremely poor (Vernon 1965; Vernon 1979). | That Blacks are less socioeconomically deprived than Hispanics or Native Americans in the US is controversial.[citation needed] The Inuit cannot be directly compared to the US population, for example they have substantially different nutrition from eating large amounts of fish.[citation needed] |
| g factor | |
| "The g-based factor hierarchy is the most widely accepted current view of the structure of abilities"[4] Correlations between an IQ subtest's g-loading, and the magnitude of the Black-White-East Asian score gap for that subtest (Peoples et al. 1995; Jensen 1993 pp. 47-8; Rushton 1995 pp. 138-9). For example, the Black-White gap is greater on backward digits span (a test where subjects repeat digits in the reverse order that they are given, and the more g-loaded test) than forward digits span (a test where subjects repeat digits in the same order that they are given, and the less g-loaded test). As predicted by Spearman's hypothesis, the B-W gap is largest on the most g-loaded tests. Narrowing of the B-W gap has been seen mostly on less g-loaded tests, such as literacy tests.[57] Arthur Jensen argues that there is no independent evidence that the environmental explanations commonly given for the Black-White gap (for example, "past history of slavery", discrimination, "caste status", "peer pressure against 'acting white'", etc) have an effect on g (Jensen 1998b, p. 510). | g-loading and the method of correlated vectors, the statistical method used in many older studies, has been criticized heavily in recent research.[citation needed] The author of multiple factor analysis, L. L. Thurstone (1947), warned "we must guard against the simple, but common, error of merely taking a first centroid factor, a first principal component, or other mean factor, in a test battery and then calling it a general factor". "Spearman's g, then, is a "statistical artifact." (C. Loring Brace, 2001) |
| Correlations between an IQ subtest's heritability or inbreeding depression and the magnitude of the Black-White-East Asian score gap for that subtest (Rushton 1989a). Environmental theories would predict the opposite.[58] | What subtest are most heritable and how to measure this is debated.[citation needed] Racialist hereditarians make assertions regarding the heritability of traits such as intelligence, to imply that a) group differences are genetic and b) intelligence is a fixed ability.[dubious — see talk page] As per Nature Reviews Neuroscience:
"The issue of race is not unique to biological investigations of intelligence, but it is more visceral in a biological context (in part because heritability can be misunderstood to imply both that group differences must be genetic and that intelligence is a fixed rather than a context-sensitive ability — both of these interpretations are incorrect)."[59] "The view that a trait is independently heritable (or heritable at all) simply because it can be separately defined and analyzed has been rendered largely obsolete by modern developments in biology" [Thorogood 1997; Lovejoy, Cohn, and White 1999:13247) |
| Theories holding that Blacks score lower than Whites because of test bias would predict the Black-White gap would be smaller on culture-reduced tests than on culture-loaded tests. Yet the reverse is true (Murray and Herrnstein 1994). | ? |
| Brain size differences | |
| editor note: this is the original entry on brain size Black-White-East Asian differences in IQ, reaction time, brain size and other physiological variables (such as skull structure, and degree of convolution of the brain) in the United States and a few other developed countries (e.g. UK, Japan). Larger brain size and higher IQ of East Asians than Whites is seen as a challenge for the primarily environmental theory. ----- Race correlates with cranial measurements (Rushton, 1990:786). ----- Skull sizes of different races have been compared since the 1800s (Morton, 1849), showing differential sizes which are assumed related to IQ (Rushton, 1996). editor note: merge with brain size discussion below | editor note: make note of critiques of Rushton's B-W-EA aggregation methodology - evidence of differences challenged The gaps may be explained by many other factors except genetics (see above). Differences among some White groups are as large as the difference between Whites and Blacks in the US. Many racial groups show great variation when tested at different times and in different places, indicating large environmental influences. The IQ scores and larger brain size of East Asians have numerous possible explanations, e.g. many East Asian nations have a very high consumption of fish.[citation needed] One study has shown larger head size at birth and higher IQ scores at 4 years of age when the mothers took fish oil supplement during pregnancy and lactation. ----- The study cited by Rushton (Beals, Smith, and Dodd 1984) actually finds that climate variables are strongly correlated with cranial variation, where as "race" had low correlations. ----- The views of Morton and Rushton have been invalidated "by a century of anthropological research" (Gossett 1965, Cravens, 1978), and themselves are inconsistent with each other (Morton putting "Caucasoids" as the group with the largest brains, and Rushton putting "Mongoloids" as the group with the largest brains). |
| In a meta-analysis of 37 studies, McDaniel 2005 concluded that total brain size correlates with intelligence. Among adults of the same sex, the average correlation is approximately 0.4. The correlation between brain size and IQ seems to hold for comparisons between and within families (Gignac et al. 2003; Jensen 1994; Jensen & Johnson 1994). However, one study found no such family-related connection (Schoenemann et al. 2000). The volume of specific brain structures also correlates with IQ. Genetics are known to influence brain structure (Thompson et al. 2001) and some aspects of cognition (Berman and Noble 1995). In one study, the correlation between gray matter volume and g is found to be mediated entirely by genetic factors (Posthuma et al. 2002). A review in Nature Reviews Neuroscience noted "Correlations between intelligence and total brain volume or grey matter volume have been replicated in magnetic resonance imaging (MRI) studies, to the extent that intelligence is now commonly used as a confounding variable in morphometric studies of disease."[60] editor note: correlation of brain size to intelligence may be necessary for the racialist-hereditarian view, but is not proof of its validity | In modern humans, intraspecific correlation between brain size and various measures of "intelligence" is nonexistent (Henneberg 1998). "What we do know is that within human families, brain size does not predict general cognitive ability; nongenetic events play a significant role in brain volume and cognitive ability associations (Schoenemann et al. 2000)." (Fatimah Jackson 2001) |
| Correlates of IQ | |
| The three-way differences in the IQ and SAT scores of children persists even after controlling for parental income or education, which seems to counter arguments that the gap is due to socioeconomic conditions.[61] In addition, some researchers have argued from studies in siblings that IQ affects socioeconomic status, rather than the other way around (Murray 1998). Studies which simultaneously control for dozens of social and economic conditions are uninformative because they assume that such differences are the cause rather than the consequence of IQ differences (Murray and Hernstein 1994; Murray 2000). SAT scores correlate with IQ as well as scores from one IQ test correlate with another (Frey and Detterman 2004. Neisser et al. concluded "it is clear that no model in which 'SES' directly determines 'IQ' will do."[4] | Adjustments for socioeconomic conditions almost completely eliminate differences in IQ scores between black and white children. The remaining difference is statistically insignificant.[62] SAT scores are not the same as IQ scores. |
| According to Arthur Jensen, environment-only explanations would predict a decreasing Black-White gap with increasing socioeconomic status of parents. Yet the opposite is true (Jensen 1998b, p. 469). | ? |
| Three-way differences in reaction times have been demonstrated (Jensen 1993; Jensen and Whang 1994; Lynn and Holmshaw 1990; Lynn and Shigehasa 1991), and it is difficult to explain differences in reaction time through lack of motivation or cultural differences on the part of the subjects. Reaction times correlate with g (Grudnick and Kranzler 2001). | Differences in reaction time or brain volume may be caused by environmental factors. As noted, there have been large changes in cranial vault size and shape during the last century in the US for both Black and Whites, far beyond what can be explained genetically. In addition, reaction time and brain size have only a low correlation with IQ test scores and are not shown to have any real-world significance. |
| Causes of individual differences in IQ | |
| Rising heritability of IQ with age, and decreasing shared-family effects (e.g., socioeconomic factors) on IQ after adolescence. An environmental cause of the IQ gap is seen as necessarily being a shared family effect. | High within-group heritability does not logically exclude the all environmental interpretation. Racialist hereditarians make assertions regarding the heritability of traits such as intelligence, to imply that a) group differences are genetic and b) intelligence is a fixed ability. As per Nature Reviews Neuroscience:
"The issue of race is not unique to biological investigations of intelligence, but it is more visceral in a biological context (in part because heritability can be misunderstood to imply both that group differences must be genetic and that intelligence is a fixed rather than a context-sensitive ability — both of these interpretations are incorrect)."[63] "The view that a trait is independently heritable (or heritable at all) simply because it can be separately defined and analyzed has been rendered largely obsolete by modern developments in biology" [Thorogood 1997; Lovejoy, Cohn, and White 1999:13247) |
| Studies using structural equation modeling find results consistent with the partially-genetic explanation (Jensen 1998b, pp. 464-467). Studies suggesting that IQ heritability and gene-environment interactions within races are the same for Blacks and Whites. That is, no race-specific statistical factors, such as an effect of White racism, have been identified in such analyses. The IQ gap exists even among middle- and upper-class Black and White families where within-race heritabilities are high and shared family effects are near zero. | Many factors that can affect IQ differ between Blacks and whites, for example duration of breastfeeding or poverty.[citation needed] Many older studies have only studied middle class families but SES has recently been shown to be relatively more important in poorer families.[citation needed] |
| The finding that when Black and White children are matched for IQ, their siblings tend to have IQs that regress towards different means (85 for Blacks and 100 for Whites). For example, among Black and White children matched with an IQ of 120, the siblings of the Black children have an average IQ of 100 whereas the siblings of the White children have an average IQ of 110. This is a stronger test of the party-genetic hypothesis than regression from parents to offspring because siblings share a similar environment (Jensen 1973). This is a novel prediction of the partly genetic hypothesis. | Regression towards the mean only shows that mean IQ scores are different which is not a new finding. That is not evidence that the cause of this difference is genetic.[citation needed] |
| The three-way difference in average IQ can be measured in very young children and before the start of schooling. For example, a one standard deviation gap is observed in Black and White 3-year olds matched for gender, birth order, and maternal education (Peoples et al. 1995). Lynn 1996 found that by age 6 the average IQ of East Asian children is 107, 103 for White children and 89 for Black children. Broman et al. (1987) found that the same trichotomy in brain size and IQ held at 4 months, 1 year, and 7 years of age. | Environmental factors can affect very young children, for example nutrition by the mother during pregnancy and breastfeeding. More breastfeeding gives IQ gains and the duration of this is known to differ between White and Black mothers.[citation needed] Two studies in Chile shows that nutritional status affects IQ, scholastic achievement, and brain volume.[64] |
| Adoption and admixture | |
| Average Black-White-East Asian differences in IQ (both positive and negative) remain following transracial adoption. Three studies of East Asian children adopted by White familes reported average IQ scores in the adopted East Asian children that are as high or higher than Whites, despite the fact that some of the children in the studies had suffered some forms of preadoptive deprivation or malnutrition and associated developmental delays (Clark and Hanisee 1982; Frydman and Lynn 1989; Winick et al. 1975). Burrow and Finley (2004) found Black-White-East Asian differences in cognitive and psychological variables among adolescents adopted by white families. They also found that Black-White mixed-race children fell in between the White and Black averages. See also the Minnesota Transracial Adoption Study. | Existing adoption studies lack behavior genetic controls needed to distinguish between genetic and environmental effects.[citation needed] Several other adoption studies finds no IQ difference between Whites and East Asians.[65] |
| Rushton and Jensen 2005b argue that these studies are "peculiarly old, the mean year of publication being 1960" and "actually very weak and nondecisive, not having been replicated even once". No studies of Black-White genetic admixture have been performed with the multi-locus DNA sequencing required to make reliable conclusions. Lynn (2002) reports that skin color is corrlated with intelligence among African Americans. | IQ have very low positive to low negative correlation with Whiteness of skin, degree of European blood groups, or self-reported degree of European ancestry among Blacks.{{cn}) |
| Jensen 1998b points out that while the study of children born in post-WWII Germany finds no difference between white and interracial children, it does find a large difference in IQ between boys and girls, suggesting that sampling artifacts have affected the results. No studies that make use of proper behavior genetic techniques have been able to identify environmental factors to explain the IQ gap. | A study which showed near-disappearance of the black-white gap among children of black and white servicemen raised by German mothers after World War II. Some, like the American Psychological Association, consider this study be strong evidence against the genetic explanation.[66] |
| High achieving minorities | |
| Theories holding that Blacks score lower than Whites because of test bias would predict that Asians would also score lower than Whites. However, the reverse is true. | Assuming that test bias must negatively affect scores of any minority group is unsupportable. Asians and Blacks do not share the same environmental or cultural influences. |
| Ashkenazi Jews have often been persecuted and discriminated against, but they still display the highest average IQ of any ethnic group, as well as SAT scores higher than those of non-Jewish Caucasians. Rowe 2005, pp. 67-68 argues that this counters arguments that depressed IQ scores of African Americans are due to discrimination or prejudice. Similarly, Jensen 1998b, p. 510, points to the examples of Chinese, Japanese, Jews, and East Indians, stating that they have been minorities, discriminated against, or even persecuted, yet do not do poorly on g-loaded tests. Murray and Herrnstein 1994 make similar arguments. | Persecution and discrimination is not always applied in identical ways with identical effects. Conflating the terms "discrimination" and "prejudice" as having both the same meaning as well as effect is a logical fallacy. Neither do persecution and discrimination encompass the entirety of culture or environmental effects.
Rowe is particularly criticized for "misuse of broad scientific concepts and incorrect or biased misinterpretation of specific scientific data."[67] |
| Lynn 1987 argues that environmental explanations cannot explain why East Asians score higher on tests of spatial reasoning than verbal reasoning. | Dichotomy in intelligence is entirely compatible with an all environmental explanation but may not be with the g theory. East Asians may have higher spatial ability for example due to their knowledge of iconographic languages. [citation needed] |
| A similar dichotomy in spatial/nonspatial intelligence test scores is present in both East Asians and several Native American and Inuit populations (Connelly 1983; Diessner and Walker 1986; Tempest 1987; Zarske and Moore 1982; McShane and Plas 1982 McShane and Plas 1984).[68] | ? |
| Significance and evolution of races | |
| A relationship between times of evolutionary emergence and brain sizes for East Asians, Whites, and Blacks. (Rushton 1996) | ? |
| Racial differences in biological characteristics such as myopia that correlate with g. Myopia is more common in Asians and Jews than in Whites, and more common in Whites than in Blacks. Myopia is about twice as common in Jews than in Gentiles. Myopia is likely pleiotropic with g (i.e., myopia and g are caused by the same genes). Arthur Jensen argues that this supports the partially-genetic explanation. (Jensen 1998b, p. 487-489) | ? |
| Partly-genetic theory is predicated on a model that the IQ gap has (the genetic) part of its origin in human evolution. Thus, it predicts that the Black-White-East Asian differences in average IQ, reaction-time, and brain size should be accompanied by a similar pattern of differences in other inherited traits. Proponents cite three-way average differences such as personality, maturation, and reproductive traits as support of this prediction; Rushton and Jensen 2005a, p. 273, cite a "matrix of 60 life-history traits". Research on racial differences in twining and testis size was the subject of a review by author and scientist Jared Diamond (1986) in the journal Nature, in which he investigated correlations between possible racial variations in testicular size and hormone levels and found one small study suggesting that dead Danish men on autopsy have larger testicles than dead Chinese men. Some studies also suggested lower hormone levels and frequency of twins among Asians than Africans. Rushton (1995) has additionally pointed to the Black-White-East Asian gradient in average hip size, arguing that nothing can explain this phenomenon except the need to give birth to children with different brain sizes. | Differences may have environmental causes and may be unrelated to one another. Many of these claims of differences have been shown to be false, for example references to scientific literature with respects to racial differences in sexual characteristics turned out to be references to a nonscientific semipornographic book and to an article in the Penthouse Forum.[69] Regarding Jared's study, he notes that smaller testicle size among Koreans was not associated with a lower frequency of sexual intercourse, which directly contradicts Rushton rK-theory. There is only an insignificant difference in frequency of twins between Whites and Blacks in the U.S (34.8 vs 34.7), also contradicting the theory.[70] Higher frequency of twins in certain African populations can be explained by large scale consumption of Yam which in rats produces such results.[71] |
| Other statistical racial differences have been reported to exist. this is a repeat of the last entry - merge | Other statistical racial differences have been found to be artifacts of poor controls. David and Collins (1997) studied birth weight and race correlations between black and white Americans. Although the correlations still held when controlled for socioeconomic variables, when they considered African immigrants to the United States, the racial pattern vanished (African-born immigrants clustered with American whites, not American blacks). "The low-birth-weight phenomenon appears to be not an endowment of the black gene pool but a consequence of the experience of growing up black in America" (Jonathan Marks, 2001) |
| Rushton asserts a "principle of aggregation" which derives his conclusions from a vast array of historical data. | The poor quality of data cited by racialist-hereditarians is strongly criticized, and all of their citations of persistent patterns are seen as unsupportable once proper controls are added and obviously invalid data is filtered out.[43] |
| "Mongoloids" have superior, larger brains because in their evolution they had to "adapt to a cognitively demanding but predictable cold Pleistocene climate (Rushton, 1997) editor note: the last entry in the table covers evolutionary explanations | "the mode of subsistence of all human populations was essentially the same over the past 200,000 years. This was conditioned by adaptation to the selective pressure engendered by the cultural ecological niche. For these reasons, then, cognitive capabilities should . . . be the same in all the living populations of the world" (Brace 1998:112). |
[edit] Other interpretations
The two most widely-known works concerning race and intelligence are The Mismeasure of Man by Stephen Jay Gould, originally published in 1981, and The Bell Curve by Richard Herrnstein and Charles Murray, published in 1994. Media controversy surrounding The Bell Curve motivated Gould to revise and expand The Mismeasure of Man to respond to arguments from The Bell Curve, publishing the book's second edition in 1996. Many current researchers think that both books are outdated due to new research.
A recent paper in the Psychological Review, "Heritability Estimates Versus Large Environmental Effects: The IQ Paradox Resolved" by William T. Dickens of The Brookings Institution and James R. Flynn presents a mechanism by which environmental effects on IQ may be magnified by feedback effects. This work may provide a resolution of the contradiction between the viewpoint of The Bell Curve's authors and the 'nurture' effects observed by others. A latter paper responded to objections.[72]
For additional relevant discussion, see: http://www.skeptic.com/eskeptic/05-02-18.html Two book reviews, by Paul R. Gross and Alondra Oubre, of Sarich’s and Miele’s book, Race: The Reality of Human Differences.
Some cite research that they believe indicates that discriminated or lower-status minorities do tend to have lower IQ, some without apparent genetic differences. Like Blacks and Hispanics in the U.S., minorities in some societies show achievement gaps (such as the Māori in New Zealand, aboriginals in Australia, scheduled castes ("untouchables") in India, non-European Jews in Israel, and the Burakumin in Japan). The most prominent finding cited is that Northern Irish Catholics used to score about 15 points lower than Protestants. Similarly, Irish, Italian and Polish immigrants in the U.S. are reported to have all scored about 80 in the beginning of the 19th century, but now tend to reach 100. The same is true of persons from rural versus urban areas in general (see e.g., this article by conservative columnist and economist Thomas Sowell and this page on European and Greek IQ. More arguments of the kind are to be found here).
[edit] Opinions of scholars and others
A survey was conducted in 1987 of a broad sample of 1,020 scholars (65% replied) in specialties that would give them reason to be knowledgeable about IQ (but not necessarily about race; Snyderman & Rothman, 1987). The survey was given to members of the American Education Research Association, National Council on Measurement in Education, American Psychological Association, American Sociological Association, Behavior Genetics Association, and Cognitive Science Society. Political and social opinions, reported in the same survey, accounted for less than 10% of the variation in responses. (Respondents on average called themselves slightly left of center politically.) Measures of expertise or eminence accounted for little or no variation in responses.
One question was "Which of the following best characterizes your opinion of the heritability of the Black-White difference in I.Q.?" (emphasis original).[73] The responses were divided into five categories:
- The difference is entirely due to environmental variation: 15%.
- The difference is entirely due to genetic variation: 1% (8 respondents).
- The difference is a product of both genetic and environmental variation: 45%.
- The data are insufficient to support any reasonable opinion: 24%.
- No response (or not qualified): 14%.
| Question | Responses |
|---|---|
| What heritability would you estimate for IQ differences within the White population? | Average estimate of 60 (± 17) percent. |
| What heritability would you estimate for IQ differences within the Black population? | Average estimate of 57 (± 18) percent. |
| Are intelligence tests biased against Blacks? | On a scale of 1 (not at all or insignificantly) to 4 (extremely), mean response of 2 (somewhat). |
| What is the source of the average Black-White difference in IQ? | Both genetic and environmental (45%, or 52% of those responding). |
The age of the survey and the anonymity of the respondents could constrain its interpretation.
In a 1988 survey, journalists, editors, and IQ experts were asked their "opinion of the source of the black-white difference in IQ" Snyderman and Rothman 1988
| Group | Entirely Environment | Entirely Genetic | Both | Data Are Insufficient |
|---|---|---|---|---|
| Journalists | 34% | 1% | 27% | 38% |
| Editors | 47% | 2% | 23% | 28% |
| IQ Experts | 17% | 1% | 53% | 28% |
[edit] The view of the American Psychological Association
In response to the controversy surrounding The Bell Curve, the American Psychological Association's Board of Scientific Affairs in 1995 established a special task force to publish an investigative report on the research presented in the book.[74]
The task force agrees that there do exist large differences between the average IQ scores of blacks and whites, and that these differences cannot be attributed to biases in test construction, nor does it "simply reflect differences in socio-economic status". While they admit there is no empirical evidence supporting it, the APA task force suggests that explanations based on social status and cultural differences may be possible. Regarding genetic causes, they noted that there is not much direct evidence on this point, but what little there is fails to support the genetic hypothesis. The January 1997 issue of American Psychologist included eleven critical responses to the APA report, most of which criticized the report's failure to examine all of the evidence for or against the partly-genetic interpretation of racial differences in IQ.
[edit] See also
- Biological determinism
- Cultural determinism
- Genetic determinism
- Nature versus nurture
- Social determinism
- Twin study
- Norms of reaction
[edit] Notes
- ^ a b c d e Race and IQ: Molecular Genetics as Deus ex Machina, Richard S. Cooper
- ^ http://www.ssc.uwo.ca/psychology/faculty/rushtonpdfs/PPPL1.pdf
- ^ http://taxa.epi.umn.edu/~mbmiller/journals/pppl/200504/2/302-2.html
- ^ a b c d e f Neisser et al. 1996
- ^ Jencks, C., & Phillips, M. (1998). The black-white test score gap: An introduction. In C. Jencks and M. Phillips (Eds.),The black-white test score gap(pp. 1-51). Washington, DC: Brookings Institution. ". . . we find it hard to see how anyone reading these studies with an open mind could conclude that innate ability played a large role in the black-white gap."
- ^ Aristotle: "Having spoken of the number of the citizens, we will proceed to speak of what should be their character. This is a subject which can be easily understood by any one who casts his eye on the more celebrated states of Hellas, and generally on the distribution of races in the habitable world. Those who live in a cold climate and in Europe are full of spirit, but wanting in intelligence and skill; and therefore they retain comparative freedom, but have no political organization, and are incapable of ruling over others. Whereas the natives of Asia are intelligent and inventive, but they are wanting in spirit, and therefore they are always in a state of subjection and slavery. But the Hellenic race, which is situated between them, is likewise intermediate in character, being high-spirited and also intelligent. Hence it continues free, and is the best-governed of any nation, and, if it could be formed into one state, would be able to rule the world." (Aristotle, Politics, ch. 7).
Cicero: "Do not obtain your slaves from Britain because they are so stupid and so utterly incapable of being taught that they are not fit to form a part of the household of Athens." Attributed to Cicero's Epistulae ad Atticum (Letters to Atticus), 68 BC-43 BC (latin text). Translation: Cicero 1918.
"Races north of the Pyrenees are of cold temperament and never reach maturity; they are of great stature and of a white colour. But they lack all sharpness of wit and penetration of intellect." Attributed to "Said of Toledo (a moorish savant)" by Benedict 1999 (p.34), originally quoted in Hogben 1931. - ^ Ogbu 1978; Ogbu 2002; Ogbu 2003
- ^ Jensen 1998b, p. 512
- ^ Joel Wiesen, "An Annotated List of Many Possible Reasons for the Black-White Mean Score Differences Seen With Many Cognitive Ability Tests: Notes to File," Applied Personnel Research, March 18, 2005.
- ^ Jensen 1998b, p. 510; Murray and Herrnstein 1994
- ^ Greek IQ
- ^ Flynn 1987, Flynn 1987b, Flynn 1999, Flynn 1999b
- ^ Colom et al. 2005
- ^ Flynn 1999
- ^ Wicherts et al. 2004 concluded that "the gains cannot be explained solely by increases at the level of the latent variables (common factors), which IQ tests purport to measure"; in other words, some of the inter-generational difference in IQ is attributable to bias or other artifacts, and not real gains in general intelligence or higher-order ability factors, unlike the B-W IQ gap. An analysis by Rushton 1999 found that the IQ increases associated with the Flynn effect did not produce changes in g, which Rushton compares to the finding by Jensen 1998a that IQ increases associated with adoption likewise do not increase g. Flynn 1999b disagrees with Rushton's analysis.
- ^ Rowe and Rodgers 2002 and others find this hypothesis unsupported by the available evidence. Dickens and Flynn 2002 respond to these criticisms.
- ^ http://scholar.google.se/scholar?as_q=&num=10&btnG=S%C3%B6k+Scholar&as_epq=How+similar+are+fluid+cognition+and+general+intelligence&as_oq=&as_eq=&as_occt=any&as_sauthors=&as_publication=Behavioral+and+Brain+Sciences&as_ylo=&as_yhi=&as_allsubj=all&hl=sv&lr=
- ^ [1]
- ^ National Center for Health Statistics: Vital Statistics of the United States (1988).
- ^ Scientific American, April 1996, p.25.
- ^ "Fat, Fitness And Performance," Peak Performance; I.B. Helland et al., "Maternal supplementation with very-long-chain n-3 fatty acids during pregnancy and lactation augments children's IQ at 4 years of age," Pediatrics 111, no. 1 (January 2003): 39–44.
- ^ "Myth: Social intervention cannot raise IQ; Intelligence Quotient, The Encyclopedia of Adoption.
- ^ Papers relating to group difference in IQ test scores & Spearman's hypothesis.
- ^ Joseph L. Graves, "What a tangled web he weaves: Race, reproductive strategies and Rushton's life history theory," Anthropological Theory 2, no. 2 (2002): 131–54; Leonard Lieberman et al., "How 'Caucasoids' Got Such Big Crania and Why They Shrank,"; Current Anthropology 42 (2001): 69–95; Zack Cernovsky, "On the similarities of American blacks and whites: A reply to J.P. Rushton," Journal of Black Studies 25 (1995): 672.
- ^ Greek IQ
- ^ Charles C. Roseman, "Detecting interregionally diversifying natural selection on modern human cranial form by using matched molecular and morphometric data" Proceedings of the national Academy of Sciences of the United States vol. 101 no. 35 (August 31, 2004):12824-12829.
- ^ http://www.mugu.com/cgi-bin/Upstream/People/Rushton/rushton-black-reply.html
- ^ http://ant.sagepub.com/cgi/content/abstract/2/2/131
- ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&list_uids=14992214&dopt=Citation
- ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1488860&dopt=Citation
- ^ http://www.mugu.com/cgi-bin/Upstream/miller-r-personality
- ^ http://www.mugu.com/cgi-bin/Upstream/Library/Miller/env-vary.html
- ^ http://www.ingentaconnect.com/search/expand?pub=infobike://els/10905138/2003/00000024/00000005/art00040&unc=
- ^ http://www.crispian.demon.co.uk/RUSHRV.htm
- ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=15638207&dopt=Citation
- ^ http://www.getcited.org/pub/103361483
- ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9626146&dopt=Citation
- ^ http://www.cdc.gov/nchs/fastats/pdf/nvsr52_10t50.pdf
- ^ http://www.azcentral.com/families/articles/0228fam_twins.html
- ^ http://links.jstor.org/sici?sici=0014-7354(200005%2F06)32%3A3%3C132%3AUOISIT%3E2.0.CO%3B2-Z
- ^ Gregory Cochran, Jason Hardy, Henry Harpending, "Natural History of Ashkenazi Intelligence," Journal of Biosocial Science (June 2005).
- ^ a b http://www.apa.org/releases/race.html
- ^ a b c d e How "Caucasoids" Got Such Big Crania and Why They Shrank, Lieberman 2001
- ^ Risch et al. 2002, Bamshad 2005.
- ^ Rowe 2005
- ^ Harpending and Rogers 2000, Bamshad et al. 2003, Edwards 2003, Bamshad et al. 2004, Tang et al. 2005, Rosenberg et al. 2005: "If enough markers are used... individuals can be partitioned into genetic clusters that match major geographic subdivisions of the globe".
- ^ Mountain and Risch 2004
- ^ Mayr 2002.
- ^ Neil Risch argues: "One could make the same arguments about sex and age! . . you can undermine any definitional system. . . In a recent study. . . we actually had a higher discordance rate between self-reported sex and markers on the X chromosome [than] between genetic structure [based on microsatellite markers] versus [racial] self-description, [which had a] 99.9% concordance. . . So you could argue that sex is also a problematic category. And there are differences between sex and gender; self-identification may not be correlated with biology perfectly. And there is sexism. And you can talk about age the same way. A person's chronological age does not correspond perfectly with his biological age for a variety of reasons, both inherited and non-inherited. Perhaps just using someone's actual birth year is not a very good way of measuring age. Does that mean we should throw it out? . . . Any category you come up with is going to be imperfect, but that doesn't preclude you from using it or the fact that it has utility" (Gitschier 2005).
- ^ Edwards 2003 cites Fisher RA. Statistical Methods and Scientific Inference. Edinburgh: Oliver and Boyd. 1956.
- ^ Risch et al. 2002, p. 5
- ^ Editorial: Census, race and science. Nat Genet 2000, 24:97-98.
- ^ Lynn 2006
- ^ IQ studies by year from IQ and the Wealth of Nations by Lynn & Vanhanen
- ^ Jensen, Arthur R. (2000) A Fuzzy Boundary of Racial Classification Attenuates IQ Difference, Psycoloquy: 11,#22 Intelligence G Factor (34)
- ^ See note 3 above.
- ^ Murray, C. (2005) "The Inequality Taboo". Commentary Magazine, September 2005.
- ^ Rushton and Jensen 2005a
- ^ Nature Reviews Neuroscience
- ^ http://www.loni.ucla.edu/~thompson/PDF/nrn0604-GrayThompson.pdf
- ^ Arthur Hu's Index of Diversity, Scholastic Aptitude Test.
- ^ "Myth: The black/white IQ gap is largely genetically caused.
- ^ Nature Reviews Neuroscience
- ^ D.M. Ivanovic et al., "Nutritional status, brain development and scholastic achievement of Chilean high-school graduates from high and low intellectual quotient and socio-economic status," British Journal of Nutrition 87, no. 1 (January 2002): 81–92; D.M. Ivanovic et al., "Head size and intelligence, learning, nutritional status and brain development. Head, IQ, learning, nutrition and brain," Neuropsychologia 42, no. 8 (2004): 1118–31.
- ^ Marinus H. van IJzendoorn, Femmie Juffer, and Caroline W. Klein Poelhuis, "Adoption and Cognitive Development: A Meta-Analytic Comparison of Adopted and Nonadopted Children’s IQ and School Performance," Psychological Bulletin 131, no. 2 (2005): 301–316.
- ^ William T. Dickens, "Behavioral Genetics and School Readiness," The Future of Children 15, no. 1 (Spring 2005): 55–69; "Intelligence: Knowns and Unknowns," Report of a Task Force established by the Board of Scientific Affairs of the APA.
- ^ Race and IQ: Molecular Genetics as Deus ex Machina, Richard S. Cooper
The technical errors contained in Rowe’s (2005) article include both misuse of broad scientific concepts and incorrect or biased misinterpretation of specific scientific data. The author’s broad argument assumes that a quantity definable as “intelligence” exists (in contradistinction to the view that multiple types of cognitive functioning can be identified that are valued and manifested differently, conditional on the setting and the observer), that intelligence can be measured with “IQ tests,” that demographic groups known as “continental races” divide humans into discrete categories on the basis of important concordant variation in genetically determined traits, that molecular genetics can (or will) make it possible to define the architecture of complex traits in terms of “genes for X or Y” (i.e., “genes for intelligence”), and that significant variation in polymorphisms in those genes overlap with the traditional demographic categories, such as those promulgated by the U.S. government.
- ^ Abstracts from the Journal of American Indian Education 1987; Rhett Diessner and Jacqueline L. Walker, "A Cognitive Pattern of the Yakima Indian Students," Journal of American Indian Education 25, no. 2 (January 1986); "Smart Fraction Theory II: Why Asians Lag," La Griffe du Lion 6, no. 2 (May 2004).
- ^ Zack Cernovsky, "On the similarities of American blacks and whites: A reply to J.P. Rushton," Journal of Black Studies 25 (July 1995): 672.
- ^ Table 50 National Vital Statistics Reports Vol. 52, No. 10, December 17, 2003. CDC.
- ^ "What's in a yam? Clues to fertility, a student discovers," Yale Medicin Summer 99
- ^ William T. Dickens and James R. Flynn, "The IQ Paradox: Still Resolved," Psychological Review 109, no. 4 (2002).
- ^ Richard Herrnstein and Charles Murray, "Race, genes and I.Q.—an apologia: the case for conservative multiculturalism," The New Republic 211, no. 11 (October 1994): 27.
- ^ http://www.lrainc.com/swtaboo/taboos/apa_01.html
[edit] References
[edit] External links
[edit] Primarily-genetic view
- Thirty Years of Research on Race Differences in Cognitive Ability J. Philippe Rushton & Arthur R. Jensen
- Black-White-East Asian IQ differences at least 50% genetic, scientists conclude in major law journal
[edit] Primarily-environmental view
- Heredity, Environment, and Race Differences in IQ Richard E. Nisbett
- Race and IQ: Molecular Genetics as Deus ex Machina Richard S. Cooper
|
Race and intelligence |
|---|---|
| Public controversy | Media portrayal | Utility of research | Accusations of bias Average test score gaps among races | Explanations | References |
