@benroyce I may have ranted a couple of times about how American adoption of birth certificates was originally motivated by trying to enforce heritage and immutability of "race" on people.
Bolsheviks did the same with "ethnicity". In late thirties, at about the same time the high-ranking politicians were being Purged, the Little Peoples' "internal passport" system was amended to record everybody's ethnicity, which would be immutable, and in the later years get sort-of-inherited (although in practice, in some places, people were able to self-identity their immutable ethnicity when they got their first passport at 16).
I don't know enough about Bolshevik history to tell if this is a strong causal link, but Stalin's experience as being tin charge of the "Ethnicities Desk" in Lenin's early cabinet makes me at least wonder. Then again, using ethnic labels for people serving in the royal court goes back centuries even in the pre-revolutionary Russian Empire.