From a structuralist perspective, there is probably no queerer theory than that of an invasion of India by Aryans or Indo-Aryans in the second millennium BC. In its nineteenth-century version, it posited a subcontinent peopled by undefined autochthons (or, the earliest known inhabitants) was suddenly submerged, in its northern parts at least, by a wave or several waves of Aryan invaders on the warpath. This view, with numerous variants, generally held until the 1960s, when US and Indian archaeologists began pointing out that such a phenomenon could hardly have taken place without leaving some traces in the archaeological record, which not only stubbornly refused to yield such evidence at site after site, but increasingly stressed continuity rather than disruption. The Hollywood-style Aryan Long March soon mutated into a leisurely stroll into India by bands of peaceful migrants in search of greener pastures.
But one central question remained: whether an invasion or a migration—and leaving aside here its assumed linguistic and cultural impact—not radically alter India’s demographic landscape? The answer, clearly, could only be a matter of proportion. Either the newcomers arrived in large numbers, or they just “trickled in,” yet somehow managed to trigger off a chain reaction, perhaps like the proverbial butterfly setting off a distant hurricane, in the spirit of chaos theory. Most proponents of the invasionist or migrationist scenario continued to prefer the former view, insisting that “the Indo-Aryan immigrants seem to have been numerous and strong enough to continue and disseminate much of their culture.” Those who, of late, have tried to trim down the numbers of Aryan tribes to the barest minimum have been compelled to do so by two formidable obstacles: the archaeological stumbling block and the growing objections raised from the 1990s by geneticists studying Indian populations, whose voice uncannily sounded like that of archaeologists.
Initially, a few genetic studies appeared to confirm the arrival of a new population from Central Asia, matching the linguistic division between Indo-Aryan and Dravidian speakers. But they were victims of the usual circularity, a priori accepting the invasionist scenario, then matching a limited strand of genetic evidence to it. As the samples studied grew larger and more diverse, and as the tools of the young science became more refined, startling new results have emerged in the last few years.
Basics of Genetic Studies
Before we briefly review those relevant to the invasion debate, let us refresh our memories. To study the ancestry of human populations, geneticists look at two types of DNA: the Y-DNA, contained in the Y-chromosome of the cell’s nucleus and transmitted from father to son; and the mtDNA or mitochondrial DNA, found in the cell’s mitochondria and transmitted by the mother alone. DNA molecules undergo slight alterations or “mutations” in the course of time, which act as specific genetic markers: thus two persons sharing an mtDNA with the same mutation must share a common ancestor somewhere in the maternal line. Those genetic markers are then grouped in categories called “haplotypes,” which are in turn organised in “haplogroups,” each of which genetically identifies a particular ethnic group. Within such a framework, “genetic distances” between several populations can be assessed, but it is important to remember that haplogroups have nothing to do with the old racial classifications, which have no scientific validity whatsoever: it is impossible to genetically define an “Aryan” race or a Dravidian one.
In India’s case, genetic studies are specially complex, not only because of entrenched prejudices on racial or linguistic divisions (and the consequent temptation to equate linguistic groups with ethnic ones), but because of the high genetic diversity of the subcontinent, next only to that of Africa. Yet a few important by-products have emerged from a dozen studies conducted by teams of biologists in Western and Indian Universities:
- One study concluded that “high castes share more than 80 percent of their maternal lineages with the lower castes and tribals” and some biologists now speak of a “caste-tribe continuum.” Another study found that “the Indian mtDNA tree in general is not subdivided according to linguistic (Indo-European, Dravidian) or caste affiliations.” In other words, geography, not caste or language, tends to define Indian genetic groups, an important conclusion that runs counter to the invasionist scenario.
- It is worth stressing that “caste populations of ‘north’ and ‘south’ India are not particularly more closely related to each other than they are to the tribal groups.” For instance, “Southern castes and tribals are very similar to each other in their Y-chromosomal haplogroup compositions.” Again, a 2009 study found Brahmins and the caste system to be of “autochthonous origin.”
- Also, studies found linguistic families to be “all much younger” than genetic lineages, and it would be “highly speculative,” at this stage to assume that a “linguistically defined group in India should be considered more ‘autochthonous’ than any other.” This knocks the bottom out of the notion of adivasi propounded by the now discredited nineteenth-century racial anthropology—and still in use in India today despite its lack of scientific validity.
- Even with India’s genetic diversity, its populations, whatever their linguistic areas or castes, share a “fundamental genomic unity” traceable to the original peopling of India by migrants from Africa some 50,000 years ago.
- Quite a few Indian populations (including tribal ones and Dravidian speakers) exhibit some connection with Central Asian populations; however, this connection turns out to date back to the migration from Africa, not to the second millennium BC.
- Indeed the “deep, common ancestry between the two regions” (India and Central Asia) is more readily explained by northward migrations from India’s Northwest some 40,000 years ago.
The conclusion is inescapable: just as the putative Aryan invasion/migration left no trace in Indian literature, in the archaeological and the anthropological record, it is invisible at the genetic level. If biologists had never been told anything about such a migration, they would be incapable of inferring it from the DNA of Indians, whether tribes or upper castes, from the South or North.
We can now view almost all Indian ethnic groups (except for known recent immigrants, in the North-East for instance) as essentially indigenous. Of course we are all ultimately descendants from Africans, but a period of at least 40,000 years should suffice to earn the label “indigenous.” Moreover, we may jocularly suggest that all non-African populations are basically descendants from Indians. As one study put it, “there are now enough reasons not only to question a ‘recent Indo-Aryan invasion’ into India some 4000 years ago, but alternatively to consider India as a part of the common gene pool ancestral to the diversity of human maternal lineages in Europe.
We must patiently await more advanced studies with larger samples and finer analytic methods. But the genetic wind seems to have turned for good, just as the archaeological wind did some forty years ago. If Indo-Aryans ever migrated to India, they only “trickled in.” But how could such small numbers revolutionise India’s cultural and linguistic landscape? That is another of the many paradoxes on which the invasionist scenario rests, ever more shakily.
 Ram Sharan Sharma, Advent of the Aryans in India (New Delhi: Manohar, 2001), p. 52.
 See for instance Michael Witzel, “Autochthonous Aryans? The Evidence from Old Indian and Iranian Texts,” Electronic Journal of Vedic Studies, vol. 7 (2001), No. 3 (25 May), § 8.
 For instance, Michael Bamshad et al., “Genetic Evidence on the Origins of Indian Caste Populations” in Genome Research, 2001, vol. 11, pp. 994-1004.
 I presented a more detailed study in my paper “Genetics and the Aryan Debate” published in Puratattva, No. 36, 2005-06, pp. 146-154 and available online:
 Among the papers referred to here (most of which are available online), the most significant ones are:
- T. Kivisild et al., “Deep common ancestry of Indian and western-Eurasian mitochondrial DNA lineages” in Current Biology, 18 November 1999, 9(22):1331-4.
- Susanta Roychoudhury et al., “Fundamental genomic unity of ethnic India is revealed by analysis of mitochondrial DNA,” Current Science, vol. 79, No. 9, 10 November 2000, pp. 1182-1192.
- Toomas Kivisild et al., “An Indian Ancestry: a Key for Understanding Human Diversity in Europe and Beyond”, ch. 31 of Archaeogenetics: DNA and the population prehistory of Europe, ed. Colin Renfrew & Katie Boyle (Cambridge: McDonald Institute for Archaeological Research, 2000), pp. 267-275.
- T. Kivisild et al., “The Genetic Heritage of the Earliest Settlers Persists Both in Indian Tribal and Caste Populations,” American Journal of Human Genetics 72(2):313-32, 2003.
- Sanghamitra Sengupta et al., “Polarity and Temporality of High-Resolution Y-Chromosome Distributions in India Identify Both Indigenous and Exogenous Expansions and Reveal Minor Genetic Influence of Central Asian Pastoralists,” American Journal of Human Genetics, February 2006; 78(2):202-21.
- Sanghamitra Sahoo et al., “A prehistory of Indian Y chromosomes: Evaluating demic diffusion scenarios,” Proceedings of the National Academy of Sciences, 24 January 2006, vol. 103, No. 4, pp. 843–848.
- Gyaneshwer Chaubey, “Peopling of South Asia: investigating the caste–tribe continuum in India,” BioEssays 2007, 29:91-100.
- Swarkar Sharma et al., “The Indian origin of paternal haplogroup R1a1* substantiates the autochthonous origin of Brahmins and the caste system,” Journal of Human Genetics (2009) 54, 47-55.