Indo-Aryan Migration - Genetic Anthropology

Genetic Anthropology

Further information: Genetics and Archaeogenetics of South Asia

Language change resulting from the migration of numerically small superstrate groups would be difficult to trace genetically. Historically attested events, such as invasions by Huns, Greeks, Kushans, Mughals and modern Europeans, may have had negligible genetic impact, and if they did it can be hard to trace it. For example, despite centuries of Greek rule in Northwest India, no trace of either the I-M170 or the E-M35 Y DNA paternal haplogroups associated with Greek and Macedonian males lines have been found. On the other hand, evidence of E-M35 and J-M12, another supposed Greek or Balkan marker, has been found in three Pakistani populations – the Burusho, Kalash and Pathan – who claim descent from Greek soldiers.

Despite the difficulties, there are claims that there is genetic evidence in support of the traditional hypothesis of Indo-Aryan migration. In the case of paternal-line Y-chromosome DNA, the Indo-Aryan migration is associated with the R1a haplogroup, especially the R1a1a subgroup, which clusters in Eastern Europe and the northern part of the Indian subcontinent, and nicely dovetails with the observed similarities between Lithuanian and Sanskrit, and more broadly, satem languages as a whole. The strongest such claims, though, are based upon studies of autosomal DNA, not only Y DNA. Several such studies have isolated two major components of ancestry amongst Indians, one being more common in the south, and amongst lower castes, and the other more common amongst upper caste Indians, Indians speaking Indo-European languages, and also Indians living in the northwest. This second component is shared with populations from the Middle East, Europe and Central Asia, and is thought to represent at least one ancient influx of people from the northwest. According to one researcher, there is "a major genetic contribution from Eurasia to North Indian upper castes" and a "greater genetic inflow among North Indian caste populations than is observed among South Indian caste and tribal populations."

Some reports emphasize the finding that tribal and caste populations in South Asia derive largely from a common maternal heritage of Pleistocene southern and western Asians, with only limited gene flow from external regions since the start of the Holocene. However, this finding alone does not rule out the possibility of an elitist and/or male-predominant Aryan invasion of the Indian subcontinent as in fact the patterns of historical conquest and migration are ultimately reflected in terms of sex-biased admixture, with the mitochondrial heritage being more stable and of more local origin and the Y-chromosomal heritage reflecting an external influence upon the population genetic structure, as can be seen in not only such regions as South Asia, but also in such regions as Northeastern Africa (Semitic Y chromosomes vs. Niger-Kordofanian mtDNA) and Latin America (Iberian Y chromosomes vs. Amerindian mtDNA). Furthermore, the majority of researchers have found significant evidence in support of Indo-European migration and even "elite dominance" of the northern half of the Indian subcontinent, usually pointing to three separate lines of evidence: the previously widespread distribution of Dravidian speakers, now confined to the south of India; the fact that upper caste Brahmins share a close genetic affinity with West Eurasians, whereas low caste Indians tend to have more in common with aboriginals or East Asians; and the comparatively recent introgression of West Eurasian DNA into the aboriginal population of the post-Neolithic Indo-Gangetic plain.

A more recent study has provided support for an influx of Indo-European migrants into the Indian subcontinent, but not necessarily an "invasion of any kind", further corroborating the findings of previous investigators, such as Bamshad et al. (2001), Wells et al. (2002) and Basu et al. (2003). For example, Reich et al. (2009) writes: "It is tempting to assume that the population ancestral to ANI and CEU spoke 'Proto-Indo-European', which has been reconstructed as ancestral to both Sanskrit and European languages, although we cannot be certain without a date for ANI–ASI mixture."

In a 2011 genetic study "confirmed the existence of a general principal component cline stretching from Europe to south India." They also concluded that the Indian populations are characterized by two major ancestry components, one of which is spread at comparable frequency and haplotype diversity in populations of South and West Asia and the Caucasus. The second component is more restricted to South Asia and accounts for more than 50% of the ancestry in Indian populations. Haplotype diversity associated with these South Asian ancestry components is significantly higher than that of the components dominating the West Eurasian ancestry palette. Modeling of the observed haplotype diversities suggests that both Indian ancestry components are older than the purported Indo-Aryan invasion 3,500 YBP However, rather than ruling out the possibility of Indo-Aryan migration, these findings suggest that the genetic affinities of both Indian ancestral components are the result of multiple gene flows over the course of thousands of years, with Indo-Aryan expansion into the subcontinent but one of many complex demographic episodes. The study authors write:

"Summing up, our results confirm both ancestry and temporal complexity shaping the still on-going process of genetic structuring of South Asian populations. This intricacy cannot be readily explained by the putative recent influx of Indo-Aryans alone but suggests multiple gene flows to the South Asian gene pool, both from the west and east, over a much longer time span."