Women make up roughly 15% of USCF members yet they only make up roughly 1.5% of grandmasters.

That means they are underrepresented by about an order of magnitude. Women on average are about 200 ELO lower than men.  It’s a very large difference and there has been research done to figure out why.

There are no real conclusive findings (as with much of this type of sociological research) but we have evidence for various different reasons. One, women are not encouraged to play chess at the same level that men are. Similar reason that more men go into Computer Science or Physics. It’s not a built in biological difference, but a cultural one.

Another one is that women are younger by 11 years on average, so their ratings haven’t peaked yet. So we should see this gap close in the coming decades. There are also various other inequities between men and women (like for example stereotype threat).

So that explains at least some of the gap. What I’m trying to say is that beyond these factors, there is also a biological difference that results in men being overrepresented in the top chess players. Notice I’m not saying average chess players, but specifically the best in the world (the grandmasters).

Why?

Well, there’s evidence for something called the "greater male variability hypothesis”. Think of every person sitting somewhere on a normal distribution. Pick a trait like aggressiveness or competitiveness.

There are the extremes on both sides of the bell curve. On the left, super passive and on the right super aggressive. Most people clump at the mean, in the center of the bell curve.

There’s evidence that more women cluster around the mean relative to men. Men are overrepresented at the extremes of the bell curve, even though the average is the same as women. Only by a little bit, but it’s statistically significant. That means that if you took a sample of all the super-aggressive and super-passive people, the majority would be men.

When you look at top chess players, they are more likely to have extreme attributes (being ultra-competitive for example helps you get better at chess).

This same effect is also theorized to be why we see that vast majority of prisoners are male. Vast majority of homeless, etc. Because extreme attributes tend to either be really good or really bad.

So that’s one biological difference. The other is the visospatial intelligence. Men tend to score better on visospatial tests when compared to women. This effect is already visible by 2 or 3 months of age, so it’s unlikely to be some sort of cultural effect.

Visiospatial cognitive ability is positively correlated with chess ability. Another biological difference between men and women that likely has some non-zero effect on chess ability.

So why are women underrepresented in grandmasters when compared to males? There is evidence for both

a) external social factors

and

b) innate biological factors

Nobody knows what % of the difference is due to a) or b). We just know there is some non-zero effect for both.

I encourage you to fact check every claim I’ve made. Don’t just look for one  research paper that confirms your argument. Each claim I’ve made I’ve seen multiple studies on. There are studies that will say the opposite, but look at it in aggregate. Look at metaanalysis studies.