It could also be communications.
Many high intelligence situations involve disorders that also have as an effect anti-social behavior. Academia is highly geared against this in some cases going so far as to evaluate people's chances for success in a PhD based on their ability to form working relationships with a peer group during their MSc. Travel is easier and correspondence is far more personal.
Would the mathematicians of the past have been as interested in this model? Perhaps some of them were the type of people that were happy to correspond by mail but found communicating face to face awkward. This wasn't a big barrier to success in the past, but it is very difficult in modern academia (particularly with most positions in most fields being teaching + research).
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.