Most Indian groups descend from a mixture of two genetically divergent populations: Ancestral North Indians (ANI) related to Central Asians, Middle Easterners, Caucasians, and Europeans; and Ancestral South Indians (ASI) not closely related to groups outside the subcontinent. The date of mixture is unknown but has implications for understanding Indian history. We report genome-wide data from 73 groups from the Indian subcontinent and analyze linkage disequilibrium to estimate ANI-ASI mixture dates ranging from about 1,900 to 4,200 years ago. In a subset of groups, 100% of the mixture is consistent with having occurred during this period. These results show that India experienced a demographic transformation several thousand years ago, from a region in which major population mixture was common to one in which mixture even between closely related groups became rare because of a shift to endogamy.
This appears quite reasonable in terms of dates and two major demographic foci. Where I suspect it will lead to confusion is that the early North Indian population would not have been Indo-European speaking, but would have spoken languages from probably 2 extinct language families (sometime grouped together as “Language X”. The residual (substrate) vocabulary in Sanskrit, etc., which is not Indo-European include two groups in phonological terms (one of which has Southeast Asian like affinities). In the vocabularies of these pre-Sanskrit languages one find the vocabulary of native trees and crops as well as introduced Near Eastern crops, and interesting a bunch of terminology relating to music and dance. The Harappan language is most likely from one of these as well. IE then is best understood as something to rose to prominence as a lingua franca later. The key linguists who have written on this include Masica (1979); WItzel and Southworth. I have drawn some botanical related conclusions and tables out in a couple of papers.
The one potential monkey wrench in the remoteness of South Indian population and Dravidian speakers—although I tend to support this view—is the continuing discussion of potential links between Proto-Dravidian and ancient Elamite. Southworth has recently come around to accepting this ide dn has started championing it (see his chapter for the Bellwood encyclopedia of human migration). As he has done really solid work on Indian languages, I think this has to carry some weight, although I have always sides in the past with those who reject Elamo-Dravidian.