Here’s the part of a Quora answer that actually made some sense:
How: Mutation of the RHD gene, resulting either in lack of expression of the protein or alteration in its structure making it less antigenic.
Where: Since there are a variety of such mutations in the human gene pool, it must have happened multiple times in multiple places.
It seems that it is not just a matter of gene mutation, but of a significant gene deletion.
See (among others) RHD gene deletion occurred in the Rhesus box
Franz F. Wagner and Willy A. Flegel
Blood 2000 95:3662-3668;
My sense is that there are a large number of mutation/deletion variations, and that it may now be possible to establish estimates for the time and place in which they occurred….a somewhat different model from identical mutation/deletions happening at the same time in different places.
I just found this. It’s from March of this year:
“Our results show a clear differentiation of Basques from the surrounding populations, with the non-Euskara-speaking Franco-Cantabrians located in an intermediate position. Moreover, a sharp genetic heterogeneity within Basques is observed with significant correlation with geography. Finally, the detected Basque differentiation cannot be attributed to an external origin compared to other Iberian and surrounding populations. ”
https://www.cell.com/current-biology/fulltext/S0960-9822(21)00349-3?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0960982221003493%3Fshowall%3Dtrue
I thought the rh- arose in several places until I read that. Now I’m not so sure. And then there’s this from 2019:
“The new model we present has forced us, furthermore, to review the amount of DNA in people of Eurasian origin that comes from Neanderthals, which could be up to three times higher than had been estimated to date using the previous models.”
https://phys.org/news/2019-04-african-populations-crossbred-extinct-humans.html
Would love to get my hands on some 411 about Neanderthal DNA %s amongst the Yamnaya.