In the beginning, it is explained, when the light-skinned ancestors of the present Hindus first came to India, they found there a darker, thicker-featured native race, the Dravidians, builders of the great temples of the South. And the priests of the newcomers desired that the blood of their people be not mixed with the native stock, but be kept of one strain. So they declared Dravidians to be unclean, “untouchable (Mayo 151).”
Mayo, Ketherine. “Less Than Men.“ Mother India, Harcourt, Brace, And Company, Inc., 1927, pp. 150-163.