Moderation of breastfeeding effects on the IQ by genetic variation in fatty acid metabolism:

…Breastfed children attain higher IQ scores than children not fed breast milk, presumably because of the fatty acids uniquely available in breast milk. Here we show that the association between breastfeeding and IQ is moderated by a genetic variant in FADS2, a gene involved in the genetic control of fatty acid pathways. We confirmed this gene-environment interaction in two birth cohorts, and we ruled out alternative explanations of the finding involving gene-exposure correlation, intrauterine growth, social class, and maternal cognitive ability, as well as maternal genotype effects on breastfeeding and breast milk. The finding shows that environmental exposures can be used to uncover novel candidate genes in complex phenotypes. It also shows that genes may work via the environment to shape the IQ, helping to close the nature versus nurture debate.

This reminds me a lot of the findings from a study of polymorphism on MAOA. One allele exhibited sensitivity toward environmental variation, while the other did not. This is a pretty simple norm of reaction, genotypes differently influenced by the same background environmental condition. Ars Technica has more detail. Check out the population differences of the two SNPs they looked at on FADS2.
Via Aziz.

Read it here.

Update: Eye on DNA has much more.

Jason M. adds: In the comments HapMap Jockey Marc again applies the wisdom from p-ter’s HapMap How-2 to the latest IQ genes:

In the study itself, there were two cohorts: a British cohort and a New Zealand cohort. In both cohorts, presence of the C allele (as either CC or CG) was associated with a hike in IQ by 6.4 and 7.0 points (from around 99-100 to around 106) in the two samples. But those without the C allele (GG) had mean IQs of 99.5 in Britain and 100.3 in New Zealand.

Incidentally, I plugged rs174575 into the ol’ Hapmap, and it seems that the C allele has a frequency rate of 72% among Utah whites, 73% among Yorubans, 89% among the Chinese, and 90% among the Japanese.

Assuming these numbers are representative, universal breastfeeding alone would lead to a gap of 1.12 to 1.225 in IQs between East Asians and whites, favoring East Asians.

On the other hand, since whites and blacks have nearly the same C allele frequency (assuming, again that these numbers are representative of white and black populations), but whites breastfeed their babies at higher rates than blacks (60% vs. 30%, according to Steve), this is pretty solid evidence that increasing the percentage of black women who breastfeed their children will have a diminishing effect on the black white IQ gap.

Since I’m already blowing off work (damn you, Gene Expression!) I might as well do the calculations. Let’s see… The 30% difference in breastfeeding is responsible for between 1.4 and 1.53 points in the black-white IQ gap! (I got these figures by multiplying the frequency rate of the C allele in Yorubans with the percentage difference in breastfeeding between blacks and whites with the effects of breastfeeding on the IQs of C allele carriers.)

Steve Sailer is vindicated!

Additional props to Rob in the comments at FuturePundit.