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560K SNP study reveals dual origin of Indian populations (Reich et al. 2009)

The paper establishes a number of different facts, that have been hinted at in previous autosomal studies, and studies based on Y chromosomes and mtDNA:

    • Modern Indians are derived from two ancestral populations. The first one, termed Ancestral North Indians (ANI) were Caucasoids, the other, Ancestral South Indians (ASI) were distinct from both Caucasoids and Mongoloids in a Eurasian context.
    • The ASI no longer exist in non-admixed form, but in various degrees of admixtures with ANI; the closest living population to the ASI are the Andaman Islanders.
    • Upper castes are higher in ANI ancestry than middle and lower castes. ANI percentages of ancestry are correlated with Western Eurasian Y chromosomes (P=0.04) and mtDNA (P=0.08).
    • Indo-European speakers are higher in ANI ancestry than Dravidian speakers.

This paper does seem to imply that Indians are a mixture of Western Eurasians and indigenous Indians. However, we should not conclude that they are a simple 2-way mix of invading Indo-Aryans and indigenous Dravidians: for example, the ANI component could be a palimpsest of different Caucasoid populations who came to the subcontinent over time. For example, we do know that South Americans are composed of Amerindians, Caucasoids, and Negroids in different proportions of admixture, but this does not mean that there was a simple mix between the three, but rather a continuous process of migration that brought (and continues to bring) people into the New World. It remains to be seen which groups participated in the diffusion of the ANI component in India.

However, the fact that ANI is correlated with caste status and language does suggest that the Indo-Aryan migration who brought Indo-European languages to India has not been totally wiped out genetically. Indo-European populations have maintained a higher degree of ancestry from the ANI component, and upper caste Indo-Europeans have maintained an even higher degree of such ancestry.