Not enough women in science?

Are women underrepresented in science?  My philosophy professor was complaining that since half of all B.Sc. grads are females, it doesn't make any sense that there are so few female science professors.  Personally, I don't see what the problem is.  It's not like scientific progress is being impeded by gender inequality.

Young women want to have kids.  I'm interning with many women who are all 22-24 years old and have a BS.  Believe it or not, the majority of them are already married.  All of them have kids on their minds.  I guarantee that none of them are willing to wait until they turn 30 to have children. 

So there you have it, biological imperative is why women don't want to get PhDs and become professors.  Can you imagine taking a maternal leave while in the middle of a project?  I mean, I'm sure it's done and it has been done, but it's probably very difficult, your projects probably suffer, and any work that had the potential of being published will become delayed.  In the world of publish or perish, I'm sure that's unacceptable.