Also the brain size/GMA correlation in Rushton’s paper is fairly consistent with Michael A. McDaniel’s meta-analysis:

http://www.people.vcu.edu/~mamcdani/Big-Brained%20article.pdf

Martin,
The number 9,006.7mm3 in this article is correct (it’s a direct cut and paste from the original article which I also have). 9,006.7 mm3 which is about ~9 cm3.

Population structure is a biatch, but… surely someone has come up with a way to control for that? Even something as dumb as partial correlation between gene of interest and trait, controlling for the (PCA’ed) rest of the genome might provide some info… Though of course you might need humongous Ns to get any signal.

Lmao. I know I did a google search like 30 minutes after I posted that. Found this:

Hurlburt:
“Even though head size also depends on factors such as the muscularity of the head and thickness of the bone, it’s very likely that a bigger head means a bigger brain.”
http://sciencenetlinks.com/science-news/science-updates/big-heads/

Would you mind posting your source for the correlation of .3 or .4 between “head size” and “brain size”?
For my own personal reference.

The biggest concern in my view in this study would be that a merely ancestry informative marker with neutral effect on intelligence is picking up of intelligence differences attributable to histories of immigration

well, as i said, the authors are not stupid :=) the samples were european.

@6

Ed, this kind of stuff is easily findable via a quick Google search. It’s been found quite a few times to be a .3 to .4 correlation.

Also, with Bastian, hope that the authors had the good sense to adjust volumes for height. Given that it was a meta-analysis, some may have and others may not.

If I had to bet, I do think the intracranial volume thing will replicate, but the IQ part probably will not.

Has anyone tried tackling IQ using genetic risk scores or other prediction models like the folks who publish on height do? A better study might be measuring native intelligence in small children. Not an easy study to do: DNA and IQ data from the under 4 set.

I think it’s generally acknowledged that height and intracranial volume correlate (Dawkins has a nice take on this in «The Ancestor’s Tale». So given the relatively small differences in volume it seems crucial to correct for the participants height if you’re going to measure the genetic influence on the volume.

Otherwise you might end up with an effect on height but no “real” effect on the intracranial volume. Especially if this gene is already known to account for height differences.

I’m a little confused by this comment. These samples are huge for an MRI-genotype association study, which often have samples sizes in the hundreds or dozens or less, which the highly significant p values reflect. Is the implication of the comment that past studies with smaller sample sizes shouldn’t have be taken as seriously as this one, or that this study in particular is too small?

Also, an MRI-genotype association study has the virtue, not common to other kinds of studies, of involving very well defined and basically indisputable data points, rather than, for example, personality surveys or IQ tests, as the core measured elements. This greatly reduces inherent systemic error associated with the measurement process, leaving only sampling error which the large sample size mutes.

I also don’t see any particularly good reason to distrust at first glance a weak association of cranial volume and IQ, as an obvious mechanism is available to relate the two, and IQ while hardly a perfect operational test is one of the best defined and most accurately operationalized metrics in psychology (certainly far more accurate than most personality measures or even than mos psychiatric diagnoseses). The claimed total effect size of the entire set of allelles appears to be less than a third of a standard deviation in any case, so it isn’t as if someone is proposing a grant overall theory of intellligence here.

The biggest concern in my view in this study would be that a merely ancestry informative marker with neutral effect on intelligence is picking up of intelligence differences attributable to histories of immigration instead (i.e. many U.S. Asian immigrants were able to immigrate due to their advanced educational degrees making them unrepresentative of Asians generally, while the African slave trade was not selective in that was and has been exacerabated by strong non-hereditary effects on IQ among the many low income African-Americans today; so any marker that is more common in Asians than Africans, even if it has no causal connection to IQ relevant brain function, is going to be associated statistically with IQ in any U.S. drawn sample).

To test that possibility, you’d really want to see if the cranial size and IQ correlations held up just as strongly within demographic subgroups as they do across demographic subgroups. Indeed, given environmental impacts due to poverty, the intragroup assocation should be stronger than the intergroup association, and the association should be stronger among middle class or better subjects than among poor subjects (which the data might contain some proxy to determine).

http://hgdp.uchicago.edu/cgi-bin/alfreqs.cgi?pos=160885986&chr=chr1&rs=rs10494373&imp=false

“We also identified a suggestive association with total brain volume at rs10494373 within DDR2. . .”

But surely you can just buy more RAM. . .

Not really sure why they didn't just look up this association in the whole meta-analysis data, given the overlap in authors.

[1] http://www.nature.com/mp/journal/v16/n10/full/mp201185a.html