Nuance my friend. Nuance. Any study based on IQ is bullshit, because IQ is bullshit. And you're making the same mistake I alluded to - lumping all forms of intelligence as the same. And I can propose all sorts of evolutionary mechanisms. I proposed one in the above comment. Again, I'm not talking about a broad conclusion that one ethnic group is smarter than another. That's preposterous, just like there isn't one ethnic group that is universally better at athletics than all others. But I can think of three physical advantages that are well documented and differ between ethnic groups:

1. High altitude breath capacity adaptation.

2. Long distance running advantages.

3. Lactose tolerance.

The brain is an organ like any other. I can think of many potential cognitive advantages one ethnic group could have over another, with very clear evolutionary mechanisms involved. These are pure speculation, but very plausible:

1. An ethnic group with a long tradition of larger than average and more tightly knit extended families may have superior social skills. In that society, the more socially skilled had an advantage in reproduction over those that were less skilled.

2. There are differences in the kind of cognitive tasks involved in farming and hunter-gathering. It would not be absurd if ethnic groups that have been farming for thousands of years have evolved an advantage on the cognitive abilities most useful to farming and a disadvantage on those tasks involved in hunting and gathering.

3. Differences in rates of neurodiversity and neurodivergence. There is a prominent theory that many "conditions" like autism and ADHD are evolutionary holdovers. The theory is that while certain neurotypes can be disabling in modern societies, these same neurotypes could have been advantageous in pre-agrarian history. If that is truly the case, why wouldn't rates of these neurotypes differ among ethnic groups? The people of North Sentinel Island still live off hunter-gathering. While there are some ethnic groups that have been farming for 10,000 years. If certain neurotypes really were more advantageous in pre-agrarian societies, ethnic groups with no or shorter histories of agriculture should be expected to have higher rates of these neurotypes. Honestly it would be extremely fascinating to test a whole bunch of people for autism and ADHD and plot that against some estimate of how long their ancestors have been involved in farming. If there is a correlation, it would be pretty slam-dunk evidence for the neurotype evolutionary advantage theory. Maybe the rates of autism among the Sentinelese are sky high.