Far enough, and I'm not even sure the "more knowledge required" is that strong an argument for some parts of math.
A scary possibility is that there are fewer people at the far right end of the bell curve. I have no idea what could case that effect, but we don't know what makes for genius of the sort which does significant creative work.
It's conceivable but unlikely that teachers' ability to recognize extraordinary minds has declined.
Perhaps genius requires extraordinary effort, which is only worthwhile if you already have nothing to lose. So maybe the hardships and obstacles that previous highly intelligent people faced actually contributed to their eventual success.
Edit: Q&A is now closed. Thanks to everyone for participating, and thanks very much to Harpending and Cochran for their responses.
In response to Kaj's review, Henry Harpending and Gregory Cochran, the authors of the The 10,000 Year Explosion, have agreed to a Q&A session with the Less Wrong community.
If you have any questions for either Harpending or Cochran, please reply to this post with a question addressed to one or both of them. Material for questions might be derived from their blog for the book which includes stories about hunting animals in Africa with an eye towards evolutionary implications (which rose to Jennifer's attention based on Steve Sailer's prior attention).
Please do not kibitz in this Q&A... instead go to the kibitzing area to talk about the Q&A session itself. Eventually, this post will be edited to note that the process has been closed, at which time there should be no new questions.