A while ago I took IQ and brain size data mostly reported by Richard Lynn and attempted to correct it to show the IQs and brain sizes the races would have if they all enjoyed First World 21st century living standards.  I called these corrected values, genetic IQ and genetic brain size, though in fairness, many actual anthropologists would call it pseudoscience.

race iq real iq (rounded) genetic iq (rounded) brain size genetic brain size
ashkenazim 108 110  110 1457
east asians 105 105  105  1416  1534
whites 99 100  100 1369  1487
arctic people 91  95  95  1443  1561
southeast asians 87  90  95  1332  1450
native americans 86 90  90  1366  1484
pacific islanders 85 90  90 1317  1435
dark caucasoids 84 85  90  1293  1411
congoids 67  75  85  1280  1398
australoids 62 65  70  1225  1343
capoids 54 60  70 1270  1388
pygmies 54 60  70 1085  1203

The problem was that the IQs Lynn reported for Bushmen, Pygmies and Australoids were so incredibly low (even after correcting for their low human development index) that I was left with a very steep slope for predicting a population’s genetic IQ from its genetic  brain size.  The absurdity of this steep slope became apparent when I tried to extrapolate the trend beyond humans and predict the IQ of chimps from their cranial capacity (about 498 cc if adjusted for their small size), and got an estimated IQ below zero!

popbrain

I decided that the problem was that Lynn’s IQ data for Australoids, Bushmen and pygmies simply isn’t credible.  You can’t give conventional IQ tests to people still living in hunter-gatherer societies and expect to get good results and there’s no credible evidence that any extant human race or ethnicity has a genetic IQ below the 80s. So after removing these three outliers, we get the following line of best fit predicting population IQ from population brain size.

solution

Now when we predict the IQs of chimps from their cranial capacity we get 26, which is within 10 points of actual laboratory research suggesting an IQ of 35.