It has been known for decades that East Asians are stronger on visuospatial than on verbal part of an IQ test, but possible explanations for this oddity have become within the reach of research only very recently. I will present a hypothesis that does not seem to have been much discussed, but which is more or less suggested by new research.
East Asians have many other peculiarities. They answer to personality questionnaires in a very different way compared to other people: they are very high on Neuroticism and very low on all other Big Five traits, Extraversion, Agreeableness, Conscientiousness and Openness, see the study in [1]. East Asians are considered diligent, yet they estimate being low on Conscientiousness? While [1] suggests that the reason can be collectivism versus individualism, I get from the answers the impression that East Asians must be exceptionally stressed people. Why should it be so?
They have higher serum testosterone levels than Europeans and even Africans [2]. In an old study [3] African men were found to have 3% higher serum testosterone than European men but also this study showed that Asian men had highest serum testosterone. This may seem strange since Asian men do not build impressive muscles or facial hair, but there is an explanation. East Asians have several copies of the human androgen receptor making them less sensitive to testosterone and they also have less of an enzyme that converts testosterone into dihydrotestosterone (DHT), a much more powerful hormone than testosterone. African men have the highest DHT:T ratio, then Europeans and last Asians. This agrees with the stereotype of masculinity but raises the question why East Asians have so high serum testosterone since it is not for building muscles?
Additionally, their physical features show higher level of adaptation to cold than Northern Europeans, who also have some cold or darkness adaptations, such as a light skin color. Were they once living further to the North?
And lastly, why do the East Asians have the highest average IQ of main races?
How to combine these all?
I think the key is hippocampus. It is important for visuospatial learning. Some 30 years ago it was noticed that in adult mammals, like rats and mice, new neurons are generated in the subgranular zone of the dentate gyrus of the hippocampus. This mechanism is called hippocampal neurogenesis. Hippocampus is one of the two regions of the brain where new neurons are born in adults, the other being the subventricular zone.
The first évidence of hippocampal neurogenesis in adult humans was found 1998, but in March 2018 Sorrells et al published a paper in Nature claiming that adult humans do not generate new neurons in detectable levels [4]. Despite the publication, the issue is not solved: Boldrini et al published in April 2018 a paper [5] which claims that adult humans do have hippocampal neurogenesis. It seems to be that whether neurogenesis in adult humans occurs in detectable or undetectable levels depends on how it is detected, but the mechanism itself probably does happen in some small rate.
The small rate of neurogenesis does not need to imply that the mechanism is unimportant in humans. It is wrong to think that the new neurons in hippocampus are the main way of creating any kind of memories. In humans normal memories are most probably stored as new synapses in the neocortex, while many unconscious skills are learned and memorized by cerebellum. What ever hippocampus does, it is not storing bulk of memories. What does the following list sound like? In rats sex social dominance, larger terrority and so on increase neurogenesis in hippocampus while social defeats and social isolation decrease neurogenesis. To me that sounds like the size of hippocampus corresponds to the size of ego, to use a disqualified term from outdated Freudian psychology. Hippocampal neurogenesis is important for the wellbeing of rats and this probably is so also for humans.
From animal studies it is known that testosterone affects neurogenesis [6]. In humans neurogenesis could either keep newly born neurons alive longer or increase the number of neurons. These effects depend on the species and the case with humans is not yet known as even the existence of adult neurogenesis in humans is disputed. However, it is not disputed that it occurs in humans in young children and that it is connected with visuospatial skills. Many new neurons are created in hippocampus in early childhood but a large portion of them die soon. Sex steroid hormones direct which neurons die and this process causes the sex differences in visuospatial abilities in humans just like it does in other mammals.
In rats and mice many environmental effects can decrease or increase neurogenesis. For instance, social isolation decreases neurogenesis in rats and mice [7]. There is emerging evidence that in humans the lack of Vitamin D influences cognitive functions in humans [8] and it is possible that it reduces neurogenesis in hippocampus. If this is so, then moving to North, which reduces sunlight and in that way reduces Vitamin D, decreased neurogenesis. Social isolation may also have decreased neurogenesis. In order to compensate this, East Asians created mutations, which increases testosterone. This balanced neurogenesis – too low neurogenesis lowers cognitive skills.
Whether the main drive was insufficiency of Vitamin D or social isolation, they adapted to the Northern environment where they were socially isolated. In more populated areas, such as Asia today is, there is more social contact. This raised neurogenesis to a too high level. Partially it was compensated by creating mutations that made them less sensitive to testosterone, but the compensation was not complete. They noticed that they cannot handle the amount of social contact that they have to face. This means, they were Introverted, felt losing energy when in groups of people. It is energy for increased neurogenesis. Introverts, when having to live with too much social contact, feel stressed and report high Neuroticism and low Agreeableness. Being too stressed they also report being low on Conscientiousness, probably because of feeling bad. Low Openness may just be true: despite their high IQ their cognitive skills do not work fully in a crowded environment, or, as I think, Openness is another unrelated trait, which they did not develop.
Being low on testosterone helps East Asian men in visuospatial tasks. The relation between testosterone and visiospatial skills is U-shaped: with too low testosterone (like women) and too high (like African men, who are high on DHT) the results are worse. They are best in the intermediate level, see e.g. [9]. This is intuitively correct: you do not expect to see many macho men or bimbo women in a mathematical department. The mathematically most talented tend to be more androgynous in character, though not always in looks.
Interestingly, Finns are good in mental rotation:
This figure is from David P. Schmitt’s blog Psychology Today [10] and originally from a paper Lippa et all 2010. Finns have the highest mean in this test (the third peak from the left), yet they are not as high in visuospatial intelligence as East Asians. This is not so strange: Mental Rotation is a test that is improved by high testosterone, while some other tests show the U-shape curve.
The Finns may be good in this test, yet have too much bioactive testosterone for East Asian visuospatial abilities; Asians have testosterone insensitive androgen receptors.
The 2D:4D finger ratio is taken as a good proxy of prenatal testosterone level and there is a clear sex difference in this ratio. The optimal ration for visuospatial intelligence sound to be close to one according to the U-curve relationship and that is what we could expect form the staff of a mathematical department. It seems that within a population the 2D:4D can be correlated with testosterone related traits, but between European populations differences in the averages of the ratio are very small. John Manning has been the main researcher on this topic. In one earlier paper he reported that Finnish men had one of the lowest 2D:4D ratios, but this is corrected in [11]: Croatia had the lowest male right hand 2D:4D ratio and Finnish men are quite on the European average, as are also Finnish women. Direct measurements show that adult Finnish men have normal European testosterone levels, which have been decreasing for some unknown reason as in all developed countries [12].
The prenatal testosterone from the mother: a boy’s brain is shaped to visuospatial abilities in the early prenatal stage. If the mother has high testosterone, girls also have high prenatal testosterone. This leads to the positive correlation between male and female 2D:4D ratio. The right had side ratio correlates more, presumably because most people are right handed. The paper [11] notices a weak correlation between low 2D:4D ratio and gender equality, suggesting that women who have been more exposed to testosterone and less to estrogen are more active in the labor market. National scores show some variance, which may be inherited from past, but it may also show present evolutionary selection. If so, it might be connected with decreasing birth rates in Europe: women with higher testosterone exposure should be less fertile, but decreasing testosterone in men does not fit to this explanation. Increasing women exposure to testosterone would also increase men exposure. Possibly testosterone binding could result to the observed effect.
Decreasing male testosterone is today seen as a risk, but originally humans may have had quite low testosterone values. One of the oldest people, !Kung San, have low levels of testosterone, and East Asian men are insensitive to testosterone.
Visuospatial intelligence is thus an old ability that can be found from all mammals and birds and even reptiles. The sex difference in this ability is created in the original way how sex differences used to be created. There is a gene in the Y chromosome, which turns the undifferentiated gonads into testes in males. Without this action gonads develop into ovaries regardless of if the individual has two X chromosomes or one X and one Y. When gonads have developed into testes, they start producing testosterone. Testosterone modifies the effect of genes in hippocampus and many other organs. Thus, if a sex difference in cognitive abilities in humans is caused by this old mechanism, there is a connection with the ability and sex steroid hormones, notably with testosterone and often also with estradiol.
If there is a sex difference, which is not associated with sex steroid hormones, we may assume that it is not created by the old Y chromosome based mechanism of sexual differentiation. There is an evolutionarily newer mechanism for sexual differences. It is based on the X chromosome. X has much more genes than Y and for that reason it has more potential for useful mutations than Y. Females mostly express only one of their two X chromosomes: in each cell one X is randomly selected. There are exceptions to this rule: for some genes women express both copies, and for some other genes the selection is not random. It can be e.g. determined by the parental origins of the gene. In the typical case, woman expresses a randomly selected X in each of her cells. Thus, the effects of X chromosome alleles are strongly diluted in women and alleles become fully expressed only if a woman is a homozygote. If some condition appears in men with the frequency p and a woman must be homozygotic to express the condition, then the trait appears in women with the frequency about 0.25p2. This is the case for recessive X chromosome alleles for mental retardation.
The typical case for X chromosome alleles is quite different. Typically the mutated allele has a small effect. It means that half of the cells of a woman express the allele and the effect of the allele is half of what it has in a man. For instance, if a mutated allele causes neurons in the brain to work a bit faster, half of the neurons in a woman’s brain are faster, while in a man all are faster. A similar effect can be expected for genes where a woman does not inhibit the other X. In that case both copies of X are expressed and the combined result should be the average of the alleles. In the case an allele is chosen not randomly but e.g. by parental origins, the average effect for women in a population is about half of that for men. Thus, for alleles that give small advantages or disadvantages, the effect of the alleles for a woman should be about half of the effects for a man and there is no connection to sex steroid hormones.
Most traits are determined by autosomal genes, but autosomal genes can have sexual dimorphism only if there is a mechanism that causes these genes to be expressed differently in men and in women. There is only one such mechanism: sex steroid hormones and close related substances. If such a mechanism is at work, then there must be some connection to hormones. If there is no such connection, the dimorphic trait must be X determined.
What differences there are in cognitive abilities between the sexes? Richard Lynn showed that the old truth that both sexes are equal in intelligence is not quite true, see [12].
Girls and boys have equal IQ between 4 and 10, girls are about 1 point better between 11 and 15, and since 16 boys have higher IQ, which grows to about 4.4 points by adulthood. In very old age women again pass men. The most interesting observation in this paper is that the difference in IQ agrees very well with the difference in brain sizes. It is known that there is a positive correlation between IQ and brain sizes within each sex. The same relation between IQ and brain size calculated from one sex leads to exactly correct IQ difference between sexes. This calculation goes as follows. The correlation between IQ and brain size measured by magnetic resonance is in average 0.38. The average male brain has a standard deviation of 128 g. As a woman brain is 100 g smaller, it is 0.78 standard deviations smaller. With 0.38 correlation we calculate that the IQ difference must be 0.78*0.38=0.273 standard deviations. With the standard deviation of 15 this gives 4.4 IQ points.
According to one web reference the average (European) brain size is about 1370 g in men and about 1200 g in women. The average brain size of Australian Aborigine men is about 1199 g, i.e., the same size as the brain of European women. Instead of being 4.4 points below the European man average IQ, the estimates for Aborigines put the figure to 61-64 points. Aborigines are not mentally retarded. They are quite well functioning in their native environment. Clearly, the brain size measures only a part of IQ variation. The brain size can correctly estimate the IQ difference between European men and women because both have the same autosomal IQ affecting genes. Aborigines do not have these genes. Their intelligence is adapted to the environment of hunter-gatherers and because of a sparse population they have not had so many IQ affecting mutations.
However, the brain size and IQ affecting autosomal genes are not the only mechanisms of genetic intelligence. There is the sex steroid related intelligence, visuospatial advantage for men and corresponding intelligence advantage for women. As can be expected, Australian Aborigine children had better visual spatial memory than white children [14], which points out to brain differences. The difference was not a larger hippocampus – indeed Aborigines have a smaller hippocampus than Europeans [15]. Their frontal portion of cerebral cortex (a part of cerebellum) was larger. This study supports the idea that hippocampus enlarged in Eurasia, some time before East Asian and Northern Europeans split, so some 50,000 years ago, and that there are different ways to improve visual spatial abilities.
The brain size, autosomal IQ genes and sex hormone related traits are still not all. There is the X chromosome. First we must find a sex dimorphic cognitive trait related to IQ.
Women are superior in most cognitive abilities, visuospatial intelligence being an exception. There is another cognitive ability where men are stronger than women in addition to visuospatial skills: Openness to ideas. Women are stronger on Openness to aesthetics, whatever that means now-a-days. Openness to ideas correlates with a higher IQ, though it is a personality trait and not part of IQ. There is an argument why it should not be connected with sex steroid hormones: the mechanism of the Y chromosome and sex hormones is very old going back to at reptiles. Reptiles are not especially open to new ideas. Ipso, this trait is new and was created in humans. Thus, as it is sex dimorphic, it is X chromosome related.
Let us notice that it is necessary that there must be X related recessive alleles that are advantageous to men. This is because there are recessive X related alleles that cause mental retardation in men and very seldom affect women. If there were no advantageous alleles, men’s IQ should be lower than women’s, but it is not. We may expect that X related recessive alleles, which are advantageous to men, become fixed in the population.
Yet, there are reasons why such alleles do not get fixed. If Openness to ideas is created by X related genes, quite obviously the trait has not got fixed as not all men have this trait. One reason why alleles do not get fixed is that there are several competing alleles. The original (wildtype) allele disappears but if several competing alleles are all good in some circumstances, they do not get fixed.
Autosomal IQ affecting alleles do not get fixed in the population because men do not choose women by intelligence. Too high intelligence is disadvantageous to women as they try to find a man, who is at least as intelligent (and tall) as they are. Genes for height have not become fixed in a population as being taller than most men is a disadvantage for a woman. The same we can assume is true for autosomal IQ increasing alleles. But X connected alleles do get fixed. The harm for women affects women less than the advantage for men helps men.
These hypothetical genes should have small effects so that a woman expressed them half of the effect in men, not so that a woman must be homozygotic to express them. The alleles are probably not fixed because of competing alleles, but even if fixed in a population there can be isolated populations which do not have these alleles. They must increase male intelligence at least as much as the X connected recessive harmful alleles decrease it. These alleles cannot be found by GWAS studies on European, possibly Eurasian, populations.
References:
[1] D. P. Schmitt, J. Allik, R.R. Mccrae, V. Benet-Martínez, “The Geographic Distribution of Big Five Personality Traits: Patterns and Profiles of Human Self-Description Across 56 Nations,” Journal of Cross-Cultural Psychology, (2007), 38(2), 173-212. full paper in:
http://journals.sagepub.com/doi/pdf/10.1177/0022022106297299
[2] Ethnic Androgen Differentials (a list compiled by blogger Ethnic Muse from 150 medical/scientific studies, it is a non-peer reviewed meta-study from around 2013)
https://ethnicmuse.files.wordpress.com/2013/04/ethnic-testosterone1.pdf
[3] Lee Ellis, Helmut Nyborg, “Racial/ethnic variations in male testosterone levels: a probable contributor to group differences in health,” Steroids (1992) vol. 57, February, 72-75. https://pdfs.semanticscholar.org/56c7/049634ac87441e8a96afc8fe34c588bdad94.pdf
[4] Shawn F. Sorrells et al, “Human hippocampal neurogenesis drops sharply in children to undetectable levels in adults,” Nature, volume 555, pages 377–381 (15 March 2018)
https://www.nature.com/articles/nature25975
[5] Maura Boldrini et al, “Human Hippocampal Neurogenesis Persists throughout Aging,” Cell Stem Cell, Volume 22, Issue 4, p589–599.e5, 5 April 2018
https://www.cell.com/cell-stem-cell/fulltext/S1934-5909(18)30121-8
[6] Maya Opendak, Brandy A. Briones, Elizabeth Gould, “Social behavior, hormones and adult neurogenesis,” Frontiers in Neuroendocrinology 41 (2016), 71-86.
https://pdfs.semanticscholar.org/45b0/c41fed422ea3ac2d19af28e50efc67a80a02.pdf
[7] Mark D. Spritzer et al, “Testosterone and social isolation influence adult neurogenesis in the dentate gyrus of male rats,” Neuroscience, (10 Nov 2011), 195:180-90.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3198792/
[8] Natalie J. Groves, Thomas H. J. Burne, “The impact of vitamin D deficiency on neurogenesis in the adult brain,” Neural Regen Res. (March 2017), 12(3): 393–394
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5399710/
[9] Ivana Hromatko and Meri Tadinak, Testosterone levels influence spatial ability: Further evidence for curvilinear relationship, Review of Psychology (2006), Vol. 13, No. 1, 27-34, http://mjesec.ffzg.hr/revija.psi/vol%2013%201%202006/Hromatko_2006_13-1.pdf
[10] David P. Schmitt’s blog Psychology Today, https://www.psychologytoday.com/intl/blog/sexual-personalities/201601/where-s-the-nearest-starbucks-sex-differences-in-wayfinding
[11] John Manning, “Digit Ratio (2D:4D) and Gender Inequalities Across Nations, www.epjournal.net–2014. 12(4): 757-768. One of the papers in:
https://pdfs.semanticscholar.org/6407/9e492e373b7fd7687b01a424497660081c32.pdf
[12] A. Perheentupa et al, “A cohort effect on serum testosterone levels in Finnish men,” European Journal of Endocrinology (2013), 168, 227–233.
http://www.eje-online.org/content/168/2/227.full.pdf
[13] Roberto Colom, Richard Lynn, “Testing the developmental theory of sex differences in
intelligence on 12–18 year olds,” Personality and Individual Differences 36 (2004), 75-82.
http://www-personal.umich.edu/~negisama/asdf.pdf
[14] Judith M. Kearins, “Visual spatial memory in Australian Aboriginal children of desert regions,” August 1981, Cognitive Psychology 13(3):434-60.
https://www.researchgate.net/publication/15961092_Visual_spatial_memory_in_Australian_Aboriginal_children_of_desert_regions
[15] J. Klekamp et al, “A quantitative study of Australian aboriginal and Caucasian brains,” J Anat. 1987 Feb; 150: 191–210.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1261675/
7 Comments
DHT is not used for muscle buildingl. Also East Asians dominate the majority of Olympic weightlifting and their physiques are much leaner thicker even the poorer nations. Just a fyi
OK, but there are very many East Asians, so it is likely that some East Asians are good in weightlifting. However, weightlifting ability can be improved by training and other things, so number of gold medals in weightlifting is not a good measure of the national average, like the number of Nobel Prizes on any topic is not a good measure of the ethnic IQ average. In general, East Asians are less muscular (which does not mean they could not grow strong muscles if they try) which means that their higher testosterone is not effective for building muscles. It has some other purpose. That is all I am saying.
I am not a scientist nor do I know much about this topic, however I find some of the questions asked here fascinating in regards to East Asians. I am Korean American and basically feel that the Northeastern Asians developed certain genetic features due to generational exposure to cold climates. From the shape of the eyes (and extra fat content above the eyes for protection), to lack of body odor, thicker hair and simply just how I feel when I am exposed to cold weather. I especially thought the hypothesis on how and why East Asians have a higher testosterone level but don’t process this testosterone as well, was interesting and deserves more thought.
That being said, I have a big problem with this report above. This is looking at select data and drawing conclusions from it from a specific perception. This is a problem because there is serious biased on the observation itself. For example, I will illustrate by giving another perspective. In Korea, Koreans are seen as the ‘norm’ and everything else is related to this normal. So whites can be seen from the perspective of Koreans and thus can be said “more” hairy, more aggressive, more violent and smelly etc. It’s this constant comparison that is flawed because what is compared gets different focus. If seen from the Korean perspective, then the way we process testosterone would be seen as “normal” and whites would be seen as not normal, therefore creating a specific list (biased) too much hair, too much aggression, violent tendencies, too much strong body odor. Whites have a selfish focus, rather than harmony with people. Whites have a higher rate of drug abuse, rape, murder, and single mothers than Koreans. I can then take this ‘observation’ and conclude that whites have all these societal problems due to their “primitive” way they process testosterone.
I fully agree that the European level of whatever, like testosterone, is not a norm, but Asians, Europeans and all other people outside Africa came originally from Africa, so there was an African normal level from which we outside Africa evolved to some direction. As Eastern Asians as the only ones have high testosterone which is not used for building muscles, this must be a feature that developed in East Asians for some purpose. That is, it is not the original African norm level from which we and you started some 50,000 years ago. I am not any expert in this topic, but for me it looked possible that there might be a connection between visuo-spatial capabilities, high testosterone that is not building muscles and cold weather. Would be good if somebody from that field would look into it. Thanks for your comment. I certainly did not intend to put any (white or other) norm to human hormonal levels.
Wonderful post however I was wondering if you could write a litte more on this subject? I’d be very thankful if you could elaborate a little bit further. Many thanks!
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Hello,
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