Ancestral North Indians and Ancestral South Indians
Middle Eastern farmers show an ancestry from a Basal Eurasian lineage that diverged from the ancestors of north Eurasian hunter-gatherers and East Asians before they separated from each other.
Two main different ancient populations are ancestral to modern Indians: the Ancestral North Indian (ANI) ancestry, a West Eurasian ancestry, and the Ancestral South Indian (ASI) ancestry. None of them exists in unmixed form, and both contribute a variable amount of the ancestry of South Asians[Reich et al. 2009].
ANI can be modelled as a mix of ancestry related to both western Iranian farmers and people from the Bronze Age Eurasian steppe, and is thus close to Middle Easterners, Central Asians, and Europeans[Lazaridis et al. 2016]. Because of that, it is possible that the ANI component was prevalent in the Mehrgarh and later Indus Valley Civilization, expanding eastward into South India in an admixture event associated with farming, as suggested by mtDNA lineages that entered India from Anatolia, the Caucasus and Iran in the earliest Neolithic sites. The ASI component would have expanded earlier, possibly in different waves, from west and south-west Asia, with the end of the last Ice Age[Silva et al. 2017].
The impact of the steppe invasion in South Asia is heterogeneous. A cline of ANI-ASI ancestry is evident, with ANI ancestry significantly higher in Indo-European than Dravidian speakers. This suggests that the ancestral ASI may have spoken a Dravidian language before mixing with the ANI.
While maternal lineages reflect earlier, pre-Holocene processes (with higher levels of autochthonous variation), paternal lineages predominantly show admixture events of the last 10,000 years, with a particularly strong male-driven invasion from central Asia during the Bronze Age[Silva et al. 2017], also reflected in the significant correlation of ANI with the Y chromosome[Reich et al. 2009]. This sex-biased pattern is much less marked in East Asian fraction, mainly focused on speakers of Tibeto-Burman and Austroasiatic language families.
Among groups, the Mala (a south Indian population) show minimal ANI and ca. 18% steppe ancestry, and the Kalash of Pakistan are inferred to have ca. 50%, similar to northern Europeans[Lazaridis et al. 2016]. Regionally the North-West Frontier populations are thus more similar to European and Central Asian populations. Among ethnolinguistic and social groups, there seems to be an influence of north Eurasian admixture (potentially from ancient Indo-European-speaking populations) in forward castes, diminishing in backward castes and Dravidian peoples[Bose et al. 2017].
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