“but my impression is that there is a growing list of likely genes”
As I said in my first comment, the list is characterized by non-reproduced associations. I have tracked this sort of research for about 10 years now, and the pattern is a consistent one where a QTL makes a big splash, but there is no follow up. As I also stated, I have friends looking for QTLs which effect normal variation. This is a well known issue in the behavior genetics community.
“My interpretation would be that neither theoretical conssiderations nor empirical studies offer much support to the idea that genes with moderate effects on IQ are particularly uncommon.”
Your interpretation is based on unfamiliarity. A literature search would validate that large/moderate QTL effects tend not to be validated over time. In your initial comment you cite ASPM. You obviously don’t know the literature, as Rushton looked to see if ASPM variation tracked IQ variation several years ago, and it does not.
Anyway, I guess this is my last comment on this thread. Hope you are more open to being less wrong in the future :-)
“What about DTNBP1, CHRM2, ASPM, NR2B, HAR1, PYDN?”
Not replicated, or nothing found. ASPM for example isn’t associated with normal variation in IQ (or the effect size too small to detect, they’ve looked). Please see my coblogger “ben g”’s post on the topic:
http://www.gnxp.com/blog/2010/02/half-sigmas-flawed-post-on-dtnbp1.php
(and no, I’m not one of the people who is excited that we haven’t been able find these genes yet)