Human Anatomy, Physiology, and Medicine. Anything human!
I was wrong about the adoption studies.
In addition to prenatal environment, the studies also fail to control for social environment.
https://en.wikipedia.org/wiki/Minnesota ... dy#Results
table of the Flynn-effect corrected results, 3rd table under Results...
It's interesting that the adopted children had a larger drop in IQ from 7 to 17, but the average drop for the adopted non-whites ((55*12.2+12*4.9+21*7.7)/(55+12+21)=10.1) was equal the drop for the adopted whites (10.1). The drop was smaller for the adopted blacks specifically (7.7), which could be due to the decline with age in the effect of "pre-adoption variables".
According to the Wikipedia article, Loehlin suggested prenatal effects, noting that among the adopted interracials, 66 of their 68 biological mothers were white. You'll notice that this group's IQ was only below the adopted whites by 6 and 8 IQ points, whereas the adopted blacks were below by 20 and 18 IQ points, more than twice below at age 17 and nearly four-times below at age 7.
Suffice it to say, the adoption studies results were influenced by many non-genetic variables, and it shouldn't be surprising that the adopted blacks still scored lower on IQ tests.
I think there is no correlation between brain size and IQ level. If compare brains of whale and elephant with humans, ours is too small. But we have very high intelligence. I think some connections between neurons or some unknown factors determine intelligence.
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