The following chart (created by some scientist(s) led by David Reich) shows the genetic divergence between hominin samples as a fraction of the human-chimp difference. So for example, all the human groups have just over a 0.12 genetic divergence with Neanderthals, meaning that the genetic difference between humans and Neanderthals is only 12% as great as the genetic difference between humans and Chimps (source: supplement of Genetic history of an archaic hominin group from Denisova Cave in Siberia.)
The purpose of the chart is to estimate how long ago the different populations diverged from a common ancestor. So since the fossil record tells us that Neanderthals and chimps diverged about 6.5 million years, then humans and Neanderthals should have diverged roughly 0.8 million years ago (12% of 6.5 million) assuming genetic divergence maps to chronological divergence in a linear way:
The above numbers make no sense to me (how could the Han and the French have separated 404 kya when the ancestors of both didn’t even leave Africa until 50 kya?).
Nonetheless, it seems to me that if you can estimate chronological divergence from genetic divergence, why not cognitive divergence?
Since I know that chimps and people of European ancestry differ by about 86 IQ points, then we can estimate how much each of these populations should differ in IQ from whites based on their genetic divergence as a percentage of the white-chimp divergence.
Using the French as the representatives for white people, we see from table S6.2 that the genetic gaps between whites and Han, Papuan, San, Yoruba, Neanderthals, and Denisovans are 0.0622, 0.0660, 0.0907, 0.0812, 0.1218, and 0.1255 respectively.
Multiplying these fractions by the 86 point IQ gap between Chimps and European ancestry people, we get the following expected IQ gaps:
Han-white IQ gap: 5 points
Papuan-white IQ gap: 6 points
San-white IQ gap: 8 points
Yoruba-white IQ gap: 7 points
Neanderthal-white IQ gap: 10 points
Denisovan-white IQ gap: 11 points
These estimated IQ gaps are much smaller than the actual IQ gaps in most cases, suggesting that IQ tests are measuring a lot of non-genetic factors.
The second point is that the expected IQ gaps between white and non-white humans is not that much smaller than the expected IQ gap between whites and Neanderthals. From a genetic perspective, Neanderthals could be just another human race, only slightly more divergent than the San, however from a morphological perspective, they’re clearly not human.
Since whites by definition have an average IQ of 100, and if we make the huge assumption that all non-white groups with the exception of Han have lower genetic IQs than whites, we get the following the figures:
Han average IQ 105
Whites average IQ 100
Papuans average IQ 94
Yoruba average IQ 93
San average IQ 92
Neanderthals average IQ 90
Denisovans average IQ 89
From these numbers we might conclude that it takes a genetic IQ of at least the mid 90s to independently invent agriculture (since everyone below that level failed to do so) and a genetic IQ of at least the high 90s to independently create civilization (since only Caucasoids and Mongoloids are credited with having done that).