A while ago, the topic of why so few women are at the top of NZ Bear's blog ecosystem. It was perhaps a bit of an echo, or at least somewhat framed by, Larry Summer's famous remarks about possible explanations for why so few women are at the top of math and science at major universities.
Of course, why there are so few women in X, when the answer isn't "because they're not allowed" or "because they're biologically incapable of it" is usually unanswerable. This is because "why do so many people do X" is itself rarely an answerable question; each person has their own reasons and their own complex history which led to it.
The discussion got me to thinking about how I got into computers (I'm a programmer by trade). I originally got interested in computers from playing computer games, but it was my friend Tom who introduced me into programming. Having him around encouraged me to get into it. He never recommended it to me that I recall, except perhaps for wanting him to do something and him telling me in exasperation to do my own damn programming. But without question I was encouraged to do it; my parents didn't particularly want me to do it but they helped me when I asked (bought me a compiler back in the bad old DOS days, let me install linux on the family computer, etc.).
Then I got to thinking about why my friend Michael never got into computers. He's a brilliant man, truly brilliant, but he has no interest in computers (that I ever saw). What he likes is philosophy of religion. He has the aptitude for computers (or math, or science), but no interest in them. I prefer theology and philosophy myself, but I like programming well enough to do them for a living (and I prefer the idea of keeping my true love unpaid so I'll never need to worry about it). So why did we each follow our paths?
Certainly temperment has something to do with it, yet I think that temperment plays less of a role in life than many people think. People are very maleable creatures, to our own will as well as to our environment. I don't mean to discount individual nature entirely, merely to take it as somewhat more general than it is often given credit for. It's an appealing theory that everyone has a profession that's their natural end (I'm as steeped in platonic idealism as the next man), but I think that we overrate it because as humans we like things to be neat and orderly. God doesn't seem to have made us in a very neat and orderly world, though.
So if we leave temperment as only a contributing factor, and not necessarily a very strong one, we're left with encouragement and discouragement. Of the two, I suspect that the former is much stronger than the latter, and I think that this is where most feminists go wrong. They (whether intentionally or not) tend to emphasize discouragement. But we've all been discouraged, and most of us have had an awful lot of discouragement. I was picked on mercilessly from kindergarden until highscool (it has a huge highschool, so most people didn't know each other, but even then I was sometimes picked on). If discouragement keeps you from doing something, you probably didn't want it enough to do it anyway. Most fields are more discouraging than social pressure anyway. For example, programming constantly makes you want to throw your computer through your monitor; compared to the discouragment involved in programming, being picked on is easy. (And that goes ten times if you have to deal with users who discover bugs.) I suspect that every other challenging field is the same way, certainly both math and computers are.
What does matter is encouragement, but not in a simple way. Being encouraged into a field is not just a matter of someone saying, "gee, you should do this for a living!" or even of a whole bunch of people saying it. The encouragement which really matters is someone helping one discover the satisfying part of a field (C.S. Lewis or Chesterton might describe it as finding joy in the field). This is complex, and almost certainly dependent on temperment — there seem to be people who cannot be interested in some fields — but it's usually a key ingredient.
But here we run into something tricky: if people are indeed maleable, what they go into depends not only on what they're introduced to, but in what order. I'm told that if I kept up with my piano lessons when I was young, I could have been a concert pianist. Having given up the piano early, I'll never know, of course, but perhaps it was true. If it was, and if I had discovered the joy of playing piano when I was young, I might well now be a pianist and not a programmer.
And this is one of the subtle reasons why social expectations for women do play a role in directing them into some fields and away from others — given that most people expect women to like certain things and dislike others, they tend to encourage women into fields incompatible with more male dominated ones (in the sense that since most fields require devotion, most fields are incompatible with each other). The very maleableness which allows people to specialise into a multiplicity of fields is what tends to direct them into some when people expect them to go there — they're more likely to find out what's enjoyable in it before they're likely to find out what's enjoyable in other fields.
This is not a conspiracy; it's not malicious. Indeed, it's so insidious about it — it's the result of people doing each other good. We are not God, so we cannot create. Thus everything we call creative is also destructive — when we open one door we close the rest. When we paint a canvas red we keep it from being green. When Michaelangelo clears the marble away from the statue he sees trapped inside of it, he destroys every other statue which was trapped inside of the marble to do it.