Some things take generations to adjust to. It is a process in which those who deal best with the conditions have a longer life, are stronger, more productive and therefore more likely to reproduce passing their genetic predispositions to the offspring. But from the moment we are presented with a new situation, our bodies often tend to do a switch right away making it possible to begin an evolutionary process from within. And this appears to be the case here. So how do the red cells and their ability to transport oxygen faster relate to the ABO group and rh factor sitting on the same red blood cells?
The people from that region have been able to deal well in high altitudes and while the rh negative blood factor runs low, it is noticable how high the percentage of people with blood type B is.
6%
https://www.rhesusnegative.net/staynegative/rhesus-negative-friends-and-organizations-worldwide/