I.Q and Human Intelligence

James Watson, winner of the 1962 Nobel Prize for the discovery of the structure of the DNA.

About 85% of variations in intelligence are genetic variations… Here are the arguments.

• 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
• Conclusion
• References

1. High Heritability

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.

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 leach^4.2“)

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 countries^4.1 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 Time^4.2

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)
East Asians	105	1416
Europeans	100	1369
Southeast Asians	90	1332
Pacific Islanders	85	1317
South Asians and north africans	84	1293
Africans	67	1282
Australian aborigenes	62	1225

Brain size and I.Q for Africans, Europeans and East-Asians⁶.

5. Isolation Time

6. Studies on Racial Hybrids

6.1 African-European Hybrids⁷

				European		Hybrids		Africans
	Location	Age	Test	N	IQ	N	IQ	N	IQ	Reference
1	Brazil	10	SPM	735	95	718	81	223	71	Fernandez, 2001
2	Germany	5-13	WISC	1,099	100	170	94	–	–	Eyferth, 1961
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
6	USA	17	WISC- R	16	102	55	94	17	85	Weinberg et al., 1992
7	USA	Adult	Otis	–	100	284	91	176	87	Codwell, 1947
8	USA	Adult	Vocab	1,245	100	304	92	146	85	Lynn, 2002
9	USA	Adult	Vocab	10,315	100	116	97	4,271	89	Rowe, 2002
10	Canada	7-12	PP	100	–	46	93	46	78	Tanser, 1941

6.2 Native American-European Hybrids⁸

Table 12.4. IQs of Native American-European Hybrids

	Location	Age	Test	Europeans		Hybrids		Amerinds		Reference
				N	IQ	N	IQ	N	IQ
1	Kansas	Adult	OTIS	–	100	536	93	179	67	Hunter & Sommermeir, 1922
2	South Dakota	10-15	OTIS	–	100	68	89	15	86	Fitzgerald & Ludeman, 1925
3	Mexico	7-10	SPM	155	98	571	94	194	83	Lynn et al., 2005
4	Bolivia	6-16	WISC4	–	–	62	94	–	–	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

Group	N	IQ
European	1000	100
Chinese	2,704	99
European-Hawallan	842	93
Chinese-Hawallan	751	91
Hawalian	621	81

6.4 East Asian-European Hybrids¹⁰

Table 10.5. IQs and brain size (cc) of East Asian-European hybrids

		East Asian	Hybrid	European	African
1	Number	63	37	17,432	19,419
2	IQ-Raw	114	103	102	90
3	IQ-Adjusted	109	98	97	85
4	Brain size	1,170	1,155	1,150	1,134

6.5 Australian Aborigines-European Hybrids¹¹.

7. Qualitative Differences in the Brain

Africans et Europeans¹²:

Australian Aborigenes and Europeans¹³:

From « Race », John R. Baker, Oxford Biology Professor¹³.

8. Adoption Studies

9. « reaction time »

	Test	Africans	Europeans	East asians
1	IQ	68	100	106
2	RT-S	398	371	348
3	RT-C	1,950	1,220	–
4	EEG	534	506	–

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.

11. European Admixture among Afro-Americans

12. 76 musculoskeletal features, proximity to homo erectus¹⁵

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

16. Inbreeding Depression

• 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.

17. Racial Differences in EEG¹⁶

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
1	IQ	68	105
2	EEG	534	506

18. Spearman’s Hypothesis

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.

http://en.wikipedia.org/wiki/Spearman’s_hypothesis

19. The Heritability of Intelligence Increases with Age

-> 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

AGE (months):	6	12	21	30
Mental Development:	0,47	0,64	0	-0,01
Motor Development:	0,94	0,24	0,06	-0,01

→ 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

AGE (months):	6	12	18	24
Mental Development:	-0.88	-0.82	-0.48	-0.23
Motor Development:	-1.06	-0.97	-0.74	-0.27

Table 14.3. Norms for Japan for the McCarthy Scales of Children’s Abilities

AGE   (Years):	2	3	4	5	6-8	Adultes
I.Q:	94,4	96,7	97,1	97,9	99,1	105

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.

21. Existence of Race Differences in Intelligence for 10.000 Years

Contemporary I.Q differences between races and between nations can be identified 10 thousand years ago from differences in terms of:

-cranial capacity

-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.

22. Race Differences in the Frequencies of Genes Linked to Intelligence

• 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 ones^4.3.

• 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)

CHRM219 gene
Location: 7q31-35.

• 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 Ashkenazi 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 noticeable that mean populations IQ are reflected in the polygenic score. Populations with higher IQs have an higher allelic frequency linked to higher intelligence.

Conclusion

•“Genome-wide association studies establish that human intelligence is highly heritable and polygenic¹⁸”

– 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. « Behavioral Genetics », Plomin, de Fries, Mc Clearn, Rutter, 1997.

2. Table inspired from a quite similar found in “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. High racial IQ stability across time and space is consequence of high heritability. Data can be found:
         4.1 -“The global bell curve. Race, I.Q and inequality worldwide”, Richard Lynn, Washington Summit Publisher, 2011.

         4.2 -J.P.Rushton to 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. Several studies were done to compare brain size. See “Race differences in intelligence, an Evolutionary Analysis” for a resume. This table can also be found in “Le quotient intellectuel, ses déterminants et son avenir” prof. 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.