Some time ago, I was building a large reference FAQ for use on Wikipedia. Unfortunately, some activist admins came along and deleted it. The archived version is here.

The background for this is that I commented on a discussion about user MjolnirPants/MPants at work, who has a very long history of breaking rules and getting away with it, while having an extreme political bias (guess which direction). He got triggered and wrote a bunch of obscenities on Wikipedia so crazy that his admin friends who had been protecting him for years could not let it off, so they had to block him. In fact, they were so bad the admins had to redact them, so the public cannot even see. In their anger, they looked for revenge, and had me blocked too on false grounds (this is despite having never previously been in trouble and editing for 8 years). After that, they looked for ways to do more damage, so they looked at my edit history for stuff they could delete and found this page I was building. Then they made a quick motion for deletion on obviously spurious grounds, and had their admin friends Ivanvector and Beeblebrox use their powers to close it immediately after less than 2 hours (!). The other members of the group are PeterTheFourth, Simonm223, and Legacypac. Because Wikipedia rules disallow people to edit as a team (WP:CANVAS, WP:TAGTEAM etc.), people of course resort to secret teams coordinated using Skype, Slack or whatever. It’s not something one can really prevent, and is a major issue with the intended system.

Leaving the drama aside, here’s a copy of the content.

This is a work in progress page that collects useful source material for commonly asked questions about intelligence research and the resulting edit disputes on Wikipedia about them. The focus here is to present mainstream science on the topic. Per Wikipedia’s policy preference for secondary literature, weight will be given this literature when available.

The page will be curated or reviewed by researchers in the field, a list of names will be given later.

Contents 1 Sources of expert opinion 1.1 Surveys of experts about intelligence research 1.2 Major textbooks or book length reviews 1.3 Multi-author handbooks

2 Genetic and environmental causation / behavioral genetics of intelligence 2.1 What does heritability mean?

3 Group differences 3.1 Race and ethnics groups 3.1.1 African American vs. European American gap in the United States 3.1.1.1 How large is the African American vs. European American gap in the United States? 3.1.1.2 Has the African American vs. European American gap in the United States changed over time? 3.1.1.3 What are the causes of the African American vs. European American intelligence gap? 3.1.1.4 What are some major reviews of the causes of African American vs. European American intelligence gap? 3.2 Sex/gender groups 3.2.1 Are there sex differences in intelligence?

4 What is the scholarly opinion of Steven Jay Gould’s work?

5 Do any researchers in the field edit Wikipedia/have Wikipedia users?

6 Recommended literature 6.1 Books by major researchers 6.1.1 Ian Deary 6.1.2 James R. Flynn 6.1.3 Richard Haier 6.1.4 Arthur R. Jensen 6.1.5 Richard Lynn 6.1.6 Gerhard Meisenberg 6.1.7 Robert Plomin 6.1.8 Heiner Rindermann 6.1.9 Stuart Ritchie



Sources of expert opinion

Similar to other scientific fields with major relevance to social policy (see evolution and climate science), there is disagreement about what experts actually believe. There are multiple ways to approach this question, including surveys of experts and collections of recent textbook content.

Surveys of experts about intelligence research

A number of surveys of expert opinion on intelligence research and related topics exist:

While it is not exactly a survey, it is a kind of concise group statement by a larger number of experts:

Note that the Rindermann surveys came from the same actual sample, just split into 2 (so far) papers. Some parts of the survey results have still not been presented in a published study, but some of them can be seen in the slides from the ISIR 2013 talk slides.

Rindermann, H. (2013). 2013 survey of expert opinion on intelligence. International Society for Intelligence Research, ISIR 2013

Major textbooks or book length reviews

A number of textbooks or book lengths of the field exist written by a variety of authors. These books are almost always in agreement about the basics, though they may disagree about the importance of specific findings or questions. Together with expert surveys, these carry considerable weight about what can be stated on Wikipedia according to secondary literature.

Multi-author handbooks

A number of multi-author edited books also exist. Caution is advised however because these are mainly edited by one person, Robert Sternberg, whose views are often not mainstream.

Genetic and environmental causation / behavioral genetics of intelligence

What does heritability mean?

Individuals differ from one another on a wide variety of traits: familiar examples include height, intelligence, and aspects of personality. Those differences are often of considerable social importance. Many interesting questions can be asked about their nature and origins. One such question is the extent to which they reflect differences among the genes of the individuals involved, as distinguished from differences among the environments to which those individuals have been exposed. The issue here is not whether genes and environments are both essential for the development of a given trait (this is always the case), and it is not about the genes or environment of any particular person. We are concerned only with the observed variation of the trait across individuals in a given population. A figure called the “heritability” (h2) of the trait represents the proportion of that variation that is associated with genetic differences among the individuals. The remaining variation (1 – h2) is associated with environmental differences and with errors of measurement. These proportions can be estimated by various methods described below.

For the complex traits that interest behavioral scientists, it is possible to ask not only whether genetic influences are important but also how much genetics contributes to the trait. The question about whether genetic influences are important involves statistical significance, the reliability of the effect. For example, we can ask whether the resemblance between “genetic” parents and their adopted offspring is significant or whether identical twins are significantly more similar than fraternal twins. Statistical significance depends on the size of the effect and the size of the sample. For example, a “genetic” parent-offspring correlation of 0.25 will be statistically significant if the adoption study includes at least 45 parent-offspring pairs. Such a result would indicate that it is highly likely (95 percent probability) that the true correlation is greater than zero.

The question about how much genetics contributes to a trait refers to effect size, the extent to which individual differences for the trait in the population can be accounted for by genetic differences among individuals. Effect size in this sense refers to individual differences for a trait in the entire population, not to certain individuals. For example, if PKU were left untreated, it would have a huge effect on the cognitive development of individuals homozygous for the recessive allele. However, because such individuals represent only 1 in 10,000 individuals in the population, this huge effect for these few individuals would have little effect overall on the variation in cognitive ability in the entire population. Thus, the size of the effect of PKU in the population is very small.

Many statistically significant environmental effects in the behavioral sciences involve very small effects in the population. For example, birth order is significantly related to intelligence test (IQ) scores (first-born children have higher IQs). This is a small effect in that the mean difference between first- and second-born siblings is less than two IQ points and their IQ distributions almost completely overlap. Birth order accounts for about 1 percent of the variance of IQ scores when other factors are controlled. In other words, if all you know about two siblings is their birth order, then you know practically nothing about their IQs.

In contrast, genetic effect sizes are often very large, among the largest effects found in the behavioral sciences, accounting for as much as half of the variance. The statistic that estimates the genetic effect size is called heritability. Heritability is the proportion of phenotypic variance that can be accounted for by genetic differences among individuals. As explained in the Appendix, heritability can be estimated from the correlations for relatives. For example, if the correlation for “genetic” (adopted apart) relatives is zero, then heritability is zero. For first-degree “genetic” relatives, their correlation reflects half of the effect of genes because they are only 50 percent similar genetically. That is, if heritability is 100 percent, their correlation would be 0.50. In Figure 6.2, the correlation for “genetic” (adopted-apart) siblings is 0.24 for IQ^ scores. Doubling this correlation yields a heritability estimate of 48 percent, which suggests that about half of the variance in IQ scores can be explained by genetic differences among individuals. (pp. 86-87)

The heritability coefficient indexes the magnitude of genetic influence (as a proportion of variance) on a quantitative (generally polygenic) trait. It tells us how much of the variance (differences among individuals) in a population is due to genetic factors.

Plomin, R., & von Stumm, S. (2018). The new genetics of intelligence. Nature Reviews Genetics.

Heritability The proportion of observed differences among individuals that can be attributed to inherited differences in genome sequence.

Group differences

Humans can be grouped into an indefinitely large number of different groups. Some of these have been investigated with regards to intelligence.

Race and ethnics groups

Linguistic conventions:

African American is taken as the current best term to refer to the group that has been referred to as US Blacks, African-descent Americans, US Negroes etc.

is taken as the current best term to refer to the group that has been referred to as US Blacks, African-descent Americans, US Negroes etc. European American is taken as the current best term to refer to the group that has been referred to as US Whites, European-descent Americans, etc.

is taken as the current best term to refer to the group that has been referred to as US Whites, European-descent Americans, etc. Hispanic American is taken as the current best term to refer to the group that has been referred to as US Hispanics, US Latino etc.

African American vs. European American gap in the United States

The gap between African Americans and European Americans is the most discussed and researched gap in the literature. Hence, we devote a special section to it.

How large is the African American vs. European American gap in the United States?

There is consensus that there is a gap, but not consensus about its current size, with a range of estimates from about 8 to 15 IQ. Most sources reiterate the 15 IQ/1 standard deviation value.

The answer to the research question of “what are the standardized difference scores between ethnic groups?” is now clearer than the [generally accepted effect size] of “1.0 SD for Blacks versus Whites” and “somewhere between .5 and .8 SDs for Hispanics versus Whites.” If one simply examines the aggregate data and ignores the moderators, the overall ds for g are 1.10 for the Black-White difference and .72 for the Hispanic-White difference. However, there are a number of important moderators that merit discussion. We discuss the Black-White moderators first.

The differential between the mean intelligence test scores of Blacks and Whites (about one standard deviation, although it may be diminishing) does not result from any obvious biases in test construction and administration, nor does it simply reflect differences in socioeconomic status. Explanations based on factors of caste and culture may be appropriate, but so far have little direct empirical support. There is certainly no such support for a genetic interpretation. At present, no one knows what causes this differential.

Has the African American vs. European American gap in the United States changed over time?

There is consensus that there is a gap, but not consensus about its historical change.

Other scholars have provided scores from Blacks and Whites who took the same test some years apart or have analyzed trends (Gottfredson, 2005; Lynn, 1996; Murray, 2005; Vincent, 1991; Wicherts, 2005). In every case, the samples lacked the quality of standardization samples. Nonetheless, all results from these other studies are compatible with our estimate of an IQ of 90.5 for Black schoolchildren in 2002. Some of the studies show little or no change during the periods they cover, and some show Black children reaching that value well before 2002, but none cast doubt on the contention that Blacks have matched our estimate (see Appendix B). All existing data suggest that since the 1960s, Black children have made large IQ gains relative to Whites, even if the precise timing of those gains is uncertain.

The differential between the mean intelligence test scores of Blacks and Whites (about one standard deviation, although it may be diminishing) does not result from any obvious biases in test construction and administration, nor does it simply reflect differences in socioeconomic status. Explanations based on factors of caste and culture may be appropriate, but so far have little direct empirical support. There is certainly no such support for a genetic interpretation. At present, no one knows what causes this differential.

Roth, P. L., Bevier, C. A., Bobko, P., Switzer, F. S., & Tyler, P. (2001). Ethnic group differences in cognitive ability in employment and educational settings: A meta‐analysis. Personnel Psychology, 54(2), 297-330.

As a whole, these studies suggest that there are observed gains for both groups, but the reduction in the between-group difference is either small, potentially a function of sampling error (Lynn, 1998), or nonexistent for highly g loaded instruments (Nyborg & Jensen, 2000).

[needs newer citations, but I found nothing useful in Hunt]

What are the causes of the African American vs. European American intelligence gap?

There is no consensus about the causes of the African American vs. European American intelligence gap. A variety of environmental causes has been proposed as well as genetic causes.

22. There is no definitive answer to why IQ bell curves differ across racial-ethnic groups. The reasons for these IQ differences between groups may be markedly different from the reasons for why individuals differ among themselves within any particular group (whites or blacks or Asians). In fact, it is wrong to assume, as many do, that the reason why some individuals in a population have high IQs but others have low IQs must be the same reason why some populations contain more such high (or low) IQ individuals than others. Most experts believe that environment is important in pushing the bell curves apart, but that genetics could be involved too.

The differential between the mean intelligence test scores of Blacks and Whites (about one standard deviation, although it may be diminishing) does not result from any obvious biases in test construction and administration, nor does it simply reflect differences in socioeconomic status. Explanations based on factors of caste and culture may be appropriate, but so far have little direct empirical support. There is certainly no such support for a genetic interpretation. At present, no one knows what causes this differential.

Hunt, E. (2010). Human intelligence. Cambridge University Press.

Neither I nor anyone else knows the cause of the differences in indices of intelligence among various racial and ethnic groups. Furthermore, there almost certainly is not any single cause, and the causes may vary for different comparisons. We do have some leads. Not surprisingly, the explanations fall into two broad categories – social and biological. The social ones will be discussed here, the biological ones in the next section.

These are the evidence on race differences in intelligence and the degree to which these differences are determined by genetic and environmental factors. It is widely accepted that race differences in intelligence exist, but no consensus has emerged on whether these have any genetic basis.

Haier, R. J. (2016). The neuroscience of intelligence. Cambridge University Press.

Finally, perhaps the major motivation for diminishing the validity of intelligence tests, and other tests of mental abilities including the SAT, is the desire, shared by many, to explain away group differences in average scores as a mere artifact of the tests. In my view, this motivation is misplaced. The causes of average test score differences among groups are not yet clear, but the differences are a major concern in education and other areas. They deserve full attention with the most sophisticated research possible so causes and potential remediation can be developed based on empirical studies. Imaging studies of brain development and intelligence are beginning to address some issues, as detailed in Chapters 3 and 4, and the goal of enhancing intelligence, discussed in Chapters 5 and 6, is something to consider.

What are some major reviews of the causes of African American vs. European American intelligence gap?

This list is not aimed to be inclusive but it tries to include major or prominent reviews of the evidence.

Sex/gender groups

Are there sex differences in intelligence?

There is consensus about the existence of differences in some group factors or specific abilities, and lack of consensus about existence of overall IQ/general intelligence differences.

Most standard tests of intelligence have been constructed so that there are no overall score differences between females and males. Some recent studies do report sex differences in IQ, but the direction is variable and the effects are small (Held, Alderton, Foley, & Segall, 1993; Lynn, 1994). This overall equivalence does not imply equal performance on every individual ability. While some tasks show no sex differences, there are others where small differences appear and a few where they are large and consistent.

What is the scholarly opinion of Steven Jay Gould’s work?

A number of prominent scholars have commented on the work by Steven Jay Gould, in particular his Mismeasure of Man book. The book is popular with outsiders, but not with researchers who work on the topic.

Jensen, A. R. (1982). The debunking of scientific fossils and straw persons. Contemporary Education Review, 1(2), 121-135.

This book concerns the biasing influence that social ideology may have on purportedly objective science- the behavioral and brain sciences especially and psychometrics in particular. Ironically, the book itself serves as a patent example of its own thesis.

[…]

In his references to my own work, Gould includes at least nine citations that involve more than just an expression of Gould’s opinion; in these citations Gould purportedly paraphrases my views. Yet in eight of the nine cases, Gould’s representation of these views is false, misleading, or grossly caricatured. Nonspecialists could have no way of knowing any of this without reading the cited sources. While ant author can occasionally make an inadvertent mistake in paraphrasing another, it appears Gould’s paraphrases are consistently slanted to serve his own message. Through hyperbole and caricature he converts real issues into straw persons, which can be easily disproved.

[…]

Gould’s book, on the other hand, is so repetitiously cluttered by doctrinaire disparagement that it can hardly provide any real enlightenment regarding mental measurement. Although Gould’s book will be warmly embraced (along with Leon Kamin’s, 1974, The Science and Politics of IQ) by the dwindling band of genetic egalitarians and neo- Lysenkoists, it is hard to see that this book makes any scientific contribution or serves to inform the general public in any responsible way about the truly important issues in mental testing today.

This is almost entirely critical of the idea of intelligence testing, especially the notion of general intelligence. It’s an odd book, because it has sold very well despite having quite a lot of technical information, about the history of intelligence testing and the statistics involved in mental measurement: it is superbly written. Note that the sections on brain size are out of date and he has refused to correct this despite being sent newly available published data by researchers. People in my research field have severely criticized his account of the statistics of mental measurement. A flawed book, but a great read.

Hunt, E. (2010). Human intelligence. Cambridge University Press.

In 1981 the Harvard paleontologist Stephen J. Gould wrote an elegant, amusing, and scathing review of this line of research, as part of a more general, and equally scathing, analysis of virtually all aspects of research on intelligence. He concluded that there was no reliable evidence relating brain size to intelligence. He also claimed that attempts to show group differences in brain size were motivated by racial prejudice. Gould had previously achieved considerable public credibility as a commentator on science, so his views were widely accepted in spite of negative reviews of his work in the technical literature.

It is impossible to know whether Gould’s imputations about investigators’ motives were correct or not. Indeed, if the early investigators’ facts were right it does not matter to science what their motives were. There have been several careful studies about the brain size-intelligence relationship. Gould had his facts wrong.

All of this is subject to vigorous and scholarly debate in the scientific literature, but some opponents of IQ testing, often driven by political concerns, have been far less fair. The most famous of these opponents was the palaeontologist Stephen Jay Gould, who wrote The Mismeasure of Man in 1981. This book, which was updated in 1996, is a sustained historical critique of early intelligence research followed by a criticism of factor analysis and the idea of general intelligence. It is a very partial summary of the literature, omitting opposing data that were readily available at the time of writing. Moreover, researchers doing a follow-up study (Lewis et al., 2011) have found that Gould’s conclusions about the accuracy of historical work on head size were simply incorrect. Unfortunately, the book was widely read and, despite now being well out of date, it still has a baleful influence over the IQ debate. There are many others: interested readers should investigate the works of long-time IQ critics such as Leon Kamin and Steven Rose, and see for themselves how their arguments stack up against the scientific research recounted in this book.

[…]

Beautifully written, as all his books are. But it’s at odds with the science and suffers from political bias.

Rindermann, H. (2018). Cognitive Capitalism: Human Capital and the Wellbeing of Nations. Cambridge University Press.

One example could be the book by Stephen Gay Gould (1981, pp. 50-69), The Mismeasure of Man. In this book, which is still credited to some extent by the public and by some ‘scientists’, Gould alleged different researchers had dishonest motives, particularly having cheated due to racist motives. One ‘case’ for him was Samuel George Morton (1799-1851), an American physician, natural scientist and anthropologist from Philadelphia. Using craniometry, Morton came to the result that Europeans have on average larger brains than Native Americans and Africans. Gould claiming that this result was based on an unconscious manipulation of the data due to ‘prejudices’ (‘finagling’). However, a student (Michael, 1988) has checked Morton’s data and found no systematic error, only deficits in precision. John Michael sent his results to Gould but he never reacted. But dealing with the results of others and dealing with questioning and critique is essential for an epistemic attitude (searching truth) and scientific progress (finding new truth). And not dealing with them, except for time and cognitive constraints, hints to a non-epistemic attitude (pursuing other aims than truth).

Psychologically interesting is that Gould alleged that others were biased in their research; however, he was himself biased. Projection is an indicator of a poorly integrated cognitive system. E.g. Blinkhorn (1982, p. 506) on Gould:

The theme of this [Gould’s] particular book is that since science is embedded in society, one must expect to find the prejudices of the age presented by scientists as fact. Most authors, given such a theme, would be content to document and catalogue instances in support of the proposition. Gould, however, goes one better by writing a book which exemplifies its own thesis. It’s a masterwork of propaganda, research in the service of a point of view rather than from a fund of knowledge.

Or Carroll (1995, p. 122), who sees Gould not only as prejudiced, but as producing prejudices:

His [Gould’s] account of the history of mental testing, however, may be regarded as badly biased, and crafted in such a way as to prejudice the general public and even some scientists against almost any research concerning human cognitive abilities. [p. 111-112]

Gould is not even mentioned in Haier (2016), Jensen (1998). Gould is mentioned and quoted in Mackintosh (2011), but no particular summary is given and his views are quoted mainly to show what critics have written, then to argued against.

Do any researchers in the field edit Wikipedia/have Wikipedia users?

One quick way to get some expert feedback is if experts are active Wikipedians. Expert here is taken more broadly to include people who have published academic literature on intelligence research. The following experts have Wikipedia profiles:

Recommended literature

The lists below contain literature that did not quite fit in the categories above, but which are otherwise of particular notice.

Books by major researchers

A loose operational definition of ‘major researcher’ here is one that is/was an ISIR board member or is/was on the Intelligence journal editorial board (current board) (the ‘flagship’ (i.e. highest impact factor) journal of the field). Listed in alphabetic order by last name.

Deary, I. J. (2000). Looking Down on Human Intelligence: From Psychometrics to the Brain. Oxford, UK: Oxford University Press.

Deary, I. J. (2001). Intelligence: A Very Short Introduction. Oxford, UK: Oxford University Press.

Matthews, G., Deary, I. J., & Whiteman, M. C. (2009). Personality Traits (3rd Edition). Cambridge, UK: Cambridge University Press.

Deary, I. J., Whalley, L. J., & Starr, J. M. (2009). A Lifetime of Intelligence. Washington, DC: American Psychological Association.

Haier, R. J. (2016). The neuroscience of intelligence. Cambridge University Press.

Lynn, Richard (2001). Eugenics: A reassessment. Praeger Publishers. ISBN 9780275958220.

Lynn, Richard; Vanhanen, Tatu (2002). IQ and the wealth of nations. Westport, Connecticut: Praeger. ISBN 9780275975104.

Lynn, Richard (2011) [1996]. Dysgenics: Genetic deterioration in modern populations. Praeger Publishers. ISBN 9780275949174.

Lynn, Richard; Vanhanen, Tatu (2012). Intelligence: A unifying construct for the social sciences. Ulster: Ulster Institute for Social Research. ISBN 9780956881175.

Lynn, Richard (2015) [2006]. Race Differences in Intelligence: An Evolutionary Analysis. Washington Summit Publishers. ISBN 1593680198.

Meisenberg, Gerhard (2007). In God’s Image: The Natural History of Intelligence and Ethics (illustrated ed.). Book Guild Publishing. ISBN 9781846240553.

Nature and Nurture: An Introduction to Human Behavioral Genetics. (1996). Brooks / Cole Publishing.

Behavioral Genetics (Seventh Edition). (2016). Worth Publishers.

Rindermann, H. (2018). Cognitive Capitalism: Human Capital and the Wellbeing of Nations. Cambridge University Press.