Or we could simply point out that with average IQs in the 70s and 80s, average mathematician IQs closer to 140s - or 4 standard deviations away, even in a population of billions we still would only expect a small handful of Ramanujans - consistent with the evidence.

It would naively seem that an IQ of 160 or more is 5 SDs from 85 , but 4SDs from the 100 , so the rarity would be 1/3,483,046 vs 1/31,560 , for a huge ratio of 110 times prevalence of extreme genius between the populations.

Except that this is not how it works when the IQ of 100 population has been selected from the other and subsequently has lower variance. Nor is it how Flynn effect worked. Because, of course, the standard deviation is not going to remain constant.