"I'd like to ask why you imagine that in any field there would be equal numbers of men and women? Or indeed why there should be any reason beyond simple preference."

Listen: "Women are choosing not to as a matter of preference so there's nothing wrong" is a cop-out. I'll grant you that the reason for the lack of equality is "simple preference." Clearly, because if women "wanted" to do startups/tech, they would. There are no laws preventing them.

"More women like milk chocolate; more men like dark (pulled that one out my arse incidentally). Does it matter?"

Intrinsically? No, of course not. But if we start from the assumption that gender shouldn't matter, we would expect a distribution that cleaves pretty closely to the gender distribution in the population. The fact that that it's doesn't isn't necessarily bad per se, but it suggests that maybe something is going on that may be worth investigating a little further. To do otherwise is intellectually lazy.

It's totally possible that the discrepancy is completely innocent, or that there's some reasonable gender-based explanation that involves no negative cultural messages, discrimination, whatever, to explain the massive differences in the number of women and men who choose to go into tech. <snark>I suppose there's a first time for everything.</snark> I just haven't been convinced by any of the pat explanations so far. None of them have explained, for example, the relatively low number of women working for large, stable tech companies (some of the best employers in the world if you're looking for benefits and stability), nor why the relative percentage of women in tech has been dropping pretty consistently over the last 30 years (actually since the early days of computing, but whatever). The point of my original post was mostly that we should go farther than saying something simple like "Women are risk averse!" and ask, well, why? Because it's not totally out of the question that cultural forces are at work, and it might behoove us to at least think about them a little bit.

"There's a natural skew I think: if both men and women equally wanted to start families then more women would normally be able to than men (artificial insemination, one-night stand, stop using birth control, decide contrary to the male to not have an abortion, whatever). This leaves more men doing startups whether they prefer that to starting a family or not."

If it were that simple then tech/CS/startups should have a gender imbalance roughly equivalent to that of the rest of the working world.

In the past, simple, personality/preference/constitution-based explanations for gender discrepancies have proven false many times - women didn't have the constitutions to be doctors, women didn't have the temperament to be lawyers, etc etc - so I'm inclined to distrust this sort of explanation, at least initially. I'm not saying "Oh because it wasn't true that women just didn't want to do law and medicine it can't be true here.", or that we need 50-50 male/female representation or I'm burning my bra, or even that we should change anything or that anyone is suffering any overt injustice at the hands of anyone else. I'm just advocating for a little critical thought about our society/culture instead of just shrugging our shoulders and assuming that there's no problem.