To me it seems that race is not a social construct but a fact of biology and the way nature begins to divide that which ought to be divided. And fighting nature is futile.
Th thing is according to Howard Bloom we should put the center of gravity on the Super-organism and the social meme that unifies it. Based on that we could say even though Sephardim and Ashkenazim have been separated by time and space still since the Torah is the social meme , therefore they can be united. Clearly that is what Bava Sali thought, even though he did sign his name 'with a (ספרדי טהור (ס''ט after it to show that he could trace his lineage to Jewish people before the mixing that began under Arab rule. Still clearly he though the main thing was loyalty towards the holy Torah. That is even though lineage is a big deal still everyone has free will. and one can still choose Torah no matter what his lineage is.
[I focused on color because that seems to be the first marker. Maybe there are others. Color is what got Darwin thinking and I also noticed the same thing. Take a species lets say squirrels and separate it. Put one set into the USA and the other into the USSR. After some time one comes out grey and the other brown. Same with birds in England. There are lots of examples.]