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Direct and indirect measures of intelligence - version 1

Main article: Race and intelligence (Average gaps among races)

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Depending on the way intelligence is measured a variety of gaps may be found between different racial and ethnic groups. Some groups that perform well on one task may do poorly on others. For example, Moroccan and North American individuals were asked in a study by Richard K. Wagner to remember patterns of Oriental rugs and pictures of everyday objects, such as a rooster and a fish. Moroccans who have long experience in the rug trade seemed to remember rug patterns better than the North American individuals. Likewise, in 1979 Robert Serpell had Zambian and English children perform a number of tasks. He found that English children did better on a drawing task, but that Zambian children did better on a wire-shaping task.

The modern controversy surrounding intelligence and race focuses on the results of IQ studies conducted during the second half of the 20th century, mainly in the United States and some other industrialized nations. On average, a difference of approximately one standard deviation was observed in the US between the mean IQ score of Blacks and Whites as adults.

Most recent attempted compilations of average IQ by race place Ashkenazi Jews at the top, followed by East Asians, Whites, Hispanics and Native Americans, and African Americans. Whether these gaps have narrowed or not, especially regarding children which may or may not later also cause a narrowing for adults, is, as noted below, debated.

Average gaps among races on direct measures - version 2

File:US Europe Minorities IQ shuttergraph.png

Average IQ scores of minority groups from North American and Europe, excluding East Asians according to Lynn 2006. No dates given for individual measurements. Lynn's datasets are criticized as being unrepresentative (Heredity April 2004, Volume 92, Number 4, Pages 359-360).

File:East Asians IQ year scatter.png

Average IQ scores of East Asians living in North American and East Asia according to Lynn 2006. Lynn's datasets are criticized as being unrepresentative (Heredity April 2004, Volume 92, Number 4, Pages 359-360).

Over the years, there has been variation in both the observed average IQ of groups, as well as the relative relationships between the average IQ of groups. Early 20th century measures typically found Blacks on the low end, and Whites on the high end. Based on studies from the 1960s and 1970s, Flynn found a slightly lower average IQ of Japanese- and Chinese American children compared to White counterparts. Recent contemporary measures place Blacks on the low end, and Asians on the high end.

IQ test score gap in the US - version 3

2003 SAT results by race/ethnicity. Redrawn from College Board statistics. College Board classifications, like other "race" classifications are not homogeneous; for example, "Asian" includes East Asians and South Asians; "White" includes Jewish Americans and other Whites. Similarly, "East Asians" are not homogenous, nor are "South Asians".

Distribution of SAT math scores by race and ethnicity. [6]

Percentage of race/ethnic groups that scored above 600 on the math SAT [7]

In the United States, the mean IQ score among Blacks has at times been measured as approximately 85 and the mean IQ score among Whites has at times has been measured as approximately 100; the mean IQ score of Latinos has been reported to be measured as approximately 89 for unspecified dates.

The mean score for people of East Asian and Jewish descent is usually higher than the mean score of Whites, but the extent of that difference is not precisely known. However, several studies place the median IQ of Ashkenazi Jews (who make up the overwhelming majority of American Jews) at approximately one standard deviation above the mean for other Whites, with the primary Jewish advantage in verbal reasoning and the East Asian advantage primarily in spatial reasoning. In The Bell Curve, Herrnstein and Murray report mean IQ scores for East Asians and Jewish Americans of 106 and 113 (on a scale where Whites = 103), respectively.

Similar gaps are seen in other tests of cognitive ability, including university admission exams such as the SAT and GRE as well as employment tests for corporate settings and the military (Roth et al. 2001).

IQ test data from various sources - version 4

Main article: Race and intelligence (test data)

NOTE: The information in the following tables is referenced to credible sources; however, it should be noted that some of these studies liberally synthesized their results from different sources and test methods. In general comparisons should only be made between similar primary sources, but this is not always possible given the wide variety of IQ tests, the fluid and debatable nature of racial categorization, and the lack of large scale representative data sets. Among the factors that invalidate comparisons across the studies are environment of the test subjects as well as inherent biases in the test procedures.

Richard Lynn, "Race Differences in Intelligence: An Evolutionary Analysis" 2006 Table 16.2 (indigenous populations)	Average IQ
Arctic Peoples	91
East Asians	105
Europeans	99
Native Americans (north & south)	86
Southern Asian & Northern Africans	84
Bushmen (southern Africa)	54
Africans (subsaharan)	67
Australians (aboriginals)	62
Southeast Asians	87
Pacific Islanders	85

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File:IQ-4races-rotate-highres.png

An example of one kind of gap found in the average intelligence of races are these cumulative IQ gaps by race or ethnicity based on 1981 U.S. distributions. According to these findings, WAIS IQs for Whites (mean = 101.4, SD = 14.7) were higher than those for Blacks (mean = 86.9, SD = 13.0); distributions for Hispanics (mean = 91), East Asians (mean = 106), and Ashkenazi Jews (mean = 112-115) are less precise because of overlap and small sample size. These curves only show scores from the 1st to the 99th percentile (covering 98% of the population).

The gaps found between the average intelligences of races or ethnicities varies depending on methods used for racial grouping, the method and setting used to test intelligence, the health and economic situation of the test takers, the interplay between the culture of the person taking the test and the culture of those who made the test, and the period in history when the test was performed.

Depending on the way intelligence is measured a variety of gaps may be found between different racial and ethnic groups. Some groups that perform well on one task may do poorly on others. For example, Moroccan and North American individuals were asked in a study by Richard K. Wagner to remember patterns of Oriental rugs and pictures of everyday objects, such as a rooster and a fish. Moroccans who have long experience in the rug trade seemed to remember rug patterns better than the North American individuals. Linkewise, in 1979 Robert Serpell had Zambian and English children perform a number of tasks. He found that English children did better on a drawing task, but that Zambian children did better on a wire-shaping task.

In modern western science controversy surrounding race and intelligence focuses on the results of IQ studies conducted during the second half of the 20th century, mainly in the United States and some other industrialized nations. IQ studies outside these nations are few and small. It is uncertain what the average IQ or subgroup IQ tests scores would be with more complete studies in the developing world. IQ test scores in the developing world are affected by factors less important in the developed world such as nutritional deficiencies (see Health and intelligence) Most of the remainder of this article refers to studies attempting to explain race differences in IQ test scores in the US, and does not refer to the world as a whole.

In the past 20 years the use of the IQ test as the sole measure of intelligence and the ability of intelligence tests to predict intelligence between people of different cultural backgrounds has fallen under increasing criticism.

“Perhaps the best way to achieve coherence in the field of intelligence is to recognize that no single correct “model” or “approach” is evident and that different ones elucidate different aspects of a very complex phenomenon (Sternberg, 2003).”

School achievement gap

Employment tests and school achievement - version 1

File:GRE by race.png

2001-2002 GRE scores - used in U.S. graduate schools - by race and ethnicity. The vast majority of the sample was White (76%), with all other groups less than 10% each. The data table also shows the majority of test takers were women (65%), and not representative of the general population. Particularly small sample sizes for minority racial groups make it difficult to make useful comparisons, especially among a self-selected group of GRE test takers

Gaps are seen in other tests of cognitive ability or aptitude, including university admission exams such as the SAT and GRE, as well as employment tests for corporate settings and the military. Measures of school achievement correlate fairly well with IQ, especially in younger children. In the United States, achievement tests find that by 12th grade black students are performing on average only as well as white and Asian students in 8th grade; Hispanic students do only slightly better than blacks.

There is wide agreement that the U.S. Black-White gap among children and adolescents on achievement tests narrowed in the 1970s and 1980s, but stalled during the 1990s. On the basis of these data, Nisbett 2005 argues that the gap in g has also narrowed to "0.6-0.7 standard deviation or approximately 10 IQ points". Both Rushton and Jensen 2005b and Gottfredson 2005b argue that "gains in scholastic achievement do not equal gains in g, and the Black-White differences in g are as large as ever, even for measures of reaction time". Charles Murray argues that the U.S. Black-White gap on the SAT has increased in size to 1 SD from the 1990s to 2005.

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Main article: Achievement gap

Measures of school achievement correlate fairly well with IQ (uncorrected correlations are highest for younger children because of restricted ranges of IQ at higher educational levels). The National Assessment of Educational Progress in the United States, find that by 12th grade Black students are performing on average only as well as White and Asian students in 8th grade; Hispanic students do only slightly better than Blacks. Closing this achievement gap is one of the aims of the No Child Left Behind act in the United States. The gap has been attributed to academic disengagement of Black students and parents and to environmental causes. Poverty in early childhood has long-lasting negative consequences for cognitive development and academic outcomes, as shown by numerous studies.

School achievement gaps between ethnic groups do not remain constant over the years a child spends in school. In a recently publicized 2005 study Deborah Wilson, Simon Burgess and Adam Briggs found that in the UK, Black children enter school at the same level as their White peers, if one controls for a number of covariates. Black children then fall behind, even controlling for covariates, in the first two years of schooling, and stay behind until secondary school where they make greater progress then their White peers substantially, but not completely closing the gap. "This suggests more systemic factors. One such often proposed is the importance of aspirations and values inculcated by families and reinforced by communities. This involves the importance of education in general, and the role of education in getting on." In the later years of schooling the study found that White pupils make slower progress than other ethnic groups.

Attempts to redress the achievement gap in the U.S. include Head Start and related early intervention programs. Neither Head Start nor most other (more intensive) programs have been able to produce lasting gains in IQ or school achievement. Gains are lost after the programs end. Supporters note that they continue as long as the programs continue. The Abecedarian Early Intervention Project is an exception to this pattern, producing an IQ boost of approximately 5 points into adulthood.

Selected IQ data

Test	Black-White gap (SD)	White mean	Black mean	N	Age	Year	Reference
Overall g	1.10	-	-	6,246,729	Adults	Various	Roth, Bevier, Bobko et al. (2001)
AFQT '79	1.21	?	?	?	Adults	1979	reported in Herrnstein and Murray (1994)
AFQT '97	0.97	?	?	?	Adults	1997	reported in Murray (2005)
WAIS R	1.01	101.4	86.5	1,880	Adults	1981	Reynolds et al (1987)
WAIS III	?	?	?	?	Adults	1997	?
WJ	1.05	?	?	?	Adults & Children	2001	reported in Murray (2005); Schrank, F.A., K.S. McGrew, and R.W. Woodcock. 2001. Technical Abstract (Woodcock-Johnson III Assessment Service Bulletin No. 2). Itasca, IL: Riverside Publishing.
WJ	0.99	?	?	?	Children	2001	reported in Murray (2005); Schrank, F.A., K.S. McGrew, and R.W. Woodcock. 2001. Technical Abstract (Woodcock-Johnson III Assessment Service Bulletin No. 2). Itasca, IL: Riverside Publishing.
WISC IV	0.78	103.2	91.7	1,745	Children	2003	Prifitera, A., L.G. Weiss, D.H. Saklofske, et al. 2005. "The WISC-IV in the clinical assessment context." Pp. 3–32 in WISC-IV Clinical Use and Interpretation: Scientist-Practitioner Perspectives, edited by A. Prifitera, D. H. Saklofske, and L. G. Weiss.
WPPSI Full-scale IQ	.23	?	?	483	5 years	1990	Ethnic Differences in Children's Intelligence Test Scores: Role of Economic Deprivation, Home Environment, and Maternal Characteristics - Jeanne Brooks-Gunn, Pamela K. Klebanov, Greg J. Duncan, Child Development, Vol. 67, No. 2. (Apr., 1996), pp. 396-408.

Is the IQ test score gap closing?

U.S. Black and White IQ - version 1

There is disagreement about whether the results of IQ tests show a narrowing of the IQ gap, or if they do who has benefited. Rushton and Jensen 2005b and Gottfredson 2005b argue that "the Black-White differences in g are as large as ever". Roth et al. 2001 found that the recent U.S. Black-White gap in g among adults is 1.1 sd, similar to characterization of the historical U.S. Black-White gap. In an analysis of standardization samples for the WAIS, WISC, SB, and AFQT, Dickens and Flynn 2006a find evidence that the U.S. Black-White gap shrunk between 3 and 6 points from 1972 to 2002. These conclusions were challenged by Rushton and Jensen 2006, and a rejoinder was made by Dickens and Flynn 2006b. Subsequently, Murray 2006 analyzed testing data from the children of the 1979 NLSY cohort, concluding that "the B-W difference did not diminish on either academic achievement or cognitive tests for children born from the mid 1970s through the mid 1990s." To reconcile the contradictory findings, Murray suggests that "the effect that Dickens and Flynn found was concentrated among subjects born before the late 1970s". In 2006, Flynn and Murray debated the shrinking Black-White IQ gap. Both agree that the gap shrunk for children born before the late 1970s, however Murray believes the narrowing stopped while Flynn believes it has continued.

Several sources have argued that the U.S. Black-White gap varies with age. Dickens and Flynn 2006b estimate that the 2006 U.S. Black-White IQ gap is 0.31 SDs at age 4, 0.63 SDs at age 12, 0.87 SDs at age 18, and 1.1 SDs at age 24. Using data from Shuey 1966, Jensen 1998 estimates that the U.S. Black-White gap is 0.70 SDs in early childhood, 1.00 SDs in middle childhood, and 1.20 SDs in early adulthood. A study of children aged eight to twelve months found a U.S. Black-White gap of 0.06 SD.

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Long term White-Black gap in NAEP math scores [8]

Long term White-Black gap in NAEP reading scores [9]

Richard Nisbett and others have argued that the Black-White gap on various ability tests has narrowed from the 1970s to the 1990s, including the Equality of Educational Opportunity (EEO) survey, the National Longitudinal Study, the High School and Beyond survey, the National Education Longitudinal Study, and the National Assessment of Educational Progress program (NAEP). The Journal of Blacks in Higher Education found that although the Black-White gap on the SAT declined from 1976-1988, it has been increasing since 1988. Other studies find that the gap has been decreasing for most of the 20th century and that this trend continued during the nineties.

Jensen has argued that the Black-White differences in g have not narrowed. In support of this claim, he presents evidence that, while there have been gains in measures of acquired competency such as scholastic achievement, these improvements do not indicate gains in g. Jensen also argues that Black-White differences in g seen in measures of reaction time have not narrowed. A large meta-analysis using 6,246,729 samples found a mean Black-White score difference of 1.1 standard deviations (ranging from 0.38 to 1.46 depending on the g loading of the test). As to whether the IQ gap is narrowing, the authors speculated that any reduction was "either small, potentially a function of sampling error ... or nonexistent for highly g loaded" tests. Gottfredson agreed that the Black-White gap observed in the National Assessment of Educational Progress test has narrowed from 1.07 to 0.89 standard deviations. However, she then argues that reduction stopped by the mid-1980s and is compatible with stable group differences in g.

A large (21,260 children) and probably the most recent (1998) study found that the Black-White gap for young children in reading and math scores was much smaller than in earlier studies, and that all of the remaining difference could be explained by a few environmental factors. One possible explanation is that the Flynn effect started earlier for Whites but has now stopped, while continuing for Blacks.

IQ gaps in other nations

World-wide IQ estimates - version 1

File:AverageIQ-Map-World.png

Calculated average IQ of indigenous populations from the book Race Differences in Intelligence by Richard Lynn. Lynn's datasets are criticized as being unrepresentative (Heredity April 2004, Volume 92, Number 4, Pages 359-360). Some of the IQ values are inferred based on a few tests in a nearby country.

One review of the global cognitive ability data is Richard Lynn's 2006 Race Differences in Intelligence, which organizes the data by nine global regions, surveying 620 published studies from around the world, with a total of 813,778 tested individuals. Lynn's meta-analysis lists East Asians (105), Europeans (99), Inuit (91), Southeast Asians and Amerindians each (87), Pacific Islanders (85), Middle Easterners (including South Asians and North Africans) (84), sub-Saharan Africans (67), and Australian Aborigines (62). Searchlight magazine criticizes Lynn's publisher, which is not an academic press and for publishing “classic” Aryan and eugenic tracts.. Lynn has previously argued at length that nutrition is the best supported environmental explanation for variation in the lower range, and a number of other environmental explanations have been advanced (see below). Ashkenazi Jews score significantly higher than other groups (107-115) in the U.S. and Britain, but estimates of the average IQ of Ashkenazim in Israel may be somewhat closer to the European mean. In other data, Hispanics average 91 and African Americans average 87, though the latter is debated. Lynn's survey is an expansion by nearly four times of the data collected in his 2002 IQ and the Wealth of Nations with Tatu Vanhanen. 'IQ and the Wealth of Nations, which dealt with the relationship between IQ and economic development, received strong criticism from some for both error and alleged bias. Lynn argues the surveyed studies have high reliability in the sense that different studies give similar results, and high validity in the sense that they correlate highly with performance in international studies of achievement in mathematics and science and with national economic development.

Related groups sometimes vary greatly in IQ in different nations. Black Africans score much lower than blacks in the US, although Black Americans average about 7-20% European admixture. Some reports indicate that the black–white gap is smaller in the UK than in the U.S. Differences between groups of whites can also be seen, ranging to the low 90s in SE Europe (with a decrease also seen in brain size). In Israel, large gaps in test scores and achievement separate Ashkenazi Jews from other groups such as the Sephardi.

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Commonly cited IQ figures
for various groups

Group	IQ avg	Citation
Jewish Americans	113	Herrnstein & Murray (1994)
East Asians	106	Herrnstein & Murray (1994) Lynn (1991a)
Whites	100	Herrnstein & Murray (1994) Lynn (1991a)
Hispanics	89	Herrnstein & Murray (1994)
Native Americans	89	Lynn (1991a)
African Americans	85	Herrnstein & Murray (1994) Lynn (1991a) Roth et al. (2001)
Subsaharan Africans	70	Lynn (1991a)

Attempted compilations of average IQ by race generally place Ashkenazi Jews and East Asians on top, followed by non-Ashkenazi Whites, other Asians, Arabs, Blacks and Indigenous Australians. See IQ and the Wealth of Nations for an attempted compilation of average IQ for different nations and a discussion of associated measurement problems.

The IQ scores vary greatly among different nations for the same group. Blacks in Africa score much lower than Blacks in the US. Studies on African Blacks have yielded results of 65 and 69. Lynn (1991a) suggests this value should be rounded up to 70. The book IQ and the Wealth of Nations gives values for African nations ranging from 59 for Equatorial Guinea to 77 for Zambia.

Studies on Native Americans yield results ranging from 70 to 90. Lynn (1991a) suggests that the mean of several studies, 89, may be a reasonable approximation. Native Americans score higher on tests of spatial than verbal reasoning, a trait also shared with East Asians.

Some reports indicate that the Black–White gap is smaller in the UK than in the U.S. Other examples are Jews who score much lower in developing nations and Koreans who score much lower in Japan. There are also other examples of IQ score differences between close neighbors in the same nation, for example between French vs. Flemish speakers in Belgium, Slovaks vs. Gypsies in Slovakia, Irish and Scottish vs. English in Great Britain, and white speakers of Afrikaans vs. white speakers of English in South Africa. In Mexico, Whites score higher than Mestizos, who score higher than Native Mexican Indians.

There has been at least one comparative study on IQ scores in different European nations. The difference between the highest and lowest average national IQ scores is 8 points. There is a not statistically significant correlation between the country's latitude and its average IQ score. Also, Southern Europeans have a larger variation than Northern Europeans. Norwegians have less than half of the variability of Whites in the US while Italians and Bulgarians have about 150%.

In Israel, there is a large gap in test scores and achievement between the Ashkenazi Jews and other groups such as the Sephardi. Gaps are seen between Israeli Jews and Ethiopian Jews. A similar gap in IQ scores and achievement is seen between the Chinese and Malays in Singapore.

Both Lynn and Rushton have suggested that high IQ is associated with colder climates. To test this hypothesis, Templer and Arikawa (in press [doi:10.1016/j.intell.2005.04.002]; see discussion [10]) compare the national IQ data from Lynn and Vanhanen with data sets that describe national average skin color and average winter and summer temperatures. They find that the strongest correlations to national IQ were −0.92 for skin color and −0.76 for average high winter temperature. They interpret this finding as strong support for IQ-climate association. Other studies using different data sets find no correlation [11][12].

World-wide scores

Cognitive ability scores for the ten global genetic clusters identified in previous genetic cluster analysis have been surveyed by Richard Lynn. Lynn regards these ten population groups as races, and extracts racial averages from 620 published studies surveying a total of 813,778 tested individuals. When taken as individual national averages, the data available, particularly regarding the developing world, is speculative due to limited sampling, year of testing, and varying type of cognitive ability test used. Lynn's previous work, including the trade book IQ and the Wealth of Nations with Tatu Vanhanen, have received widespread and strong criticism for both bias and error.

In general, Lynn lists East Asians and Europeans as demonstrating the highest average IQ, indigenous Americans and other Eurasians with intermediate average IQ, and Africans and Australian Aborigines with the lowest average IQ. According to Lynn, when the studies are grouped and taken as averages for the ten racial groups, the argument for their reliability is that, though additional evidence may be required to confirm some of the more limited estimates, many have very high reliability in the sense that different studies give similar results, as well as that they correlate highly with performance in international studies of achievement in mathematics and science and with national economic development. Lynn argues established environmental hypotheses can explain a substantial amount of these differences. The data set for sub-Saharan Africans around the world, the one most often criticized, is drawn from 155 different studies with a combined sample of 387,286 people. 57 of the studies are from countries in Africa, 54 from western countries, and 16 from non-western countries outside of Africa.

Some Ashkenazi Jews score significantly higher than any other group. An IQ of 70 is often associated with mental retardation, but deficits in adaptive behavior, such as telling the time, interacting socially, and looking after oneself, have only limited correlation with IQ, and are more important than IQ in determining whether a person is able to live an independent life.

IQ scores vary greatly among different nations for related groups. Blacks in Africa score much lower than Blacks in the US. Some reports indicate that the Black–White gap is smaller in the UK than in the U.S. American Blacks average about 7-20% European admixture; UK admixtures are not as well-studied. Many studies also show differences in IQ between different groups of Whites. In Israel, large gaps in test scores and achievement separate Ashkenazi Jews from other groups such as the Sephardi.

IQ and Retardation

The low average IQ of Blacks in Sub-Saharan Africa is often met with incredulity. Among whites, almost everyone with an IQ of 75 is also retarded, but among groups with lower average IQs this association no longer holds. The reason is that mental retardation describes both an inability to solve problems (what IQ measures) and an inability to perform everyday tasks (e.g. daily living skills, communication skills, and social skills). Many whites with very low IQ have a genetic disorder (e.g., Down syndrome), whereas that level of reasoning ability is nearer to the average for sub-Saharan Africans. Jensen (1998) describes this phenomenon at length, including his great surprise at finding that people with normal social skills can perform so poorly on tests of fluid reasoning.

An IQ of 70 is often associated with mental retardation, but deficits in adaptive behavior, such as telling the time, interacting socially, and looking after oneself, have only limited correlation with IQ, and are more important than IQ in determining whether a person is able to live an independent life (Mackintosh 1998, p. 177). Mercer 1973 reported that on the basis of IQ alone 10 times as many Blacks as Whites would be classified as retarded, but when adaptive behavior measures are added to the criterion, this difference completely disappears. Some ethnic differences in cognitive ability appear in some aspects of cognitive ability and not others (see below; Mackintosh 1998, p. 178). The Black-White disparity seen in IQ does not appear in some basic cognitive functions that don't involve more than minimal elaboration, transformation, or other mental manipulation (Mackintosh 1998, p. 178; Jensen 1973).

Hybrid vigor

Intelligence is associated with the degree of "hybrid vigor" (heterosis) manifested by offspring of cross-ethnic matings. Children of Japanese–Caucasian cross-ethnic matings score .26 SD higher on several cognitive tests than those from within-ethnic matings, despite having virtually identical parental educational and occupational backgrounds. The increase in scores tends to be higher on cognitive tests that are more g-loaded, suggesting that hybrid vigor improves g. Heterosis may be partially responsible for the Flynn effect.

Reaction time

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Average racial differences have been asserted to exist on tests of response time, although it is also argued that some of these differences can be explained by cultural phenomena. Jensen has used reaction time as a proxy for IQ, despite the low correlation.. The use of reaction time as a proxy for race has been disputed by others in the field. Leon J. Kamin and Sharon Grant-Henry used Jenson's work as an example of "claims about racial differences in intelligence that are not supported by scientific evidence" in thier study Reaction Time, Race, and Racism.

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

Jensen 1993 has stated that this allows for an extension of Spearman's hypothesis to include reaction time. Based on these results, they have concluded that the observed East Asian-White-Black differences have a neurological basis.

Brain size & structure

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An 1839 drawing by Samuel George Morton who wrote that the difference between humans was one of species. Drawing of "a Negro head… a Caucasian skull… a Mongol head" showing skull size.

Many studies report that IQ has a moderate correlation with various measures of brain size. For example, a 2005 meta-analysis found that brain size correlates with IQ by a factor of approximately .40 among adults. The correlation was also found in some studies to hold true within families (where environmental factors can be considered to be similar), but in one study of 36 sibling pairs essentially zero correlation between brain size and IQ was found when comparing within families. Some studies have found racial differences in brain size. Professor Ulric Neisser claims that the studies comparing brain size by race "exhibit many internal inconsistencies", but that "there is indeed a small overall trend".

There are several hotly debated studies which have concluded that there are race differences in brain size. These studies are criticized as having not found racially-based difference, with critics arguing instead the the variation better explained in terms of geography. Perhaps the largest single study, Beals et al. 1984 analyzed more than 20,000 skulls from around the world, finding that brain size varied with latitude of biogeographic ancestry. Lieberman (2001) explains "...the relationship between latitude and cranial size is an example of Bergmann’s principle that crania are more spherical in cold climates because mass increases relative to surface area to conserve core temperatures...Beals, Smith, and Dodd emphasize that this relationship is independent of 'race'.".. By this they mean that brain size varies with latitude both within and between races. The biogeographical variation in brain size is widely described as an evolutionary adaptation to climate. Lieberman and other anthropologists (2001) have also made several other criticisms.

In 1970 Philip V. Tobias listed a number of difficulties involved in measuring and making meaningful comparisons of brain weight. These included equating subjects on age, sex, body size, temperature etc. In addition, brain development is plastic, and brain size may be affected by early environmental factors. Because of all these difficulties, Tobias concluded that no adequate racial comparative studies had actually been conducted.

The brain size of American Blacks reported in Tobias’s summary were larger than any White group, (which include American, English and French Whites) except those from the Swedish sub sample (who had the largest brains of any of the 77 national groups measured), and American Blacks were estimated to have some 200 million more neurons than American Whites (See Tobias 1970; Weizmann et. 1990).

Possibly related to the Flynn effect[13] is, as also previously observed by Boas, increase in cranial vault size and change in shape during the last 150 years in the US. Brain size has increased for both American Blacks and Whites probably due to improved health and nutrition.

According to Lieberman, Rushton and others combining the correlations between race, IQ and brain size to establishes a correlation between race and IQ. This conclusion is strongly objected to by Lieberman and other scientists, both on the basis of the initial correlation asserted between race and brain size, and the progressively weak correlation as the studies are combined.

see also Craniometry, Neuroscience and intelligence

Mean cranial capacity (cc)

Measurement	East Asian	European	African
Autopsy	1351	1356	1223
Endocranial volume	1415	1362	1268
External head measurements	1335	1341	1284
Corrected for body size	1356	1329	1294
Mean	1364	1347	1267
Redrawn from Jensen 1998b, Table 12.1

Some historical and modern studies, using skull and head measurements, weighing of brains at autopsy, or more recently, magnetic resonance imaging, report racial differences in average brain size similar to those for IQ. Other studies have not found these results. These studies are usually accompanied by a great deal of controversy.

Old studies

Several studies from the 19th century and early 20th century found racial differences. Some showed that whites had the largest measurements, which was the expected view at the time. This is different from more recent results [14][15](Rushton, 1991, 2000). As noted later, brain size and shape has changed greatly in the last century.

In his 1839 Crania Americana, anthropologist Samuel George Morton reported that the mean cranial capacity of the skulls of Whites was 87 in³ (1426cm³), while that of Blacks was 78 in³ (1278cm³). Based on the measurement of 144 skulls of Native Americans, he reported a figure of 82in³ (1344cm³).

Morton's work has been criticized by Stephen Jay Gould, who alleged in his 1981 book The Mismeasure of Man that Morton was guilty of fudging data and "overpacking" the skulls with filler. Despite Gould's retabulation of Morton's data, however, the differences in brain size among different races still persist, with the data still showing a difference of about four cubic inches between modern Caucasians and Africans. Gould writes that the differences are "trivial", but current head of the controversial Pioneer Fund J. Philippe Rushton (1996) responds that a difference of only a single cubic inch equates to millions of neurons. In 1988, J. S. Michael remeasured a random sample of Morton's skulls and concluded that Morton had made very few errors. J. Philippe Rushton (1989) additionally reanalyzed Gould's retabulation, concluding that Morton had shown a pattern of decreasing brain size proceeding from East Asians, Europeans, and Africans.

Cortical neurons (billions)

East Asian	European	African
13.767	13.665	13.185
Source: Rushton 2000

In 1873, Paul Broca found the same pattern by weighing brains at autopsy. Other historical studies showing a Black-White difference in brain size include Bean 1906, Mall 1909, Pearl 1934 and Vint 1934. In 1888, H.D. Rolleston reported that the brain of the Australian Aborigine weighed less than the brain of Blacks (44.3 oz, 1256 g) , which in turn weighed less than the brain of Whites (49 oz, 1389 g). He also found that the Australian brain was less convoluted than those of Whites (p. 33).

Some 19th century studies have also found that the brains of Whites are more convoluted than those of Blacks [16][17] or Australian Aborigines (Rolleston 1888, p. 33). It is often assumed that convolutions are associated with increased intelligence because they allow a greater surface area to be packed into a smaller volume. However, dolphins, who have shown no signs of super-human intelligence, have more convoluted brains than do humans (Ridgway, S.H. (1986). Dolphin brain size. p. 59-70 In: M.M. Bryden and R.J. Harrison (Eds) Research on Dolphins. Clarendon Press, Oxford. 478 pp.).

Recent studies

File:Cranial capacity-IQ.png

Relationship between group IQ and cranial capacity. Redrawn from Jensen 1998b, Fig. 12.4

In his controversial 1995 work Race, Evolution, and Behavior, J. Philippe Rushton reported an average endocranial volume of 1,415 cm³ for "Orientals [sic]", 1,362 for Whites, and 1,268 for Blacks. When adjusted for average body size, the differences become more pronounced; i.e., the encephalization quotients (EQ) display greater differences than do absolute brain sizes (Jerison 1973, Jerison 2000; Rushton 1991). Rushton 1991 found an EQ of 7.26 for East Asians as compared to 6.76 for Caucasians. Differences in brain size between Asians and Europeans sometimes do not appear until adjusted for body size (Rushton 1997). In some cases Europeans averaged higher absolute brain sizes than East Asians but lower relative brain sizes when adjusted for body size. It needs to be added that these brain sizes are "mean" averages, not actual brain size. East Asians have a much higher endocranial measurement than any other race. This means they have much more dura matter (the 3 layer membrane that protects the brain). That might explain the more spherical brain shape. This membrane does not contain neurons. Many contest that brain/body ratio's should only include actual brain size. Also European and American "whites" are not separated into different categories in these studies as East Asians are from other orientals. For example, darker traited whites as opposed to lighter traited whites (only 30% of white people in Europe and America have blue eyes, due to heterosis).

Ulric Neisser, who co-authored the American Psychological Association's Task Force Report on Intelligence, examined Lynn and Rushton's data and writes, "although those studies exhibit many internal inconsistencies (and the within-groups variabilites are always much larger than the between-groups differences), there is indeed a small overall trend in the direction they describe."

File:HRSM.png

Findings of Ho et al (1980, Table 1). Left to right: Brain weight distributions for 222 Black females (μ=1158, σ=119), 395 White females (μ=1252, σ=125), 228 Black males (μ=1286, σ=138), and 416 White males (μ=1392, σ=130).

One other study showing similar patterns in average brain weight is Ho et al. 1980 which analyzed autopsy records from Case Western Reserve University (N=1,261) to determine the effects of age, gender, and race on brain weight. The authors found that while there was a large amount of overlap among the groups, there were also statistically significant differences between the groups, and found that White males had the largest brain weight, followed by Black males, White females, and Black females. For a discussion of gender differences in brain size see sex and intelligence. Ho et al. 1980 also discovered that mean brain mass decreased over a five year period fastest for White males, followed by Black males, White females, and Black females.

Other studies have shown the same pattern in average head size, including Rushton 1992, Rushton 1994, and the National Collaborative Perinatal Project (described by Broman et al. 1987) which collected anthropometric data, including head measurements and IQ, on approximately 35,000 children from 1959 to 1974 (although the study began with over 50,000 subjects, some attrition occurred as with many longitudinal studies). Analyses of the data found the East Asian ? White ? Black pattern in head size and IQ at 4 months, 1 year, and 7 years of age.

File:Mcshane1983.png

Distribution of skull distance measurements for various racial groups. (F=Frontal skull distance measurement, O=Occipital skull distance measurement. From McShane 1983

East Asian brains have greater width and breadth (i.e., are more brachycephalic) and are more spherically shaped than those of Europeans (it should be noted that theirs has more angles or a diamond shape, as well as a more developed frontal region of the skull). Africans tend to have longer and narrower (more dolichocephalic) brains. Beals et al. proposed that the longer and narrower African brain evolved for better heat dissipation in a warmer climate, while East Asians and Europeans evolved comparatively shorter and wider brains for thermoregulatory purposes in a cooler climate. Rushton and Ankney 2000 (pp. 612-613) question the thermoregulatory hypothesis, instead positing that brachycephalization and sphericalization allow for greater brain size. At the same time, Rushton and Ankney believe it is possible that the need to thermoregulate in Africa may have selected against increasing brain size. Rushton and Ankney 2000 found a pattern of descending prognathism, glabella size, postorbital constriction, and temporal fossae in African, European, and East Asian skulls and propose that these structures shrank over the course of evolution to allow greater brain size.

Rushton has been accused by other researchers of misrepresenting the data. When they have reanalyzed the data, Zack Cernovsky et al. argue that many of Rushton's claims are incorrect. [18]

Extensive statistical analyses by Beals et al. showed that cranial size varies primarily with climatic zones (e.g.,distance from the equator), not race. According to Beals et al., the correlations of brain size to race are spurious: smaller crania are found in warmer climates, irrespective of race. Several other studies found that North American Blacks were superior to American Whites in brain weight, that they had cranial capacities that compared favorably to the average for various samples of Caucasians, and that they had excess neurons larger than many groups of Caucasoids, for example, the English and the French. In general, skulls from people in countries with poverty and infant malnutrition are smaller regardless of race. [19]

Modern studies using MRI imaging shows a weak to moderate correlation between brain size and IQ and have shown that brain size correlates with IQ by a factor of approximately .40 among adults. The correlation between brain size and IQ seems to hold for comparisons between and within families. although one study found no correlation within family. A study on twins showed that frontal gray matter volume was correlated with g and highly heritable. A related study has reported that the correlation between brain size (reported to have a heritability of 0.85) and g is 0.4, and that correlation is mediated entirely by genetic factors. Note that none of the MRI studies have studied racial differences.

In a 2005 review of the literature [20], Rushton and Jensen claim that MRI studies show racial differences in brain size. The cited study (Harvey et al. 1994) compared brain size between a group of 26 persons with bipolar disorder and a group of 48 persons with schizophrenia and also included 34 healthy controls. The distribution of age and race was approximately equal across the three groups and consisted of Caucasians, Blacks, and West Indians (p. 692, table 1). Harvey et al. write,

Over the entire sample intracranial volume was related to height (P=0.0001), gender (P=0.001), ethnicity (P=0.007), and IQ (P=0.03), but not age; larger volumes generally occurred in those subjects who were taller, male, and Caucasian" (p. 693).

(Note that East Asians were not included in the study, that there was a sex ratio imbalance among the schizophrenic group (p. 692), that intracranial volume is not the same thing as brain size, and that the sample where most have serious mental disease may not be representative for population as a whole.)

Cranial vault size and shape have changed greatly during the last 150 years in the US. These changes must occur by early childhood because of the early development of the vault. The explanation for these changes may be related to the Flynn effect.

References

Main article: Race and intelligence (References)

Commenting out the categories

{{Race and intelligence}} [[Category:Race and intelligence controversy| ]]