It may be worth noting that no part of the human (etc) genome varies nearly as much as our immune system; (particularly the major histocompatibility complex - M

It may be worth noting that no part of the human (etc) genome varies nearly as much as our immune system; (particularly the major histocompatibility complex - MHC) for the obvious reason that we're in a very active arms race with the small minority of microbes that are pernicious to us. So very sharp variations in immune function are not unexpected. https://en.wikipedia.org/wiki/Major_histocompatibility_complex#Evolutionary_diversity https://en.wikipedia.org/wiki/Major_histocompatibility_compl...