I don't think this is true, logically or socially. We have dense clusters that are slowly merging as the world enjoys this extremely new concept of travel and intermingling world populations. I've seen many people describe themselves as "mixed race", directly or indirectly by describing their ancestry. Of course, the number of basis vectors required to accurately describe a person is increasing with time, but it seems that medical science has chosen to ignore this "easy" way to describe and treat people for some reason. But, is it all that surprising, considering not even women were represented fairly in medical trials, even 15 years ago?