The Black-White IQ Gap: 100 Years Of Research [Abridged]

Blacks and whites differ in average intelligence, and they’re poorly explained by environmental factors

Since the inception of the Boas Cult (refer to MacDonald, 2002) and the denial of race and race differences after World War 2, any comment that refers to race differences in intellectual ability, morphological features or anything else is automatically denounced as “scientific racism” and as being discredited without showing any evidence, or flimsy at best, that it was (e.g. Burmila, 2018; International Socialist Review). The hereditarians, people who support the hypothesis that race differences in a variety of features are influenced by genetics, are accused of racism and being supporters of white supremacy. For example, in a review of Michael Levin’s book Why Race Matters, Levin, who is Jewish, was accused of being a

“Jew who fights in the same trenches of white supremacists”

J.P. Rushton, a Canadian psychologist who wrote the book Race, Evolution and Behavior, had people accuse him and his book of being “racist works of pseudoscience.” Gottfredson (2012) documents the attacks on Rushton and his work, most notably how critics of his attack his motives by calling it “evil,” and calling his work “pseudoscience.” Once a respected psychologist, Rushton was shunned simply for speaking about race differences. The same thing happened to Arthur Jensen and Charles Murray. Hereditarians are accused of implying that whites as superior and other minorities, like blacks, inferior due to race differences in intelligence – which are assessed by IQ tests. The denial of race, IQ differences and a genetic influence seems to rest more on the basis of a moral ground (e.g. Shanks, 2018) .

For example, Turkheimer (1990) claims:

“If it is ever documented conclusively, the genetic inferiority of a race on a trait as important as intelligence will rank with the atomic bomb as the most destructive scientific discovery in human history. The correct conclusion is to withhold judgment.”

The Root, a pro-black site that attacked IQ tests with bad arguments, claimed that IQ tests were racist because of the sins of the original creators (a tactic also used by Gould [1980]):

“Some people say that even the idea of IQ tests are inherently racist because IQ testing derived from the eugenics movement—the idea that it is possible to improve the human race by preventing certain people from breeding.
The man who invented the first IQ test, 
Alfred Binet, even argued that his own tests couldn’t adequately measure intelligence. The Scholastic Aptitude Test (SAT) and the Advanced Placement Exam have similar originsin racism and eugenics.”

Harriot (2019)

In referring to the debate on race as a valid biological concept, Pigliucci (2013) states:

Of course, anyone who has seriously looked into this endless debate knows very well that here is where the stakes really lie: it is not about small genetic differences that may or may not help build a more individualized medicine; it is not about forensic anthropologists and how well they do their work; it is about claims that one race has superior or inferior intellectual capabilities than other one.

I defend the hereditarians and their positions for two reasons:

(i) Just because someone claims that whites are more intelligent than blacks, this doesn’t mean that they think that intelligence equals superiority. By saying that “whites have higher IQ’s than blacks,” critics automatically associate higher intelligence with racial superiority. It is not the hereditarians like Rushton and Levin, for example, who are associating intelligence with superiority, it is the critics who are because they automatically associate high intelligence with superiority. There is no cosmic scale by which differences in intelligence make one race superior to another. A gap separates the facts from judgement of value.

(ii) The evidence supports the hereditarian hypothesis rather than the environmentalist one to a larger degree. We shouldn’t throw away evidence on the basis of a publication date (something many critics like to do; i.e. “this study is invalid because it was published in 1964“, for example) or because it maybe harsh for someone hear. If whites are accused of being responsible for the lack of intelligence amongst blacks, then whites have a right to defend themselves against these accusations. Whites have a right to argue the genetic hypothesis and counter the accusations made against them. The hereditarian hypothesis has withheld critiques made by others for years – while the environmentalist position , while nice in theory, has been shown to not hold (Rushton and Jensen, 2005b).

Some readers may be quick to blame all of this on scientific racism and disregard the evidence because of when it was published, but this is fallacious in nature. In respects to the latter, either the evidence is right or wrong, but appealing to the publication date is a quick cop out to counter the evidence. When it comes to the former, Wade (2014) summed it up best:

“By referring to anyone who explores the biological basis of race as a ‘scientific racist’ and thus in essence demonizing them as racist, the academic left has managed to suppress almost all discussions of human differentiation.”

An Emergence of Controversy

Since the 18th century, European philosophers and scientist proposed that there may be race differences in intelligence. During the 19th and early 20th century, it was though that race differences in the brain were responsible for the race differences in intelligence (Galton, 1839).

During this time there were no IQ test, so people like Francis Galton estimated the intelligence of various racial groups from traveler observations, intellectual achievements, and using the percentage of eminent men in their respected racial groups. According to Galton, intelligence was distributed normally in all racial and ethnic groups, but that distribution varied between groups.

Lewis Terman in the Stanford-Binet Intelligence Scale handbook noted the higher frequency of “morons” amongst non-white American groups, and that more research needed to be done on race differences in intelligence (Benjamin, 2006).

In the 1920s – 1960s, psychologists started questioning the causes for race differences in IQ. During this time, race differences in intelligence were used to support the idea of racial eugenics. The hereditarian hypothesis also started to change due to eugenicist claims regarding race differences in behavior and morality.

From the 1960s – 1980s, the hereditarian position grew stronger thanks to the works of Arthur Jensen. In 1965, William Shockley made a public statement at the Nobel conference, stating that social programs helping the disadvantaged wouldn’t work, and that the most competent group in the U.S. were from the original European settlers. During this, Shockley also supported eugenics, and claimed that his arguments were backed by statistics. Shockley was supported by the Pioneer Fund, a group dedicated to the study of heritability and eugenics in the human race.

One of Shockley’s lobbying campaigns involved educational psychologist Arthur Jensen, from U.C. Berkeley. Jensen, surprisingly, was an environmentalist – but changed his mind in 1966 – 1967. Jensen stressed the importance of genes for intelligence, and that the black-white performance gap had a genetic component to it in his article “How Much Can We Boost IQ and Scholastic Achievement” (Jensen, 1967). Jensen stated that

“various lines of evidence, no one of which is definitive alone, but which, viewed all together, make it a not unreasonable hypothesis that genetic factors are strongly implicated in the average Negro-white intelligence difference. The preponderance of the evidence is, in my opinion, less consistent with a strictly environmental hypothesis than with a genetic hypothesis, which, of course, does not exclude the influence of environment or its interaction with genetic factors.”

Sesardic (2005)

Thanks to Jensen, an academic interest in the hereditarian viewpoint on race differences in intelligence sprung up once again. In 1971, Richard Herrnstein, an American psychologist and sociologist, wrote an article on The Atlantic discussing IQ differences between social classes rather than races. Much like Jensen, he took a strong hereditarian stance on the issue of intelligence. Although the hereditarians simply tried to counter the environmentalist position, a storm of hate against them ensued.

Jensen and Herrnstein were charged with accusations of racism. Jensen was protested by Berkeley’s Students for a Democratic Society. They staged protest against Jensen at U.C. Berkeley, chanting to “Fight Racism. Fire Jensen!” (Jensen, 1972). While teaching at Berkeley, Jensen required bodyguards even though he denied accusations of racism. In 1972, 50 academics – which included Jensen and Herrnstein, signed a statement entitled “Resolution on Scientific Freedom Regarding Human Behavior and Heredity.” The statement criticized the

“suppression, punishment and defamation of scientists who emphasized the role of heredity in human behavior”

Badcock (2015)

Since Jensen’s publication of his article, rebuttals were made against his positions; many of these he has responded to (Jensen, 1980).

After his 1967 article, Jensen became more open on his views on race differences in intelligence. He stated that

“something between one-half and three-fourths of the average IQ differences between American Negroes and whites is attributable to genetic factors.”

Brody (2013)

Critiques against Jensen, for example from the American Psychological Society, American Anthropological Association and Genetics Society of America, all seem to be to simply label Jensen a racist and for simplifying such a complex issue.

In the 1980s – 2000s, hereditarian research continued. Richard Lynn and J. Philippe Rushton, with help from the Pioneer Fund, released their work on race differences in intelligence. Rushton’s 1994 book Race, Evolution and Behavior sparked controversy. He was under police investigation for complaints of promoting racism and white supremacy, something he denied (Rushton, 1994).

In 1994, Richard Herrnstein and Charles Murray reignited the topic on race differences in intelligence with their book The Bell Curve. After its publication, countless articles and books were released in an effort to debunk the book (Gould, 1980; 1994; Jacoby and Glauberman, 1995; Fischer, 1996). The criticisms against the book were mostly stock arguments: correlation doesn’t equal causation, misuse of statistics, and that it wasn’t submitted for peer review (even though books don’t get peer reviewed). Defenses of the Bell Curve and their use of their statistics have also been published (Goodnow, 2014; Hu, 2015; Murray, 1995; Winegard and Winegard, 2017; Heresy, 2019).

Since Herrnstein and Murray’s work, other hereditarian works arguing for a larger genetic influence on IQ have since been released (Levin, 1997; Jensen, 1998). The debate still goes on.

Before we can move onto the data, we have to define race and talk about IQ tests. Since in order for differences in IQ between races to have a racial basis race must first exist, the short discussion on race will be given.

Race: A Biological Reality

Social Construct or Biological Reality?

A popular position in the social sciences it to take the position that race is merely a social construct (e.g. American Anthropological Association, 1998; Thompson, 2006). The problem with the the social construction argument is that they concede that race exists in social sense – but not a biological sense. Thus, both race realist and social constructionist agree that race exists, but they differ on how race exists exactly.

For example, Ashley Montagu, a student of Franz Boa’s, the founder of American Anthropology, wrote the book “Man’s Most Dangerous Myth: The Fallacy of Race” (Montagu, 1997). The title suggests that race is merely a myth, but even in the book Montagu says that race is real according to biology:

If were are asked whether in this sense [the biological sense] there exists a fair number of races in the human species, the answer is that there do.

Even Gould (1996) admits that there are differences in gene alleles between different races, something that shows the biological reality of race.

The Biology of Race

Race is our genetic ancestry, something that we can see simply by looking at someones genomes. Since some race denialist sometimes make the argument that race has meant many different things throughout history, and thus the word race is useless (e.g. Vox, 2015), the word race can be substituted with genetic ancestry or population. So everything you’ll read about IQ differences can be seen as IQ differences between people of European and African ancestry, or different populations that differ in their genes that correlate with classical anthropological views on race.

Witherspoon et al. (2007) found that analyzing gene allele frequency over thousands of loci finds that someone in one racial population is similar to someone in the same population as them. So a European is more genetically related to another European than to an African.

One of the earliest attempts to study DNA differences came in 1994 when looking at tandem repeats (sites on the genome where the same pair of DNA units are repeated several times in tandem), in this case CA repeats, also known as cytosine which is then followed by adenine. When analyzing their subjects on the basis of then number of CA repeats at each genomic location, they found that people clustered together well with their continent origin: Africa, Europe, East Asia, the Americans and Australasia (Bowcock et al., 1994).  Furthermore, Li et al. (2008) applied a clustering program and looked at 1,000 people from 51 populations from around the world. Each person had their genome looked at 65,000 SNP sites; the people sampled from around the world clustered into 5 continental groups. One of new clusters that formed was of the people from Central and South Asia, including India and Pakistan. The second new cluster formation was of people from the Middle East. This, of course, shows how the number of races aren’t fixed, and there could be a large number of races. Genetic clustering analysis have been replicated multiple times (see Bamshad, 2003Rosenberg et al., 2002Tang et al., 2005).

It’s important to note that races aren’t simply genetic clusters, but rather divisions of organisms that all share common gene alleles. Biological races are a group of organisms, and the genes of these organisms cluster together. Thus, genetic clusters show biological races, but clusters are not races in themselves.

We know race has a genetic basis, but people like Lewontin (1972) and others argue that race is meaningless because there’s more variation between groups than within groups. This has become to be known as Lewontin’s Fallacy. The argument goes that since there’s more variation within groups than between groups, race doesn’t mean anything in a biological sense. This is true, but that’s because you’re only looking at a small number of gene alleles at a small number of loci. When you analyze gene alleles over a higher frequency of locus, you start to see that this statement becomes false, a critique made by Edwards (2003) against Lewontin. According to Edwards,

“This conclusion, due to R.C. Lewontin in 1972, is unwarranted because the argument ignores the fact that most of the information that distinguishes populations is hidden in the correlation structure of the data and not simply in the variation of the individual factors.”

Regardless of Lewontin, we can tell someones race by their genes, something that has been replicated many times with cluster analysis.

There are of course other critiques against the concept of race and against genetic clustering, but looking at the history of race, race differences and responding to critiques deserves an article of its own. The evidence shown in this passage should be enough to justify race as a biological reality. What comes next is a brief history of IQ tests, the g-factor, responding to critiques against IQ tests and race differences in intelligence.

A Brief History of IQ Tests

The first IQ test, named the Binet-Simon scale, of course, was developed by Alfred Binet and Theodore Simon in 1904. The French Ministry of Education asked these researchers to develop a test that would allow them to distinguish mentally retarded kids from normally intelligent, but lazy kids. Binet and Simon began working on a test that wasn’t specifically about things taught in school, but that also focused on attention, memory, and problem solving skills.

Binet himself, however, believed that IQ tests couldn’t be used to measure a single permanent level of intelligence. He also said that intelligence was far too broad of a concept to express with a single number. He suggested that intelligence changed over time due to a number of factors and could only be compared to people from similar backgrounds.

After Binet’s original IQ test, Stanford psychologist Lewis Terman took Binet’s original IQ test and standardized it with a sample of American participants. This adapted test was published in 1916, and was called the Stanford-Binet Intelligence Scale. This wouldn’t be the first time that a new version of an intelligence test was created.

Building on the Stanford-Binet test, American psychologist David Wechsler created a new IQ test. Wechsler also believed that intelligence also involved different mental abilities. Since he wasn’t satisfied with the Stanford-Binet test, he published his new IQ test in 1955 called the Wechsler Adult Intelligence Scale (WAIS), the Wechsler Intelligence Scale for Children (WISC) and the Wechsler Preschool and Primary Scale of Intelligence (WPPSI).

Understanding the g-Factor

General intelligence, also known as the g-factor, refers to the existence of a broad mental capacity that influences performance on cognitive ability measures. In 1904, Charles Spearman first described the existence of general intelligence. According to Spearman, g was responsible for someone’s overall performance on IQ test. Spearman noted that while some people could and often excel in certain things, most people who did well in one thing tended to do well in other things, too. A person who did well in a test on verbal intelligence, for example, did well on a test of spatial intelligence.

IQ tests measure cognitive abilities that are thought to make up general intelligence. These include things like:

  • Quantitative Reasoning: ability to solve numerical problems
  • Fluid Reasoning: flexible thinking to solve problems
  • Visual-Spatial Processing: ability to put together puzzles and solve complex shape; tell where objects are in space, how far something is, read maps etc.
  • Knowledge: an individual’s knowledge about a vast array of topics
  • Working Memory: capacity of short term memory, like repeating a set of numbers

All these things are supposed to correlate with g, according to Spearman, and they do. Jensen (1998) found that all these sub tests correlate with g, which vindicate the theory put forth by Charles Spearman.

To extract g, people performed a technique called factor analysis. To quote Gottfredson:

“factor analysis determines the minimum number of underlying dimensions necessary to explain a pattern of correlations among measurements. A general factor suffusing all tests is not, as is sometimes argued, a necessary outcome of factor analysis. No general factor has been found in the analysis of personality tests, for example; instead the method usually yields at least five dimensions (neuroticism, extroversion, conscientiousness, agreeableness and openness to ideas), each relating to different subsets of tests. But, as Spearman observed, a general factor does emerge from analysis of mental ability tests, and leading psychologists, such as Arthur R. Jensen of the University of California at Berkeley and John B. Carroll of the University of North Carolina at Chapel Hill, have confirmed his findings in the decades since. Partly because of this research, most intelligence experts now use g as the working definition of intelligence.

It’s recognized that a general cognitive factor appears in data from every human culture (Warne and Burningham, 2018). Some people have tried to deny the reality of g by claiming that it’s only a statistical artifact (Gould, 1996), especially Hampshire et al. (2012) . Hampshire et al. is especially noteworthy as articles have ran with the headline that, according to Hampshire et al.’s findings, “IQ test are fundamentally flawed” (Connor, 2012). The claims Hampshire et al. make are specially similar to Gould’s claims and Bowles and Ginitis (1973). In the Connor article for The Guardian, Hampshire et al. claim that:

The results disprove once and for all the idea that a single measure of intelligence, such as IQ, is enough to capture all of the differences in cognitive ability that we see between people,”

“Instead, several different circuits contribute to intelligence, each with its own unique capacity. A person may well be good in one of these areas, but they are just as likely to be bad in the other two.

In their paper, they cite Stephen J. Gould, a popular race-denialist who wrote the book The Mismeasure of Man. Gould’s work has been used to discredit the book The Bell Curve – and it seems that the authors are aware of Gould’s work on the topic of race and intelligence as they cite his work.

It remains unclear, however, whether population differences in intelligence test scores are driven by heritable factors or by other correlated demographic variables such as socioeconomic status, education level, and motivation” (Gould, 1981).

More relevantly, it is questionable whether they relate to a unitary intelligence factor, as opposed to a bias in testing paradigms toward particular components of a more complex intelligence construct” (Gould, 1981).

Gould makes the argument in his book that g is just a statistical artifact. Focusing on Gould, though, isn’t worthy for this article as refutations to his attack on g have already been done (Carroll 1995Hunt 1995Jensen and Weng 1994).

Going back to Hampshire et al., Hampshire et al. has been responded to by Haier et al. (2014a; 2014b); their response highlights key issues against this study. To quote the paper:

The authors issued a press release from their university (The University of Western Ontario in Canada) the day before the Neuron publication on December 20th. This press release is in Appendix C. The title is: “Western University-led research debunks the IQ myth.” The press release received some attention mostly in non-science media outlets and hyped the study as demonstrating definitively that IQ was a meaningless concept. For example, the senior author, Adrian Owen, was quoted as saying: “When we looked at the data, the bottom line is the whole concept of IQ — or of you having a higher IQ than me — is a myth… There is no such thing as a single measure of IQ or a measure of general intelligence.” Of course, most psychologists understand that this is a classic “straw man” argument since no one claims that an IQ score (which is a composite of a test battery) measures the whole of human intelligence. It is also widely understood that the g-factor is not synonymous with IQ.”


The study’s design appears to have suffered from a conceptual confusion that sometimes appears in studies using factor analysis. Hampshire et al. used averaged voxel activations (in a limited set of brain areas) across all 12 tests and all 16 subjects as the basis for identifying the two brain networks but then related these average across-subject voxel activation differences to individual differences in task performance in the much larger internet sample. The interpretation of these associations as indicating that neurological factors underlie variation in task performance is questionable.”

In laymen’s terms: it’s recognized that IQ test do not measure all of human intelligence, and Hampshire et al. start off with this straw man regardless. They used average voxel activations (voxels are 3-dimensional images in fMRI that represent a tidy cube of brain tissue, and each voxel can represent a million brain cells) in a limited set of areas on the brain on across all the 12 test used and 16 people for identifying two brain networks. The flaw is that they used these two brain network averages across-subject voxel activation in task performance for the much larger internet sample. Largely making a blanket conclusion.

Trying to deny the reality of g is a losing battle as Spearman’s hypothesis has been confirmed in 25 large independent samples (Jensen, 1998). According to Dragt (2010),

“Spearman’s hypothesis can now be considered to be an empirical fact. Mean differences in intelligence between ethnic groups can be largely explained by the complexity of the subtests in an IQ battery. So, the present study shows clearly that there is simply no support for cultural bias as an explanation of these ethnic group differences. Apart from subtests with a strong language component, IQ batteries appear to be excellent measures of intelligence for all groups studied in our meta-analysis.”

It’s important to note that the races differ in g, according to Jensen. This is important as we continue, especially for critiques like the Flynn Effect.
Rushton and Jensen (2005) found a positive correlation between how well a question measures general intelligence and how the races differ in it. This means that the racial gaps in intelligence are primarily gaps in general intelligence.

Critiques Against IQ Tests

Defining “Intelligence

A common tactic by some people is to first ask “what is intelligence?” From my personal experience, this is usually a tactic that leads to the argument that there is no universal agreement on what intelligence actually means. This, of course, is absolutely true. There is no uniform agreement on what the word means, but we can look at what other researchers have defined intelligence as and use that as a proxy.

Rindermann, Becker, and Coyle (2016) surveyed intelligence researchers to see what was the cause of international differences in IQ tests. In their introduction, they defined intelligence as

the ability to think (intelligence), the disposition of knowledge (the store of true and relevant knowledge), and the intelligent use of this knowledge.”

Plomin and Stumm (2018) , two psychologists, define intelligence as

“the ability to learn, reason and solve problems”

Neisser et al. (1996) found that researchers regard intelligence as efforts to organize a complex set of phenomena, including the

ability to understand complex ideas, to adapt effectively to the environment, to learn from experience, to engage in various forms of reasoning, to overcome obstacles by taking thought.”

The most comprehensive data on what defines intelligence, that I could find, comes from Legg and Hutter (2007). They looked at definitions of intelligence from organizations, psychologists, and AI researchers. While they do say that there is no uniform agreement on what intelligence means, the definitions they got could all be summed up:

Intelligence measures an agent’s ability to achieve goals in a wide range of environments.”

Baker (1974) also uses intelligence to mean the ability to solve problems and understand concepts.

So from this point on, intelligence would be taken to mean the ability to solve problems and understand concepts. A good way to understand this is from a simple thought experiment:

Think of 2 people of whom you know. Which one is intelligent and which one is less intelligent than the other? Why is this so? I assume that even the reader can see that one friend has a faster time understanding and solving stuff, while the other friend takes longer.

“Intelligence Means Different Things in Different Cultures”

A common argument is that different cultures have different definitions on what they classify as intelligence. Sternberg (2004) makes the argument that intelligence can not be understood without understanding its cultural context. He has a small section arguing that a child’s talent may go unnoticed that in academic test. Benson (2003) writes in the American Psychological Association that

“…Taiwanese-Chinese conceptions of intelligence emphasize understanding and relating to others–including knowing when to show and when not to show one’s intelligence.”

Researchers also looked at what intelligence is in Africa. According to Benson,

“When rural parents in Africa talk about the intelligence of children, they prefer not to separate the cognitive speed aspect of intelligence from the social responsibility aspect.”

What this argument tries to do, much like the theory of multiple intelligence, is to stretch out what the word “intelligence” means. For example, “even though Bill has a PhD in astrophysics, that doesn’t mean that Bob is less intelligent than him since Bob has social skills.” Sternberg and others loosen the definition of intelligence so that it can fit in things like talents and skills. No person would make the argument that someone who understands music theory is as intelligent as Newton or Einstein. It is generally recognized that skills and talents can not be substituted for someone’s intelligence, but it seems that as you loosen a word up to fit multiple things, it loses its original meaning.  Because someone may have social skills or can fish, this doesn’t tell us anything about their intelligence. This line of reasoning is just an ad-hoc, it to tries to lump talents, skills and other things to try to invalidate what intelligence is (Levin, 1997).

“There Are Multiple Types of Intelligence”

Much like the argument taken up above, the theory of multiple intelligence also tries to expand the word intelligence to fit things like talents and skills. The proponent of multiple IQ theory,  Howard Gardner, claims that IQ could be broken down into multiple things:

  • Visual-spatial
  • Bodily-Kinesthetic
  • Musical
  • Interpersonal
  • Intrapersonal
  • Linguistic
  • Logical – Mathematical

The first thing that should be obvious is how musical talent is taken to be a type of intelligence of its own, rather than just that – a talent. There are problems proving Gardner’s theory in the first place as he’s opposed to psychometric testing. Waterhouse (2010) found no support for the theory of multiple intelligence.

“Although Gardner and Moran (2006)…… claimed that there was a wealth of empirical support for their theories, Gardner and Moran offered no research evidence to validate MI.”

Again, all this tries to do is stretch out the word intelligence to fit stuff that it doesn’t even align with. Talents do not equal intelligence.

The Flynn Effect

Supposedly, IQ has been raising for all races and even for countries – which should mean that the racial IQ gap should narrow soon and that environmental changes can cause large IQ gains. Even conservative commentator Thomas Sowell said that

“Since the black-white difference in IQ is 15 points, this means that an even larger IQ difference has existed between different generations of the same race, making it no longer necessary to attribute IQ differences of this magnitude to genetics. In the half century between 1945 and 1995, black Americans’ raw test scores rose by the equivalent of 16 IQ points.” 

Sowell (2002)

What the Flynn-Effect measures is things that aren’t g. So it’s telling us nothing about how races differ in general intelligence. Rushton and Jensen (2005) looked at the Flynn Effect in their work on race differences in intelligence:

One culture-only hypothesis currently enjoying much support is based on the secular increase in test scores, known as the Flynn effect because of the repeated demonstration by James Flynn (1984, 1987, 1999) that the average IQ in several countries has increased by about 3 points a decade over the last 50 years. Some have suggested that the Flynn effect implies that the 1 standard deviation difference in the mean Black–White IQ difference in the United States will gradually disappear over time (Flynn, 1999). However, one statistical analysis shows that the Flynn effect is not on the g factor, the principal source of the mean Black–White group difference.

Even Flynn (2011), an egalitarian in the IQ debate, and who the Flynn Effect is based on, has said that it is not on g.

The magnitude of white/ black IQ differences on Wechsler subtests at any given time is correlated with the g loadings of the subtests; the magnitude of IQ gains over time on subtests is not usually so correlated; the causes of the two phenomena are not the same.”

Since the Flynn Effect is not on g, that means that there should be a negative correlation between score gains in IQ and g-loadings. Nijenhuis and Flier (2012) found a negative correlation between score gains and g-loading, and that the Flynn Effect and group differences have different causes – this suggests that the Flynn Effect is on item specific cognitive abilities and not g. This holds true even when assessing the Flynn Effect on scholastic achievement (Jensen, 1998).

The Validity of IQ Test Scores

IQ tests simply don’t measure how well someone does on IQ tests, but it also measures real world outcomes. Some commentators, like the internet personalities on The Majority Report with Sam Seder, argue that IQ tests only measure how well you do on IQ tests. In reality, IQ scores correlate with many things, which can be seen in the chart below.

StudyItemCorrelation (r)
Strenze (2006)Educational Attainment0.53
 Occupational Prestige0.45
Strenze (2015)Becoming a leader in
a group
 Popularity among
group members
 Physical attractiveness-0.4
 Number of children-0.11
 Academic performance
in primary education
Schmidt and Hunter (2004)Job Performance0.51
Jensen (1980)Occupational
0.5 – 0.7
 Scholastic Achievement0.50
Rushton and Templer (2009)Rape, 1990’s *n-0.29
 Assault, 1990’s *n-0.21
 Homicide, 1990’s *n-0.25
Herrnstein and Murray
Socio-economic Status0.4
 Dropping out of HS0.58
Lynn and Vanhanen (2012)Economic Freedom *n0.52 – 0.76
 Income Inequality *n-0.51 – -0.60
Rinderman (2007); Lynn et al.
National School
Achievement *n
0.87 – 0.92

n = national level

Since IQ scores on IQ tests measure outcomes in the real world, they are not simply tests that only measure how well someone does on IQ tests. More IQ correlates can be found in Herrnstein and Murray (1994) and Levin (1997).

Race Differences in IQ: The Black-White IQ Gap

Shuey (1966) in The Testing of Negro Intelligence reported on 382 studies involving 80 different tests administered on hundreds and thousands of black and white children, high school and college students, military personnel, civilian adults, deviates, and criminals. The average black IQ score in these studies were a bit below 85, and the average for whites was also a bit above 100. The average black-white difference was always close to a 1 SD.

Coleman et al. (1966) reached identical conclusions:

“…the Negroes’ averages tend to be about one standard deviation below those of whites.”

The National Academy of Science reported:

“Many studies have shown that members of some minority groups tend to score lower on a variety of commonly used ability tests than do members of the white majority in this country. The much publicized Coleman study provided comparisons of several racial and ethnic groups for a national sample of 3rd, 6th, 9th and 12th grade students on tests of verbal and nonverbal ability, reading comprehension, mathematics achievement, and general information. The largest difference in group averages usually existed between blacks and whites on all tests and at all grade levels. In terms of the distribution of scores for whites, the average score for blacks was roughly one standard deviation below the average for whites. Differences of approximately this magnitude were found for all given tests at 6th, 9th and 12th grades… The roughly one-standard deviation difference in average test scores between blacks and white students in this country found by Coleman et al. is typical of results of other studies.”

Garner and Wigdor (1982)

Lynn (2011) reviewed the overall literature on the black-white IQ gap in the United States. In all the studies Lynn reviewed on American blacks, they averaged an IQ of 85. Whites, on the other hand, averaged an IQ of 100.

In regards to whites (Column broken down by: row, location, age, sample size, test used, IQ score, source):

Herrnstein and Murray (1994) introduced the general population to race differences in IQ. The general evidence showed a 1 SD IQ difference between blacks and whites:

The findings for race differences in intelligence have been found in Rushton and Jensen (2010)Rushton and Rushton (2001)Lynn (2011), and Lynn (2008). For blacks and whites specifically, the race differences in IQ have been replicated (Levin 1997; Pesta and Poznanski 2008).

The gaps in IQ shouldn’t be controversial as Roth et al. (2001), which was a large meta-analysis which included more than 6,000,000 individuals in the meta-analysis, found that blacks score 1 SD lower than whites. Chuck (2013) looked at 100 years of testing done on black intelligence, and every study looked at found lower intelligence amongst blacks.

From all the studies reviewed, there’s a 1 SD (15-point) gap between blacks and whites. Rushton and Jensen (2005) note:

Currently, the 1.1 standard deviation difference in average IQ between Blacks and Whites in the United States is not in itself a matter of empirical dispute. A meta-analytic review by Roth, Bevier, Bobko, Switzer, and Tyler (2001) showed it also holds for college and university application tests such as the Scholastic Aptitude Test and the Graduate Record Examination, as well as for tests for job applicants in corporate settings and in the military.”

Race differences in intelligence are also not new. In fact, contrary to some beliefs, it’s been recognized for a very long time that blacks are less intelligent. The historical view on race differences in IQ seem to have been consistent with modern day evidence: blacks are less intelligent than whites.

“Where, oh, tell me where, sir, has the pure-blooded negro, unassisted by the white man, exhibited any of the triumphs of genius? Where have we found that race producing a Homer, a Phidias, a Praxiteles, a Socrates, a Demosthenes, a Virgil, or a Milton, or a Shakespeare? Where has it produced any great architect like Michael Angelo ? Where any great poet, where any heroic soldier like Alexander, Caesar, or Napoleon ? Where any wonderful mechanic ? What negro of pure blood ever started a steam-engine, or a spinning-jenny, a screw, a lever, the wheel, or the pulley? What negro has invented a telegraph, or discovered a star, a satellite, or an asteroid ? What negro ever constructed a palatial edifice like this in which we are assembled, these Corinthian columns, these frescoes walls ? Negro history makes no mark in the great world’s progress. That history is all a blank, blank, blank, sir. The negro can never rise above a certain range of intelligence. The children of the negro, up to ten or fifteen years of age, may be as bright and as intelligent as white children. They acquire knowledge as rapidly ; but after that early age the negro youth does not advance as does the white youth. While the white man is increasing in knowledge till the day of his death, the negro reaches before the age of maturity a point beyond which he cannot well advance in anything save in the arts, of mere imitation.”

James Brook (1867); Speech in the House of Representatives

“The negro mind, in essential respects, is always that of a child, the intelligence, as observed, is more rapidly developed in the negro child, those faculties more immediately connected with sensation, perception, and perhaps memory, are more energetic ; but when they reach twelve and fifteen, they diverge; the reflective faculties in the white are now called into action, the real Caucasian character now opens, the mental forces fairly evolved, while the negro remains stationary, a perpetual child. The negro of forty or fifty has more experience or knowledge, perhaps, as the white man of that age has a more extended knowledge than the man of twenty-five, but the intellectual caliber the actual mental capacity in the former case is no greater than it was at fifteen, when its utmost limits were reached.”

Van Evrie (1853)

Philosophers such as Kant and Voltaire have also given their inputs on the intelligence of blacks. Kant writes that

“The Negroes of Africa have received from nature no intelligence that rises above the foolish. Hume invites anyone to quote a single example of a negro who has exhibited talents. He asserts that among the hundred thousands of blacks who have been seduced away from their own countries, although very many of them have been set free, yet not a single one has ever been found that has performed anything great whether in art or science or in any other laudable subject; but among the whites, people constantly rabble and acquire esteem through their superior gifts. The difference between these two races of man is thus a substantial one: it appears to be just as great in respect of the faculties of the mind as in colour.”

Kant (1764)

In the case of Voltaire, Voltaire writes:

“Their round eyes, their flat nose, their lips which are always thick, their differently shaped ears, the wool on their head, the measure even of their intelligence establishes between them and other species of men prodigious differences.  If their understanding is not of a different nature from ours, it is at least greatly inferior.  They are not capable of any great application of ideas, and seemed formed neither in the advantages nor the abuses of our philosophy.”

Voltaire (1756)

Pieterse (1992) recorded the agreement of European cultures that blacks are less intelligent, brutal and highly sexed. Lewis (1990) describes how medieval Arab slave traders saw their black slaves as rhythmic, highly sexed, unintelligent, and prone to merriment.

Even the strongest egalitarian who believes that the races don’t differ in IQ should concede that there are race differences in IQ after seeing all this evidence – if they do not, then they should offer evidence showcasing that there is no difference between blacks and whites in intelligence. The fact that no egalitarian has shown evidence to support their case shows that the evidence doesn’t agree with them.

Race Differences in IQ at A Young Age

What’s most striking is that IQ differences between racial groups can be seen at a young age. In row 19 in the tables from Lynn, 2 year old blacks averaged an IQ of 92. This shouldn’t be seen as a huge blow to the hereditarian position given the fact that blacks mature faster than whites (Lynn, 1998; Rushton, 2000). This IQ score, of course, actually drops by the age of 3 – 4.

By the age of 3, the intelligence of blacks drops from its original 92 to 85 – 86 (Montie and Pagan, 1988; Peoples, Fagin, and Drotar, 1995). At the age of 3 – 3.4, blacks infants averaged an IQ score of 85 – showing that even before they’re put into school, blacks are still less intelligent than whites.

This doesn’t support the hypothesis that racism or education could drop IQ scores – as blacks have a moderate IQ score at 2, but it drops by the age of 4.

Using cross-cultural studies, race differences in intelligence are fully present in pre-school children outside of the US also. This further verifies the fact that race differences in intelligence are present at an early age as African 3 year olds in Dominica average an IQ of 67 (Lynn, 2011), and black kids at the age 4 in St. Lucia average an IQ of 62 (Murray, 1983).

Environmental Factors in IQ

Culture Bias in IQ Testing

A popular belief in the social sciences is that IQ test are biased against minorities. Sternberg (1986) states:

We must also recognize the limitations of present day intelligence tests. Largely developed and standardized on white middle-class children, these tests tend to be biased against black children to an unknown degree.

It is plausible that IQ test made by whites could be biased against minorities, but this isn’t the case. Jensen (1980) exhaustively reviewed the overall literature on bias in mental testing. He found that IQ test were not biased against blacks.

Reeve and Charles (2008) found that 73.3% of experts surveyed said that there is no cultural-bias in IQ test.

The National Research Council and The National Academy of Science concluded that cultural bias was not an issue in cognitive testing among racial groups in the US:

“The Committee further concluded that ability tests predict
equally well for all groups of test takers. Research evidence does not support the notion that tests systematically underpredict the performance of minority group members.”

Gottfredson (1994) noted that IQ test aren’t biased against blacks and people of different social classes:

Intelligence is a very general mental capability that…can be measured, and intelligence tests measure it well. They are among the most accurate (in technical terms, reliable and valid) of all psychological tests and assessments….While there are different types of intelligence tests, they all measure the same intelligence….Intelligence tests are not culturally biased against American blacks or other native-born, English-speaking peoples in the U.S. Rather, IQ scores predict equally accurately for all such Americans, regardless of race and social class.

Neisser at al. (1996) found that IQ test aren’t “biased against African Americans.” It’s worth noting that Neisser et al. was also released after the book The Bell Curve, which was heavily critiqued by people such as Gould. Referring to bias, Neisser et al. states that

none…contributes substantially to the Black/White differential in intelligence test scores.”

Dyck (1995) states that

The evidence indicates that cognitive test are equally reliable across races, are of equivalent item difficulty across races, yield similar sub-test correlations…and factor analyses yield similar results. The question of biased has been answered: they are not.

Brown and Whitaker (1999) did what Jensen did and reviewed the literature on test bias in IQ test; they looked at claims that they were biased, not biased, and critiques against Jensen. They state that

“…claims of bias should be met with skepticism and evaluated critically according to established scientific principles.”

Thus, low performance from minorities can’t be explained away simply by point to culture bias, which doesn’t seem to even be a factor in IQ testing. A similar argument has been that self-esteem, test anxiety, and stress could also make someone perform bad on IQ tests, but these have never been consistently confirmed (Jensen, 1980).

Adoption Studies and Socio-Economic Status

Adoption Studies

Twin studies have shown that poor kids put into higher SES have had their IQ raised by x points. Schiff et al. (1978) found that poor french children put into higher SES homes had their IQ raised by 15.5 points.

Moore (1986) compared the average IQ of 23 black children adopted into white homes. The children, aged 7 and 10, had an IQ score of 117 compared to an IQ of 103 for those in black homes. The sample size in this study is incredibly small, making it an unrepresentative sample. Since the IQ’s of those in black homes high were already high, it’s very likely likely that Moore was studying on a sample where there were no differences IQ – making this study useless for the race and IQ debate.

Moore also noted the differences in behavior in how whites and blacks were treated. White adoptive mothers reduced stress by joking, laughing and grinning, where as black mothers reduced stress in less positive ways by coughing, scowling, and frowning. She also states that the white adoptive mothers gave more positive reinforcements than the black mothers, and attributes this to culture rather than genetics (Rushton and Jensen, 2005).

Efyerth (1961) looked at the IQ scores of out-of-wedlock children fathered by U.S. soldiers in Germany reared by white German mothers during WW2. The mean IQ for the white children was 97, and 96.6 for the mixed race children, respectively. The problem with this study, of course, is that the children were really young and there was no follow-up done. This matters due to Wilson Effect, dictating that the heritability of IQ increases with age. So only testing kids at a young age may mask genetic effects. Also, 20 – 25% of the black fathers in this study were French North Africans (Caucasian). This shows why the mixed kids had a higher IQ (Rushton and Jensen, 2005).

Scarr and Weinberg (1983) found that the IQ of kids put into higher SES homes also increased:

From these findings, it should be that better SES does increase IQ, but a drop happens by the age of 17. As can be seen in the chart above, the IQ of blacks actually dropped near to their original IQ by age 17 – showing a possible 2nd regression to the mean when the environment is changed. The IQ’s of hybrid blacks/ Caucasians seems to be between the average IQ of non-mixed blacks and non-mixed Caucasians.

While studies do find an increase in IQ, these aren’t permanent. The gains end up dropping later in life. This could possibly be attributed to the Wilson Effect (this will be talked about later in the section that discusses biological factors in IQ).

Scarr, one of the researchers, claimed that education was important in raising IQ, but it seems that the gains don’t last forever. Scarr and Weinberg came to a conclusion with a stake in the debate on race and intelligence.

“The test performance of the Black/Black adoptees [in the study] was not different from that of ordinary Black children reared by their own families in the same area of the country. My colleagues and I reported the data accurately and as fully as possible, and then tried to make the results palatable to environmentally committed colleagues. In retrospect, this was a mistake. The results of the transracial adoption study can be used to support either a genetic difference hypothesis or an environmental difference one (because the children have visible African ancestry). We should have been agnostic on the conclusions”

Socio-Economic Status

The evidence does suggest that smarter people come from higher SES homes. Sirin (2005) meta-analyzed data on roughly 100,000 students and found that the correlation between IQ and SES is .26. Which is weak to moderate for r. The problem is that SES is also heritable at .42% (Hyytinen et al. 2013). Regardless, controlling for SES doesn’t close the black-white IQ gap.

The effect on poverty on race differences in IQ don’t seem to hold across racial lines as a 9-12 point gap remains when status is controlled for (Jensen 1980; Neisser et al. 1996); white children have higher Peabody Vocabulary Test scores at all income levels (Currie and Thomas 1995); lower class whites consistently do as well or better than middle and upper class blacks (Jensen 1980; Scarr 1981). Herrnstein and Murray (1994) found that as Black  IQ scores go up with SES, it doesn’t close the black-white IQ gap.

What if studies controlled for SES like Jensen did? Shuey (1966) looked at 42 studies carried out between 1913-1966 in which blacks and whites had the same SES. 95% found that whites still had higher IQ’s; 2 found no race differences when SES was controlled for, but none found that blacks were smarter than whites. Loehlin, Lindzey, and Spuhler (1975) also looked at 7 studies between Shuey’s work and 1973. All 7 studies showed that whites had higher IQ’s than blacks even when comparing blacks and whites in the same SES.

Even using the SAT, which is a highly g-loaded test (Hambrick, 2011), it shows race differences in IQ between blacks and whites at all income levels (which fits in line with the findings presented by Shuey and Currie and Thomas).

Cottrell (2015) claims that the black-white IQ gap is caused family income, maternal education, maternal verbal ability/knowledge, learning materials in the home, parenting factors (maternal sensitivity, maternal warmth and acceptance, and safe physical environment), child birth order, and child birth weight are responsible for the black-white IQ gap.

This should also be met with high doubt as Sesardic (2005) notes that some of these variables fall short in explaining the between-group IQ gap, and the rest can be found in Rushton and Jensen (2005). For example, Rushton and Jensen note that

“Racial-group differences in IQ appear early. For example, the Black and the White 3 year-old children in the standardization sample of the Stanford–Binet IV show a 1 standard deviation mean difference after being matched on gender, birth order, and maternal education.

The most recent study I could find claiming that poverty reduces IQ is Mani et al. (2013). They claim that lack of resources, or scarcity in economic terms, triggers something that impedes cognitive function. Graves (2015) tried replicating what Mani found, but instead they said that “experimental results do not find that mental and financial scarcities significantly impact test performance.” Although in the literature results do suggest that scarcity may hinder problem solving abilities, but more research is needed.

A personal critique of Mani et al. is that they introduced two studies: one looked at shoppers and the other at farmers. With the former, they separated New Jersey shoppers into two groups: poor and rich. They found that showing the poor thoughts on finances reduced cognitive function, but not for the rich. The problem is that they didn’t even measure the IQ of the poor shoppers before hand, so we have no idea if they were already less intelligent before hand. Regardless of my critique, Dang, Xiao, and Dewitte (2015)looked at Mani et al. and Vohs (2013) – which found similar results as Mani et al.

To quote Dang, Xiao, and Dewitte:

Although these authors went through great efforts to safeguard external validity of their independent variable, we contend that they paid insufficient attention to that of the dependent variable. First, the cognitive tasks they used (e.g., IQ tests, the Stroop task) are irrelevant to participants’ daily life. It is possible that the poor do not have sufficient motivation to fully engage in these tasks while worrying about their financial situation.

They conclude:

Further, we suggest poverty does not necessarily lead to self-regulation failure. Previous studies demonstrated that engaging in a concurrent inhibitory task (e.g., retrenching expenditure within limited budget) would facilitate self-regulation through an inhibitory spillover mechanism (Tuk et al., 2015) or by blocking individuals from recognizing the tempting value of attractive stimuli (Van Dillen et al., 2013). From this perspective, the poor may excel in self-regulation under certain circumstances. Future studies are needed to specify.

McClelland et al. (2015) note some statistical errors in Mani et al., such as median splits, and how critiques made by Wicherts and Scholten (2013) against Mani et al. were correct even after Mani et al. responded to them. When replying to Wicherts and Scholten, Mani et al. just made the argument that “other people did the same thing we did, so it’s alright.” According to Wicherts and Scholten,

the stronger cognitive impediment experienced by the poor could merely be the result of an inappropriate statistical test and an overly easy cognitive control measure. The latter could obscure an equally “threatening” effect in the rich, simply because they were unable to obtain higher scores when not threatened. With such methodological issues remaining to be addressed, the authors’ proposal of far-reaching policy changes, such as timing HIV educational campaigns to harvest cycles, seems premature” (Wicherts and Scholten 2013).

Intervention Studies and Education

Intervention Studies

The question on if early childhood  intervention increases IQ should be taken up in this article as all environmental factors, or at least most, should be considered in the race and IQ debate.

Skuy et al. (2002) looked at 1st-year psychology students and found that an intervention actually increased the black and non-black IQ in Ravens. The IQ score for blacks went from 83 to 97, and for non-blacks it was from 103 to 107. The problem with this study is that it taught people how to solve questions on Raven’s Progressive Matrices; this is called studying for the test – which shows people how to solve specific questions that you’d find on an IQ test (which defeats the purpose of an IQ test). Regardless of this critique, no follow-up was done to see if these IQ scores were permanent gains. Luckily, the Head Start program study did give a follow-up.

Currie and Thomas (1995) looked at black and white kids who were part of the Head Start program. According to the study:

“When selection is controlled in this way, Head Start has positive and persistent effects on the test scores and schooling attainment of white children, relative to participation in either other preschools or no preschool. In contrast, while the test scores of African-American children also increase with participation in Head Start, these gains are quickly lost, and there appear to be no positive effects on schooling attainment.”

Thus, it seems that Head Start actually helped whites, but for blacks it wasn’t permanent. These findings are further confirmed by a meta-analysis finding that intervention does raise IQ, but there’s a fade out in IQ gains over time (Protzko, 2015).

According to Nisbett (2009), blacks have closed the IQ gap by about 5.5 points between 1970 – 1992. At the same time, blacks also closed the educational achievement gap by 35%. According to Nisbett, intervention can narrow the black-white IQ gap. However, it’s very unlikely this is the case since Chuck (2013) and, using Nisbett’s data, Rushton and Jensen have found that the black-white IQ gap has remained constant at about 1.1 SD’s. Using a wider array of tests, no narrowing of the black-white IQ gap has been found (Murray, 2009).


Since intervention studies, or at least this one with a follow-up, don’t show long term effects (for blacks, at least), it should be asked if education plays a role in the race and IQ debate, especially since many commentators claim that minorities get less school funding – which decreases their IQ.

In reality, school funding is pretty progressive, and for a more technical analysis, RCA (2017) does that justice. He finds that school funding by race is actually somewhat progressive. Richwine (2011) looked at school funding by race and found that blacks actually get more school funding per-pupil:

So if blacks get more school funding per student, why are they being outperformed in IQ tests by Asians who get less funding? A good critique of this is that quality of education and allocation of funds is responsible for this disparity, but this falls short in explaining the black-white IQ gap. For example, if there exists a 1 SD gap between blacks and whites by the age of 3, even before they’re put into schools, then maybe education doesn’t have a large effect on IQ tests as environmentalist want it to be.


Multi-vitamins do affect IQ, but it seems to be for small stuff – not g (general intelligence [Grima et al. 2012]). It’s hard to make the argument that blacks have worse nutritional habits given their overall athletic performance, and given the fact that surveys shows that blacks consume more fruitsvegetablesmeat and sugar than do whites in the US, but also have a higher obesity rate.

Stereotype Threat & Motivation

Stereotype Threat

Stereotype threat refers to situations in which people might feel at risk to confirming to their groups stereotype, and then this causes them to do bad on test. In theory, this should hold true for race and gender.

Wei (2009) looked at 64 papers on race and gender stereotype threat, and stereotype threat was replicated only 58.4% of the time. This shows replication bias, and it was only produced almost 60% of the time, and 30% of the time it wasn’t. To quote an article looking at the replication of stereotype threat:

In conclusion, a replicability analysis with the R-Index shows that stereotype-threat is an elusive phenomenon. Even large replication studies with hundreds of participants were unable to provide evidence for an effect that appeared to be a robust effect in the original article. The R-Index of the meta-analysis by Flore and Wicherts corroborates concerns that the importance of stereotype-threat as an explanation for gender differences in math performance has been exaggerated. Similarly, Ganley, Mingle, Ryan, Ryan, and Vasilyeva (2013) found no evidence for stereotype threat effects in studies with 931 students and suggested that “these results raise the possibility that stereotype threat may not be the cause of gender differences in mathematics performance prior to college.” (p 1995).

Pennington et al. (2019) found that stereotype threat didn’t harm student performance, further leading to the argument that this isn’t a problem in IQ test.


Another argument taken up is that race differences in IQ test are caused by motivation (refer to Nauret, 2018). First of all, in general there are race differences in motivation. Mau and Lynn (1998) looked at standardized scores on math, reading and science, and number of hours devoted to working on homework per week.

It is suggested that motivational differences expressed in the amount of homework undertaken contribute to the group differences in educational achievement. Statistically significant correlations between the amount of homework and educational achievement support this hypothesis. There are also group differences in intelligence parallel to those in educational achievement, suggesting both intelligence and motivation are involved in racial and ethnic differences in educational achievement.”

If we use academic achievement as a substitute for motivation and control for IQ, we find that cognitive ability is a better predictor of academic achievement than motivation, and that students’ “self-assessments of their motivation were not related to their academic achievement” (Gagne and Pere 2002).Jensen (1980) also notes how motivation in IQ scores are inconsistent in explaining the black-white IQ gap.

Reaction Time

Reaction time simply consists of the speed of a reaction to a simple stimulus, like clicking a light when it turns on. A simple understanding of this can be seen in games – ones for children and ones found within application stores. Any game that requires you to react to something, for example clicking a tile when it lights up or placing your foot on top of a light when it lights up, is an example of a stimulus that requires a quick reaction. Jensen (1998) and Deary (2000) have found that the correlation between reaction time and intelligence is at 0.2 to 0.3. If the races differ in reaction time, then it can show race differences in brain efficiency and to see if motivation can really explain race differences in IQ.

Jensen (1993) looked at 585 Europeans and 235 African 10 year old children in the United States whose IQ’s were assessed by using Raven’s Progressive Matrices. Within the study, Jensen used computer-controlled apparatuses so that no human error can potentially fudge the data. Three different kinds of reaction times were measured: Simple reaction time (SRT), which consists of reactions to a single light; Choice reaction time (CST), which consists of reaction to one of eight lights; and finally Odd-man reaction time (OMRT), which consists of reaction to one of three lights that was farthest from the other two. Each of the three reaction times were measured for four components consisting of the reaction time proper (the decision time), the movement time (time it takes to move the finger to the button), and the standard deviations of the reaction and movement time. A similar study was also carried out by Lynn and Holmshaw (1990). The results can be seen in the table below.

Correlation Between RT and IQ Differences Between Blacks & Whites (Jensen; Lynn and Holmshaw)

SRT0.053; 0.11-0.003; -0.40
SMT0.042; 0.150.114; 0.01
SRT: SD0.174* ; 0.09-0.167* ; -1.17*
SMT: SD0.114* ; 0.10*-0.097; -0.60*
CRT0.116*; 0.14*0.053; -0.12
CMT0.072; 0.20*0.063; 0.47*
CRT: SD0.132*; 0.02-0.086; -1.50*
CMT: SD0.072; 0.16*0.063; -0.62*
OMRT0.203*; 0.09-0.189*; -0.38*
0.090; 0.21*

-0.057; 0.49*
OMRT: SD0.203*; 0.07-0.258*; -0.49
OMMT: SD0.187*; 0.15*0.009; -0.18*

Statistically Significant= * ; d= Difference between blacks and whites, negative signifies a faster RT in whites

Correlations between RT and IQ are all positive, and all the data in 16 of the 24 correlations are statistically significant but the correlations are also low. Reaction times in row 1, 5, and 9 are faster in whites than in blacks except for CRT in Jensen. Simple movement time shows no race differences, but Africans are significantly faster than whites in both CMT and in OMMT in the Lynn and Holmshaw data. The SD’s are consistently greater in blacks in the Lynn and Holmshaw data than in Jensen’s data. In Lynn and Holmshaw’s data, the mean difference of the 6 reaction times and SD’s between blacks and whites amount to only 0.67j as compared to a 2.5d difference in IQ.

This means that approximately a quarter of the black-white IQ gap maybe attributable to race differences in the speed of neurological processing. Reaction time has a heritability of 50% (Deary, 2000).

Child Abuse & Home Environments

Home Environments

If the races differ in IQ, then this could explain race differences in home environment and child abuse which could affect intelligence.

In the case of IQ and home environments, it maybe that low IQ parents make bad environments for their kids by treating them worse. Herrnstien and Murray found that the evidence suggest that child mistreatment is mostly from low income families (most low income families tend to be blacks and other minorities).

A summary will be given based off of their findings from different studies.

  • A national study of child abuse reports found that more than 65% of the mothers and 56% of the fathers didn’t complete high school.
  • 480 infants of women registered for prenatal care at an urban hospital for indigent persons and their children found that less educated mothers, even with this disadvantaged population, were more likely to neglect their children.
  • A quantitative study of 113 two-parent families in the Netherlands found that parents with a high level of reasoning complexity (a measure of cognitive ability) responded to their children more flexibly and sensitively, while those with low levels of reasoning complexity were more authoritarian and rigid, independently of education and occupation.

Since low IQ parents are more likely to neglect their kids, it explains why child abuse is higher in black families than in white families, considering their 1 SD gap in IQ.

Child Abuse

Being a victim of child abuse increases the chances of criminality and having lower IQ even after controlling for SES (Currie and Tekin, 2006; Paolucci, Genius, and Violata, 2001). Race differences in child abuse seem to be larger in black families than in white families.

Child Abuse by Race (Statista, 2017)

Using twins, Currie and Tekin found that when one twin is abused and the other is not, the abused twin is, on average, more criminal and less intelligent (Koenen et al. 2003). This holds true even after controlling for birth order, maternal education, paternal criminality, religion and family structure, according to Currie and Tekin.

A problem with this is that parents might be abusing their kids because of their behavior. So if a child is violent and lacks self-control, their parent might use physical force on them. This might be why blacks have a higher child abuse rate considering black kids act out more and have less self-control than whites:

“Teachers reported better social adjustment and less hostility-aggression from Mongoloid children than from Caucasoid children, who in turn were better adjusted and less hostile than Negroid children.”

Rushton (1999)

Mischel (19581961) found that black children had lower self control than matched white children. He reported undertaking the study because informants suggested that

“Negroes are impulsive, indulge themselves, settle for next to nothing if they can get it right away, do not work or wait for bigger things in the future.”

I am aware of no study controlling for race differences in behavior. To the degree that child abuse, specifically, is responsible for the black-white IQ gap is maybe 3-4 points as that’s how much child abuse lowers IQ by (Paolucci, Genius, and Violata, 2001 ; Klika and Herrenkohl, 2013;
Koenen et al. 2003).

Lead Exposure & Intelligence

It should be no surprise that lead exposure affects intelligence in a negative way (Stewart et al., 2007). Since Hood (2005) found that lead exposure is higher amongst poor communities, and poorer communities tend to black, it makes sense as to why blacks have 27% higher lead exposure in their tibia:

likely because of sustained higher ongoing lead exposure over the decades

Theppeang et al. (2008)

Nevin (2012) showcases that blacks, regardless of SES, were more likely to have higher exposure to lead than whites.

The answer on if lead plays a role in lower IQ is an obvious yes, but the question is: “By how much does it lower IQ by?”

Luckily, we have data on blood level by race with a national representative sample. CDC (2005) data goes all the way back to 1991:

The difference between blacks and white varies by age group, but the most important is the 1-5 year old age range. The difference is about 2 micro grams. A difference in 2 micro grams give a difference of about 2 IQ points, and Nevin cites a study saying that IQ declined by 7.4 IQ points as lifetime average blood lead concentration increased from 1 to 10 ug per deciliter.

A meta-analysis on 7 studies by Lanphear et al. (2005) found that

“The estimated IQ point decrements associated with an increase in blood lead from 2.4 to 10 µg/dL, 10 to 20 µg/dL, and 20 to 30 µg/dL were 3.9 (95% CI, 2.4–5.3), 1.9 (95% CI, 1.2–2.6), and 1.1 (95% CI, 0.7–1.5), respectively. “

Using their model and race differences in lead exposure, lead exposure explains less than 1 IQ point. This means that the 1 SD gap in IQ (15 points) goes down to 14 points after lead exposure is taken into account.

Slavery, Segregation: Can They Explain IQ Differences?

An environmentalist position that could explain race differences in intelligence are past historical injustice like slavery, segregation, and racism. This line of argument could be brought up as a counter to the hereditarian hypothesis, but looking at the evidence should cast strong doubts to this position.


One hypothesis that could make sense is the fact that Africans were brought to the U.S. by force and were forced to live their lives as slaves. In turn, slavery somehow could’ve caused the black-white IQ gap as slavery could’ve stunted their IQ. In order to make this hypothesis true, Africans in Africa would’ve needed to be intelligent in the first place – and the evidence suggest that this isn’t the case.

The strongest case against this is the fact there have always been racial differences in intelligence even before slavery happened. Lynn (2009) looked at race differences in brain size, since they correlate with IQ, cold winters theory, and Bakers (1974) criteria for civilization. He found that race differences in intelligence have been present for the past 10,000 years.

Even in modern times, Africans are less intelligent than whites. Lynn (2011) did a meta-analysis on studies looking at the average IQ of sub-Saharan Africans.

Out of all the studies looked at, all found evidence of low intelligence amongst Africans; the studies average to an IQ of 75. It would make no sense to believe that Africans, even before slavery, were even intelligent to begin with.

Even if we were to disregard Lynn’s data, accounts from early explorers to Africa showcase a lack of intelligence. Baker (1974) gives us quotes from Livingstone on the intelligence of Africans:

“No science has been developed, and few questions are ever discussed, except those of which have an intimate connection with the wants of the stomach.”
“All that Africans have thought of has been present gratification.”


Livingstone (2010)

Thus, from all this evidence, like IQ data and historic accounts, slavery could not have caused the black-white IQ gap as it seems lower intelligence amongst Africans has always been there.


Since blacks and whites were both segregated for a time, it makes sense to think that the type of education given to each race was “unequal,” a position supported by Hammond (1998); of course, some individuals like Sowell contest to this and argue that de-segregation didn’t improve black performance and that blacks did better academic wise under segregation (Sowell, 2006). In order to test this argument, we can compare IQ scores during and after segregation. If there is a shift in the gap after segregation ended, then the segregation argument will be shown to hold merit.

While we have no IQ data prior to 1918, we can use data from 1918 – 1954 and so on (when school segregation was overturned by Brown v. Board of Education). Luckily, Shuey (1966) reviewed studies ranging from 1916-65.

Black IQ (During Segregation & After)

1916-653-61,70087Shuey (1966)

As can be seen from the chart above, the IQ’s of blacks from ages 3-18 has remained constant since 1916 all the way to 1965. Rivkin and Welch (2006) analyzed studies on the effects of de-segregation on blacks, and two study found that de-segregation did not have a large effect on the black-white academic achievement gap. The change caused by de-segregation was very small. Herrnstein and Murray (1994) also found similar results supporting the fact that the black-white IQ gap didn’t close after de-segregation.

If the IQ of blacks from 1916-65 didn’t shift at all, and if desegregation didn’t close the black-white IQ gap or narrow it, then this argument from the environmentalist position can be thrown away.

The Biology of Intelligence

An argument frequently assessed by egalitarians and those alike is that race is not tied to intelligence. For example, just because someone may have black skin it doesn’t mean that it’s their skin color that causes low IQ; race, your genetic ancestry, is not tied to IQ directly. Meaning that just because you’re of European ancestry, it doesn’t mean that that’s what determines your intelligence. This is a point many hereditarians concede to, but an argument can be made against this position.

If the races evolved differently from one another to have different morphological and genetic traits that directly influence intelligence, then race, as you can classify them by morphological and genetic differences, is tied to intelligence differences.

In order to understand the genetics of intelligence, we first need to establish what a gene is and other things related to genes and how they express themselves. To put it simply, a gene is a unit of heredity. Much like blueprints, genes are instructions for characteristics of individuals like eye color, height, intelligence, temperament and so on. Genes are small sections of DNA that contains the instructions for a specific molecule like protein. The purpose of genes is to simply store information, and each gene contains the information required to build a specific protein needed for an organism.

When a gene comes in different forms, it’s referred to as an allele. Alleles for a particular gene often come in pairs on each chromosome. When genes express themselves, they express themselves phenotypically (the physical traits and characteristics of an individual/ organism that’s a result of their genetic makeup). So an individual’s phenotype is a result of the combination of gene alleles they have.  

Think of someone’s height. For a gene that determines height, there may be different alleles. One allele may result in being short, and another may result in being over 6’ foot. Someone’s full height would be a result of how many alleles they have and how they interact. It’s important to note that the result of a phenotype are a result of the genes and the environment. The characteristics associated with a particular allele can sometimes be dominant or recessive. A gene is said to be dominant when the dominant alleles show their effect phenotypically even when there is only one copy in the genome, and a gene is said to be recessive when the effects of an allele only show its effects when when there are two copies in the genome.

In cells, long strands of DNA are compacted into form units called chromosomes. Humans inherit two sets of chromosomes from their mother and their father. Genes are inherited through chromosomes.

A gene can express itself differently in different environments. This is referred to as the gene-environment expression. Despite the interaction of genes and the environment, it is wrong to say that environmental manipulation can make a gene express itself in any way. So if blacks are found to have a higher frequency of genes associated with lower intelligence, it’s wrong to say that changing the environment would make said gene express itself in a way where it makes it control for higher intelligence. Along with the gene-environment expression comes the gene-environment correlation.

The gene-environment correlation means that genes shape the environment (DeFries, Loehlin, and Plomin, 1977). The gene-environment correlation can be divided into three types. A correlation is said to be active when a gene affects its environment via its phenotypic expression. Someone genetically predisposed to knowledge will seek environments that encourage the consumption of education. A correlation is passive when the gene that causes it is not a correlate. High IQ parents making environments that encourage education (such as making their kids room filled with books on mathematics, science, etc.) is a passive/ gene environment. The final one is reactive when the phenotypic expression of a gene causes others to modify their behavior towards the gene’s bearer. For example, a kid who may be predisposed to playing music will encourage his parents to buy him a guitar or a piano. This particular reaction will cause a feedback loop. The reaction caused by the phenotype changes the phenotype so that it elicits a further reaction. The feedback may be positive, amplifying the phenotype provoking its reaction, which encourages the kids musical curiosity. Or the reaction may be negative, which will diminish the phenotype. So someone predisposed to depression will shape their environment so it encourages depression, causing a feedback loop.

The Heritability of Intelligence

It’s important to note what heritability actually is. As the Rushton and Jensen paper cited notes:

“Heritability refers to the genetic contribution to the individual differences (variance) in a particular group, not to the phenotype of a single individual. Heritability is not a constant that holds for all groups or in all environments. A heritability of 1.00 means all the observed differences in that group are due to genetic differences and not at all to their differences in the environment. A heritability of zero (0.00) means the converse. A heritability of 0.50 means the observed variation is equally the result of genetic and of environmental differences. The heritability of height in modern industrial populations, for example, is about 90%, which means that most of the differences in height among the individuals are due to their genetic differences.”

As mentioned in the SES section of this article, the Wilson Effect dictates that the heritability of IQ increases with age. This means that as you get older, your genes start playing a large role and the environmental effects start canceling out.

The same genes that explain intelligence during childhood are there during adulthood (Trzaskowski, Visscher, and Plomin, 2014). 

When it comes to the heritability of IQ, it seems to be at .8. In non-statistical terms, that means that IQ is 80% genetic and 20% environmental. More recent estimates put it at almost .9.

Heritability of IQ

Studyh2 Estimate
Burt (1966)0.77

Sniekers et al. (2017)

Hunt (2010)
0.86 (MZ)
0.55 (DZ)

Panizzon et al. (2012)

Plomin and Deary (2015)

Pederson et al. (1992)
0.78 – 0.8

When it comes to Burt, Kamin (Princeton, 2018) and Gould (1996) assert that Burt fabricated his figures on the heritability of intelligence. The main evidence of fraud has been the high concordance of Burt’s figures over time and the elusiveness of his co-authors. Joynson (1989), Fletcher (1991) and Rushton (2001) indicate that Burt’s figures were stable because of his re-use of the same data. While not the best science, it is not fraud. Some witnesses also do remember Burt’s collaborators.

Turkheimer et al. (2003) found that heritability of IQ is actually lower for those in lower SES positions. Since blacks are more likely to be in lower SES positions than their white counterparts, this should mean that genes play a smaller role for them than for those in higher SES. While Turkheimer et al.’s findings should be a huge blow to the hereditarian position, their findings have failed replication – showing that the heritability of IQ doesn’t differ by SES (Nagoshi and Johnson, 2005; Asbury, Wachs, and Plomin, 2005; Bates et al., 2015; McGue et al., 2005).

Brain Size and Intelligence

Race and Differences in Brain Size

Cranial Capacity by Race (in cm^3)

StudyBlackWhiteAsianSample SizeB-W Diff.
Ho et al. (1980)12671370—–1,261.92

Gould (1981)
Beals et al. (1984)12761362138020,000.93
Rushton (1993)12951421145150,000 (males).91
Rushton (1994)122812841312“tens of

Brain size in general has a heritability estimate of 87% (Pepers et al. 2007), and race differences in brain size can be seen at a young age, too. Schultz (1922) found that white fetuses had a larger cranial capacity than black fetuses, and Kirkegaard (2018) noted that race differences in brain size could be see in children as young as 3. Similarly, Rushton (1997) found that, at birth, Asians had larger brains than whites, and whites had larger brains than blacks.

Fitting the hereditarian position, mixed black-white individuals actually have brain sizes that fell between that of blacks and whites (Pearl, 1934; Bean, 1906).

A common objection to race differences in brain size is to cite Boas (1912), the founder of American Anthropology. Boas looked at European immigrant children and their parents: he found that the brain size of kids matched, not their parents, but non-immigrant kids. It turns on that Boas didn’t even control for brain size differences with the function of age. Sparks and Jantz (2002) re-looked at Boas’s findings and controlled for the age difference between the kids and their parents. The brain size of the parents and their kids didn’t differ – the statistical findings were negligible.  The brain size of the immigrant kids and non-immigrant kids also did differ. Boas and his study are still cited in the most updated anthropology textbook I could find (e.g. Larsen, 2017).

These findings could be attributed to the fact that poverty may decrease brain size, a position akin to Noble et al. (2015). They found that poor children scored worse when compared to rich children, but the gap shrunk – but didn’t reduce completely – when controlling for brain size. These results suggest that nutrition and the pre-natal environment cause poor children to have poor cognitive skills than rich children. The researchers didn’t falsify the more likely explanation between brain size and SES. Namely that the parents with larger brains tend to make more money, and then they in turn pass on the genes that control for brain size onto their children which makes them more intelligent. Instead, the authors gave possible hypothesis for their findings with insufficient support.

Brain Size & Intelligence

Three meta-analysis on over 100 studies have found that people with bigger brains are more likely to score higher on IQ test; they produced correlations ranging from  .24 to .40. (McDaniel 2005;Rushton and Ankey 2009; Pietschnig et al 2015).

McDaniel (2005) found a correlation of .21 – .41 in his meta-analysis for brain size and IQ. Using MRI scans on brain size and IQ on college students after body size was controlled for, Willerman et al. (1991) found an r of .35 between brain size and IQ.  Andreason et al. (1993) obtained r’s ranging from .26 to .56 between IQ and the size of  specific brain structures, and an r of .38 between IQ and full-scale IQ and grey matter volume. Raz et al. (1993)and Wickett, Vernon, and Lee (1996) got replications ranging from .41, .47 – .49. Overall, the data does suggest a significant correlation ( .21 <r< .56).

Andreason et al. (1993)  suggest that the remainder of variance is due to

aspects of brain structures that reflect quality rather than quantity of brain tissue: complexity of circuitry, dendritic expansion, number of synapses [or neurotransmitter] efficiency.”


Race Differences in Brain Neurons and Brain Development

If the races differ in brain size, then they should also differ in other aspects of the brain that influence intelligence.

Rushton (1997) looked at brain neurons (in millions of excess neurons) by race, and found that blacks, on average, have less brain neurons than whites and Asians:

Neurons by Race (in millions of excess neurons)


This difference in 100-200 million neurons would be enough to show racial differences in achievements. Since whites have larger brains that do blacks, it maybe that larger brains have a higher chance of having more neurons than the smaller brain.

The genes associated with brain development may also not be equal across racial lines. Wu and Zhang (2011) found that the races differ in genes associated with brain development at a higher frequency than they do in genes that control for skin color:

Through all of this, it seems that race differences in brain size explain a small portion of race differences in intelligence. The reason that the correlation between brain size and IQ isn’t 1 could be attributed to stronger forces at play.

Race Differences in IQ Related Genes

Piffer (2015) used data from the 1000 Genomes project and world IQ data from Lynn and Vanhanen (2012). The goal was to see how these 9 SNPs differed between populations.

Gene VariantAssociation with IQFrequency Among East AsiansWhiteBlacks
Rs104…Positive (+)41.7%53.3%19.5%
Rs175..Negative (-)62.2%51.1%69.9%
Rs101…Positive (+)90.4%71.3%.62.1%
Rs115…Positive (+)31.7%22.9%5.7%
Rs485…Positive (+)55.4%38.7%10.4%
Rs236…Positive (+)86.2%76.7%34%
Rs175…Positive (+)86%62.8%15.1%
rs792…Positive (+)86%48.7%29%
rs272…Negative (-)48.7%53.9%77.2%

From this, we can see that Asians and Europeans have a higher frequency of genes associated with higher IQ, while blacks have a higher frequency of genes associated with lower IQ’s.

It is true that IQ is a highly polygenic trait (meaning that it’s influenced by many genes), and that these 9 SNPs aren’t all the genes that control for IQ, but if these genes differ by race – then there should be no reason to think that all the other genes that control for high and low IQ won’t differ by racial populations.

Genetic Admixture and IQ

According to the hereditarian hypothesis, black admixture will lower IQ while European admixture would actually increase it. Luckily, we have some evidence showing that this maybe the case.

It maybe that American blacks have a higher IQ than pure blooded blacks due to European admixture. Reed (1971) and Chakraborty, Kamboh, Nwamko, and Ferrell (1992) estimate that American blacks have 25% white ancestry. Lynn (2011) estimates that IQ would increase 0.2 points for every 1% of European genes, and that American blacks with 50% European admixture would have an IQ of 90. As the European admixture increases, for example to 75%, it would lead to an IQ of 95.

In Scarr and Weinberg (1983) , they found that mixed black/ white kids had an IQ between those who were black and those who were white. This is well expected and falls inline with the hereditarian hypothesis. Shuey (1966) found that in 16/18 studies were skin color could be used as a proxy for amount of admixture, blacks with lighter skin had a higher IQ than those with darker skin color (although, the correlation was small at only .10).

Templer and Arikawa (2006) also found a negative correlation of -0.92 between IQ and skin color of 192 countries; meaning that the darker the skin color, the lower the intelligence.

A counter to the admixture hypothesis is that Scarr et al. (1977), Loehlin, Vanderberg, and Osborne (1973), and Neisser et al. (1996) found no link between skin color and IQ, but these studies don’t actually test this hypothesis (Reed, 1997).

From all this evidence using biological traits and how they differ by race, it’s enough justification to defend the position that race is tied to IQ. No matter how much someone wants to deny it, race is tied to IQ if morphological and genetic features that influence IQ differ by groups.

This is an excerpt from the book “The Forest and The Trees: A Collection Essays.” In this book, the question on “why IQ matters” is taken up and so are other critiques like individualism and outliers to a larger extent. The book is still in the works and contains more information on race and IQ differences. To think of it in another way, this article is essentially a rough draft.

One thought on “The Black-White IQ Gap: 100 Years Of Research [Abridged]

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