If that's actually correct, we should be able to just breed a superintelligence. Maybe not one as powerful as an AI gone foom, but still orders of magnitude higher than us mortals.
Unless he claims at some point that humans reached some sort of hard limit, but it seems vastly more likely that huge brains are costly and we're the point where the tradeoffs balanced.
Supposedly human brain size is limited by the skulls that will fit out of our mothers, and human babies are actually born premature relative to other species because it's only when we are premature that our skulls will still fit out.
Of course, we have cesarean births now, so...
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.