Women, Math, and the Y Chromosome

I was working on this post about how Les Mis is totally communist, but then I remembered this is a blog about evolution, not pop culture ramblings.

Women, math, and genetics.

Many people have wondered why mathematicians are disproportionately male. Some have wondered if Larry Summers got nudged out of being president of Harvard for saying it might just be biological.

Of course it’s biological.

Sex differences in math performance are probably just a side effect of the Y Chromosome.

Let’s back up a speck. First, let’s be clear what we’re talking about.

Last time I checked, women and men performed, on average, about equally well on highschool math. Little girls seem to do slightly better on elementary school math, but elementary school is largely a test of how long you can sit still, so that’s no mystery. But by highschool, the boys have gotten a little better at sitting, and the testing is probably a little more reliable. (See the Wikipedia for way more details.)

And yet, more men than women end up in lucrative, high-status math professorships.

I’m being sarcastic. Math is nerdy and low-status, so women avoid it like the plague except to complain that there aren’t enough women in it.

Anyway, you might be wondering how, if men and women have the same average ability, more men than women end up as math professors. The answer, of course, is that while there are more men than women at the extreme tail of high math ability, there are also more men than women at the extreme tail of low math ability.

After all, more men than women are retarded. Boys dominate special ed classes 2 to 1–that is, they are 2/3s of special ed students, and not just because they’re more aggressive.

Anyone who thinks there’s a vast male conspiracy to keep women out of those sexy, lucrative math jobs needs to explain why those same conspirators think so many little boys are retarded. If society is somehow magically convincing little girls that they suck at math, then it is doing an even better job of convincing little boys that they’re even worse. And which should we be most concerned about, society causing a slight dearth of women at the very top end of a profession that doesn’t pay very well, or a massive over-representation of boys among the retarded?

If society’s not to blame, then what else could cause men to both under and over-perform at math?

Their Y chromosomes.

You see, for women, every chromosome comes as part of a matched set. In the slightly simplified view, you have one eye-color gene from your mom, and one from your dad. Together, they determine your eye color. If one is wonky, the other at least is still there, functioning properly. This has a moderating effect on gene expression–you get fewer extremes.

But males only have one Y chromosome. If something goes wrong with it, well, there’s not a lot your X chromosome is likely to do about it.

The result is that men show greater spread on a lot of traits that involve the Y chromosome. Height is an obvious example: while most men are taller than most women, men have a wider range of heights. Women are more narrowly clustered around their average, while men are more spread out:

We can figure ut something else from thi graph: men lie about their heights

Even allowing that some of these people are probably lying (some of those 5’7″ guys are probably actually 5’6″, and probably one of the 6’s is actually 5’11”,) there are far more women at 5’6″ than men at 5’10”. The men are more spread out, with more of them, therefore, at the tails of their distribution.

The Y chromosome contains the code that makes men taller than women, but since they only have one copy of this code, there’s nothing to moderate it. If they happen to get one gene for short, well, then they’re short. If they get one for tall, then they’re tall.

It’s the same with math. The Y chromosome has an effect on brain development (it must, otherwise males brains couldn’t create the sex hormones they need for proper genital development and function.) A woman who is lucky enough to get a good math gene from one of her parents has decent odds of getting a mediocre math gene from her other parent, bringing her back toward average. A woman who gets a particularly bad math gene is likely, again by chance, to get a better one from her other parent, again bringing her back toward average.

By contrast, a man is stuck, for better or worse, with one gene. If it’s a good gene, he’s good at math. If it’s a bad gene, he ends up in special ed.

(Note: in reality, there are a lot of genes involved, not just one or two. This is a simplified model to highlight the effect of the Y chromosome in decreasing individual genetic variation in men.)


Why does any of this matter? It doesn’t, except that humans think it matters. There’s been a huge push, socially and legally, to force more women into fields where they aren’t yet 50% or greater. To the extent that math departments have been partially protected, it’s just because math, unlike medicine, is low-status and so not all that attractive to women; they just feel insulted by the claim that they’re bad at math.

Of course, women aren’t “bad at math.” For all of the normal sorts of math people do in everyday life, women and men are equally competent. And plenty of women are math professors–I know some personally. They are just less than 50% of math professors.

No one should be picking math professors based on gender. Male or female, pick ’em based on their math skills.

The beauty of math, the thing I love about it, is its objectivity. You can’t bullshit your way through math; culture doesn’t matter. An answer is correct or it is not. The other thing I love about math is that it is cheap. Of all the subjects, math requires the least $$$ to teach–as my relatives who lived through the Great Depression have impressed on me, reading requires heavy, expensive books (heavy is a concern when your penniless family is fleeing the Dust Bowl,) but you can do math with a stick and some dirt.

This is (among other things) why Asian immigrants do so well in math–it’s cheap, culture-independent, and objective. There are no environmental factors other than brain damage that can be reasonably argued to interfere with math performance.

Frankly, I think arguing about whether people are bad at something or inundating them with messages that essentially say, “Everyone thinks you’re bad at this, but don’t worry, it’s totally not true!” causes way more insecurity than just not saying anything and letting people just be.

Much of American advertising works like this; take something people weren’t thinking about at all, then go out of your way to tell them that of course they shouldn’t be concerned about it until they’re so concerned that they go buy your products.

Maybe we’d be better off not stressing out and just letting kids do their homework without imposing political ideas either way on them.



15 thoughts on “Women, Math, and the Y Chromosome

  1. It’s not just about different distributions and wider margins. Generally men tend to think in a more “systematizing” manner than women, which should indicate an enhanced mathematical capacity. This could affect (or be extrapolated to) IQ as well; while there are both more male geniuses and male retards than female ones, it can be argued that the non-genius, non-retarded man is still more intelligent than the average woman (although not significantly so, if we are to trust test scores), at least when intelligence is measured objectively, similarly to men being taller than women regardless of the existence of giants and dwarves. There must have been an evolutionary and sex-selective pressure on men to develop a sharper intelligence than that of women. Another point that should be made here is that there are more male retards than male geniuses, as mutations are usually maladaptive, which skews test scores. Finally, measuring the same age brackets is faulty: male brains keep developing into the 30s, at a slow pace; female brains mature much faster; it’s more productive to compare 30 y/o men with 20 y/o women. I believe we’ll then see an advantage for men due male brains developing further than female ones.


    • These are all decent points. I do suspect that a certain % of low-IQ boys are more likely to drop out of highschool than low-IQ girls, so that may have a slight effect of raising the overall male average at that age.


  2. Eh, it’s rather about the X chromosome than Y, directly, as the X contains two orders of magnitude more gene loci than Y in general, IIRC. But your explanation about one copy vs two copies still holds, even then. About 3% more variation among men than women could be explained by functional mosaicism of female tissues caused by stochastic X-inactivation (Barr body formation) that occurs in their every cell.

    https://www.psychologytoday.com/blog/the-how-and-why-sex-differences/201101/how-womens-brains-are-calico-cats – pop-sci explanation for those too lazy to trawl Wikipedia. :)


    • Thanks.
      I also considered after the writing the idea that there’s just something on the Y that activates or deactivates things elsewhere in the genetics, but as you say, the general idea still holds.


      • Personally, I find molecular genetics to be a fascinating subject. For example, have you ever wondered why AFAIK all autosomal monosomies are lethal, but there are several trisomies that are not? Even a deletion of a part of a chromosome usually introduces severe abnormalities, sometimes lethally severe ones:
        Notice that “A ‘de novo’-situation appears in about 75% of the cases.” Apparently, haploinsufficiency resulting from copy-number variation is almost always detrimental to survival and fertility/virility of affected individuals.

        https://en.wikipedia.org/wiki/Y_linkage – not many genes in general.
        https://en.wikipedia.org/wiki/X-linked_intellectual_disability – obviously, these affect more severely men than women. Gene variants located on the X chromosome that boost intellectual capacity would also more strongly affect men than women.


      • All good/interesting points. Also, a lot of the genes on the Y chromosome (and maybe the X?) have an effect on the activation/expression of genes elsewhere. So as I understand it, both men and women have, for example, the code for breasts, but men have additional code that prevents theirs from fully developing. Ovaries and testes are created via basically the same code getting activated differently, etc. (I am not an expert her, so I am probably getting the terminology completely wrong, but hopefully you know what I mean.) Whereas I am not aware of there being any female equivalent of the prostate, so the code for that seems more likely to be localized on the Y chromosome–and that, in turn, might have something to do with the relative prevalence of prostate cancers, if that code just isn’t subject to the same repair/purging of bad mutations as the rest of the code.


      • Differences in ‘brain wiring’ (neural network topology) between men and women are not solely the result to exposure to different concentrations of sex-related neurosteroids during brain development:
        You might find this extremely interesting as well:

        “PCDH11X and PCDH11Y, respond in different ways to Retinoic acid, a chemical involved in the development of embryos. The acid stimulates the activity of PCDH11Y but suppresses PCDH11X. This is likely one of the explanations for the differences between the brains of men and women.”

        PCDH11X is located on the X chromosome, and PCDH11Y on the Y chromosome, so that clearly demonstrates that ‘sex reassignment’ hormone replacement therapy would never be able to fully transform a man into a woman and vice versa (a position that is practically a heresy nowadays :) ).


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