Genetics and archaeogenetics of South Asia
The geographic position of the Indian subcontinent makes its biodiversity important for the study of the early dispersal of anatomically modern humans across Asia.
[7] The West Eurasian ancestry, which is closely related to Mesolithic hunter-gatherers and Neolithic farmers who lived on the Iranian Plateau (who are also closely related to Caucasus hunter-gatherers), forms the major source of the South Asian genetic makeup, and combined with varying degrees of AASI ancestry, formed the Indus Periphery Cline around ~5400–3700 BCE, which constitutes the main ancestral heritage of most modern South Asian groups.
The Indus Periphery ancestry, around the 2nd millennium BCE, mixed with another West Eurasian wave, the incoming mostly male-mediated Yamnaya-Steppe component (archaeogenetically dubbed the Western Steppe Herders) to form the Ancestral North Indians (ANI), while at the same time it contributed to the formation of Ancestral South Indians (ASI) by admixture with hunter-gatherers having higher proportions of AASI-related ancestry.
[8] The Andamanese people are among the relatively most closely related modern populations to the AASI component and henceforth used as an (imperfect) proxy for it,[6][10] but others (Yelmen et al. 2019) note that both are deeply diverged from each other, and propose that the AASI type ancestry is closest to the non-West Eurasian part, termed S-component, extracted from the South Asian samples, especially those from the Irula tribe.
[22][6][11][15][16][26][24][28][29][30] According to an international research team led by palaeogeneticists of the Johannes Gutenberg University Mainz (JGU), the main ancestry component of South Asians is derived from a population related to Neolithic farmers from the eastern Fertile Crescent and Iran.
[33] Tätte et al. 2019 estimated that the Austroasiatic language speaking people admixed with Indian population about 2000–3800 years ago, which may suggest arrival of Southeast Asian genetic component in the area.
The major South Asian Y-chromosome DNA haplogroups are H, J2, L, R1a1, R2, which are commonly found among other West Eurasian populations, such as Middle Easterners or Europeans.
[43] In South Asia, R1a1 has been observed often with high frequency in a number of demographic groups,[39][38][73] as well as with highest STR diversity which lead some to see it as the locus of origin.
[75] The distribution of M417-subclades R1-Z282 (including R1-Z280)[76] in Central and Eastern Europe and R1-Z93 in Asia[75][76] suggests that R1a1a diversified within the Eurasian Steppes or the Middle East and Caucasus region.
[85] It is found at 86.6% among Tamangs of Nepal, with similarly high frequencies, 75% to 85%, among the northeastern Indian Tibeto-Burman groups, including Adi, Naga, Apatani, Nyishi, Kachari and Rabha.
[80] The Indian Genome Variation Consortium, divides the population of South Asia into four ethnolinguistic (not genetic) groups: Indo-European, Dravidian, Tibeto-Burman and Austro-Asiatic.
[5]: 04 Most of the studies based on mtDNA variation have reported genetic unity of South Asian populations across language, caste and tribal groups.
[2] According to Kivisild et al. (1999), "Minor overlaps with lineages described in other Eurasian populations clearly demonstrate that recent immigrations have had very little impact on the innate structure of the maternal gene pool of South Asians.
While Kivisild et al.[43] proposes an ancient and shared genetic heritage of male lineages in South Asia, Bamshad et al. (2001) suggests an affinity between South Asian male lineages and modern west Eurasians proportionate to upper-caste rank and places upper-caste populations of southern Indian states closer to East Europeans.
Closest-neighbor analysis done by Mondal et al. in 2017 concluded that Indian Y-lineages are close to southern European populations and the time of divergence between the two at least in part predated Bronze-Age Steppe migration into India:[79]These results suggest that the European-related ancestry in Indian populations might be much older and more complex than anticipated, and might originate from the first wave of agriculturists or even earlierResults of studies based upon autosomal DNA variation have also been varied.
[94] Gallego Romero notes that Indians who are lactose-tolerant show a genetic pattern regarding this tolerance which is "characteristic of the common European mutation".
The study concluded that "almost all groups speaking Indo-European or Dravidian languages lie along a gradient of varying relatedness to West-Eurasians in PCA (referred to as "Indian cline")".
[96] A 2013 study by Chaubey using the single-nucleotide polymorphism (SNP), shows that the genome of Andamanese people (Onge) is closer to those of other Oceanic Negrito groups than to that of South Asians.
[70] The geneticist PP Majumder (2010) has recently argued that the findings of Reich et al. (2009) are in remarkable concordance with previous research using mtDNA and Y-DNA:[98] Central Asian populations are supposed to have been major contributors to the Indian gene pool, particularly to the northern Indian gene pool, and the migrants had supposedly moved into India through what is now Afghanistan and Pakistan.
Consistent with the above findings, a recent study using over 500,000 biallelic autosomal markers has found a north to south gradient of genetic proximity of Indian populations to western Eurasians.
This feature is likely related to the proportions of ancestry derived from the western Eurasian gene pool, which, as this study has shown, is greater in populations inhabiting northern India than those inhabiting southern India.Chaubey et al. 2015 detected a distinctive East Asian ancestral component, mainly restricted to specific populations in the foothills of Himalaya and northeastern part of India.
Highest frequency of the component is observed among the Tibeto-Burmese speaking groups of northeast India and was also detected in Andamanese populations at 32%, with substantial presence also among Austroasiatic speakers.
It is found to be largely absent in Indo-European and Dravidian speakers, except in some specific ethnic groups living in the Himalayan foothills and central-south India.
[97] Lazaridis et al. (2016) notes "The demographic impact of steppe related populations on South Asia was substantial, as the Mala, a south Indian Dalit population with minimal ANI (Ancestral North Indian) along the 'Indian Cline' of such ancestry is inferred to have ~ 18% steppe-related ancestry, while the Kalash of Pakistan are inferred to have ~ 50%, similar to present-day northern Europeans."
[23]: 15 According to Narasimhan et al., this mixed population, which probably was native to the Indus Valley Civilisation, "contributed in large proportions to both the ANI and ASI", which took shape during the 2nd millennium BCE.
[23]: 15 The authors propose that the AASI indigenous hunter-gatherers represent a divergent branch that split off around the same time that East Asian, Onge (Andamanese) and Australian Aboriginal ancestors separated from each other.
[7] Two genetic studies (Narasimhan et al. 2019 & Shinde et al. 2019) analysing remains from the Indus Valley civilisation (of parts of Bronze Age Northwest India and East Pakistan), found them to have a mixture of ancestry, both from native South Asian hunter-gatherers sharing a distant root with the Andamanese, and from a group related to Iranian farmers.
The authors found that the respective amounts of those ancestries varied significantly between individuals, and concluded that more samples are needed to get the full picture of Indian population history.
A 2011 study published in the American Journal of Human Genetics[28] indicates that Indian ancestral components are the result of a more complex demographic history than was previously thought.
However, if one were to rule out the possibility of a large-scale 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.
