I think children and the whole biological clock thing are a huge factor in this (and in the low percentage of women in any job that has crazy long hours, like law or medicine). But I also believe that the effect is both more subtle and far-reaching than is generally appreciated.
There are studies that show that people from a racist culture who believe "racism is wrong" will still tend to believe secondary and tertiary things that are basically racist but aren't directly about skin color per se -- like conversations I have had with people who say they would vote for or hire a black person if they were articulate enough and claim it is not racist, it is just that most blacks aren't educated/articulate enough. My reply to that is "If articulation were the issue, then George W Bush should have never been elected president. He is infamous for butchering the English language." Of course, he's white and male and went to the right schools and came from the right family. It makes people very uncomfortable to point out the flaw in their logic and point out that this is a social form of "Jim Crow Law".
So, basically, I think there is kind of a female version of social "Jim Crow Law" going on: Even women who don't specifically want to have kids may still make choices that are rooted in the goal of having mom available to the kids. Or may be discouraged by subtle social things that are rooted in those assumptions. People who make such assumptions usually don't even realize they are making them. So it gets hard to root out.
There are studies that show that people from a racist culture who believe "racism is wrong" will still tend to believe secondary and tertiary things that are basically racist but aren't directly about skin color per se -- like conversations I have had with people who say they would vote for or hire a black person if they were articulate enough and claim it is not racist, it is just that most blacks aren't educated/articulate enough. My reply to that is "If articulation were the issue, then George W Bush should have never been elected president. He is infamous for butchering the English language." Of course, he's white and male and went to the right schools and came from the right family. It makes people very uncomfortable to point out the flaw in their logic and point out that this is a social form of "Jim Crow Law".
So, basically, I think there is kind of a female version of social "Jim Crow Law" going on: Even women who don't specifically want to have kids may still make choices that are rooted in the goal of having mom available to the kids. Or may be discouraged by subtle social things that are rooted in those assumptions. People who make such assumptions usually don't even realize they are making them. So it gets hard to root out.
My 2 cents.