If a trait is being selected for, the alleles with large positive effects will compound with a faster growth rate than those with small effects (even if there are initially many more small-effect alleles) and tend to account for a large portion of the heritability of that trait (at least until they have almost swept the population).
You suggest that psychological traits such as personality and cognition have been subject to recent positive selection, so why haven't GWAS (or targeted investigations, e.g. microcephalin) found much in the way of common large effect alleles for psychological traits? What are your best guesses on the genetic architectures of personality and cognition?
Yikes! This is worse than my PhD orals.
There have been some (tentatively) identified like the 7-repeat version of the D4 dopamine receptor, the serotonin transporter, and others that Greg will be able to dredge up from his memory.
We may have found others but not identified them. Imagine that it would be highly beneficial to have a little bit less of substance s. If so then a mutation that broke the gene producing s would be favored a lot and would sweep until people with two copies of broken s started being born. How likely is it now that two broken ...
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.