Intelligence is Determined Primarilly by Genes
James Watson, winner of the 1962 Nobel Prize for the discovery of the structure of the DNA.
85% of variations in intelligence are due to genetic variations… Here are the arguments that demonstrate it without a shadow of a doubt.
- 1. High Heritability
- 2. High Stability of Racial I.Q in all Environments
- 3. Stability Over Time
- 4. I.Q Differences are Reflected in Brain Size Differences
- 5. Isolation Time
- 6. Studies on Racial Hybrids
- 7. Qualitative Differences in the Brain
- 8. Adoption Studies
- 9. Race Differences in Reaction Time
- 10. Race Differences in Inspection Time
- 11. European Admixture Among Afro-Americans
- 12. 76 Musculoskeletal Features, Proximity to Homo Erectus
- 13. Intelligence is Part of a Set of Evolutionary Traits
- 14. Position in Evolution
- 15. Regression to the Mean
- 16. Inbreeding Depression
- 17. Racial Differences in EEG
- 18. Spearman’s hypothesis
- 19. Heritability Increases with Age
- 20. Racial Differences in Intellectual Maturation Speeds
- 21. Existence of Racial Differences in Intelligence for 10 Thousand Year
- 22. Differences in Gene Frequencies linked to Intellignece
1. High Heritability
Table extracted from « Behavior Genetics », Plomin, Fries, Mc Clearn, Rutter, 1997.
-> Clearly points out the genetic causality of intelligence (polygenic trait)
On the other hand, the intellectual correlation between adoptive siblings makes it possible to estimate the importance of the environment. The correlation is from 0 to adulthood. As surprising as it may seem, the living environment or education has no impact on general intelligence in adulthooh1.
Table extracted from « Behavioral Genetics », Plomin, Fries, Mc Clearn, Rutter, 1997.
What is the heritability of intelligence?
-> Heritability of the intelligence = part of the variance attributable to genetic factors. There are several ways to estimate it… pointing all to an heritability of about ~ 0.8 in adulthood.
Illustration of the genetic and « environmental » part of intelligence.
If everyone were raised in the same environment, intellectual differences between individuals would be reduced to 80% of the current differences.There are 3 ways to estimate it … pointing to an heritability > to 0.8 in adulthood.
1. Studies of true twins reared in different environments (Data summarized by Bouchard, 1993, p.58). In adults, the data are based on 5 studies summarized by Bouchard. The weighted average correlation for the sample size is 0.75. This figure must be corrected for test reliability (attenuation correction), (Bouchard, 1993, p.49, Machintosh, 1998). This correction increases the correlation to 0.83.
2. A second method for estimating heritability is to compare the degree of similarity between identical twins and non-identical twins of the same sex, raised in the same family. The correlation is 0.88 for identical twins and 0.51 for non-identical twins of the same sex. After correcting these figures for test reliability (mitigation correction), corrected correlation becomes 0.98 for identical twins and 0.56 for non-identical twins.
Heritability can be calculated by Falconer’s (1960) formula by doubling the difference between the correlations of identical and non-identical twins of the same sex. The difference between the two correlations is 0.42, doubling this difference gives a heritability of 0.84.
3. A third method for estimating heritability is to examine the I.Q correlation between children of different biological parents adopted and raised in the same families. This makes it possible to estimate the magnitude of the effect of the family environment (« between family effect »). The summary of the literature on the subject was done by Bouchard (1998) who concludes that in adults the correlation is 0.04, indicating an heritability of 0.96.
-> The first two methods are more precise and give an estimate of 0.84 and 0.85 for heritability of intelligence.
The conclusion of a high heritability for intelligence implies that there are genes that determine intelligence. The first was discovered by Chorley et al. (1998). It is located on chromosome 6 and the possession of one of the alleles of this gene contributes up to 4 Q.I. Since then, thousands of alleles involved in intelligence have been highlighted.
2. High Stability of Racial I.Q in Different Environments4
-> supports genetic causality (Arabs in Europe of first and second generation, immigration …)
Slight increase (84 to 88 for Arabs … genes « hold improvement on leach4.2« )
1. Ashkenazi Jews (110) (America, Europe …)
2. East Asians (105) (Asia, Europe, America …)
3. Europeans (100) (Australia, America, Europe …)
4. Inuit (91)
5. Caucasian-African Hybrids (90) (Europe, America …)
6. Southeast Asians (90) (Europe, America, Asia)
7. Native Americans (87) (North and South America)
8. North African and South Asian (86) (Middle East, America, Europe …)
9. Africans (80) (Europe, North and South America, Africa)
10. Australian Aborigines (62)
This hierarchy remains rigorously unchanged and is reflected in all multiracial countries4.1 In almost all social parameters (wages, socio-economic levels, level of crimes and offenses, prevalence of talented people, prevalence of mental retardation … see » Intellectual Hierarchy Around the World « )
3. Stability Over Time4.2
4. I.Q Differences are Reflected in Brain Size Differences5
Table 9.8. Race differences in brain site (cc) and intelligence
|Race||IQ||Brain Size (cc)|
|South Asians and north africans||84||1293|
Brain size and I.Q for Africans, Europeans and East-Asians6.
5. Isolation Time
When two populations evolve in isolation from one another during such a period, there are differences that occur in all areas where there are possibilities of genetic variation. The extreme environmentalist position, postulating that there are no intellectual differences between two races, defies the general principle of biological evolution and can be seen as impossible.
6. Studies on Racial Hybrids
6.1 African-European Hybrids7
|3||South Africa||10-12||AAB||10,000||100||6,196||83||293||65||Fick, 1929|
|4||South Africa||13||GSAT||746||100||815||86||–||–||Claassen, 1990|
|5||South Africa||15||SPM||1,056||100||778||80||1,093||74||Owen, 1992|
|16||102||55||94||17||85||Weinberg et al.,
6.2 Native American-European Hybrids8
Table 12.4. IQs of Native American-European Hybrids
|Hunter & Sommermeir, 1922|
|Fitzgerald & Ludeman, 1925|
|Lynn et al., 2005|
|Virues-Ortega et al., 2011|
6.3 Pacific Islander-European Hybrids9
I.Q of Hawallan-European hybrids and Hawallan-Chinese hybrids.
Table 9.3. IQs of Europeans, Chinese, and Pacific Islander Hybrids
6.4 East Asian-European Hybrids10
Table 10.5. IQs and brain size (cc) of East Asian-European hybrids
6.5 Australian Aborigenes-European Hybrids11.
7. Qualitative Differences in the Brain
Africans et Europeans12:
-The cortex of Africans is on average 15% thinner than that of Europeans.
-Africans have a smaller frontal and occipital lobe and a wider parietal lobe.
-Africans have a lower proportion of pyramidal neurons than Europeans.
Australian Aborigenes and Europeans13:
From « Race », John R. Baker, Oxford Biology Professor13.
8. Adoption Studies
Koreans adopted by Belgians: 106 of average I.Q.
For children who are all adopted by European parents, there is a difference of 16 I.Q between African and European, the same as this found in whole America.
Raising black children in a middle-class white family has no effect on their I.Q at 17 years old.
Education has no more effect on East Asians adopted by Caucasians, their average I.Q remaining higher.
-> Genetic factors.
9. « reaction time »
Reaction time is correlated with I.Q, as both are signs of central nervous system efficiency. Caucasians react on average faster to a stimulus than Africans.
The tested individual is placed in front of a small lamp that will light up. Whenever this is the case, he simply presses the button in front of him as quickly as possible.
This is a sign of the efficiency of the nervous system since it is a basic treatment of information that must go back to the brain and then back down to press the button. Reaction times are measured in milliseconds.
Reaction Times and EEGs among African, European and East Asians4.3.
10. « Inspection time »
« L’inspection time » measures the speed of processing visual or auditory information. The « inspection time » measures are correlated +0.7 with I.Q.
High I.Q people process visual or auditory information more quickly. They have smaller inspection times.
There are significant race difference in inspection time.
11. European Admixture among Afro-Americans
• Correlation of -0.91 between skin pigmentation and I.Q (Larivée, 2009)
• Average I.Q of Africans: 80
• 25 percent of European descent: 85 (African-Americans)
• Mean I.Q for hybrid people with 50% european descent: 90
• Mean I.Q for people with 75 percent of European ancestry: 95
12. 76 musculoskeletal features, proximity to homo erectus15
Racial differences in brain size are correlated with 76 musculoskeletal traits identified in standard works of evolutionary anatomy as being systematically related to an increase in cranial capacity and intelligence in hominids.
• Among these differences, we find:
– The transverse diameter of the pelvis: The increase in brain size and intelligence go with an increase of the pelvic transversal diameter to allow the passage of the skull at birth. Africans have a significantly smaller pelvic diameter than Europeans (27.4 cm against 24.6 for Africans). Asians have a diameter greater than that of Europeans.
As a consequence of a larger pelvis, the femur, which inserted itself at the level of the pelvis, curved since it was overflown from a growing pelvis, especially the femoral inserons and causing an angle greater for the release of the two objects, it was imperative that the character be involved in a proper junction with the peron, causing a risk incurvation. Europeans have a significantly higher femoral angle than Africans and significantly less than East Asian incarnation.
-While intelligence and brain size have increased, rights are now more spherical and deep. Europeans have significantly more spherical brains, deeper and bigger than Africans.
The increase in sphericity has therefore reduced the protuberances, in particular the mastoid process. Whites have a significantly smaller mastoid process than blacks.
– The increase in generic capacity occurred towards the front of the skull, it appeared as a decrease in prognathism and an increase in orthognathism (flatter face). Europeans have a significantly less prognathic and more orthognathic face than Africans.
Consult the full study « Progressive Change in Brain Size and Muskulo-Skeletal Traits in 7 Hominoid Populations » Human Evolution (2004) Vol. 19
In detail …
13. Intelligence is Part of a Set of Evolutionary traits
East Asians and Africans are at the two ends of a continuum with Europeans in an intermediate position, not only on the mean scores of cognitive tests and brain size, but also on 60 variables including the ripening speed, personality, reproduction and social organization. It seems unlikely that social factors can produce this coherent model across such a diverse set of behaviors. This shows that intelligence is part of a larger evolutionary process rooted in evolution.
From « Rushton’s contributions to the study of mental ability » Arthur R. Jensen, Personality and Individual Differences, 2012.
Africans are in fact more r-selected than Europeans, who are more r-selected than East Asian (zoological gradient r / K). For more details see Rushton’s comparative perspective.
14. Position in Evolution
15. Régression to the Mean
Regression to the Mean for Stature
Regression to the Mean for Intelligence
How to understand the phenomenon of regression to the mean?
Imagine two beans of the same size: beans A and beans B.
Bean A comes from a breed (= variety) of large beans. The bean B comes from a breed of small beans.
The seeds of beans A and beans B are planted. What is observed in the offspring?
The progeny of bean A will show a « regression » to its higher average size: the beans will be bigger.
The progeny of bean B will regress towards the racial average of B, namely a smaller size.
This phenomenon is found exactly in terms of I.Q and intelligence: take two couples with an average I.Q of 110, an African couple and a European couple.
The children of the European couple will regress towards the European intellectual average of 100: they will have on average I.Q. The children of the African couple will regress towards the African I.Q mean of 80: they will have on average I.Q of 95.
This phenomenon of regression to the mean is also noticeable among low IQs: a child of a European couple with an average IQ of 75 will have an I.Q of 87.5 (regression towards the average of 100), whereas a child of an African couple with a mean I.Q of 75 will average 77.5 IQ (regression to the mean of 80).
-> Signature of the European genotypic average at 100 and the African genotypic average at 80.
Regression to the mean for intelligence
-> Signature of genetic causality of intelligence
-> Additive genetic model
• Decreased « fitness » in the offspring of the crossing of individuals (or animals … man is an animal) genetically too close
• 7-I.Q-point deficit in the offspring of first-generation cousin crosses
-> Point the genetic causality of intelligence.
As explained (see here) the evoked potentials of smarter individuals have a smaller « score »: The frequency of alpha waves is greater.
In other words, the transmission of information is faster in bright people.
There is a significant difference, in terms of EEG score, between races.
Table 4.10. EEGs of Africans and Europeans
|Test||Africans in Africa||Europeans in Europe|
The magnitude of the intellectual difference between two races, observed in cognitive skill tests, is proportional to its saturation in g.
Example of the difference between European and African-Americans. The difference is 1 SD = 15 Q.I.
In other words, the more a test is saturated in g (the more it will imply a cognitive complexity), the more the difference will be marked.
-> A difference in g is mainly responsible for the racial intellectual differences observed.
-> This points to the genetic causality of intelligence.
If the environment had an impact, its importance should increase with age, but the opposite is happening.
The non-shared environment essentially targets in utero environment.
20. Racial Differences in Intellectual Maturation Speeds
→ (1) Fastest intellectual development among Australian Aborigines and lowest final intelligence (mean I.Q 62)
→ (2) Intellectual development among Africans a little slower than among Aborigines and final intelligence a little higher (mean I.Q 71)
→ (3) Intellectual development among Europeans slower than Africans and higher final intelligence (Mean I.Q 100)
→ (4) Least fast intellectual development among East Asians and highest final intelligence (mean I.Q 105)
Africans are ahead of the Europeans in their intellectual and motor development until around 30 months (2.5 years) then they are caught and exceeded.
Table 14.2. Differences between the means of South African Black and American White Infants on the Bay Scales of Infant Development, expressed as ds
→ Australian aborigines also have a low Q.I (62) and similarly show early infant maturity. They are more advanced than Caucasians in controlling the neck, back and legs (Freedman, 1974).
→ Slower intellectual development among East Asians and higher final intelligence
European children are ahead of East Asian (for intellectual and motor development) until about 8 years old.
Table 14.4. Norms for Taiwan for the Bayley Scales of Infant Development
Table 14.3. Norms for Japan for the McCarthy Scales of Children’s Abilities
It’s a well-known principle of evolutionary biology is that infants of more developed species have a longer childhood in which they depend on their mothers. As soon as baby reptiles hatch from their eggs, they can move and fend for themselves, while monkeys have a few years of maternal dependence. Among the primates, the most primitive are the lemurs, who have 2 years of maternal dependence; macaques are a little more developed and have 4 years of care by the mother; chimpanzees are even more developed and require about 8 years of maternal dependence; and humans are the most developed and have about 14 years of maternal dependence (Lovejoy, 1981, Rushton, 2000, p.205).
J.P.Rushton shown that this principle extends to the three main races of homo sapiens: East Asians have a slower development, a longer period of dependence, and the highest final intelligence; Caucasians (Europeans, South Asians, and North Africans collectively) mature faster, while Sub-Saharan Africans grow fastest, have the shortest period of maternal dependency, and the lowest final intelligence. These differences are present in physical, motor and mental development. Regarding physical development, Africans have greater skeletal maturity at birth, faster dental development in childhood, and faster sexual development with earlier adolescence (measured by breast appearance in girls and by genital development in boys). Rushton’s theory was confirmed by the Japanese anthropologist Kunihiko Kimura (Eiben, 1998).
These differences in the speed of intellectual maturation point again the genetic causality of racial differences in intelligence, which are part of an evolutionary pattern.
Contemporary I.Q differences between races and between nations can be identified 10 thousand years ago from differences in terms of:
-in the ability to make the Neolithic transition from hunting and gathering to sedentary agriculture 8000 years ago
-in the development of early civilizations 6000 years ago
-in scientific, mathematical and technological advances of the last 2500 years
“Consistency of Race Differences in Intelligence over Millennia”, Richard Lynn, Personality and Individual Differences 48 (2010) 100–101.
• Intelligence is highly genetic and polygenic. It implies it’s dictated by certain genes that have a higher frequency in smarter races than in less intelligent ones4.3.
• Lots of genes (thousands) have already been linked to intellectual gain and they actually show a racial frequency parallel to racial I.Q.
The gene of congenital myopia17
The gene of congenital myopia: gain of 7 points of Q.I. (homozygous recessive)
-Highest frequency among Ashkenazi (mean I.Q 110)
-Second highest frequency among East Asians (mean I.Q 105)
-Third highest frequency among Europeans (mean I.Q 100)
-Less frequent among South Asian / North African (Middle Eastern, average I.Q 84)
-The least frequent among Africans (average I.Q 71)
• Gain of 6.89 Q.I points in individuals carrying the rs2061174 A allele in the adult population.
The allele appears in 45% of Africans, 80% of Europeans and 100% of East-Asians, following the hierarchy of Q.I.
Dysbindin-1 gene (DTNBP1) 19
• There are 6 different alleles of this gene. Frequency differences between races would explain a third of the intellectual differences between blacks and Europeans.
• An allele of this gene would show a particularly strong correlation with Q.I.
It is present in 93 percent of East Asians (Chinese and Japanese), 82 percent of Europeans and 63 percent of Africans, which follows the hierarchy of Q.I.
Polygenic Score (GWAS)
A recent study20 published in the journal Intelligence looked at all the genetic variations increasing intelligence discovered to date, highlighted by GWAS (Genome Wide Association Study, allowing the illumination of many different genetic variants involved in a phenotypic trait).
The study then evaluated racial differences in the frequency of these alleles, and showed that they were parallel to I.Q differences between populations; In other words, higher I.Q races actually have a higher frequency of alleles increasing intelligence in their genetic background (table below).
AFR for Africans, AMR for Native Americans, ASN for East Asian, EUR for Europeans and SAS for South Asians and North Africans.
Taking into account all the genetic variants that increase the intelligence highlighted so far, these alleles are more common among East Asians (average IQ 105), followed by Europeans (average IQ of 100). Amerindians (AMR, middle Q.I of 86) and South and North African Asians (SAS, middle Q.I of 84) have a lower frequency and sub-Saharan Africans have the lowest frequency of these alleles.
The frequency of these genetic variants increasing the intelligence is in agreement with the average intelligence of the populations.
The study also estimates more precisely the frequencies of these alleles for different countries and shows the close link between the national I.Q and the frequency of these alleles in the population.
Fig. 2 and Fig. 1 from « A review of intelligence GWAS hits: Their relationship to country IQ and the issue of spatial autocorrelation » Intelligence 53 (2015) 43–50.
Below is a graph of educability genetic scores based on over 2400 allelic variations. These scores are highly correlated with intelligence, they are even currently better intelligence estimators than purely intellectual scores, because studies have been done on larger samples (Plomin, 2018).
As can be seen, these educability genetic scores are parallel to racial I.Q.
East Asians have the highest frequencies of favorable alleles, followed by Europeans. Africans have the lowest frequencies of these alleles.
In 2019 Kirkegaard, Dunkel and al. show that Ashkenasi Jews have an higher PGS score for intelligence.
Dunkel, Kirkegaard et al. (2019) “Polygenic scores mediate the Jewish phenotypic advantage in educational attainment and cognitive ability compared with Catholics and Lutherans” Evolutionary Behavioral Sciences.
This 2019 study corroborate 2018 results get by Piffer D. already showing highest PGS score for intelligence among Ashkenazi Jews.
Piffer D. (2018) Evidence for recent polygenic selection on educational attainment and intelligence inferred from GWAS hits: a replication of previous findings using recent data.
It is again clearly noticable that mean populations IQ are reflected in the polygenic score. Populations with higher IQs have an higher allelic frequency linked to higher intelligence.
– Nature, 2011.
« Intelligence — the ability to learn, reason and solve problems — is at the forefront of behavioural genetic research. Intelligence is highly heritable and predicts important educational,
occupational and health outcomes better than any other trait »
– Nature, 2018.
References for the Whole Page
1. « Des gènes au comportement », Plomin, de Fries, Mc Clearn, Rutter, 1997.
2. Tableau inspiré de celui trouvé dans « The I.Q argument. Race, intelligence and education », Hans Eysenck, 1971.
3. « Race differences in intelligence. An evolutionary Analysis », Chapter 4 pp.29-73, Richard Lynn, Washington Summit Publisher, 2006.
4. La haute stabilité des Q.I raciaux à travers le temps et quel que soit le milieu est la conséquence logique d’une haute héritabilité. Ces informations se retrouvent entre autre dans:
4.1 -« The global bell curve. Race, I.Q and inequality worldwide », Richard Lynn, Washington Summit Publisher, 2011.
4.2 -Conférence de J.P.Rushton à American Renaissance « The Heritability of World I.Q Differences », 2010.
4.3 -« Race differences in intelligence. An evolutionary Analysis« , Richard Lynn, Washington Summit Publisher, 2006.
5. De nombreuses études ont été effectuées pour comparer les volumes craniens dans les différentes races. Consulter « Race differences in intelligence » pour un résumé de ces études. Ce tableau récapitulatif se retrouve également dans « Le quotient intellectuel, ses déterminants et son avenir », sous la direction de Serge Larivée, Montréal, 2009.
6. Graph from « The g factor », 1998, Arthur R. Jensen.
7,8,9,10 et 11. « Race differences in intelligence. An evolutionary Analysis« , Richard Lynn, Washington Summit Publisher, 2006. 7. pp.64 8. pp.161 9. pp.119 10. pp.141 11. pp.105
12. « The Science of Human Diversity », Richard Lynn, University Press Of America, 2001.
13. « Race », John R. Baker, Oxford university press, 1974.
14. « Race, evolution and behavior », J.P. Rushton, Charles Darwin Research Institute, 2000.
15. Rushton, J. P., & Rushton, E. W. (2004). Progressive changes in brain size and musculo-skeletal traits in seven hominoid populations. Human Evolution, 19, 173-196.
16. Sonke C.J (2000). Cross cultural differences in simple cognitive tasks:a psychophysiological
investigation. Tilberg: university press.
17. Karlsson, Jon L. (2009) Major Intelligence Gene Tied to Myopia: A Review. Mankind Quarterly, Vol. 49, No. 3-4 (Spring-Summer 2009).
18. G Davies, A Tenesa, A Payton, J Yang, S E Harris, D Liewald, X Ke, S Le Hellard, A Christoforou, M Luciano et al. (2011) Genome-wide association studies establish that human intelligence is highly heritable and polygenic. Molecular Psychiatry 16, 996-1005 (October 2011).
19. Roth B.M. (2010) « The perils of diversity. Immigration and human nature », Washington Summit Publishers.
20. Piffer D. (2015) « A review of intelligence GWAS hits: Their relationship to country IQ and the issue of spatial autocorrelation« Intelligence 53, 43–50.
21. Plomin R. et Van Stumm S. (2018) « The new genetics of intelligence« Nature genetics, 2018.
22. Altmann A. et al (2018) Evidence for bias of genetic ancestry in resting state functional MRI. BioRxiv.
23. Fan C.C. et al. (2015) Modeling the 3D Geometry of the Cortical Surface with Genetic Ancestry. Current Biology 25, 1-5.