Peter Bellwood in First Farmers presents a hypothesis for the expansion of the Dravidian languages into southern India in the late Neolithic through the spread of an agro-pastoralist lifestyle through the western Deccan, pushing southward along the Arabian sea fringe. At the time I was skeptical, but now I am modestly confident that this is close to the reality.
There is always talk about “steppe” ancestry on this weblog. But there are groups that seem “enriched” from IVC ancestry, as judged by the Indus Periphery samples. The confidence is lower since we don’t have nearly as good a sample coverage…but I think I can pass on what we’ve seen so far: groups in southern Pakistan, non-Brahmin elites in South India, and some Sudra groups in Gujarat and Maharashtra, seem to be relatively enriched for IVC-like ancestry. Then there is the supposed existence of Dravidian toponyms in Sindh, Gujarat, and Maharashtra. And, their total absence in the Gangetic plain.
There have been decades of debate about Brahui. I’ve looked closely at Brahui genetics, and they are no different from the Baloch. Combined with evidence from Y chromosomes (the Baloch and Brahui have some of the highest frequencies of haplogroups found in IVC-related ancient DNA), I doubt the thesis they are medieval intruders (if they are, their distinctive genes were totally replaced).
Genetically, we know that some southern tribes, such as the Pulliyar, have some IVC-related ancestry. But other groups, such as Reddy in Andhra Pradesh, have a lot more. How does this cline emerge? My conjecture is that there were several movements of “Dravidian” people from Sindh and Gujarat into southern India, simultaneous with the expansion of Vedic Aryans to the north into the Gangetic plain. The region the Vedic Aryans intruded upon, Punjab, was not inhabited by Dravidian speakers. Like Mesopotamia, the Indus Valley Civilization was probably multi-lingual, despite broad cultural affinities developed over time.