Race and intelligence
Construct for the Social Sciences
The relationship between race and intelligence has been the subject of a large and complex scientific and public debate, often influenced by political correctness. Human races/ethnicities differ on average measured IQ according to large scale testing. The role of genetics as a cause for these measured differences has been examined in numerous scientific studies. The differences are argued to be responsible for numerous important societal effects.
- 1 History
- 2 Measured average IQs
- 3 General race and intelligence research issues
- 4 The genetics or not debate
- 5 Evolutionary explanations for racial differences
- 6 Race, sex, and intelligence
- 7 Interventions affecting IQ
- 8 Significance of IQ differences
- 8.1 Significance of IQ and g
- 8.2 Significance of environmentally caused IQ changes
- 8.3 Very low average IQ values
- 8.4 Personality and apparent IQ
- 8.5 Historical societies
- 8.6 Modern societies
- 8.7 Future
- 9 External links
- 10 References
Early scientific research started in the nineteenth century and included methods such as skull and brain measurements.
Francis Galton, half-cousin of Charles Darwin and an important eugenicist and differential psychologist, was also an important early pioneer in intelligence research as well as in race and intelligence research. Arthur Jensen has stated that "Although the conclusions Galton drew from his empirical studies were seldom compelling for lack of the needed technology and methods of statistical inference in his day, contemporary research has generally borne out most of Galton’s original and largely intuitive ideas".
The first IQ test was created in 1905. By the end of the twentieth century, many hundreds of studies measuring the IQs of racial/ethnic groups had been published. The number of studies discussing these results is much larger.
Race research in general, including also race and intelligence research, became increasingly a taboo subject after WWII. The influential 1950 declaration "The Race Question" contributed to this.
The Pioneer Fund was influential during this postwar period in keeping some research and debate alive
In 1969, Arthur Jensen caused great public controversy with the article "How Much Can We Boost IQ and School Achievement?" in which he argued for genetics being an important explanation for the measured differences.
In 1987, a survey of the opinion of IQ experts was published. One question concerned what caused the US Black-White IQ gap. The survey found a large support for a partial genetic, partial environmental explanation. The survey was later used in the book The IQ Controversy, the Media and Public Policy (1988), which argued that the general public was misled by the media regarding the expert opinion.
The Bell Curve public debate
Further public debate ensued after the publication in 1994 of The Bell Curve, a book primarily focusing on IQ and not on race, but which did state the existence of race differences regarding measured average IQ and argued for these being an important explanation for many social differences between the races, such as regarding crime, education, unemployment, etc. Such arguments were not new in the scientific literature, but The Bell Curve made such arguments more known to the general public. A frequent misrepresentation is that the book made many new and controversial claims, which had never been made before, implying that they were new and fringe views with little support, ignoring that the book cited an extensive existing academic literature.
In response to the Bell Curve debate and perceived false and highly misleading views in the public debate, the statement "Mainstream Science on Intelligence" was signed by 52 professors.
The American Psychological Association also responded to the debate by creating a committee which in 1995 published the report "Intelligence: Knowns and Unknowns". It acknowledged the gap between the average measured IQ scores of Whites and Blacks, the importance of IQ, and stated that both genetic and environmental explanations had inadequate support. It concluded "In short, no adequate explanation of the differential between the IQ means of Blacks and Whites is presently available."
Jensen commented that "As I read the APA statement, [...] I didn't feel it was contradicting my position, but rather merely sidestepping it. It seems more evasive of my position than contradictory. The committee did acknowledge the factual status of what I have termed the Spearman Effect, the reality of g, the inadequacy of test bias and socioeconomic status as causal explanations, and many other conclusions that don't differ at all from my own position. [...] Considering that the report was commissioned by the APA, I was surprised it went as far as it did. Viewed in that light, I am not especially displeased by it."
The leftist and highly political American Anthropological Association in 1994 issued a "Statement on "Race" and Intelligence" and in 1998 issued a "Statement on "Race"". Neither of these brief, politically correct statements cited any sources for the claims made, unlike the many sources cited by the long report by the American Psychological Association.
The debate also caused other responses, such as popular science books aimed at the general public. The Jewish Stephen Jay Gould published a second edition of The Mismeasure of Man (originally published in 1983) and the Jewish Jared Diamond published Guns, Germs, and Steel in 1997. Both denied genetically caused racial IQ differences, both became international bestsellers among the general public, and both were translated into numerous languages. Their impacts on the academic debate among IQ researchers were much smaller. (More generally regarding the views of Jewish scientists on genetic race differences, see Arguments regarding the existence of races: Views of scientists.)
The 2000s saw a widening of the debate from mainly being about US racial differences to also more systematically include worldwide racial differences. Richard Lynn published several books which systematically reviewed earlier worldwide IQ testing. He estimated the average IQs of races and the average IQ of countries as well as argued for many and important practical effects due to the IQ differences. Many other researchers have published further studies on these subjects.
In 2013, another survey of expert opinion was done. It and the 1987 survey are discussed in more detail below in the sections "Opinion of experts in 1987" and "Opinion of experts in 2013".
The 2010s saw studies starting to use genetic data, reflecting the continued rapid advance in genetic research. This may in the near future definitely settle the debate regarding whether the measured racial IQ differences are partially genetic or not.
Measured average IQs
Note that the below values are measured average IQs for different groups, according to the given sources. Individuals may differ greatly from these values and individuals with high and low IQs exist in all groups.
Richard Lynn in his 2006 book Race Differences in Intelligence reviewed the literature on worldwide IQ testing and calculated the average IQs for different races based on earlier IQ test results (citing hundreds of different studies testing the average IQ of different races).
|Race: Measurement region||Measured average IQ||Number of samples||Number of countries|
|Aborigines: New Guinea||63||5||1|
|Amerindians: North America||86||19||2|
|Amerindians: Latin America||86||10||5|
|Arctic Peoples: North America||91||15||2|
|Bushmen: South West Africa||54||3||1|
|East Asians: East Asia||105||60||7|
|East Asians: United States||101||26||1|
|East Asians: Elsewhere||102||9||5|
|Europeans: Outside Europe||99||23||12|
|Pacific Islanders: Pacific Islands||85||14||9|
|Pacific Islanders: New Zealand||90||12||1|
|South Asians and North Africans: South Asia||84||37||17|
|South Asians and North Africans: Britain||92||16||1|
|South Asians and North Africans: Europa||85||18||3|
|South Asians and North Africans: Africa||86||6||2|
|South Asians and North Africans: Fiji, etc||85||3||3|
|Southeast Asians: Southeast Asia||87||11||6|
|Southeast Asians: United States||93||7||1|
|Sub-Saharan Africans: Africa||67||57||17|
|Sub-Saharan Africans: Caribbean||71||14||6|
|Sub-Saharan Africans: United States||85||29||1|
|Sub-Saharan Africans: Netherlands||85||7||1|
|Sub-Saharan Africans: Britain||86||18||1|
These are measured (phenotypic) average IQs. Differences for the same race between different regions were explained by factors such as malnutrition being prevalent in developing nations, race mixing, as well emigrants for a variety of reasons possibly having different average IQ than that of their region of origin. Thus, Lynn estimated that the genotypic average IQ of Sub-Saharan Africans is 80 rather than the measured phenotypic 67. The genotypic average IQ of Blacks in the United States was estimated to be somewhat higher at 85 due to some interbreeding with Europeans.
There were also some groups differences regarding the profile of narrower mental abilities. East Asians and Amerindians had a pattern of relatively high non-verbal reasoning/spatial IQ and relatively low verbal IQ (compared to the overall average measured IQs of the groups).
Regarding various criticisms and counter-criticisms of such literature reviews and measured average IQ scores (in particular the average measured IQ of Sub-Saharan Africa), see the related discussions in the article about Countries and intelligence.
Very large scale international student assessment tests are regularly performed in many countries. Such testing may often be much larger and more recent than formal IQ testing. These and other country level tests may not directly test racial differences, but results from such testing are sometimes used for indirect or related studies. Again see the article Countries and intelligence.
World average IQ
The average IQ of the world as of 2000 has been estimated to be 90 based on estimated average country IQs and country population sizes.
United States Black-White gap
Review articles by Rushton and Jensen (2005 and 2010) stated that in the United States, Blacks and Whites have been the subjects of the greatest number of studies. These studies have shown that the Black-White IQ difference is about 15 to 18 points or 1 to 1.1 standard deviations (SDs).
Such a difference means that the White average IQ is higher than that of 80-85% of Blacks. However, it should be noted that for "bell curve" distributions ("normal distributions"), such as for IQ and many other traits, if there is an average difference between two groups, then it will be amplified at the extremes. One example is regarding height where the men:women ratio becomes increasingly larger with increasing height. Similarly, IQ differences will be most pronounced at extreme IQs.
Roth et al. (2001) in a meta-analysis reviewed the results of over 6 million participants on tests of cognitive ability or aptitude and found a Black-White gap of 1.1 SD. Consistent results were found for college and university application tests, such as the Scholastic Aptitude Test (N = 2.4 million) and the Graduate Record Examination (N = 2.3 million), as well as for tests of job applicants in corporate sections (N = 0.5 million) and in the military (N = 0.4 million).
Some studies have argued that the gap has narrowed by up to a third, but has been criticized for selective exclusion of opposing results, incorrect calculations, or for this occurring on the tests measuring the g factor less well. If a narrowing has occurred, then it may have stopped in recent times. Some narrowing is compatible with the gap being partly environmental. Other studies have found no narrowing. The meta-analytic review by Roth et al. stated that any narrowing was "either small, potentially a function of sampling error...or nonexistent for highly g loaded instruments”. A 2017 study stated that "It is safe to conclude there is no gap narrowing with respect to vocabulary scores and that Huang & Hauser’s (2001) findings were the result of statistical artifacts."
See also the section Race and intelligence: The genetics or not debate: Shared and unshared environmental factors regarding the gap being argued to have narrowed for children, and especially young children, but this narrowing almost completely disappearing as the individuals age.
A 2013 review stated that "a gap of 1 full standard deviation is already apparent on IQ tests at 36 months of age, and that there has been no obvious convergence in this early performance difference over time."
A factor that could possibly cause a change in average cognitive ability score for a group (including immigrant groups) is if an increasing number of mixed-race individuals tend to identify themselves as members of this group (such as mixed Black-White individuals tending to identify themselves as Black). However, such a cognitive ability score change could reflect the average genetics of the group changing.
Another view is that the Black-White IQ is actually larger than 1 SD and that the average Black IQ is likely 78 (a 22 point Black-White gap). This is argued to be supported by testing such as the military draft testing during WWII, which is argued to be the most representative testing ever done. It is argued that higher results than 78 may be due to unrepresentative samples caused by factors such as non-participation in voluntary testing by the very lowest scoring segments of the Black population in inner cities.
The US group "Hispanics" is a diverse group that may have Amerindian, European, and Sub-Saharan African origins in varying proportions. Most are of mixed Amerindian/European origin.
In the US, the tested average IQ of "Hispanics" is typically intermediate between that of Blacks and Whites. Both the above mentioned 2001 meta-analysis and the book Race Differences in Intelligence found an average IQ of 89.
Several studies of the IQ of Gypsies, a people of South Asian origin living in Europe since several centuries but with little intermarrying with other groups, have found average IQs ranging from 70 to 83. A 2015 meta-analysis stated an average IQ of 74.
See also Gypsies: Intelligence.
Several studies have stated that the measured cognitive ability test scores of immigrants are generally similar to those from their region of origin and that this generally persists for at least several generations. There are also discussions regarding some specific immigrant groups, such as West Indians of African origin immigrants to the United States and African immigrants to the United Kingdom. See Race and intelligence: The genetics or not debate: Immigrants on this topic.
The book The Nature of Race: the Genealogy of the Concept and the Biological Construct’s Contemporaneous Utility stated that "As Baten and Juif (2013) note, the international cognitive ability differences are not new and they precede the event of mass schooling. As such, Baten and Sohn (2013) found that Korea, China and Japan had high numeracy levels in the 1600s; Juif and Baten (2013) found that Spanish and Portuguese had higher numeracy levels than Amerindian Incas in the 1500s. Juif and Baten (2013) also found that 1820 cohort ethnic/national cognitive ability levels predicted 21st century national levels."
There are also several variables associated with IQ which can also be measured (such as brain size, reaction time, and different results on different kinds of tests/subtests) and which have been measured in different groups. They are discussed in the article Race and intelligence: The genetics or not debate.
General race and intelligence research issues
Ad hominem, straw men, and guilt by association
Those arguing for a genetic explanation, sometimes referred to as "hereditarians", are frequently subjected to various forms of ad hominem personal attacks. This may include accusations of being "racist" (in some extremely negative sense), associations with claimed "racists", claimed "racists" using the research, etc. Obviously, ad hominem personal attacks are not scientifically valid arguments regarding what causes the racial IQ differences.
A somewhat more sophisticated ad hominem attack method is more or less openly insinuating that the researchers are bribed by the Pioneer Fund. This despite many hereditarians never having received any research funding by the Pioneer Fund. The argument may then be that these researchers are relying on earlier research funded by the Pioneer Fund. This ignores the often completely independent research done by these researchers. This also ignores that a researcher may have a far easier career and even physical security if being politically correct. One example being that the Nobel Prize winner and discoverer of DNA James Watson was essentially fired for publicly expressing a hereditarian view. Finnish police considered starting a criminal investigation of Tatu Vanhanen, co-author of IQ and the Wealth of Nations, for expressing hereditarian views.
Stephen Jay Gould's book The Mismeasure of Man became an international bestseller. It has been criticized by hereditarians as largely attacking straw men, such as possibly problematic results from early intelligence research that are not relevant for the modern debate. The book has been argued to be an attempt to discredit modern research and modern researchers by using guilt by association and to have many other problems. Furthermore, an important criticism in the book was regarding the early nineteenth century researcher Samuel George Morton. Gould accused Morton of manipulating the results regarding average racial cranial capacities. However, a 2011 study made new measurements of the skulls used by Morton and analyzed Morton's and Gould's claims. The study stated that Morton had not manipulated the results. On the other hand, Gould had done several remarkable errors.
Race research and the origin of racism
The existence of races
Denying the existence of races may be used as an attempted argument against race and IQ research. However, it should be noted that even if races in the sense of subspecies were proven to be incorrect, then this does not actually make the debate disappear. It is possible to study IQ differences between groups that are not races (for example, IQ differences between criminals and non-criminals, IQ differences between different age groups, and so on). Even those claiming that races are social constructs still argue that it is possible to study, for example, average income differences between Blacks and Whites, so average IQ differences could also be studied. Simply demanding that a more politically correct label than "race" should be used, such as "ethnicity" or "population", will not change this.
Blacks and Whites differ genetically regarding, for example, the genes for skin color and sickle-cell anemia. So they could differ also regarding IQ genes. Furthermore, IQ is likely affected by a very large number of genes. This means that even if the population differences regarding the population frequencies of individual gene variants affecting IQ are all small, but these population frequencies correlate, then the total effect of many such small but correlated differences may be that the population differences regarding genetic effects on IQ are very large.
It is perfectly possible to study the role of genetics as an explanation for differences between groups that are not subspecies or even between groups that no one has claimed to be races. Current examples would include the enormous amount of medical research regarding the genetic differences between those having a certain disease and those not having this disease.
The genetics or not debate
The scientific debate regarding whether the measured racial IQ differences (in particular the well-studied US Black-White gap) are partially genetic involves numerous different scientific studies using many different kinds of evidence. It sometimes uses non-trivial mathematics. The debate is discussed in the article Race and intelligence: The genetics or not debate.
This section will only briefly mention two aspects: surveys of expert opinion and the recent direct genetic evidence which may soon resolve the issue.
Opinion of experts in 1987
The 1987 "Survey of Expert Opinion on Intelligence and Aptitude Testing" was published in American Psychologist (the official journal of the American Psychological Association). It surveyed 1020 IQ experts, 661 of which completed the questionnaire. One question was "Which of the following best characterizes your opinion of the heritability of black-white differences in IQ?"
- 14% declined to answer the question.
- 24% voted that there was insufficient evidence to give an answer.
- 1% voted that the gap was "due entirely to genetic variation".
- 15% voted that it "due entirely to environmental variation".
- 45% voted that it was a "product of genetic and environmental variation".
Opinion of experts in 2013 / 2014
In 2013/2014, a similar survey was done and found that 40% of experts favored a more environmental explanation, 43% a more genetic one, and about 17% a 50-50 split. 84% of experts stated that genes are influential. This despite their political views on average being leftist. Experts were those who had published at least one article after 2010 in journals covering cognitive ability. Compared to the 1987 survey, there was an increase in the willingness to ascribe intelligence differences to genetic causes.
Opinion of experts in 2016
A survey published in 2016 surveyed experts who had published articles on or after 2010 in journals on intelligence, cognitive abilities, and student achievement. A total of 1345 people were invited. 71 responded and answered the questions on cross-national cognitive ability differences. Those surveyed were asked to state a percentage rating indicating the importance of 15 possible causes of measured cognitive ability differences.
Many of the 15 possible factors included in the survey may be influenced by genetics and genetic groups differences. The survey did not include a single binary question on which overall factor, genetics or environment, is the more important explanation for the differences. Thus, it cannot be compared in that respect with the 1987 and 2013 surveys.
Also, cross-national differences are not the same as the US Black-White differences asked about in the 1987 and 2013 surveys. Also supporters of a partially genetic explanation generally argue that environmental factors are more important in developing countries than in developed countries.
"Seventy-one experts rated possible causes of cross-national differences in cognitive ability based on psychometric IQs and student assessment studies (e.g., PISA, PIRLS, TIMSS). Genes were rated as the most important cause (17%), followed by educational quality (11.44%), health (10.88%), and educational quantity (10.20%) [...] Only 5 of 71 experts (7%) who responded to the genetic item thought that genes had no influence. [...] Items with lower percentages (< 10%) included wealth, culture, and modernization (7–9%). Methodological bias factors (sampling error, test knowledge, test bias) were rated as less important (3–6%, together 11.78%). [...] The low ratings for methodological factors suggest that international assessments were perceived to be valid indicators of cognitive ability and cross-country patterns. [...] Because environmental theories are rarely questioned in research, their corroboration by an expert survey is not astonishing. More important is the support for the frequently hotly disputed genetic explanations. Assuming that the survey is representative of expert opinions, genetic factors should receive more attention in future research and public debates."
There were also similar questions on some more specific groups such as "Immigrants from the Middle East (Arabian and Muslim countries) [...] In the current study, experts attributed the low test results primarily to genetic factors (23.01%) and culture (17.26%). Discrimination was rated as relatively unimportant for Middle Eastern immigrants (2.27%) and for other groups and countries (1.25%)."
Evolutionary explanations for racial differences
Assuming that the average measured IQ differences are partially due to genetic differences, several evolutionary explanations for these differences have been proposed. One is that living in a cold climate has been argued to have been cognitively challenging for much of human history. This is argued to be supported by high correlations between average country IQ and colder average temperature, higher latitude, lighter skin color, and larger cranial cavity volume.
The book The Nature of Race: the Genealogy of the Concept and the Biological Construct’s Contemporaneous Utility stated that this "model has interesting theoretical and empirical support. Regarding theory, in (at least some) non-human species, climate is associated with between population variation in cognition, brain size, and heritable neural functioning (see, for example: Roth et al., 2010; Roth et al., 2012; Roth et al., 2013); cold evolved populations are, apparently, sharper. For humans, models which assume a simple relationship between selection conditioned on cognitive ability and climatic harshness over the last 60,000 years reasonably predict current global cognitive capital (see: Hart, 2007; relatedly: Grall, 2012). Regarding empirical findings, climate by way of cranial size explains a non-trivial portion of the National IQ variance (see: Meisenberg and Woodley, 2013). Generally, cognitive and cognitively related somatic differences are in agreement with the cold weather model; this model is also in agreement with the literature regarding other species."
The theory has been argued to be further supported by several studies which have found larger cranial cavity volumes in pre-human hominids who lived in colder climates compared to pre-human hominids who lived in warmer climates.
New genetic mutations, which could include ones causing higher IQ, would be more likely to arise in large populations. This can be combined with the cold temperature theory. This would explain why Arctic People who live in very cold areas, but only as small populations, did not evolve a very high IQ. Europeans and East Asians who had large populations and lived in relatively cold areas evolved a higher IQ.
J. Philippe Rushton in his book Race, Evolution and Behavior argued that the differential K theory explains many examined differences between human races, including intelligence. The differential K theory also argues that different climate is an important evolutionary cause of the racial differences.
A 2016 study argued that genetics influence motivational factors related to the differential K theory rather than intelligence ability itself.
Another theory is that living in more evolutionary novel environments in general would have favored higher intelligence.
For example the books The 10,000 Year Explosion: How Civilization Accelerated Human Evolution and A Troublesome Inheritance: Genes, Race and Human History have argued that there may have been evolutionary factors causing group differences also in relatively recent human history, caused by different selection pressures in different human societies.
Another is that in relatively recent European and East Asian societies three key elements are argued to have existed: 1. Class differences that reflect differences in intellectual performance. 2. A higher level of reproductive success in higher social classes than in lower ones. 3. No barriers to downward social mobility. The lower classes are argued to have been gradually replaced by people of higher social origin (and IQ). This is argued to have caused a relatively recent increase in IQ in these societies. Other societies are argued to have lacked stratification, or to have been too rigidly stratified, or to have favored other characteristics than IQ as causes of social mobility. There are also criticisms of the theory, such as regarding such societal elements argued to differ between different East Asian societies.
Different castes and other groups in India have been argued to have different average IQ, which has been argued to reflect different ancestral origins and/or recent different evolutionary pressures for different groups. See the article on India and the external links there.
Evolutionary theories have also been proposed for more narrow abilities, such as the relatively high spatial abilities of Amerindians and East Asians. See Other race differences: Visual memory.
Race, sex, and intelligence
Some studies have found differences in average measured intelligence between the sexes, with the results varying for different populations. A 2014 study stated that higher average intelligence in a population is associated with higher average intelligence differences between the sexes in the population. An evolutionary explanation for these and other population differences is that intelligence is a trait influenced by sexual selection.
Interventions affecting IQ
Both hereditarians and non-hereditarians in principle agree on that measures should be implemented against certain environmental factors that are known to negatively affect IQ. Such factors include certain nutritional deficiencies (such as iodine deficiency) and certain diseases during pregnancy/childhood (such as malaria). Such factors are particularly prevalent in developing countries.
However, many non-hereditarians and advocates of political correctness tend to avoid mentioning (and may even actively censor mentioning) the measured average IQ differences and their importance, which may contribute to such interventions not being done or being done less forcefully.
Another problematic aspect (according to hereditarians) is that non-hereditarians (despite arguing that IQ differences are due to 100% environmental factors and an unjust society) have regarding the IQ differences in developed countries had difficulty in finding the societal interventions required to close the gaps or even had difficulty in finding interventions causing any lasting narrowing the gaps. See Race and intelligence: The genetics or not debate: Intervention programs.
Significance of IQ differences
Significance of IQ and g
The importance of IQ may be attacked, which would make IQ differences unimportant. The America Psychological Association's report "Intelligence: Knowns and Unknowns" rejected this argument and stated that IQ predicts several important life outcomes and achievements. This is also why IQ tests and closely correlated tests are used widely in many educational and occupational settings. Also, IQ has been argued to be the best single predictor of academic and job performance and attainment and one of the best predictors of a plethora of other outcomes. If predicting the life outcomes of a teenager based on only one fact about them, nothing is argued to be nearly as informative as their IQ.
The g factor (general factor) is the underlying general mental ability that is measured more or less well by different cognitive tests The existence of g does not exclude the existence also of narrower cognitive abilities (that correlate with one another and g as explained in the IQ article). g has sometimes been criticized for reasons such as being a claimed statistical artifact. Supporters argue that such attempted criticisms have a long history, but that all have ultimately failed. For example, there have been many unsuccessful attempts to find important forms of intelligence that do not correlate with g. Furthermore, g is argued to have a very high heritability, to be unchanged by training such as taking repeated IQ tests, to account for almost of all of the predictive ability of cognitive tests, and findings in neurobiology “establish a biological basis for g that is firmer than that of any other human psychological trait”. Furthermore, successfully discrediting g as a statistical artifact would change the situation much less than some may expect. Different races would continue to systematically differ on numerous different tests of various correlated cognitive abilities as well as to continue to systematically differ on various correlated life outcomes and achievements and there would still continue to be correlations between cognitive tests and life outcomes and achievements.
Also the anti-hereditarian IQ researcher James Flynn has rejected attacking g in order to discredit racial IQ differences and has stated regarding Stephen Jay Gould’s book The Mismeasure of Man (which attacked the hereditarian Arthur Jensen) that "Gould’s book evades all of Jensen’s best arguments for a genetic component in the black-white IQ gap, by positing that they are dependent on the concept of g as a general intelligence factor. Therefore, Gould believes that if he can discredit g, no more need be said. This is manifestly false. Jensen’s arguments would bite no matter whether blacks suffered from a score deficit on one or 10 or 100 factors."
Significance of environmentally caused IQ changes
Some opponents of a genetic explanation for IQ differences seem to think that if only the differences are due to environmental factors, then the differences are unimportant, and can be dismissed. However, a lowered IQ due to, for example, iodine deficiency during childhood/pregnancy causing lifelong lowered IQ is important for individuals and societies, despite the cause being completely environmental.
Very low average IQ values
Some average measured IQ values, such as the 54 for Bushmen, (see the section "Worldwide") have been seen by some as implausible low, since it would imply a diagnosis of mental retardation in European countries. Counter-criticisms include that, besides this value being based on only three studies, Europeans with more severe forms of mental retardation often have genetic diseases that cause many other problems beside the low IQ. A better comparison is argued to be with European children with comparable IQ. An IQ of 54 is equivalent to the average IQ of European 8 years old children. These can learn to read, write, and do arithmetic. Historically, the great majority European children worked productively at this age. This is also the case today for many children of this age in developing nations.
Personality and apparent IQ
Some low average IQ groups on average also have been argued to have an extrovert, self-assured, talkative personality (possibly related to the Differential K theory), which may cause some people to overestimate the average IQ of such groups and to be reluctant to accept as valid the results from IQ testing.
The book Understanding human history: An analysis including the effects of geography and differential evolution as one theme argued for differences in average intelligence between human races as a major factor in the course of human history and prehistory. For example, the book states that advanced Stone Age inventions such as cave painting, sewing needles, bows and arrows, harpoons, fishhooks, and pottery, which appeared from 32,000 to 13,000 years ago, were all made north of Sub-Saharan Africa. Furthermore, the book states that in Sub-Saharan Africa before 1500 AD, with the exception of some regions having contacts with the Muslim world or with the European world, there were no written languages, no mathematics other than simple arithmetic, no advanced building construction methods, no domes or arches, no wheeled devices, no draft animals, no potter's wheel, no woodworking joints, and no mechanical contrivances with moving parts, such as scissors or hinges. This despite the presence of some other technologies invented elsewhere, such as agriculture and iron metalworking/weapons, spread in association with the Bantu expansion.
Mesoamerica (before the Age of Discovery) has been argued to have had more unfavorable environmental factors than Sub-Saharan Africa, such as Sub-Saharan Africa having had contacts with the regions to the north and their technologies and useful flora/fauna, but Mesoamerica is argued to despite this to have been a more advanced region, one example being the Maya who lived in a jungle region. This has been argued to be explained by average intelligence differences.
Population expansions and conquests
Early examples of when a non-European group has conquered/colonized other non-European group(s), with there today being measured IQ differences between the groups or, if one of the groups is today missing, such a difference has been argued to have existed earlier, include:
- The Bantu expansion against groups such as the Khoisan and Pygmies.
- The Dravidian expansion in India against groups who may have been related to Australoids. See also the article on Caste.
- The Han Chinese expansion to Southern China.
- The Mongol Empire expansion, and other earlier and later expansions of other East Asians, to non-East Asian territories.
The Austronesians colonized the islands in Pacific Ocean and the island of Madagascar close to Africa but far from the Pacific Ocean, islands which had not been colonized by groups who for a long time had been close to these islands, such as the Australoids and Sub-Saharan Africans, which has been argued to be related to average IQ differences.
Race differences in intelligence can explain why most conquests of people(s) by another people throughout human history have involved a northern people conquering southern people(s). This despite the northern regions usually being less populous due to harsher climates. For example, China was never threatened by southerners but repeatedly conquered by northerners. Similarly, India was repeatedly conquered by northerners, Europeans conquered various southern peoples but not East Asians, and so on.
Known inventors and scientists
Regarding the race of known inventors/scientists, the overwhelming majority of the most well-known are Europeans, according to Human Accomplishment: The Pursuit of Excellence in the Arts and Sciences, 800 B.C. to 1950.
Lynn has argued that East Asians, despite having slightly higher average IQ, have produced much less creative discoveries and innovations in the arts and sciences than Europeans. One possible explanation is that East Asians have lower average creativity than Europeans. Lynn argues that this is supported by Northeast Asians scoring lower on the personality trait openness to experience.
Fertile river valley civilizations
Differences regarding average IQ is also one argued explanation regarding various aspects of civilizations. However, non-hereditarians have pointed out that some of the earliest civilizations occurred in regions that today do not have a very high average IQ. One response is that hereditarians have never argued that IQ (or genetics) is the only explanation for differences between human groups. The earliest civilizations occurred in very fertile river valleys, which at the early stages of technological development likely were the only regions that allowed the high population density necessary for the development of civilization. In contrast, factors such as the long, harsh winters and the very hard clay soils in Northern Europe for a long time prevented a high population density. Technology had to advance greatly before this changed, one example being that the technologically much more advanced heavy plough, necessary to take advantage of such clay soils, was first introduced in the Medieval period.
After the early developments leading to civilizations, which occurred slowly over very long time periods, several of these fertile river valley civilizations stagnated and produced few new innovations and technologies, with such developments instead occurring in areas such as those inhabited by populations of at least partial Indo-European descent.
Furthermore, despite their large populations and early civilizations, these fertile river valley civilizations never created large empires extending very far from the fertile river valleys, with the exception of China. Instead, it was various people of at least partial Indo-European descent (such as Romans, Indo-Aryans, and Persians), who created very extensive empires and who also conquered these fertile river valleys, despite presumably having started with much smaller population sizes. See also the Indo-European article on a high average IQ as an argued explanation for the Indo-European expansion.
Another view is that the average IQ of the populations creating the first civilizations may have been very different from the average IQ of the populations now inhabiting these areas. These areas have often seen extensive invasions and immigrations and it has even been argued that many of the first civilizations were created by groups completely different from the groups now living in the corresponding areas. Even if not, the average IQ may have been substantially changed by factors such as interbreeding with slaves from low IQ groups, dysgenic practices such as high IQ persons having fewer children, or dysgenic effects caused by society/religion not rewarding intellectual curiosity.
Racially different cognitive elites
Another factor is that the ruling/cognitive elite in early civilizations may have been from a very different racial group than the rest of the population. Conquering peoples have often formed a ruling elite racially different from the rest of the population and many of the more cognitively demanding tasks have in many societies been performed by foreigners or minority group(s) racially different from the rest of the population.
A well-documented example of such an elite were the small minorities of Greeks/Romans in Egypt during the Ptolemaic dynasty/Roman empire, who ruled the country and who made many important scientific and mathematical contributions, such as Euclidean geometry. Another example is the so-called "slave soldiers" in many Islamic empires, who were often from high IQ groups, such as East Asians or Europeans, and who despite the name often were the top administrators or even the rulers of the empires. The Janissaries and the Mamluks are well-known examples, but "slave soldiers" dominated the army and the government already during the Abbasid dynasty (the "Islamic Golden Age") and similar groups played important parts in the Islamic expansion before this.
Morphological evidence based on for example statues, paintings, skeletal remains, or mummies have often been used to argue that various ancient populations or cognitive elites were racially different from the current populations living in the same area. Even if historical records are available, practices such as religious conversion are often accompanied by changing personal and family names, which often makes it difficult to identify the correct race from the name of persons. The earlier presence of racially different cognitive elites or internal dysgenic changes in a population may be difficult to detect by genetic studies of the current populations living in these areas.
Dysgenics and the fall of civilizations
Dysgenic changes including regarding IQ have been suggested to be an important explanation for the fall of various civilizations. The book Why Civilizations Self-Destruct is one often mentioned example of such arguments.
A significant part of the debate following The Bell Curve was regarding how important the IQ group differences were for the future achievements of the groups in the US. The book argued for the strong importance of IQ for numerous factors, such as future educational achievements, employment, income, divorce rates, and crime. See the links to the right regarding tables from the book on this.
A 2016 analysis of US data found a substantially larger effect of IQ on permanent income than some previous investigations.
Furthermore, a high IQ has been argued to be more important for group outcome differences than for individual outcome differences. A 2011 study presented "four different channels through which intelligence may matter more for nations than for individuals: (i) intelligence is associated with patience and hence higher savings rates; (ii) intelligence causes cooperation; (iii) higher group intelligence opens the door to using fragile, high-value production technologies; and (iv) intelligence is associated with supporting market-oriented policies."
A 2013 study found that the ability of tests to measures the g factor was higher in low scoring countries than in high scoring countries, implying that the predictive ability of tests may actually be higher for low average IQ countries than for high average IQ countries (where most studies of predicative ability have been done).
The book Guns, Germs, and Steel by Jewish biologist Jared Diamond, written as one response to the Bell Curve, argued that geographical differences caused differences in available resources, which caused some groups to get a head start, which explains today's differences in achievement between different parts of the world. One problem with Diamond's book is that it contains no actual arguments against the IQ explanation but simply describes an alternative explanation regarding worldwide developments. He also states that the populations in question separated a long time ago and that they faced different environments thereafter. These facts have been argued to virtually guarantee that the populations diverged genetically. Rushton notes, "It seems incredible that, as an evolutionary biologist, Diamond seems unaware that it is different environments that cause, via natural selection, biological differences among populations." Furthermore, hereditarians have not denied that geographic and other non-IQ factors may be important. For example, IQ and the Wealth of Nations argued that average IQ, natural resources such as oil, and the presence or not of Communist economic systems have been major determinants of economic growth after WWII. Also, Diamond's argument does not explain why the different races in the same country achieve differently. See also the article on the book Guns, Germs, and Steel.
Lynn in the 2008 book The Global Bell Curve, named after The Bell Curve, argued that the same racial hierarchies exist in all countries that have several races, with the different races differing similarly, regardless of country, regarding variables such as crime, income, school results, education, etc. It does not matter if some groups were very poor when they arrived to a new country. After a while, the same consistent racial hierarchies as elsewhere are established. Furthermore, mixed-race groups almost always place intermediate between their two ancestral races on such variables. A group that is particularly difficult to explain using political correctness is East Asians in Latin America and other areas. They often arrived very poor, in order to work as plantation workers and in similar occupations, but now usually have a high socioeconomic status, despite never having any political power or receiving any preferential treatment.
"Market-dominant minorities", a concept introduced by the book World on Fire, include Chinese, Jews, and Whites in various countries where they are minorities, Indians in Southeast Africa, and Lebanese in West Africa. As stated above, The Global Bell Curve argued that average IQ differences is one explanation for the economic influence of such minorities.
There are also some countries that are racially different from the surrounding countries and that perform very differently from these surrounding countries on various variables. Examples include Haiti (predominantly Sub-Saharan Africans) and Singapore (predominantly East Asians).
One explanation for such group differences are different "cultural values". This is however also a politically problematic explanation, since it implies that all cultures are not equal. Hereditarians have criticized such explanations as being very difficult to test and likely also partially genetically influenced. See Other race differences: Values and Other race differences: Personality traits. There are also general arguments against such environmental factors, at least in developed countries, see Race and intelligence: The genetics or not debate: Shared environmental factors and Race and intelligence: The genetics or not debate: Environmental factors specific to only one (or some) race(s).
See also Confucianism on this as an important cultural explanation for East Asian high average measured IQ.
"From a more historical perspective, based on an analysis of 123 countries, 54 of which were European colonies, Prayon and Baten (2010) found a European colonial migrant human capital effect. European migrants to Africa, South Asia, Oceania, and the Americas had to begin with higher levels of developed cognitive ability (as indexed by age heaping) than the peoples indigenous to those regions. The authors found that the contemporaneous benefits of the historic human capital infusion, resulting from European migration to these areas, varied as a function of the ratio of European migrants to non-European natives. The implication is that historic European migrants brought their region of origin abilities with them and that this historic migrant effect persists still today. As one might expect from the above discussion, genomic racial ancestry, which varies extensively in the Americas due to historic migrant waves, predicts cognitive and/or cognitive related outcomes across the Americas, between nations, between regions within nations, and between individuals within national ethnic groups (Fuerst and Kirkegaard, 2015)."
Several IQ researchers have expressed very pessimistic views regarding the future of Western civilization due to mass immigration of low-IQ groups and other dysgenic trends. See Dysgenics: Pessimism regarding the future of Western civilization.
- Vincent Sarich och Frank Miele. Race: The Reality of Human Differences. 2004. Westview Press.
- J. Philippe Rushton. Race, Evolution, and Behavior: A Life History Perspective. 1997. Transaction Publishers.
- Richard Lynn. Race differences in Intelligence. 2006. Washington Summit Publishers.
- Jensen AR (2002) Galton's legacy to research on intelligence. J Biosoc Sci 34 (2):145-72. http://pubmed.gov/11926452
- Jensen, Arthur R (1969). "How Much Can We Boost IQ and Scholastic Achievement?". Harvard Educational Review 39: 1–123. http://hepgjournals.org/doi/abs/10.17763/haer.39.1.l3u15956627424k7
- Rushton, J. Philippe; Jensen, Arthur R. Thirty years of research on race differences in cognitive ability. Psychology, Public Policy, and Law, Vol 11(2), Jun 2005, 235-294. http://dx.doi.org/10.1037/1076-89126.96.36.199 http://psychology.uwo.ca/faculty/rushtonpdfs/PPPL1.pdf
- Mark Snyderman and Stanley Rothman. Survey of Expert Opinion on Intelligence and Aptitude Testing. February 1987. Vol 42. No 2. 137-144. American Psychologist.
- Mark Snyderman and Stanley Rothman. The IQ Controversy, the Media and Public Policy. 1988. Transaction Books.
- Miele, Frank (2002). Intelligence, Race, and Genetics: Conversations with Arthur R. Jensen. Oxford: Westview Press. ISBN 0-8133-4274-0
- Richard Lynn & Tatu Vanhanen. Intelligence: A Unifying Construct for the Social Sciences. 2012. Ulster Institute for Social Research.
- John Fuerst ("Chuck"). (2013, January 15). Secular Changes in the Black-White Cognitive Ability Gap. Human Varieties. http://humanvarieties.org/2013/01/15/secular-changes-in-the-black-white-cognitive-ability-gap/
- J. Philippe Rushton and Arthur R. Jensen. Race and IQ: A Theory-Based Review of the Research in Richard Nisbett’s Intelligence and How to Get It. The Open Psychology Journal, 2010, 3, 9-35. http://dx.doi.org/10.2174/1874350101003010009 http://psychology.uwo.ca/faculty/rushtonpdfs/2010%20Review%20of%20Nisbett.pdf
- Steven Pinker, The Blank Slate, 2002, Viking Penguin, Chapter 18 Gender
- Neisser, Ulric; Boodoo, Gwyneth; Bouchard Jr., Thomas J.; Boykin, A. Wade; Brody, Nathan; Ceci, Stephen J.; Halpern, Diane F.; Loehlin, John C.; Perloff, Robert; Sternberg, Robert J.; Urbina, Susana. Intelligence: Knowns and Unknowns. American Psychologist, Vol 51(2), Feb 1996, 77-101. http://dx.doi.org/10.1037/0003-066X.51.2.77
- Linda S. Gottfredson, Mainstream science on intelligence: An editorial with 52 signatories, history, and bibliography, Intelligence, Volume 24, Issue 1, January–February 1997, Pages 13-23, ISSN 0160-2896, http://dx.doi.org/10.1016/S0160-2896(97)90011-8.
- Roth, P. L., Bevier, C. A., Bobko, P., Switzer, F. S., III, & Tyler, P. (2001). Ethnic group differences in cognitive ability in employment and educational settings: A meta-analysis. Personnel Psychology, 54, 297–330. http://dx.doi.org/10.1111/j.1744-6570.2001.tb00094.x
- J. Philippe Rushton, Arthur R. Jensen, The rise and fall of the Flynn Effect as a reason to expect a narrowing of the Black–White IQ gap, Intelligence, Volume 38, Issue 2, March–April 2010, Pages 213-219, ISSN 0160-2896, http://dx.doi.org/10.1016/j.intell.2009.12.002 http://www.psychology.uwo.ca/faculty/rushtonpdfs/2010%20Editorial%20for%20Intelligence.pdf
- An Update on the Secular Narrowing of the Black-White Gap in the Wordsum Vocabulary Test (1974-2012) http://www.mankindquarterly.org/archive/issue/58-2/11
- Jason Malloy. (2013, May 26). The Onset and Development of B-W Ability Differences: Early Infancy to Age 3 (Part 1). Human Varieties. http://humanvarieties.org/2013/05/26/the-onset-and-development-of-b-w-ability-differences-early-infancy-to-age-3-part-1/
- General mental ability in South Asians: Data from three Roma (Gypsy) communities in Serbia, J. Philippe Rushton, Jelena Cvorovic and Trudy Ann Bons, Intelligence, Volume 35, Issue 1, January–February 2007, http://dx.doi.org/10.1016/j.intell.2006.09.002
- Marginal tribes, disparate outcomes. https://drjamesthompson.blogspot.com/2015/05/marginal-tribes-disparate-outcomes.html
- Intelligence of the Pygmies http://www.mankindquarterly.org/archive/issue/51-4/2
- John Fuerst. (2015). "The Nature of Race: the Genealogy of the Concept and the Biological Construct’s Contemporaneous Utility". Submitted: December 25, 2014. Published: June 18, 2015. Open Behavioral Genetics. http://openpsych.net/OBG/2015/06/the-nature-of-race/
- Andrea Pitzer. Controversial comments taint Watson's legacy. USA Today November 21, 2007. http://abcnews.go.com/Technology/story?id=3895028&page=1#.UEvH5I3ZA-E
- Helsingin Sanomat - Comments in interview could bring charges of inciting racism against PM Vanhanen's father.
- J. Philippe Rushton. Race, Intelligence, and the Brain: The Errors and Omissions of the 'Revised' Edition of S.J. Gould's The Mismeasure of Man (1996). Personality and Individual Differences. Vol 23. No 1. pp. 169-180. 1997. http://psychology.uwo.ca/faculty/rushtonpdfs/Gould.pdf
- Arthur R. Jensen. The Debunking of Scientific Fossils And Straw Persons. Contemporary Education Review Summer 1982, Volume 1, Number 2, pp. 121- 135. http://www.debunker.com/texts/jensen.html
- Lewis JE, DeGusta D, Meyer MR, Monge JM, Mann AE, et al. (2011) The Mismeasure of Science: Stephen Jay Gould versus Samuel George Morton on Skulls and Bias. PLoS Biol 9(6): e1001071. doi:10.1371/journal.pbio.1001071 http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.1001071
- Davide Piffer, Estimating the genotypic intelligence of populations and assessing the impact of socioeconomic factors and migrations., The Winnower 2:e142299.93508 (2015). DOI: 10.15200/winn.142299.93508 https://thewinnower.com/papers/estimating-the-genotypic-intelligence-of-populations-and-assessing-the-impact-of-socioeconomic-factors-and-migrations
- Progress in Intelligence Research https://www.amren.com/blog/2019/11/progress-in-intelligence-research/
- Rindermann, Coyle, and Becker, ISIR 13, 14-XII 13, Expert Survey. Discussed in: J Thompson. (2013, December 14). ISIR What do intelligence researchers really think about intelligence? http://drjamesthompson.blogspot.com/2013/12/isir-what-do-intelligence-researchers.html
- Rindermann, H., Becker, D., & Coyle, T. R. (2016). Survey of Expert Opinion on Intelligence: Causes of International Differences in Cognitive Ability Tests. Frontiers in psychology, 7. http://journal.frontiersin.org/article/10.3389/fpsyg.2016.00399/full
- Lynn, R., & Vanhanen, T., National IQs: A review of their educational, cognitive, economic, political, demographic, sociological, epidemiological, geographic and climatic correlates, Intelligence (2012), http://dx.doi.org/10.1016/j.intell.2011.11.004
- Richard Lynn and Tatu Vanhanen. 2012. Intelligence: A Unifying Construct for the Social Sciences. Ulster Institute for Social Research.
- Becker, D., & Rindermann, H. (2016). The relationship between cross-national genetic distances and IQ-differences. Personality and Individual Differences, 98, 300-310. http://www.sciencedirect.com/science/article/pii/S019188691630174X
- Minkov, M., Welzel, C., & Bond, M. H. (2016). The impact of genes, geography, and educational opportunities on national cognitive achievement. Learning and Individual Differences, 47, 236-243. http://www.sciencedirect.com/science/article/pii/S1041608016300267
- Kenya Kura, Japanese north–south gradient in IQ predicts differences in stature, skin color, income, and homicide rate, Intelligence, Volume 41, Issue 5, September–October 2013, Pages 512-516, ISSN 0160-2896, http://dx.doi.org/10.1016/j.intell.2013.07.001 http://www.sciencedirect.com/science/article/pii/S0160289613000949
- Richard Lynn, In Italy, north–south differences in IQ predict differences in income, education, infant mortality, stature, and literacy, Intelligence, Volume 38, Issue 1, January–February 2010, Pages 93-100, ISSN 0160-2896, http://dx.doi.org/10.1016/j.intell.2009.07.004 http://www.sciencedirect.com/science/article/pii/S0160289609000956
- R. Lynn. North–south differences in Spain in IQ, educational attainment, per capita income, literacy, life expectancy and employment. Mankind Quarterly, 52 (2012), pp. 265–291. http://www.mankindquarterly.org/spring_summer2012_lynn.html
- Elijah L. Armstrong, Heitor B.F. Fernandes, Michael A. Woodley, SD–IE and other differentiation effects in Italy and Spain, Personality and Individual Differences, Volume 68, October 2014, Pages 189-194, ISSN 0191-8869, http://dx.doi.org/10.1016/j.paid.2014.03.043 http://www.sciencedirect.com/science/article/pii/S019188691400213X
- Jason Malloy. 2014. Human varieties. HVGIQ: Vietnam. http://humanvarieties.org/2014/06/19/hvgiq-vietnam/
- Grigoriev, A., Lapteva, E., & Lynn, R. (2016). Regional differences in intelligence, infant mortality, stature and fertility in European Russia in the late nineteenth century. Intelligence, 55, 34-37. http://www.sciencedirect.com/science/article/pii/S0160289616300150
- Peter Frost. East Asia's Farewell to Alms. Evo and Proud. http://evoandproud.blogspot.com/2013/03/east-asias-farewell-to-alms.html
- Peter Frost. Does the Clark-Unz model apply to Japan and Korea? Evo and Proud. http://evoandproud.blogspot.ro/2013/03/does-clark-unz-model-apply-to-japan-and.html
- Ron Unz. China: Chinese Eugenics? http://www.theamericanconservative.com/china-chinese-eugenics/
- The Evolution Of Chinese IQ http://akarlin.com/2012/08/the-evolution-of-chinese-iq/
- Davide Piffer. (2014). Sexual selection as a mechanism behind sex and population differences in fluid intelligence: an evolutionary hypothesis. Open Behavioral Genetics. Published: August 9, 2014. http://openpsych.net/OBG/2014/08/sexual-selection-as-a-mechanism-behind-sex-and-population-differences-in-fluid-intelligence-an-evolutionary-hypothesis/
- Marc Dalliard. Is Psychometric g a Myth? Human Varieties. http://humanvarieties.org/2013/04/03/is-psychometric-g-a-myth/
- Marc Dalliard. Some Further Notes on g and Shalizi. http://humanvarieties.org/2013/04/14/some-further-notes-on-g-and-shalizi/
- J. Philippe Rushton: Solving The African IQ Conundrum: “Winning Personality” Masks Low Scores http://www.vdare.com/articles/solving-the-african-iq-conundrum-winning-personality-masks-low-scores
- Hart, M. H. (2007). Understanding human history: An analysis including the effects of geography and differential evolution. Washington Summit Publishers.
- John R. Baker. Race. Oxford University Press, New York. 1974.
- A Real Diamond: Michael Hart`s Understanding Human History. August 12, 2007, 9:00 am. Vdare.com. http://www.vdare.com/articles/a-real-diamond-michael-harts-understanding-human-history
- Richard Lynn, Race Differences in Intelligence, Creativity and Creative Achievement, Richard Lynn, Mankind Quarterly, Vol. 48, No. 3 (Spring 2008) pp. 299-309, http://www.mankindquarterly.org/spring2008_lynn.html
- Andersen, Thomas Barnebeck & Jensen, Peter Sandholt & Skovsgaard, Christian Stejner, 2013. "The heavy plough and the agricultural revolution in medieval Europe," Discussion Papers of Business and Economics 6/2013, Department of Business and Economics, University of Southern Denmark. http://ideas.repec.org/p/hhs/sdueko/2013_006.html
- Donald I. Templer. The Comparison of Mean IQ in Muslim and Non-Muslim Countries. Mankind Quarterly, Vol. 50, No. 3 (Spring 2010) pp. 188-209 http://www.mankindquarterly.org/spring2010_templer.html
- Daniel Pipes. Slave Soldiers and Islam. New Haven and London: Yale University Press, 1981. http://www.danielpipes.org/books/slave.php
- Elmer Pendell. Why Civilizations Self-Destruct. 1977.
- Marc Dalliard. IQ and Permanent Income: Sizing Up the “IQ Paradox”. Human varieties. http://humanvarieties.org/2016/01/31/iq-and-permanent-income-sizing-up-the-iq-paradox/
- Jones, Garett, National IQ and National Productivity: The Hive Mind Across Asia (June 2011). Asian Development Review, Vol. 28, No. 1, pp. 51-71, 2011. Available at SSRN: http://ssrn.com/abstract=1869472
- Thomas R. Coyle, Heiner Rindermann. (2013). Spearman’s Law of Diminishing Returns and national ability. Personality and Individual Differences, Volume 55, Issue 4, August 2013, Pages 406–410. https://www.sciencedirect.com/science/article/pii/S0191886913001530
- Rushton, J. P. (1999). [Book Review of J. Diamond: Guns, germs and steel. New York: W.W. Norton, 1997]. Population and Environment, 21, 99-107