The unspectacular brain size of Ashkenazim has long bothered me because if brain size plays a substantially causal role in IQ, then whatever selected for high Jewish IQ should have also selected for bigger brains by proxy, so the absence of larger brains makes the high Jewish IQ seem more cultural than biological.
Fortunately Dr. Henry Harpending, Greg Cochran, and Jason Hardy came to the rescue by linking the high Ashkenazi IQ to four other biological traits: Tay-Sachs, Niemann-Pick, Gaucher, and mucolipidosis type IV.
The New York Times reported:
Ashkenazic diseases like Tay-Sachs, they say, are a side effect of genes that promote intelligence.
The explanation that the Ashkenazic disease genes must have some hidden value has long been accepted by other researchers, but no one could find a convincing infectious disease or other threat to which the Ashkenazic genetic ailments might confer protection.
Why Jewish high IQ is linked to disease while East Asian high IQ is linked to brain size is something of a mystery, but may relate to the fact that Jewish IQ had to evolve with lightning speed and evolved in a much smaller population, or it may relate to verbal IQ vs spatial IQ. Who knows? So much research needs to be done and so few scientists are doing it.
I have long argued that height is to weight as brain size is to IQ. The taller you are, the more room there is a for a heavy body, just as the bigger brained you are, the more room there is for a high IQ mind, but in both cases, other factors determine how much of that room is used.
So in order for me to feel better about Jews having big IQs despite having slightly small brains, I needed to find a race that had big weights, despite having small heights.
In a study where white males averaged 177 cm (SD = 6.4), Samoan men averaged 173 cm. Translating this to an IQ (Intelligence Quotient) type scale where the mean and SD in the white population are defined as 100 and 15 respectively, Samoans had a HQ (Height Quotient) of 91.
And yet, when it comes to weight, white males averaged only 80.3 kg (SD = 11.9) while Samoan men averaged 94.7 kg. Once again, setting the white mean and SD at 100 and 15 respectively, Samoans enjoyed a WQ (Weight Quotient) of 118!
So just as Ashkenazi Jews may have brains slightly smaller than the white mean set at 100, (Brain-size quotient = 94) despite having an average IQ that is higher (110), Samoans have heights well below the white mean, despite having weights that are way above.
Because just as Jews makeup for their brain size with Tay-Sachs, Niemann-Pick, Gaucher, and mucolipidosis type IV, Somans make up for their height with big muscles, big fat, and big bones.