Sub-caste intermarriage bars cannot rest on eugenic logic

Evidence

If caste is eugenic in origin, then the origin of sub-castes must also be eugenic. But can anyone seriously maintain that the origin of sub-castes is eugenic? I think it would be absurd to contend for such a proposition, and for a very obvious reason. If caste means race, then differences of sub-castes cannot mean differences of race, because sub-castes become ex hypothesi sub-divisions of one and the same race. Consequently the bar against intermarrying and inter-dining between sub-castes cannot be for the purpose of maintaining purity of race or of blood. — Ambedkar, B R, Annihilation of Caste_ The Annotated…, 867