The Cambridge History of India, Vol. I: Ancient India v1.c17.142

v1.c17.142

It seems probable enough that among the Çūdras themselves there were rules of endogamy; for we may generally assume, in the absence of anything to the contrary in the texts, that the Vedic Indians and the aborigines alike married within the tribe. The Çūdras seem often to have been subjugated by whole tribes, such as the Baindas, the Parṇakas, the Paulkasas, and perhaps the Chaṇḍālas, who may originally have been members of small and degraded tribes living mainly by fishing or hunting: such tribes have survived in the Central Provinces and near the Himālayas until the present day, and they must have been much more numerous in the first millennium B.C. Thus from below as well as from above, from the practices of the conquered aborigines as well as from the class prejudices of the Āryans, may have come the impulse to the development of caste.