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Originally Posted by simplicitus
Now, consider evolution. One might be able to tell some BS story of the type so beloved by armchair evolutionary biologists that people in Africa (who, again, show major genetic variation) lacked the selection pressures that caused their Asian counterparts to develop "better" cognitive functions. Can one tell that evolutionary story for 1200 distinct genes, a sample that accounts for maybe 10% of "cognitive performance"? Were the evolutionary selection pressures for this subset of genes (or, say, the assumed superset of, say, 10k genes that account for most of "cognitive performance"), all in the same direction that selected for Asian "cognitive performance" over African "cognitive performance". That would be pretty damn incredible from an evolutionary standpoint. One would seemingly expect differences in these 1.2k or 10k genes to vary randomly among the populations, such that the "higher cognitive performance" variant was as likely to be found in one population or another. (And, one wonders what sorts of significant uni-directional variation could take place over say, 50-100k years, a pretty limited time scale but about the longest possible period since the common ancestors of groups were cohabiting.)
Selection is on the basis of phenotypes - traits, behaviours etc so it's not surprising at all that multiple genes involved in one phenotype could exhibit selection in the same direction. For example, if fast running ability were being heavily selected for, we would expect multiple disparate genes all conferring some running advantage to all display selection pressure. Worth noting also that "determine ethnic ancestry by analysing a large number of SNPs" describes the business model of Ancestry, 23andme etc. You can have it done for $99.
Your last sentence is pretty "wat". 50-100K years is a giant amount of evolutionary time. Speciation from H. Erectus to H. Sapiens is thought to have taken place only about 300,000 years ago. From the
op-ed by the genetics professor at Harvard which I have linked before:
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You will sometimes hear that any biological differences among populations are likely to be small, because humans have diverged too recently from common ancestors for substantial differences to have arisen under the pressure of natural selection. This is not true. The ancestors of East Asians, Europeans, West Africans and Australians were, until recently, almost completely isolated from one another for 40,000 years or longer, which is more than sufficient time for the forces of evolution to work. Indeed, the study led by Dr. Kong showed that in Iceland, there has been measurable genetic selection against the genetic variations that predict more years of education in that population just within the last century.
The whole op-ed is basically a gentle warning that the idea that populations separated for that long aren't going to have differences is almost impossible, so we might not want to rely on that as a premise on which political equality is built.