If the genetic explanation is true and environment makes no contribution, then I think one should find that IQ is more highly correlated with myopia than academic achievement
It's like saying "if evolution is true, crocoducks should exist". You are (deliberately?) misrepresenting opponent's views. He meant that of all genetic variation affecting IQ, only small, but non-negligible, subset affects both myopia and IQ. However I still don't quite get how larger brain can cause myopia rather than hyperopia.
Maybe the larger brain leads to more intelligence, and people with more intelligence read more, and reading more leads to myopia. (Whether reading actually leads to myopia can be questioned, but that doesn't affect the point.)
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.