So, are $POORETHNICGROUP so poor, badly off and socially failed because they are about 15 IQ points stupider than $RICHETHNICGROUP? No, it may be the other way around: poverty directly loses you around 15 IQ points on average.
Or so says Anandi Mani et al. "Poverty Impedes Cognitive Function" Science 341, 976 (2013); DOI: 10.1126/science.1238041. A PDF while it lasts (from the nice person with the candy on /r/scholar) and the newspaper article I first spotted it in. The authors have written quite a lot of papers on this subject.
So, I totally buy the "cognitive load decreases intellectual performance, both in life and on IQ tests" claim. This is very well replicated, and has immediate personal implications (don't try to remember everything, write it all down; try to minimize sources of stress in your life; try to think about as few projects at a time as possible).
I don't think it's valid to say "instead of A->B, it's B->A," or see this as a complete explanation, because the ~13 point drop is only present in times of financial stress. Take standardized sch...
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.