FAQ (Frequently Asked Questions) on Intelligence
> What Is Intelligence?
> Can We Measure Intelligence?
> Different Types of Intelligence?
> What IQ Means?
> Each Population Its Own Intelligence?
> What Is the Impact of Racial Differences in Intelligence on Global Geopolitics?
> What Is the g Factor?
> What “Indifference to Indicators” Means?
> What Are the Average g in the Animal World, Including Homo Sapiens?
> Is IQ Hereditary?
What’s Intelligence?
To discuss an issue, it must first be identified and defined.
Qualitatively everyone perceives roughly what intelligence is, a “very general ability generated by the brain”.
Is there a way to quantify and hierarchize this ability? One of the criticisms often heard against IQ is that it is not possible to hierarchize intelligence.
What does science say? What to think of this statement?
Can We Measure Intelligence?
Intelligence is a biological, physiological, organic characteristic, just like height (current neurosciences consider the Cartesian body-mind dualism as erroneous). Current neurosciences are monistic and could take up this quotation by Pierre Jean Georges Cabanis, French doctor of the 18th century “The brain secretes thought as the liver secretes the ball”, in fact the spirit is inseparable from the brain, it is an emanation). Intelligence as a biological trait is hierarchical according to the very simple following diagram:
-> Intelligence (efficiency of the central nervous system) is more important in great apes’ brains (which have the average mental age of Europeans of 2-3 years, average IQ 22) than in dogs (which have an IQ average of 12).
-> Intelligence is more important in a 5 years old children (IQ 35) than in great apes.
-> Intelligence is more important in 10 years old children (IQ 70) than in 5 years old children.
-> Intelligence is more important in adults (average IQ 100) than in 10 years children.
So far, nothing very surprising.
But is there a way to hierarchize in a finer and less coarse way, for example between two European adults?
To be able to quantify, you have to know what to quantify …
Different Types of Intelligence?
If there are different types of intelligence it means that a person considered to be very intelligent in one area would not be in another? In this perspective there will be no way to quantify or hierarchize.
It was quickly realized that:
-> All cognitive skills (totally disparate!) Are positively inter-correlated
-> People who perform well on some tasks tend to perform well on all others
-> All mental faculties are partially determined by a common factor that was called g for ‘general intelligence factor’
-> IQ is an attempt to measure general intelligence = g
-> It is enough to measure some aptitudes to correctly extrapolate ‘intelligence in general’ = g = general intelligence
Figure 2: General intelligence (g) and its correlations.
In fact, you can measure as much type of intelligence as you want: spatial intelligence, verbal intelligence, verbal intelligence, mathematical intelligence, social intelligence, musical intelligence … or I1, I2, I3, I4, I5, I6, I7 … the fact is that a person gifted in one area has a high probability of being in all the others while a person with low intelligence in a field has a high probability to be low in all areas (which is at the origin of the concept of “mental retardation” for example: would be impossible if general intelligence didn’t exist)
The segregation of general intelligence into several types of intelligence (literary, mathematical, artistic, social, musical, economic …) is a cultural construction without biological or neurological base. The biological basis of human intelligence is a characteristic with a large single component, measured by g.
“One of the most remarkable discoveries of all psychology … that scores on all tests of each variety of mental ability are positively inter-correlated for any representative sample of the general population” -Jensen
“g is to psychology what carbon is to physics” -C. Brand
“IQ is to sociology what gravity is to physics” -R. Lynn
“IQ is a fundamental part of a society. We must stop the dysgenic trend in America “-William Shockley, Nobel Prize in physics for the development of the transistor, the man who allowed the transition to the era of electronics.
Absolutely all cognitive activities have a certain saturation in g (= correlation with IQ), even the most basic ones (it is ubiquitous of all processes transiting through the central nervous system).
-Reasoning
-Space visualization
-Memory
-Music
-Languages
-Vocabulary
-Basic cognitive tasks …
But also for example:
– auditory distinction of sounds show correlation with g (higher IQ people can distinguish closer sound tones!)
– visual colors distinction show correlation with g (higher IQ people can distinguish closer color tones!),
– simple reaction time to a stimulus.
-> All cognitive activities have a certain correlation with the IQ (= g loading, equivalent to the implication of the processor of a computer in a program -> Some programs are more greedy in speed of processor but all show a proportionality to clock speed)
Some examples of cognitive activities and their g loading …
Figure 3: Different cognitive activities and their ‘g loading’ (correlation with general intelligence)
From The g factor, 1998, A. Jensen
All mental activities are as good estimate of general intelligence (g). Take for example a simple addition, the result of such a test will not be a very good estimate of the general intelligence of a person (g loading of only 0.23) In contrast the Raven’s Matrices have a high g loading (0.94), which means that they require a high cognition (abstraction, links, reflection) and that a good result in Raven’s Matrices will be predictive of high intellectual results elsewhere (because a good result to Raven testifies to a high general intelligence).
If you want to know the speed at which a computer runs, you will not run a low-end program, because even if it runs very well, it will not predict the performance of the computer in others conditions … Conversely, you will test the computer with a program that requires high performance, this way you will know if your computer is powerful or not.
Raven’s Matrices: one of the highest g loading at 0.94 (one of the best estimators of the IQ ie of the general intelligence).
To pass an IQ test, it is thus to pass a series of tests which are good estimators of general intelligence, in the same way that one would make pass a computer program asking for high system resources on a computer for deduce his power.
IQ validity is accredited by being generally one of the best predictor of a considerable number of social parameters, such as the socio-economic status or level of education predicted on the basis of the IQ of a child, or even many other social parameters. IQ is also accredited by its many biological correlations like brain size (the higher the IQ, the bigger the brain, on average, correlation is 0.35), the speed of the nerve impulse (the higher the IQ, the higher nerve conduction velocity) or many other biological parameters. For further discussion on the intrinsic validity of IQ as a measure of intelligence see section
“Validity of IQ: biological and social correlations of IQ”
General intelligence (g) increases in childhood with the natural crescendo of the cranial capacity, reaches its maximum towards 25 years, then decreases slowly from 30 years then more quickly after 80 years.
Evolution of brain weight and intelligence with age (below)
Intelligence increases in childhood until around 25 years, then slowly declines.
The most basic processes, such as simple reaction times (on the graph below) or inspection times, will follow the same route: the physiological power of the brain increases until around 25 years of age.
Reaction Time at Different Age
The speed at which information is processed by the brain increases with age until around age 25 (graphs below).
IQ shows a distribution called bell or Gauss curve, with many individuals with an IQ close to 100 (the average intelligence of a European) and fewer and fewer people while moving away from 100, one size or another. It is exactly the same for height: many men will have a height around 1m75 and there will be few people of very small size and few people of more than 1m95. This type of distribution makes it possible to accurately predict the frequency of individuals exceeding a certain intelligence, we know for example that for a IQ of more than 130, we will find 2% of the european population.
IQ remains highly stable over the course of life. The correlation between IQ measured at age 11 and the measured IQ at the same individual at age 80 is 0.72 (Deary, 2004 and Hailer, 2016).
What IQ Means?
| IQ or g Factor: | Potential Activities : | Intelligence Level : | % in the European population with an I.Q = or > : | Average Cranial Capacity of a European Population with this Intelligence (N large and random) : |
| 200 | Polymath | Ceiling of what has been measured in homo sapiens. (Blaise Pascal, Francis Galton, Isaac Newton, Marilyn Von Savant) | ||
| 175 | Great philosophers or writers (Cox, 1926) | (one european on 4 million) | ||
| 165 | Estimated average of great composers (Cox, 1926) | 1640 cc | ||
| 158 | Average Nobel science prize, measured | (one european on 31 thousand) | ||
| 145 | Highly Gifted | 0.14 | ||
| 135 | 1 | |||
| 130 | Average Physicists, Surgeons, Civil Engineers, University Professors | Very Superior Intelligence, Mensa Level | 3 | 1494 cc |
| 125 | Average of doctors or post-docs | Intellectual precocity | 5 | |
| 120 | Average pharmacists | 9 | ||
| 115 | Average of university graduates (science) | Superior Intelligence | 16 | 1432 cc |
| 110 | Average among European university students | 25 | ||
| 105 | 37 | |||
| 100 | Average IQ among Europeans | Normal Intelligence | 50 | 1369 cc |
| 95 | Average IQ among car dispatchers | 63 | ||
| 90 | 75 | |||
| 85 | Difficulty learning. repeated failures. Capable of finishing high school. Manual work. | Borderline Intellectual Fonctionning (IQ between 70-85) | 84 | 1307 cc |
| 80 | Not able to work below 80 | 91 | ||
| 75 | ||||
| 70 | Beginning of intellectual disability (DSM5, American Psychiatric Association) | 98 | 1244 cc | |
| 50-70 | -Learning difficulties appear quickly. -Generally in special education. Can learn to read, write and calculate. – Satisfactory social autonomy, with occasional help. Rigidity, little creativity. Absence of curiosity. |
Mild mental retardation | ||
| 35-50 | Very little school learning. Language late and incomplete. Lives without significant autonomy. Need a watch for his social acts. Capable of daily actions (eat, dress alone). |
Moderate mental retardation | ||
| 20-35 | Acquire only late or not at all asyntactically spoken language, almost no autonomy. | Severe mental retardation | ||
| <20 | Need for continuous nursing, often associated with motor disorders. Communication essentially nonverbal. Most often in specialized institutions . | Deep or extreme mental retardation |
Corroborating Montesquieu’s thesis in his “theory of climates”, scientific psychology and evolutionary biology have now exhaustively demonstrated the innate genetic causality of a large number of human behaviors and psychological characteristics, including intelligence. (see “Intelligence is essentially genetic”) and the role played by climate, especially during the main ice age, on the growth and development of racial differences (see “Cause of race differences”). and “Evolution of intellectual differences”)
General intelligence (g) is correctly evaluated by IQ, its predictive power of individual or collective achievements as well as its reliability and its various correlations including biological traits make it a tool of first importance.
Each Population Has It’s Own Intelligence?
It seems interesting to consider the concept of adaptive intelligence. All living beings present today on earth, effectively because they still exist today on the planet as it exists today, have some form of adaptability to perpetuate. This ability to adapt and perpetuate the form of life can be called “intelligence,” but it is an expanded form of the concept. Bacteria have a high adaptive intelligence; Temperatures could go up or down by several tens of degrees that they would survive. Chameleons are endowed with remarkable camouflage abilities, thorn hedgehogs, cheetahs reach crazy speeds, so many biological characteristics that can be called “adaptive intelligence”. It is not this intelligence that is gauged by IQ. Intelligence here is cognitive. Cognitive intelligence, commonly called intelligence, is a form of adaptive intelligence. It is this form of intelligence, measured by IQ, which is hierarchical.
Do you consider a cat or dog as intelligent as homo sapiens? Probably not and that’s because you are referring to the primary meaning of the term intelligence, cognitive intelligence, involving brain processes. If on the other hand the question was “do you consider that man and the cat or dog have the same adaptive intelligence as man? You could tell, provided you define adaptive intelligence as the ability to perpetuate yourself, that to the extent that both are still on earth my faith is difficult to position. But of two things one, or are you talking about cerebral cognitive intelligence and it is clear that homo sapiens surpasses other animals, or you speak of adaptive intelligence and you can consider all living beings as equal on this earth , from the bacterium to the man.
This is of course the cognitive intelligence of which this site speaks, an intelligence that can be quantify according to Figure 1. This type of intelligence is not identical in all homo sapiens races/populations.
The average IQ are:
1. Ashkenazi Jews (110)
2. East Asians (105)
3. Europeans (100)
4. Southeast Asians (92)
5. Inuit (91)
6. Caucasian-African half-breeds (81-90)
7. Native Americans (86)
8. North African and South Asian (84-88)
9. Africans (67-80)
10. Australian Aborigines (62)
11. Bushmen (54)
These differences are essentially of genetic origin. See “Intelligence Is Highly Genetic”
Higher IQ populations have a higher frequency in alleles for high intelligence in their genetic inheritance, a consequence of greater natural selection on intelligence in cold climates. These genes encode for the brain size and neurophysiological processes that varies from one population to another.
Each people has different assets, this is called culture. Take a computer and compare it to a human brain. The power of the computer, that is, its central processor, is the electronic counterpart of biological human intelligence; it is, in a way, the intelligence of the computer. On this computer you can have different operating systems and different other programs, it is the acquired, it is somehow the culture of the computer, which he assimilates from the outside.
It is at the level of this central processor that the different races of homo sapiens vary. It is not a “cultural bias”. Australian aborigines show the lowest IQ, they also have the smallest average cranial capacity and a slower nerve conduction velocity. Eastern Asians have the highest average IQ, the largest average cranial capacity, the fastest nerve conduction velocity, and the highest allele frequencies for high intelligence. On the other hand, the IQ shows an equivalent predictive power for all races. In identical IQ, the average salary of an African-American and a European is for example identical. This is because on average the different races do not have the same intelligence that we find social disparities in societies, this was demonstrated for the United States by Muray and Hernstein (professor of sociology at Harvard) in “The Bell Curve”, then this has been demonstrated for all the multi-ethnic countries of the planet in “The Global Bell Curve”, 2009, Lynn. For a summary see “Intellectual Hierarchy Around the World”
| Computer | Brain | |
| Information processing | Hardware | Intelligence measures by g (central nervous system efficiency) |
| External acquisitions by: | Softwares | Various learning (speech, numbers, studies …) |
What is the impact of racial differences in intelligence on global geopolitics?
It is central and directly causal. 75% of the differences in average wages per capita, for example, can be explained by the differences in IQ between nations.
See the summary table “From Genes to Civilization”
See also “IQ by country and economy”
What Is the g Factor?
As seen previously, the factor g is in fact almost a synonym of the IQ, but the pedagogy is the repetition and it is necessary to understand what the factor g is. The factor g (g for general intelligence) is a biological, organic, person-to-person characteristic underlying all the processes that pass through the central nervous system.
It was discovered by Charles Spearman who realized that all mental processes were inter-correlated so that someone who performed well in one area tended to perform better everywhere else while a mentally deficient person for example had tend to be weak in all cognitive processes. What had astonished Spearman at the time was that the finesse of sound frequency recognition (A test where sounds of different frequencies are heard and the highest sound is heard. Increasingly, the hierarchy obtained by this auditory test was identical to that obtained by a classical IQ test: in other words, the fineness of the auditory spectrum seemed to correlate with the factor g and the people with a high g factor (a high IQ) have on average a finer auditory and visual spectrum The factor g is in a way a measure of the power and complexity of the central nervous system.
The phenomenon of positive inter-correlations in the set of mental abilities (called “positive manifold”) has been described as “probably the most reproduced result of all psychology” (Deary, 2000).
The factor g is measured in IQ units and is usually extracted from a conventional test battery.
What Means “Indifference of Indicators”?
Take the example of a computer. Imagine that you have before you ten different computer cubic machines and you do not know the power. To extrapolate the speed of the processor, you will run computer programs and try to distinguish if these programs run more or less quickly, this is exactly what is done to compare competing machines. Any program or almost will be good to make a comparison because all programs are dependent on the central processor. After having tested only a limited number of programs, it will be possible to correctly estimate the speed of the processors of the ten machines and to make a correct hierarchy of their powers.
It is the same for the factor g which is ubiquitous of the processes passing through the central nervous system: cognitive tasks, visual finesse (ability to distinguish closer color tones), auditory, speed of processing information. so that the type of test is not important to identify a person’s g-factor, because all cognitive tests of any kind involve the factor g.
Since all cognitive results are intercorrelated, it suffices to do a few types of tests in order to extract, by factor analysis, the g-factor of an individual.
The factor g extracted from any type of test bank will always be the same, within the limits of the measurement error.
All types of tests, whatever they are, contain a certain saturation in g. As a result, a composite score of different tests will have more and more saturation in g, because the composition in g accumulates in the composite score while the non-correlated elements in g cancel each other out.
The factors g extracted by different test batteries show correlations between 0.95 to 1. Basically, it is the same entity that is measured, underlying all the processes passing through the central nervous system.
What are the average g in the animal world, including homo sapiens?
Ashkenazi Jews: 110 (2/3 with a IQ between 93 and 127 ie a standard deviation of 17)
East Asians or Mongoloid: 105 (2/3 between 90 and 120)
Europeans or Caucasians: 100 (2/3 with an IQ between 85 and 115)
Southeast Asians: 92
Inuit: 91
Average homo sapiens: 90
Native Americans: 87
North African and South Asian: 84-88 (2/3 with an IQ between 71 and 97)
12 years old European: 75
Sub-Saharan Africans: 67-80 (2/3 with an IQ between 56 and 78 for the natives of Africa)
Aborigines of Australia: 62
Bushmen: 54
European of 8 years: 50
Great apes: 25 (some gifted monkeys reach g factors of 80 or even 90)
Border collars: 15 (there too there is an internal variation!)
To go further Validity of IQ: Biological and Social IQ correlations
Is IQ Hereditary?
Yes, essentially. But the term hereditary means ‘influenced by genetic factors’ and not ‘identical to parents’! You may very well have blue eyes while both of your parents have brown eyes. The intellectual variations between individuals and between ethnic groups are mainly of genetic origin. They are consequent to variations in the frequencies of alleles for high and low intelligence. These alleles begin to be discovered little by little.
For a more detailed argument, see Intelligence Is Highly Genetic.
References (not exhaustive)
Deary Ian J. (2010) « The neuroscience of human intelligence differences » Nature Review, Neuroscience, Volume 11, pp.201-211.
Jensen A.R. (1998) « The g factor: the science of mental ability »
Jensen A.R., Langan C. and LoSasso (2002) « Discussion on genius and intelligence. Mega fundation interview with Arthur Jensen »
Larivée S. and al. (2009) « Le quotient intellectuel, ses déterminants et son avenir »
Lynn R. (2006 and second edition 2015) « Race differences in intelligence. An evolutionary analyse »
Wikipédia (2018) « g factor »