Race and intelligence (Comparison of explanations)

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[edit] Comparison of explanations

Main article: Race and intelligence (explanations)

The Black-White IQ gap in the U.S. may be explained by a variety of explanations on various axes of dispute. There are questions as to the magnitude, direction and causes of gaps, as well as questions regarding the fundamental assumptions of how to frame the question.

This table includes arguments put forward by a wide variety of sources on a wide variety of positions, and also includes some rebuttal and counter-rebuttal on those arguments. Neither column represents a single major point of view.

Adoption and admixture
Some Black-White-East Asian differences in IQ (both positive and negative) remain following transracial adoption. Burrow and Finley (2004) reported 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. Two studies of Asian children adopted by White families reported average IQ scores in the adopted Asian children that are higher than Whites.(Clark and Hanisee 1982; Frydman and Lynn 1989.	Nisbett (2005) reports the results of the three three major adoption studies that address the question of genetic contribution to the Black-White IQ difference. Two of the studies shows unambiguous lack of support for the hereditarian model and one study showing at most ambiguous support for it.^[1] Several other adoption studies finds no IQ difference between Whites and East Asians.^[2]
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.	There are numerous studies of the association between skin color and IQ. The correlation between lightness of skin and IQ, averaged over a large number of studies reviewed by Shuey (1966), is very low (0.1). The average correlation between IQ and judged “Negroidness” of features is even lower. ^[3] A 2002 reanalysis of Lynn's data concluded "that his bivariate association disappears once childhood environmental factors are considered. Therefore, a genetic link between skin color and intelligence among African Americans cannot be supported in his data."^[4] IQ have very low positive to low negative correlation with several studies concerning the degree of European blood groups, or self-reported degree of European ancestry among Blacks. ^[5]
Jensen 1998b points out that while the study which showed near-disappearance (difference of 0.5 IQ points) of the multiracial-white gap among children of black/North African and white servicemen raised by their genetic white mothers after World War II, it does find a large difference in IQ between boys and girls, suggesting that sampling artifacts and the effects of heterosis(4 IQ points^{[citation needed]}) in mixed race children have affected the results. Rushton & Jensen (2005) also state "One third of the children were between 5 and 10 years of age, and two thirds were between 10 and 13 years...behavior genetic studies show that while family socialization effects on IQ are often strong before puberty, after puberty they dwindle, sometimes to zero. Second, 20% to 25% of the “Black” fathers were not African Americans but French North Africans (i.e., largely Caucasian or “Whites” as we have defined the terms here). Third, there was rigorous selection based on IQ score in the U.S. Army at the time, with a rejection rate for Blacks on the preinduction Army General Classification Test of about 30%, compared with 3% for Whites." ^[6]	A study which "examined the IQs of several hundred German children fathered by Black GIs during the post-1945 occupation and compared them with the IQs of children fathered by White GIs. The children of the Black GIs had an average IQ of 96.5. The children of the White GIs had an average IQ of 97." Some, like the American Psychological Association, consider this study be strong evidence against the genetic explanation.^[7] Because the Black-White gap in the military was similar to that for the U.S. population, these data imply that the Black-White gap in the U.S. population as a whole is not genetic, even in part (Flynn, 1980, pp. 87-88). The results seem particularly telling because it seems highly likely that environmental conditions were inferior for Black children. He argues that "one would have to assume preposterously high IQ scores on the part of the North African portion of the Black fathers to make up for the substantial difference between offspring of Blacks and Whites predicted by their hereditarian theory. Second, Rushton and Jensen assume that Black soldiers were more rigorously selected than Whites and so might have had IQs nearly as high as those of the White soldiers. Blacks in the military did indeed have higher IQs than did Blacks in the general population, but the same was true of White soldiers compared with the general White population. Flynn (1980) has argued that the evidence indicates that the gap in IQ between Black and White soldiers was the same as that in the U.S. population at large."^[8] Regarding heterosis, if breeding with close relatives such as in isolated, small rural communities, then this depresses IQ. As for the beneficial effects of outbreeding, 3 IQ points is the advantage of not breeding with one's cousins.^[9] Regarding the argument about the disappearance of the shared family effect, this is discussed in a section below.
Because the White mother-Black father pairs averaged 1 year more of education than the Black mother-White father pairs, the study is uninterpretable.	If the Black-White IQ gap is largely hereditary, then children having one Black and one White parent should have the same IQ on average, regardless of which parent is Black. But if one assumes that mothers are particularly important to the intellectual socialization of their children and if the socialization practices of Whites are more favorable to IQ development than those of Black mothers, then children of White mothers and Black fathers should have higher IQs than children of Black mothers and White fathers. This could of course not have a plausible genetic explanation. In fact, it emerges that children of White mothers and Black fathers have IQs 9 points higher than children with Black mothers and White fathers (Willerman, Naylor, & Myrianthopoulos, 1974). This result in itself suggests that most of the Black-White IQ gap is environmental in origin. But because mothers are not the only environmental influence on the child's IQ, the 9-point difference might be regarded as a very conservative estimate of the environmental contribution to the gap. There can be no basis for assuming that 1-year's difference in education on the part of the parents could possibly translate into an expected 9 IQ point difference for the children.^[10]
Utility of racial categories
Some geneticists argue categories of self-identified race/ethnicity or biogeographic ancestry are both valid and useful.^[11] 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."^[12] They find that these categories correspond with clusters inferred from multilocus genetic data..^[13] Moreover, they conclude that this correspondence implies that genetic factors might contribute to unexplained phenotypic variation between groups.^[14] 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."^[15] Risch and colleagues (2002) argue that "much of this discussion does not derive from an objective scientific perspective."^[16] 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."^[17]	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 reported that the concept of race was rejected by 69% of physical anthropologists and 80% of cultural anthropologists (Lieberman and Kirk n.d.)"^[18] "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)."^[18] "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."^[19] "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)."^[19] "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."^[19]
"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."^[20]	"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."^[21] "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?"^[19]
IQ differences
Black-White-East Asian differences in culture-fair IQ test scores exist world-wide despite international differences in social, cultural, and economic conditions.^[22] 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).	The only nationwide IQ tests have been done in a few developed countries, and the attempted aggregations of smaller studies in other nations, most of which do not have any all, have been severely criticized, see IQ and the Wealth of Nations. Regarding China and African Americans, and developing vs. developed nations more generally, there are numerous environmental and social factors which could differ, such as those mentioned elsewhere in this article. For example, child-rearing practices and attitudes differ greatly between East Asians nations and the US.^[23] Many East Asian nations have a high consumption of fish. Fish oil supplementation to pregnant and lactating mothers has been linked to increased cognitive ability.^[24] See also Health and intelligence. Assertions of Black-White-East Asian differences are based on invalid "aggregation" of data.^[18]^[off-topic?]
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.	One argument of many against the reliability of the IQ scores in developing nations is that in some such countries a majority of the population would be classified by the IQ scores as mentally retarded. People with a score below 75 will often, but not always, have difficulties with daily living skills, which would include the majority of people in Sub-Saharan Africa, arguably absurd. The most extreme exampke is 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.
Several studies argue that the Black-White IQ gap in the US has remained constant at approximately one standard deviation since it was first measured despite social and economic change during that time, including the civil rights movement and Brown v. Board of Education.^[25] Average IQ scores gaps internationally have been stable since they were first measured in the early and mid 20th century.^[26](Lynn and Vanhanen 2002 ).	Several other studies show that the gap in the US is narrowing. See Race and intelligence (test data)#Is the IQ test score gap closing.3F. Moreover, the extent of concrete social and economic change is debatable; for example, Jonathan Kozol, in his 2005 book Shame of the Nation, reported that public schools are more racially segregated today than they were in 1969. Considering the few studies outside some developing nations, and other problems as described in the article about IQ and the Wealth of Nations, any claim regarding an internationally stable gap is doubtful. The given source, [1], a blog site, is highly questionable considering the absence of the Flynn effect in the graph.
Some studies find that 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 reported 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) reported that the same trichotomy in brain size and IQ held at 4 months, 1 year, and 7 years of age.	A recent, large, and nationally representative data set find only very small (0.06 SD between whites and blacks) racial differences on measures for mental function 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."^[27] Environmental factors can affect very young children and affect black and white children differently, for example breastfeeding and environmental toxins such as lead, as discussed in other sections in this article. In developing nations there are factors affecting children, like severe malnutrition and tropical diseases, not present in developed nations, see Health and intelligence.
One statistical analysis suggests that the Flynn effect is qualitatively different than the Black-White IQ gap (Wicherts et al. 2004).	The Flynn effect is the finding that IQ scores have been increasing very rapidly worldwide, in particular on "culture-fair" and highly g-loaded tests such as Raven's Progressive Matrices. Average IQ in the US in 1932 was 80, well below the current black-white gap. Many environmental influences has been suggested as an explanation, and it seems not unlikely that the effect started earlier and may end sooner for Whites in the US compared to Blacks and for developed nations compared to developing nations. This may happen regardless of whether the gaps have been stable or not until now. 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.
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 is incorrect, see Household income in the United States. The Inuit (Eskimo) cannot be directly compared to the US population, for example they have substantially different nutrition from eating large amounts of fish.^[28] Fish oil supplement to pregnant and lactating mothers has been linked to increased cognitive ability, see Health and intelligence.
?	Results from the US, which include almost all studies and findings, cannot be generalized to the world as whole. Blacks, East Asians, Hispanics, and Whites in the US are not a random sample of the worldwide popultion. The environment in the US differs from other nations. For example, some studies find that the Black-White gap in the UK is about half that in the US.^[29] In developing nations there are many factors, like severe malnutrition and certain diseases, that affect IQ that are not present in developed nations.
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.	Jews and East Asians have been discriminated against in the past, but arguably far less now, compared to African Americans. 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."^[30]
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 various all environmental explanation. For example, East Asians may have higher spatial ability for example due to their use of logographic writing systems. One study found that g does not differ between Greek and Chinese pupils. The Chinese did outperform the Greeks in visuo/spatial ability, but this difference was smaller at earlier ages, grew during the first years of schooling and decreased later. The authors suggest that this pattern can be explained as follows: the Chinese students train their visuo/spatial ability during their early school years, as they have to learn many logographic characters of the Chinese writing system. Later in life, the Greek students adopt compensating strategies to deal with visuo/spatial information, and therefore the difference decreases.^[31]
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).^[32]	Again, there are numerous possible environmental explanations, like greater emphasis on spatial ability rather than verbal ability among hunter-gatherers.
Claimed attributes of the US black-white gap not compatible with only environmental factors
"The g-based factor hierarchy is the most widely accepted current view of the structure of abilities"^[33] 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.^[34] 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).	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) 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), in turn used for many studies regarding g, 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"^[35] This leaves the validity of Spearman's hypothesis, considered a central justification for the genetic explanation, an unresolved question.
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.^[36]	The correlations are not statistically significant.^[37]
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).	Outdated methodology. If anything, the results show that test bias exists.^[38]
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.	See the section on heritability at the beginning of the article. Regarding the disappearance of effects from the shared family environment seen in US studies, see the section on this above. In brief, there are alternative models incorporating the shared maternal (foetal) environment that may better fit the available data, more recent studies suggest that earlier studies may have been biased, and the Dickens and Flynn model allow very large environmental influences also for adults.
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.	Dickens (2005) argues that the same arguments can be applied to the Flynn effect to show that the large and rapid US gain in IQ scores is substantially due to genetic factors which is extremely unlikely. He and Flynn have instead presented an alternative model explaining such contradictions. He argues that it is unlikely that the black-white gap has a large genetic component.^[39] There are many factors that can affect IQ that differ between Blacks and whites, for example breastfeeding and blood lead levels, as noted elsewhere in this article. Many older studies have only studied middle class families but SES has recently been shown to be relatively more important in poorer families.^[40] Several studies have shown that environmental differences between blacks and whites can, in a statistical sense, “explain” nearly all of the difference in cognitive ability between black and white children.^[41]
Studies of US comparisons of both parents to children and siblings to each other finding regression to differing means for different races (85 for Blacks and 100 for Whites) across the entire range of IQs despite the fact that siblings are matched for shared environment and genetic heritage, with regression unaffected by family socioeconomic status and generation examined.^[42] For example, the children of wealthy, high IQ Black parents score lower than the children of poor, low IQ White parents (Jensen 1998b, p. 358); and for Black and White children with an IQ of 120, the siblings of the Black children average an IQ of 100 whereas the siblings of the White children average an IQ of 110; in comparison, for Black and White children with an IQ of 70, the siblings of the Black children average an IQ of 78 whereas the siblings of the White children average an IQ of 85 (Jensen 1973, pp. 107–119))	Does not exclude environmental explanations, it may only make them more difficult.^[43]
Possible differences in brain size and other correlates of IQ
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 reported 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 reported 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."^[44]	These studies do not not refer to racial differences. A correlation of 0.4 explains only 16% of the variance.
Black-White-East Asian differences in 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). (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).	In principle, assuming brain size and IQ are related, then all environmental factors that can affect IQ can also affect brain size. Better nutrition can affect brain growth, as can cognitive stimulation. A larger brain is not by itself evidence for genetics any more than IQ scores are. See the article regarding the Flynn effect for studies showing that brain and skull size has been increasing. 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). The only study cited as evidence for race differences using MRI is an old study primarily looking at a small sample of subjects with serious mental disease (Harvey et al. 1994).
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). Neisser et al. concluded "it is clear that no model in which 'SES' directly determines 'IQ' will do."^[33]	One study found that adjustments for socioeconomic conditions almost completely eliminate differences in IQ scores between black and white children. The remaining difference is statistically insignificant.^[45] A 2002 study looked at how much of the correlation between parent and offspring income different factors accounted for. It found that the offspring's inheritance of wealth, inheritance of a high status race, and having received more years of schooling are important factors, but having received a higher IQ is not a major contributor and having received a higher IQ due to genetics is even less important.^[46] Neisser et al. suggested several other environmental factors, such as being a caste-like minority.
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).	Affirmative action legislation could cause this.
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).	As for brain size, the correlation explains very little of the variance. Similarly, differences in reaction time is by themselves not evidence for genetics and could, for example, be caused by differences in nutrition.
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)	A correlation between IQ and myopia can have other causes than genetics. For example, high IQ and reading may be associated, which increase the risk for myopia. The prevalence of myopia has recently increased, suggesting an environmental influence. While there may also be a genetic component to myopia, this is not necessarily evidence for racial genetic differences in IQ.^[47] A strong genetic association would greatly decrese the value of intelligence in a societies without glasses.