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Sex diffs in brain size Ritchie

Pity the poor blogger’s lot: there are more interesting papers being published every week than any essayist, however diligent, can possibly cope with. And there will be more, as the vast genetic databases give up their secrets. No sooner does one team scoop the others with a savage novelty than their rivals counter-attack with their own surprising findings. If you are curious about mankind, it is the best time to be alive. We are likely to learn more about ourselves in the next few decades than was possible in the last few centuries.

So back we go to an old theme, but with a new twist: how do women’s brains work?

To sort out this mildly contentious issue, Stuart Ritchie, up and coming member of the Edinburgh crew and its international affiliates, has provided intrigued men with a map of women’s brains. Smaller, of course, as many a man has surmised in the midst of an unexpectedly heated domestic discussion, but apparently able to function as well, or almost as well, as the male variety. Let us dig deeper into these mysteries, in the calm and measured way which befits this distinguished audience.

Sex Differences in the Adult Human Brain: Evidence from 5216 UK Biobank Participants
Stuart J Ritchie, Simon R Cox, Xueyi Shen, Michael V Lombardo, Lianne M Reus, Clara Alloza, Mathew A Harris, Helen L Alderson, Stuart Hunter, Emma Neilson, David C M Liewald, Bonnie Auyeung, Heather C Whalley, Stephen M Lawrie ,Catharine R Gale, Mark E Bastin, Andrew M McIntoshIan, J Deary.
Cerebral Cortex, bhy109, https://doi.org/10.1093/cercor/bhy109
Published: 16 May 2018

https://academic.oup.com/cercor/advance-article/doi/10.1093/cercor/bhy109/4996558

The authors say:

Sex differences in the human brain are of interest for many reasons: for example, there are sex differences in the observed prevalence of psychiatric disorders and in some psychological traits that brain differences might help to explain. We report the largest single-sample study of structural and functional sex differences in the human brain (2750 female, 2466 male participants; mean age 61.7 years, range 44–77 years). Males had higher raw volumes, raw surface areas, and white matter fractional anisotropy; females had higher raw cortical thickness and higher white matter tract complexity. There was considerable distributional overlap between the sexes. Subregional differences were not fully attributable to differences in total volume, total surface area, mean cortical thickness, or height. There was generally greater male variance across the raw structural measures. Functional connectome organization showed stronger connectivity for males in unimodal sensorimotor cortices, and stronger connectivity for females in the default mode network. This large-scale study provides a foundation for attempts to understand the causes and consequences of sex differences in adult brain structure and function.

There is much to discuss here, but my attention was drawn by two phrases “considerable distributional overlap” (which in my experience means that one group is pretty different from another) and “generally greater male variance” (which agrees with most of the observations on sex differences indicating that men are leptokurtic (more variable), women more platykurtic (less variable).

Women are more at risk of dementia, depression, schizophrenia and dyslexia. Men are better than women at mental rotation tasks, and are more physically aggressive; women are more interested in people than in things, are more neurotic and more agreeable.

One of the most interesting sex differences is intelligence. Here is their introduction to the topic:

There is more to sex differences than averages: there are physical and psychological traits that tend to be more variable in males than females. The best-studied human phenotype in this context has been cognitive ability: almost universally, studies have found that males show greater variance in this trait (Deary et al. 2007a; Johnson et al. 2008; Lakin 2013; though see Iliescu et al. 2016). This has also been found for academic achievement test results (themselves a potential consequence of cognitive differences, which are known to predict later educational achievement; Deary et al. 2007b; Machin and Pekkarinen 2008; Lehre et al. 2009a, 2009b), other psychological characteristics such as personality (Borkenau et al. 2013), and a range of physical traits such as athletic performance (Olds et al. 2006), and both birth and adult weight (Lehre et al. 2009a). To our knowledge, only two prior studies have explicitly examined sex differences in the variability of brain structure (Wierenga et al. 2017; Lange et al. 1997), and no studies have done so in individuals older than 20 years. Here, we addressed this gap in the literature by testing the “greater male variability” hypothesis in the adult brain.
[]
We tested male–female differences (in mean and variance) in overall and subcortical brain volumes, mapped the magnitude of sex differences across the cortex with multiple measures (volume, surface area, and cortical thickness), and also examined sex differences in white matter microstructure derived from DT-MRI and NODDI. We tested the extent to which these differences were regionally-specific or brain-general, by adjusting them for the total brain size (or other relevant overall measurement; for instance, adjusting volume differences for total brain volume and cortical thickness differences for mean cortical thickness), and examining whether the differences found in the raw analyses were still present. We tested the extent to which these structural differences (in broad, regional, and white matter measures) mediated sex variation in scores on two cognitive tests, one tapping a mixture of fluid and crystallized reasoning skills (skills previously found to be linked to brain volumes; Pietschnig et al. 2015) and one testing processing speed (previously found to be linked to white matter microstructural differences; see Penke et al. 2012). At the functional level, we also examined large-scale organization of functional networks in the brain using resting-state fMRI functional connectivity data and data-driven network-based analyses.

The study compared 2750 females (mean age = 61.12 years, SD = 7.42, range = 44.64–77.12) and 2466 males (mean age = 62.39 years, SD = 7.56, range = 44.23–76.99). These are extremely large samples, two orders of magnitude larger than the early studies in the 1980s, and way larger than many of the studies that the Press report so frequently. Consider them “Foxtrot Oscar” samples.

The first result is startling: male brains are very much bigger, a colossal 1.4 effect size. 92% of men will be above the mean for women. On average men have 117.8 cm3 more brain than women. All this extra brain must be doing something for men, you might surmise, other than just helping them perpetually contemplate the relative advantages of the more complicated positions adopted during sexual intercourse. Perhaps not. Broadly the same effect of male advantage can be found in all the brain region sub-comparisons. Male brains are both larger, and also vary more in size. Greater male variability seems a fact of nature. If there were a direct relationship between brain size and cognitive ability, there would be many, many more bright men than bright women.

The cognitive test was limited to a 13-item verbal-numerical test to be completed in 2 minutes, which ought to be enough to grade the general population. The mere notion of such a test will discomfort those citizens who regard their own intellects as more wide-ranging and multi-faceted than could ever be measured by mere earthly means, and who rank their brainpower of greater value to Western Civilization in ways that could not possibly be assayed in 120 seconds. Personally, I quail at the thought of having to subject myself to such a harsh evaluation. I mean, 13 into 120 is, let me see, well, not very long at all to solve each item. On reflection, 9 seconds to pass each question. Can such people exist?

The test might be a little crude if the purpose is to detect sex differences across the broad range of different cognitive tasks, and also a bit limited if the volunteers are, as one might expect of this database, somewhat brighter volunteers interested in contributing to science. However, these are minor quibbles. All intellects can be evaluated in 2 minutes. I like it. Here are the details:

Verbal-numerical reasoning. This test (UK Biobank data field 20016) consisted of thirteen multiple-choice items, six verbal and seven numerical. Participants responded to the items on a touch-screen computer. One of the verbal items was: “Stop means the same as: Pause/Close/Cease/Break/Rest/Do not know/Prefer not to answer”. One of the numerical items was: “If sixty is more than half of seventy-five, multiply twenty-three by three. If not subtract 15 from eighty-five. Is the answer: 68/69/70/71/72/Do not know/Prefer not to answer”. Participants had a two-minute time limit to answer the thirteen questions. The “prefer not to answer” option was considered as missing data for the purposes of the present analyses. The scores from the test formed a normal distribution.

Reaction Time. This test (UK Biobank data field 100032), which followed immediately after the verbal-numerical reasoning test, was modelled on the game of ‘snap’: participants responded by pressing a button on a button box as quickly as possible with their dominant hand whenever the symbols on two ‘cards’ displayed to them on the computer screen matched. The test had twelve rounds; the first four rounds were considered ‘training’ (or practice) rounds so were not included in the calculation of the final score, and four of the remaining rounds did not include matching symbols. Thus, the final score was calculated on the basis of the four rounds with matching symbols (the mean time in ms to press the button across these four trials was the score variable). We excluded the scores of 8 participants who had Reaction Times of 1100ms or longer. After this exclusion, the Reaction Times formed an approximately normal distribution. Note that, for analyses, we reflected the raw scores so that higher scores meant better performance (this meant that the two cognitive tests correlated positively with each other).

The choice reaction time task should be a good measure of mental alertness, though 4 out of 8 trials is on the short side. However, there is a case for saying that all reaction time tests should have only one trial. If the person responds very slowly, in real life he would be dead. That is what reaction times are for. Here are the results for the two cognitive tests:

Ritchie sex diff cognitive measures

The insert above shows: female mean, male mean, t-test, probability, d (effect size), and finally the Bayes Factor showing the probability there is a sex difference. The full results for Table 2 are in the paper.

Sure enough, Table 2 shows that the cognitive tests are only an effect size of about 0.2 in favour of men. Where did all the male brain size advantage go? 0.2 of a standard deviation works out to 3 IQ points. Nothing much, you may say, considering that the test-retest reliability of the Wechsler is 4 IQ points, but if this is a true representation of male-female differences, then we can calculate what it would mean for the male/female balance at the higher levels of ability. As you may have seen in previous posts, if men are really 3 points brighter than women, and women’s standard deviation is narrower than men, say 14 rather than 15 points, then this makes a big difference at the higher reaches of intelligence.

Here are the estimates, if one assumes men have an IQ of 102, (sd 15) and women an IQ of 99, (sd 14).

At IQ 130: 69.8% men
At IQ 145: 80.3% men

The authors correctly point out that the sample, though the biggest collected for scanning, may not be a perfect representation of the population at large (though I doubt this directly affects sex differences).

This is a very substantial paper. It shows a massive sex difference in brain size of 1.4 d, and when one factors in that brain size relates to intelligence at a correlation of about 0.28, then the predicted intelligence difference will be a large 0.39 d, but the observed difference is only half that. Paradoxical. One implication is that there are sex-linked differences in brain structure and dendritic arborization which overcome pure size differences. If so, how is this balancing act achieved? Why don’t all people have the smaller, more craftily wired version of the human brain, which presumably requires a smaller blood supply. On the other hand, it might be that the cognitive testing has not been wide enough, and has ignored tasks in which males have an advantage. By the way, if one sex has an advantage in one skill, this is not an error of testing, it is a triumph of testing that a real difference has been revealed.

It is possible that, in a rush to ensure that men and women’s mental ability scores can be presented as equal, in general men’s stronger subject areas have been under-sampled. Test producers are under pressure to minimize sexual and racial differences. This may have suppressed the size of real differences. In defence of any group who think that their specialist strong points have been ignored, we should set the sampling frame for cognitive tests as wide as possible. These points do not invalidate the findings of this fine paper on brains, but they leave open the possibility that there is a small but real male advantage in intelligence which a broader scope of tests would reveal.

And now I must leave you. The opportunity to sit quietly in a room, mentally rotating three-dimensional objects, is too good to be missed.

.

 
• Category: Science • Tags: Brain Scans, Gender, Sex Differences 
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  1. j2 says:

    You can think like this. There are enormously many potentially interesting papers coming out, but as a blogger, you have the chance to write your own ideas. I do not have enormously many new ideas, neither probably do you. Papers are just the material do create the new ideas. The ideas in scientific papers do not need to be retold, as they already have been published.

    Then about male and female differences in IQ, as your post is of it. As men have only one X chromosome, deleterious gene alleles in X are expressed in men and full 300 cause mental retardation. We may assume that a larger number of mutations in X decrease IQ. If both sexes had the same average IQ without this disadvantage of men (women do not express recessive gene alleles in X), then men had to have a lower IQ, but they do not. The reason must be that without these bad alleles men had higher IQ, as the size difference tells us.

    Now, the second thing, what stops men from collecting more of these deleterious alleles in X? the simple fact that women do not like a man to be more stupid. Such men do not easily find a mate, as in general, women try to find a bit smarter man. This stops men from getting more stupid in average than women, and indeed it fixes the IQ difference to a very small male advantage. Naturally this implies that the smartest women stay single as they cannot find a smarter man, while the most stupid men seldom manage to have children.

    As this old rule is not any more followed, many women accept a more stupid man. This destroys the balance – male intelligence can drop as low as you want because there are mutations in X all the time. Soon the difference is to the other direction, despite of male larger brain, but still there will be men without these bad genes, and they are smarter than women.

    Just an example theory what you could do with published papers, add something to them. Just like with publishing papers, only easier written as it does not need to pass a demented referee.

    • Replies: @res
    , @Semperluctor
    , @Bill jones
  2. res says:
    @j2

    This paper has an interesting look at detecting X-linked associations in GWAS using the increased variance for heterozygous females (because of the random aspect of X-inactivation). X-inactivation informs variance-based testing for X-linked association of a quantitative trait https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4381508/

    One interesting bit:

    Most GWAS studies of X-linked variants either ignored X-inactivation [12,30] or addressed it by simply changing the male genotype coding from 0/1 to 0/2, i.e. considering hemizygous males as equivalent to female homozygotes [13,28].

    Looking through the Lee SSGAC EA SNPs it appears they just ignored the X chromosome. Does anyone know for sure? Based on Figure 5 in the Hsu Compressed Sensing height paper I think the X chromosome is ignored there as well.

    I wonder if it would be possible to use the increased variance in males for X-linked associations to help detection.

    Does anyone know of any work assessing the different variances (and their relative magnitudes) resulting from homo/heterozygous females and males? Would it make sense to look at the different homozygous female and male alleles separately?

    • Replies: @J2
    , @Atavisionary
  3. res says:

    Thank you for the interesting paper and your analysis.

    It shows a massive sex difference in brain size of 1.4 d, and when one factors in that brain size relates to intelligence at a correlation of about 0.28, then the predicted intelligence difference will be a large 0.39 d, but the observed difference is only half that.

    I think part of that is attributable to body size. Table S1 adjusts the volume data for height. This reduces the TBV d to -0.42 (which overcompensates by your calculation giving an IQ d of 0.12 or 1.8 IQ points) and gives a VR of 0.84 (similar to 0.82 of full analysis).

    Using that VR to estimate relative IQ SDs (assuming male IQ SD is 15) gives
    0.84^0.5 * 15 = 13.75 which is close to your 14 number.

    I wonder if it would make more sense to map height to “weight” (e.g. using https://onlinelibrary.wiley.com/doi/pdf/10.1002/ajhb.1310010412 – do this rather than actual weight to exclude impact of obesity) and then map that to the curve in https://en.wikipedia.org/wiki/Brain-to-body_mass_ratio
    then use that number to adjust the brain volume data.

    The paper has 47 pages of supplemental material in a Word document. Some of the tables are just references to Excel spreadsheets at the OSF. I wonder why Table S2 was deleted: https://osf.io/w3u8e/

    Table S7. Correlation matrix for overall brain variables and cognitive variables
    is interesting. The correlations of cognitive variables with others are small. VNR (Verbal Numerical Reasoning) correlates 0.177 with TBV (Total Brain Volume). RT (Reaction Time) correlates 0.122 with VNR and 0.099 with TBV.
    7. General orientation dispersion is an intriguing outlier. It has opposite of the typical correlations (e.g. positive r with female) for all of the other variables.

    Could someone with expertise in brain anatomy comment on Table S12. Percentage mediation of the sex-cognitive relation for each brain subregion selected by the LASSO model, for verbal-numerical reasoning and reaction time? Superior temporal volume and surface area and Rostral middle frontal surface area appear especially important for VNR sex differences.

    Speaking of VNR sex differences, did the authors unpack V and N sex differences anywhere? That seems like a very interesting analysis to try.

    Figure S2a. Shift functions for each of the overall and subcortical variables. is a novel (this plot type was new to me) look at the distributional differences for all of the variables by sex.

    More on shift functions (including links to R code to create plots like this): https://garstats.wordpress.com/2016/07/12/shift-function/
    I need to try this out in some of my work.

  4. @res

    Interesting. You are ahead of me on this enquiry. I was wondering about the within sample correlations of brain size and intelligence test results. Not sure of what is going on. Might be a restriction of range problem (volunteers for brain scans brighter than average?) or perhaps a consequence of the restricted 13 item test.
    Jumping the other way, if the correlation between intelligence and brain size is low precisely when brain size is measured very accurately, perhaps…….there is not much of a correlation.

    • Replies: @res
  5. All this extra brain must be doing something for men, you might surmise, other than just helping them perpetually contemplate the relative advantages of the more complicated positions adopted during sexual intercourse.

    Jesus Christ,
    and he is a devot christian… yess

    I’m more polite than this.

    Viagra makes miracles!!

    Bigger and asshole brains, great!!1

    This sexual club fights is so ridiculous, so NORMIE-tard…

    Yes the sample is mostly white*

    On the other hand, it might be that the cognitive testing has not been wide enough, and has ignored tasks in which males have an advantage.

    The simple fact that 90% of problems in the word is caused by human males, yiees, specially white/jewish male$$… put all women of all races and religions in the same place and you will be very little conflict if compared with men.

    Yes, since you gals decided to remove emotional intelligence from the existence…

    • Replies: @Santoculto
  6. @Santoculto

    … you will have… iiiiiir

  7. Interesting, I will have to take a closer look at this study when I get some time.

    The greater variability of males is explicable if you consider intelligence (and other behavioral traits) as being strongly X-linked. In other words, a lot of the genes influencing those traits seem to be on the X chromosome and because of the phenomenon of pseudo-dominance the same traits get expressed at different frequencies in men and women. If intelligence alleles are often recessive (both those that boost and lower intelligence) then men as a population should vary from the average more. The most commonly known trait that follows this pattern would likely be color blindness. The reason it affects men more is that the relevant gene is on the X chromosome. Now, you can imagine how other genes working on the nervous system and on the X could cause quite a different expression pattern in the population of men vs. women. If you are really interested in knowing more detail about this, you need to read “Smart and SeXy” by Roderick Kaine. This book goes into great detail about how it works, and has plenty of citations showing the intelligence does seem to be substantially X-linked. You can read a review of the book below:

    https://www.counter-currents.com/2016/11/why-most-high-achievers-are-men/

    • Replies: @res
  8. @res

    I have always been a little leery about the use of adjusting figures to body weight. I mean, you could adjust for weight in comparing the torque of a mack truck to a honda civic, but in what context is that helpful? Obviously, the truck has way more torque and is going to haul things better. A bigger brain is going to think better.

    • Replies: @res
  9. res says:
    @James Thompson

    volunteers for brain scans brighter than average?

    Do you have any idea what the selection criteria were? Based on the age ranges: “MRI data from 5216 participants were available for the present study (mean age = 61.72 years, SD = 7.51, range = 44.23–77.12)” I was thinking they were looking for late in life changes.

    We can infer a bit from the Table 1 summary statistics for the VNR test.
    Mean (SD) – Females 6.80 (2.10), Males 7.14 (2.13)

    We can see VNR (Verbal Numerical Reasoning test) statistics for the full (well, 190k participants anyway) UKBB sample at https://biobank.ctsu.ox.ac.uk/crystal/field.cgi?id=20016
    Mean = 6.11557 Std.dev = 2.16093
    So the test actually has a fair bit of ceiling (> +3 SD) as long as it is accurate. Your speculation about the sample being brighter (for whatever reason) was on target. For reference scoring 9 is 90th percentile. Both 60th and 70th percentiles are included in a score of 7.

    Regarding the correlation of brain size and intelligence test results. From Table S7 the correlation of TBV with sex (female=0) is -0.571. I think this decreases the apparent correlation of TBV and VNR for the whole sample. It would be interesting to see separate sex based correlations, or perhaps even better, a regression of VNR on TBV and sex.

    It would be interesting to also try looking at TBV normalized by body size and the relation of that to VNR.

    • Replies: @Atavisionary
  10. res says:
    @Atavisionary

    I have always been a little leery about the use of adjusting figures to body weight.

    Agreed.

    but in what context is that helpful?

    If you care about acceleration (or top speed) the Honda Civic might do better with much less power. Because of its smaller size.

    A bigger brain is going to think better.

    ceteris paribus. Which I don’t think is necessarily the case here. But the only real body size correlate I see is with sensory and motor nerve interfacing. How much of the brain is dedicated to that? I am guessing not all that much?

    Then there are whatever other variables matter: architecture, structural integrity, …

    This issue is one where my engineer side comes through. If adjusting for body size gives a better model fit (e.g. see TBV ~ VNR correlation comment above) then it seems reasonable to me to make the adjustment until we have theoretical justification to guide us.

    It would be very interesting to see a study similar to this which also measured things like myelination, neural conduction velocity, and whatever other variables we could come up with.

    • Replies: @Atavisionary
  11. res says:
    @Atavisionary

    Thank you for that link. The book review was interesting in itself and the book sounds even more so.

    This was especially interesting in the context of my GWAS and X chromosome comment above:

    The X chromosome contains only about 3.4 percent of the genes in the human genome, but 16 percent of the genes known to be involved in IQ and 23 percent of those involved in retardation. Research on this point is ongoing, and these percentages may rise. But it is already safe to say that the overrepresentation of genes expressed in the nervous system on the X chromosome lies between a factor of three and seven.

  12. J2 says:
    @res

    Thanks,

    I will look at that paper. X inactivation happens in each cell and usually randomly, so in average a female brain has half of the cells expressing one X associated allele, half the other, meaning that if one is better in some respect (like faster signal transmission) the result is still only half of what would be if the allele is expressed in all cells, as in a male.

    I do not know the answers to your questions, but will think of them.

    Most of the found IQ genes are in autosomal chromosomes, which makes sense since both sexes are about as intelligent. The differences are that males have 10% larger brains, that they express X genes, and that testosterone changes the brain structure (that is something that can be studied as there are hormonal abnormalities). I have been interested in X chromosomes as they have a clear connection with male mental retardation. I assume there must be X associated alleles that cause less severe drops in intelligence. These three differences (size, X alleles, testosterone) must be the cause of higher IQ variance and different abilities, but for the average IQ the mechanisms can be sexual selection which keeps the average IQs very close.

  13. @res

    That book, smart and sexy, has a short chapter on X-inactivation. One interesting thing is that Human X chromosomes don’t fully deactivate, one study found that up to 25% of the inactivated X in humans wasn’t completely deactivated, which was seemingly a lot larger than in the case of mice.

    >Does anyone know of any work assessing the different variances (and their relative magnitudes) resulting from homo/heterozygous females and males? Would it make sense to look at the different homozygous female and male alleles separately?

    Not sure about any gwas, but I do know that a female heterozygous for a trait on the X is very usually just like the homozygote dominant and thus the pattern for X linked traits in women is similar to autosomal inheritance. You can actually show that yourself at home by looking at rates of colorblindness. The percentage is pretty well documented, and if you plug it into the hardy-weinberg equation you find that only a very small number of heterozygous women show the color blindness trait due to X mosaicism. About .1% more women demonstrate colorblindness than would be expected if only homozygous recessive women had it.

    You can actually do a little math and see that you would expect greater variability in males than in females when there are dominant and recessive alleles for X linked genes. I quote a study called “A role for the X chromosome in sex differences in variability in general intelligence” Wendy Johnson,1,2 Andrew Carothers,3 and Ian J. Deary1

    Before focusing on general intelligence in a speculative way, it makes sense to review briefly the reasons that genes on the X chromosome can be expected to create greater variability in males in any trait they influence. This material is not speculative. The reasons have nothing to do with general intelligence per se. Males carry one X chromosome and one Y chromosome, whereas females carry two X chromosomes. The X chromosome is of medium size and contains 3.4% of the total amount of genetic material in the haploid human genome (McKusick, 1966; Skuse, 2005). In contrast, the Y chromosome is very small and carries little beyond the genetic instructions for maleness. This alone will tend to produce greater variability in males than in females. This is because males carrying alleles that are expressed in proportion to their presence in the genome will either present the trait or they will not. Female heterozygotes who carry one copy of each allele, however, will present some intermediate level of the trait, reducing their population variability. Males more often express traits from recessive alleles that are expressed only if unopposed. This is because males will express the trait at the level of the allele frequency in the population, whereas females will express it at the square of this frequency. For example, if the population gene frequency is 10%, the trait incidence in males will be 10%, but the incidence in females will be 1% (0.1 0.1). This also means less variability in females than in males. For dominant alleles that are expressed regardless of the other allele, males will express the trait at the level of the allele frequency in the population, but females will express it at a higher level. The maximum variance for both sexes will occur when the allele frequency is 0.5, and even then the male variance of 0.25, 0.05 (1.0 0.5), will be greater than the female variance of 0.188, 0.75 (1.0 0.75).

    So, if intelligence is X linked, and has a fair number of recessive alleles boosting it that gap between the number of males and females at the highest levels of ability could stack pretty large.

    If we do a thought experiment starting with the above example, 1 allele 10%, 10% of males would express that boost while only 1% of females. If there were two alleles both at that same frequency, then males expressing both would be at 1% and females would be at .0001%. As you add more genes, the frequency of appearance for both sexes decreases, but the rate of female appearances decreases much more dramatically. Now imagine 50 or 100 X-linked genes with recessive intelligence boosting alleles. In short, it isn’t a surprise at all why the highest achievers throughout history have almost all been men. However, it also isn’t a surprise when that rare very gifted female appears. Its all there in the genes, and statistics.

    • Replies: @j2
    , @res
  14. dearieme says:

    The headline of an article in my morning paper said that MRI scans could detect which children would want to change “gender”. I shan’t bother reading the article, I’ll just wait for this blog to dissect it.

    That gives me more time to study the sports pages.

    Apparently there’s going to be a big football competition this summer. Did you ever?

    • Replies: @res
  15. @res

    Here are some studies which compare brain size to IQ. Most found a correlation between .3-.5. So there is definitely something to it.

    154 McDaniel, M. A. (2005) Big-brained people are smarter: A meta-analysis of the relationship between in vivo brain volume and intelligence. Intelligence. 2005 Jul– Aug. Vol. 33 Vol. 4, 337– 346.

    155 Rushton, J. P., Ankney C. D. (2000) Size matters: a review and new analyses of racial differences in cranial capacity and intelligence that refute Kamin and Omari. Personality and Individual Differences. 2000 Oct. Vol. 29 Vol. 4, 591– 620.

    156 Wickett, J.C., Vernon, P.A., Leeb, D.H. (2000) Relationships between factors of intelligence and brain volume. Personality and Individual Differences. Vol. 29 No. 6, 1095– 1122.

    157 Brouwer, R. M., Hedman, A. M., van Haren, N. E., Schnack, H. G., Brans, R. G., Smit, D. J., Kahn, R. S., Boomsma, D. I., Holshoff, P. (2014) Heritability of brain volume change and its relation to intelligence. NeuroImage. 2014 Oct 15. Vol. 100, 676– 683.

    Kaine, Roderick. Smart and SeXy: The Evolutionary Origins and Biological Underpinnings of Cognitive Differences between the Sexes (Kindle Locations 4375-4384). Arktos Media Ltd.. Kindle Edition.

    • Replies: @res
    , @phil
  16. @res

    I am not a big car guy, and that analogy might not be the best any way, but I am under the impression that if the goal is speed, then bigger engines built for speed do better than smaller ones built for speed. Ditto when you switch to torque.

    >It would be very interesting to see a study similar to this which also measured things like myelination, neural conduction velocity, and whatever other variables we could come up with.

    Studies of testosterone during fetal development suggest that it is very important for the development of white matter (myelination). And in fact, the larger male brain is largely driven by this increased amount of white matter. You always hear that women have more grey while men have more white. Well, that’s true after adjusting for size but in absolute terms, men and women tend to have about the same amount of grey matter, whereas men have much more white matter. (Obviously, male variability is in play here, but you get the idea.) Interestingly, Simon Baron-cohen has persuasively, in my opinion, shown that Autism is likely related to an excess of testosterone during fetal development and that their differences likely result from an extreme male patterned brain phenotype. Again, they tend to have more white matter than normal males.

    Autism appears at all parts of the IQ spectrum, and that is probably explained by an interaction between X-linked intelligence and fetal testosterone.

    • Replies: @res
  17. j2 says:
    @Atavisionary

    Atavisionary,

    You are right about fully recessive X linked gene alleles, then a woman expresses a trait only as homozygote aa while a man expresses the trait always. In this case (fully recessive allele), if the carrier frequency is p and the population is in Hardy-Weinberg equilibrium, then me express the trait with probability p and women express it as about (1/4)p^2+(1/4)p^3. But this is not always true for X linked genes since there is X inactivation. Each woman’s cell makes a choice which of the two copies of a gene to express. There are also two sections where X inactivation does not happen and both copies are partially expressed, but let us talk of the case when there is X inactivation.

    If the allele is nonfunctional, as can be the case with a gene allele causing severe mental retardation, the cells that express the non-fuctional gene are often excluded and the woman works with the functional genes. Then the recessive defect is not necessarily seen at all. Like, if in a woman brain half of the neurons were defective, the half good ones are quite enough for everything, no mental retardation is seen.

    But assume now that there are two functional copies and one is slightly better than the other. Both are used, but the effect of this gene allele is half of what it would be in a man where all cells have one allele. If the higher male variation of IQ were caused by X associated genes and they would be fully recessive, then the female variation would be extremely small. It is not so small, only a bit smaller than for men. Thus, these alleles are not fully recessive.

    Indeed, the majority of the variation of genetically determined IQ in both sexes must be due to autosomal genes. X related genes are only some 12% of all IQ related genes. It is not explanation of the variance, but a part of the explanation why male variance is larger than the female variance.

    I suggest this explanation. Because of a larger male brain size and because sex hormones give male brain a different structure (testosterone boosts spatio-visual ability and supresses female context switching, also called multiprocessing or inability to concentrate), males initially have a higher IQ, which is mostly decreased by X associated alleles (most mutations are harmful). Male IQ drops as low as selection allows and in humans assortative mating forces average IQs to be almost the same with a small male advantage.

    I wrote a post of this some time ago:

    http://www.pienisalaliittotutkimus.com/2018/04/20/men-inherit-male-intelligence-from-mom-but-not-the-iq-variance/

    The effect of testosterone is that in very early childhood babies have a huge number of neurons, which fast die. Testosterone level determines which cells die and this very old mammal/reptile mechanism gives males an advantage in visuo-spatial and females an advantage in taking care of offspring. As this is a very old mechanism and recently nature has preferred the X chromosome method over the Y-linked testosterone method for making sex differences, I would not look for very high mental capabilities from this direction. I wrote some time ago a post of it in:

    http://www.pienisalaliittotutkimus.com/2018/05/11/why-east-asians-have-iq-profile-skewed-to-visual-spatial/

    • Replies: @res
    , @Atavisionary
  18. res says:
    @Atavisionary

    I am not a big car guy, and that analogy might not be the best any way, but I am under the impression that if the goal is speed, then bigger engines built for speed do better than smaller ones built for speed. Ditto when you switch to torque.

    Agreed about that, but the point I was trying to make is that the size (weight) of the body the engine has to drive makes a difference in the performance achieved. The question then is whether there is a similar size relationship for the brain/body.

    The pithy car guy (I am not much of one either, but have spent time in that world) version of your comment is “there is no substitute for cubic inches.”

    In terms of the size/power (either HP or torque) relationship for engines (and brains) there is a reason HP per cubic inch is considered an important (though not all important) metric. It might be interesting to define an IQ/cc metric and do a GWAS on that.

    P.S. Interesting testosterone comments.

  19. res says:
    @j2

    Interesting well referenced blog posts. Thanks for the links. It looks like there is much more on your site as well.

  20. res says:
    @Atavisionary

    Thanks for the references. 154 looks like a good overview. One thing they find is that the single sex correlations are a bit larger than the mixed sex correlation (more so for women, for adults correlations were: all 0.30, M 0.34, F 0.38). This is the expected effect (if body size matters) I mentioned above. Though the change is not as large as I would have guessed.

    Does anyone know of any looks at the IQ vs. brain size correlation in humans that attempt to account for body size?

    This 2015 paper has a comprehensive table of studies they used in their meta-analysis: http://www.larspenke.eu/pdfs/Pietschnig%20et%20al_in_press_-_Meta-analysis_brain_volume_intelligence.pdf
    Might be useful…

  21. res says:
    @dearieme

    LOL! For those intrigued by your comment: http://www.dailymail.co.uk/sciencetech/article-5757349/Scientists-say-MRIs-pick-transgender-people-gender-dysphoria.html
    I am not finding the paper itself, but here is a press release: https://www.ese-hormones.org/media/1506/transgender-brains-are-more-like-their-desired-gender-from-an-early-age.pdf

    In all seriousness, their premise makes sense to me. I am curious how the usual suspects will reconcile this with the idea that men and women are the same.

    P.S. The version of your comment I am familiar with is “How about them ?” https://www.urbandictionary.com/define.php?term=how%20about%20them%20_______________

  22. res says:
    @Atavisionary

    Good comment. One thought about

    I do know that a female heterozygous for a trait on the X is very usually just like the homozygote dominant and thus the pattern for X linked traits in women is similar to autosomal inheritance.

    My understanding is this is generally true for Mendelian traits. For quantitative traits I would expect the X linked traits to also be similar to autosomal traits except for the heterozygous case not existing for men.

    There are of course odd exceptions like calico cats. I don’t know how many cases there are where the mosaicism is relevant phenotypically.

    The Johnson paper is interesting: http://journals.sagepub.com/doi/pdf/10.1111/j.1745-6924.2009.01168.x
    Thanks.

    • Replies: @j2
  23. Drake says:

    There’s a typo when you write

    The insert above shows: male mean, female mean, t-test, probability, d (effect size), and finally the Bayes Factor showing the probability there is a sex difference. The full results for Table 2 are in the paper.

    The table lists the female mean first, then the male mean.

    • Replies: @James Thompson
  24. j2 says:
    @res

    “I do know that a female heterozygous for a trait on the X is very usually just like the homozygote dominant and thus the pattern for X linked traits in women is similar to autosomal inheritance.”

    Logically thinking, heterozygotes on X associated gene alleles are always expressing both alleles if the alleles differ only little, unless the gene is parentially imprinted. That is:

    If the gene is one of the genes without X inactivation, both alleles are expressed.

    If the gene has parental imprinting, only one allele is expressed.

    Assume the gene has X inactivation and the expressed allele is randomly chosen. Consider a homozygote female. In this case each cell of the female expresses a randomly one of the alleles. As these alleles are identical, both are expressed in the phenotype and we cannot see it.

    Now, change one allele just a bit, infinitesimal amount to any direction. It does not change much and both alleles are again expressed in the phenotype. Go on changing more. At some point one allele becomes so nonfunctional that it is not expressed in the phenotype. Then the allele is expressed in the female just like fully recessive autosomal allele. But if there is only a small change, then both alleles are expressed as a female body is always a mosaic if half of the cells are not so nonfunctional that they die, and they are both expressed unless they differ so much that one becomes fully dominant. That is, alleles in X female that differ very little must be co-dominant.

  25. But what does this do to restrain the monstrous regiment of women?

    • Replies: @Dieter Kief
  26. @j2

    How can it make sense that ‘the smartest women will stay single as they cannot find a smarter man’,when at the margins (IQ higher than 145) there are 4 times more 145 IQ men than women? Super smart women would have their pick of even smarter, and much more numerous, men; but for, perhaps, the tendency of very smart men not to marry 145 IQ + women, they marry nurses etc, …hmmm…..as very smart women marry carpenters.

    • Replies: @j2
    , @sabril
  27. @Drake

    Thank you for spotting that. I have corrected it.

  28. @j2

    I basically agree with everything your saying.

    One thing though, it is very possible you are underestimating the number of genes involved in cognition on the X chromosome. Figures I have seen range from 10-20%, and if you consider known genes involved in mental retardation, 90 of the 300 link to the X, which is 23% of the total. And this is when the X only makes up 3.4% of the genome. My guess is that we aren’t finished discovering cognitively important genes on the X.

    Then there is the dosage. less genes could have a larger impact if the dosage for them is higher in the brain, insinuating that whatever they are doing is very important to mental function. Again, the X punches above its weight in this category. This is an excerpt from the book “Smart and SeXy”

    “Though there are an unusually large number of genes related to brain function on the X chromosome compared to individual autosomes, just looking at the number of genes actually underestimates the relative effect of those genes on cognition. One reason is because genes on the X chromosome are expressed at higher concentrations in brain tissue than they are in other tissues and relative to autosome gene expression within brain tissue. The ratio of expression levels between the X chromosome and theautosomes (X:Autosomes) was found to be greater than 1 (1.1– 1.2) in humans when all genes were considered. For tissues other than the brain, the ratio was less than one. The proportion of individual genes with double the level of expression in the brain relative to other tissues was 2.8 times greater for X chromosome genes than for autosomal genes in humans. 110 For brain-specific genes (a gene with double the expression in brain tissue compared to other tissues), the X:autosome ratio was 1.43 in humans. 78, 119 About 12 % of all X chromosome genes qualify as brain specific genes. In other words, it has been unambiguously demonstrated by several studies that the X chromosome contains regions with an unusually high density of genes expressed in the brain, and that many of those genes are expressed at an unusually high level in the brain compared to other tissues. 120″

    Kaine, Roderick. Smart and SeXy: The Evolutionary Origins and Biological Underpinnings of Cognitive Differences between the Sexes (Kindle Locations 1511-1514). Arktos Media Ltd.. Kindle Edition.

    The of course is the fact that the X chromosome genes involved are much larger than typical, and then the “junk” is cut out. It is very possible that regulatory RNAs are being produced with some unknown important function.

    As far as X inactivation, selective inactivation is mostly only relevant for mutations severe enough to harm cell viability. If the cell isn’t harmed in that way, then normal mosaicism ensues which quite closely approximates autosomal inheritance patterns.

    • Replies: @j2
  29. Hey, honest question But, where does one find all of these papers? I would like to read some papers, not only on genetics but of all different sorts.

    What websites/databases Are worthwhile to browse to find some of these?

    • Replies: @res
    , @smellyoilandgas
  30. phil says:
    @Atavisionary

    Res,

    Also note the importance of this issue for East Asians (slightly larger brain volume on average, but also smaller body size, so the brain-size difference is greater if we adjust for body size)

    East Asians (on average) are particularly good at 3D reasoning, which is also suspected to be a strength of males vs females.

    • Replies: @res
    , @Atavisionary
  31. phil says:

    Ritchie’s reaction-time finding is important because it indicates a male-female difference in g, whereas Meisenberg has posited that the male-female difference is not on g.

    Consider mechanical sense and ability. If women are relatively bad at mechanical tasks, is it because they are not very interested in them (as suggested by the work of Simon Baron-Cohen), or would they be bad at them even if they were interested? Ritchie’s work suggests that the answer may be both; they are are not so good in any case AND they are not so interested. When one adds in the greater variability in male abilities, one can start to explain very large differences between the number of elite men and the number of elite women with respect to mechanical ability.

    Meisenberg’s work suggests that women could be equally good at mechanical work–IF they were interested in it and/or more encouraged to do it.

    • Replies: @res
  32. res says:
    @phil

    Good point. Thanks.

    Has anyone done similar MRI studies on East Asians? If so, it would be interesting to compare the results with this study.

  33. @quasi_verbatim

    Are such questions as yours now rather matters of the heart?

  34. res says:
    @phil

    Could you elaborate a bit on why you find the reaction-time data more compelling than the VNR data as an indication of male-female g differences? The RT difference does appear to be a bit larger:
    VNR d = -0.18, VR = 0.97
    RT d = -0.21, VR = 0.92
    Speaking of those numbers, that VNR VR=0.97 seems a bit too close to 1 to be supportive of a female IQ SD ~= 14.

    Any thoughts on how much relative (profiles within group, e.g. M vs. V in women) abilities and interests matter for group differences in outcome compared to the absolute differences? It seems to me there is a good comparative advantage argument to be made there in addition to the absolute advantage argument.

    I am having trouble finding references to Meisenberg’s work in this area. The closest I see is this letter: https://www.researchgate.net/publication/308765268_Sex_Differences_in_Intelligence
    but I don’t see that referring to his own work. Can you point me to any?

    • Replies: @phil
  35. @UrbaneFrancoOntarian

    before google and Disney copyright and Patent law enhancement acts, you could find fascinating articles everywhere, all over the Internet, in the public domain, free for the reading, now you must pay and pay and pay.
    If you have access to them through the library of an educational institution you are lucky.

  36. @j2

    I look forward to the no doubt numerous papers comparing women’s intelligence with other attributes and those of the men they marry.

  37. @phil

    A good way to find interesting studies is to read one that you find interesting (say you hear about it on the news or something), and then any of the points in there that also looks interesting and has a citation should link you to another one. So you look that one up too.

    Reddit has a sub called /r/scholar. It has a link to a russian website called libgen which should have just about any study you could possibly want to read, and without the paywall. In the rare case they don’t have it, you can post a request to the sub and usually someone will add it to libgen or provide you a direct link.

  38. phil says:
    @res

    res,

    I do not regard the reaction time difference to be the only relevant evidence for g differences, but I found Ritchie’s finding interesting because, measured in standard deviation units, the difference was about equal to the IQ difference for the other part of the study.

    Meisenberg has an interesting article in the issue of Mankind Quarterly devoted to sex differences (published within the last 12 months). He argues that the IQ difference between men and women does not represent a difference in g.

    I agree that relative abilities and interests (including non-g considerations) may affect group outcomes and, I would say, country outcomes as well.

  39. j2 says:
    @Atavisionary

    You write: “As far as X inactivation, selective inactivation is mostly only relevant for mutations severe enough to harm cell viability. If the cell isn’t harmed in that way, then normal mosaicism ensues which quite closely approximates autosomal inheritance patterns.”

    It is exactly this which is the difference with X associated genes and autosomal genes. When the cell is not harmed in any way by either allele, X inactivation causes one copy to be expressed in every second cell of a female. That is, for normally working alleles of X associated genes you expect that women express both alleles 1/2 strength, while men express what they have.

    The new way (in the time scale of evolution) is to develop sex differences through the X chromosome, the old way was through the Y chromosome with the help of sex hormones. When talking of human intelligence (and not spatial-visual capabilities of all males, which is testosterone and hippocampus influenced, like the superios visual-spatial intelligence of East-Asians, ancient stuff) we have to look at the X chromosome for sex differences. You are completely right in this, we have to look at X in order to understand the larger variation of IQ in men. As both men and women have IQ variation, not all variation is due to X associated genes. There are many autosomal IQ genes. They must have a similar effect on both men and women and they explain a large part of human IQ variation, but here we are interested on sex difference in variation and average.

    I think average for both sexes is basically the same with a small male advantage, which is smaller than the brain size difference would imply. I explain it by male intelligence being volatile. It can sink or increase depending on how stupid men are accepted as spouses. And that is because IQ decreasing genes are expressed in males and there always are mutations creating them, so if women accept stupid men, there will be stupid men. Assortative mating has so far kept male intelligence from sinking below female intelligence, but it is just a custom.

    What I want to point out is that these X associated genes do not behave as recessive genes on autosomal chromosomes, that is, if some X chromosome associated genetic trait in men has the frequency p, it is not that women have the frequency about (1/4)p^2. They have about half of the trait in men and this is due to X inactivation. It is not so for very harmful gene alleles, but it is so for IQ genes, which each have a very minor IQ rising effect.

    Notice that having blue eyes is caused by a recessive allele. Why is it recessive? An allele becomes recessive if it is harmful. Thus, blue eyes gene was once harmful, like it is in albinos, it is associated with poor eyesight. Now there must be a compensating mutation because having blue eyes does not cause bad sight. This compensating mutation is not known to the cells, which conclude that the blue eyes allele is defunct, if they have a choice, they express the brown eyes allele. But after the compensating allele was created, there is really no difference with having eyes blue or brown. This is the way to think of recessive alleles. They are recessive because they do not do the original job, but a mutation elsewhere may compensate for the loss.

    • Replies: @utu
  40. res says:

    I do not regard the reaction time difference to be the only relevant evidence for g differences

    Understood and I did not mean to suggest otherwise.

    I found Ritchie’s finding interesting because, measured in standard deviation units, the difference was about equal to the IQ difference for the other part of the study.

    That makes sense. What did you think about the VR difference between VNR and RT? I suppose it is small enough it could be noise (errors in opposite directions).

    Meisenberg has an interesting article in the issue of Mankind Quarterly devoted to sex differences (published within the last 12 months). He argues that the IQ difference between men and women does not represent a difference in g.

    Thanks! Not sure why it did not show up in my earlier searches, but here is a link: http://www.mankindquarterly.org/archive/issue/58-1/8

    I found the wording in the abstract oddly equivocal (am I imagining that?):

    On the other hand, neither the sex differences themselves nor their developmental changes are related in any consistent way to the g loadings of the subtests.

    Now I need to go read the article.

  41. j2 says:
    @Semperluctor

    I think you just said it. Just by numbers very smart women like over 145 could find an even smarter man like 155, but in practice it is not so easy. Men do not much care of the IQ of the woman and marry the beautiful and kind nurses and so the smart women can either stay single or marry carpenters. That could be symmetric, but more women stay single in this scenario, so it is not symmetric.

    Anyway, an average woman prefers to marry up rather than down in the scale of social success and high IQ is linked to success. No woman will marry the most stupid men as they are seriously retarded. That alone (ignoring what happens to smart women) keeps male IQ average just a bit over average IQ of women.

    This is the mechanism that keeps the average IQ of the two sexes almost equal with a very small male advantage.

  42. utu says:
    @j2

    Thus, blue eyes gene was once harmful

    When the first mutation that lead to blue eyes occurred it had no way of knowing it was harmful or not but for some reason it was recessive. Or are you saying that perhaps it was not recessive at first but became later because it was harmful?

    • Replies: @j2
    , @j2
  43. j2 says:
    @utu

    This, I admit, was just an idea I got while writing the comment. I do not have a proof for it.

    I reason like this: why is one allele recessive? If both copies are identical neither should be recessive. If they differ very little, again neither should be recessive. If one is very bad, like causing mental retardation, meaning it is not working correctly, the allele is usually recessive . (Let us ignore the gene for the Down Syndrome, which I remember is dominant. There is needed some special argument for these cases, but almost all genes for mental retardation are recessive.) From this I speculated that an allele becomes recessive if it does not do its job in the cell. It may still work if there are compensating mutations elsewhere that do the necessary job elsewhere.

    From this I speculated, but it is simply speculation, that the blue eye gene that is common in Northern Europe was originally rather similar to an albino blue eye gene. Harmful as it did not do its job in the cell, but later it was compensated by another mutation and after that blue eyes saw quite clearly. Albino blue eyes do not see that well.

    I do not know what makes one allele recessive, but there must be some reason for it. I understand it does not code proteins that are used by the organism if there is a dominant allele and that is why it is recessive. So the reason should be in the cell. For instance, the recessive allele codes proteins, but wrong ones which are destroyed and the other allele also codes proteins and these are good and used. That scenario would appear as one allele being fully recessive. But this far surpasses my limited knowledge on the topic.

  44. j2 says:
    @utu

    Still about the blue eyes. I guess you know of the anti-White theory that whites were originally black albinos. This is debunked by stating that the mutation for blue eyes is not the albino mutation and that the Cheddar man had brown skin and blue eyes as it had mutations for blue eyes and brown skin, but is it that simple?

    Black albinos have the allele for dark skin and an allele causing albinism. Likewise, we cannot conclude that Western Hunter Gatherer had dark skin because it possessed a gene for dark skin. If it had uncompensated albino mutation, it had a gene for dark skin, a gene for blue eyes, white skin and blue eyes, and it did had some problem with eyesight. A compensating mutation fixed the eye problem and the gene for dark skin was replaced by a better allele for white skin form Eastern Hunter Gatherer through Caucasus Hunter Gatherers, who were a mixture of WHG and EHG.

    The allele for blue eyes is different from the most common albinism gene, but still, it is recessive. Why is it recessive if it is not worse than the brown eye gene on a cell level? It may code correct proteins, but in a slower pace. That might also work to make it recessive.

    • Replies: @utu
  45. Maybe it’s just me. While found this specifics here informative. The knowledge that male female brain size, chemistry and operation are different is not new, at least not to me.

    But some the confirming data provides more detail than I was familiar with.

  46. utu says:
    @j2

    Thanks but I have no opinion on the issue.

    Just one comment: the belief that evolution and DNA and all that is correct does not make stories we weave within this narrative correct. Sometimes we do not know and often we will never know, nevertheless everybody and his uncle tries to weave an explanatory story. Perhaps sometimes we should admit that we do not know and stop instead of weaving stories that become as ridiculous as just-so stories of Kipling. The difference is that evolutionists take themselves so damn seriously that they do not notice when they themselves became central characters of the joke they created.

    • Replies: @j2
  47. j2 says:
    @utu

    I accept what you say of not creating speculative theories. But I want to add just one thing.

    After writing the comment I looked at what is known of blue eyes genes. It is pretty much what I suspected, though more complicated. A gene has a protein coding part and a control part. The control part tells when to code proteins and how much. This control part can be controlled yet by another gene’s control part. This is the case with blue and brown eyes. It appears as Mendelian (recessive and dominant gene) but it is actually much more complicated, and there are special genes for other eye colors, like green, hazel and so on.

    But about blue eyes. There is OCA2 gene, which causes albinism that turns the skin lighter and eyes blue. This gene is now controlled in Europeans by HERC2 gene. This control gene controls the control part of OCA2 and works only with eyes. Thus, modern Europeans do not get light skin from ORC2. They have special light skin genes. The Cheddar man (Britain 9200 BP) did not have these special light skin genes but had ORC2. It very possibly was olive color and blue eyes become common because they at that time were connected with a lighter skin. I think it was the lighter skin that was selected as it helps in getting vitamin D, not the blue eyes for sexual selection as in other places there are blue eyes as a minority (why are blue eyes not strongly selected in Caucasus if it is sexual selection, must be selection for D vitamin). Later mutations changed this and now blue eyes and light skin are not so closely connected.

    But this is not the important thing what I wanted to say. It was just an example of what a recessive gene is. It is so that the HERC2/ORC2 gene in eye color is recessive because the recessive variant does not produce protein P for making melanin in eyes. If you have one original allele making this melanin, then you have brown eyes. If you have two alleles which do not work, then you have blue eyes. A recessive gene is one which does not work: it does not do everything that the original gene did. The problem can be in the control part as in eye color, or in the protein coding part which means that the gene makes incorrect proteins because of a mutation. Again, it does not work.
    We conclude, an allele is recessive if it does not do everything the original allele did.

    Inversely, a dominant allele either turns on protein coding more often that in the original (you can get e.g. larger ears and longer face as in X associated dominant disease Fragile X, I made a mistake in the previous comment, I meant Fragile X, not Down Syndrome), or turns on some atavistic features that should be off. Good, this just modifies what there was and turns on what was not supposed to be on. We conclude, an allele is dominant if it does more that the original allele did.

    So how do you get a completely new property what is needed for evolution? Like how do you create an eye when there was no eye in the beginning? It is very difficult with random mutations. Recessive mutations turn off something what there was, that does not help. Dominant mutations turn on what there was but was turned off, that also does not help. I can see only that some piece of DNA gets multiplied and then a mutation makes it nonfunctional, which does not harm as there is the original piece still working. The nonfunctional piece accumulates in a long time new mutations and miraculously it will one day produce something totally new, like an eye. As can be seen, this is nearly impossible. It is indeed a monkey hitting keys and producing a new working gene.

    I think it is important to think how these mutations actually could work, as it reveals that evolution of new species and new properties is not explained. Mutations only explain turning on and off existing functionalities. Natural selection is a fact, but it also does not explain evolution of species to the extent that is believed. I understand that creating a theory out of almost nothing probably will not lead to the correct theory, but the insight that it gives may lead to a correct insight of larger things. Like, you cannot in an armchair guess how eye color genes work, but you may become convinced that evolution in large cannot produce life out of non-life, even with mutations.

    But I admit that this is not my field and one should not weave explanations like Poirot in Agatha Christie’s books, that is, in comments on somebody’s blog. I wrote my first comment as the author of the post seemed to be wondering if a blogger should report every new scientific article, so I suggested that a blogger might propose a new idea, but maybe that was stupid from me. I will write this in my own blog, there it can be as nobody reads it anyway. Thank’s for your comments.

  48. sabril says:
    @Semperluctor

    Based on my observations, I would say that smart women have their pick of men, until they hit their early to mid-30s. Pretty much all of these “smart women who cannot find men”are in their late 30s or older. Evidently, having a high IQ does not save a woman from self-deception about the Wall or about other differences between men and women.

    To put it another way, all things being equal a high-IQ woman will have more opportunities with men, but all things are not equal. Today’s society will push that high-IQ woman into spending her 20s pursuing education and career. And will not tell her that for women, youth is all-important in attracting men, far more important than intelligence.

    • Replies: @Corvinus
  49. Respect says:

    It is a complicated and difficult to understand paper , and as I understood an UK one . This is relevant because for obvious reasons I sistematically do not believe anylonger studies made in the UK , unless they really prove clearly whatever they are saying ( remember the ” earth warming ” hoax , ” the climate change ” ? ) .

    The same applies for many US ” scientific ” papers . After nearly 3 decades of selling brain image and chromosomes galore at great expense and with mimimal results , I hope you will understand my scientific skepticism .

    Well , they say demencia is more frequent in women , right , yeaaa, but women live about 5 or 6 years more than men , and with age there is more demencia , and more illnesses in general , till you die , so .

    Women have more depressions , true , as well as anxiety disorders , women double the men´s prevalence of anxiety and depressive disorders , but men have more alcohol and drug abuse than women , a 10 to 1 ratio , thus presenting a lot of mental illnesses derived from alcoholism and drug addiction .

    Schizophrenia has a similar prevalence in men and women , with an early onset in men .

    Dislexias ( or specific development disorders ) are not more frequent in women but in men . They are more frequent in low IQ people . If you see the Gauss curve of intelligence you will see that 2,2 % of the population has an IQ lower than 70 , qualifying as mentally retarded , men are overrepressented here . Dislexias are more frequent in these people , as well as in borderline IQ ( about 15 % of the population )

    On the other side of the Gauss curve of intelligence we have 2,2 % of the population with an IQ of more than 130 , men are also overrepresented here , and society depends of this bright people ( male or female )

    Men problably have more spatial inteligence ( have you seen your wife trying to read a map ? ) , and probably also ” military ” skills . And women have probably more verbal intelligence .

    Also it is important to remember that girls mature a couple of years faster than boys , what in the disgraceful western egalitarian school system of mixed schooling puts the boys at a disadvantage in mixed school , sometimes with bad consecuences for the rest of their lives and for society as a whole .

  50. Corvinus says:
    @sabril

    “Based on my observations, I would say that smart women have their pick of men, until they hit their early to mid-30s.”

    You’re leaving out an important factor here–men have to deem those women as being intelligent AND attractive enough to earn their attention.

    “Pretty much all of these “smart women who cannot find men”are in their late 30s or older.”

    I would say some of these smart women, just like their male counterparts, are way too picky and thus complain about not finding someone they want to have a long-term relationship.

    “Evidently, having a high IQ does not save a woman from self-deception about the Wall or about other differences between men and women.”

    Talk about self-deception. This “wall” is a figment of the manosphere’s collective imagination. Men and women as they become older gain weight, do not age well, or have health problems that take away their physical attractiveness. It is a combination of biological and environmental factors.

    “Today’s society will push that high-IQ woman into spending her 20s pursuing education and career. And will not tell her that for women, youth is all-important in attracting men, far more important than intelligence.”

    For some men, absolutely, the youthful appearance of a woman may be their defining criteria. But each man decides for himself what in a female most catches their eye.

  51. EH says:

    Great post, Dr. Thompson.

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