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Article Dans Une Revue Journal of Biosciences Année : 2006

Ancient Indian roots?

Denise Carvalho-Silva
  • Fonction : Auteur
Chris Tyler-Smith
  • Fonction : Auteur

Résumé

Ancient Indian roots? A study published in the February issue of The American Journal of Human Genetics (Sengupta et al 2006) provides the most thorough investigation to date of the genetic origins of the Indian people. It suggests that the origins are largely indigenous, dating back to the Palaeolithic period, and that the genetic influence of the Indo-European-speakers who established the caste system was small. How have they come to these conclusions? We humans seem to have an insatiable curiosity about our origins. Surprisingly, perhaps, we know quite a lot about the distant past: populations all over the world originated in Africa, with those outside Africa being largely if not entirely derived from the exodus of a small number of Africans around 50,000-60,000 years ago (Jobling et al 2004). We also know a lot about the last few centuries from historical records. But we know much less about the period in between. And a lot happened: the climate fluctuated enormously, including a glacial maximum ("ice age") around 20,000 years ago, while after 10,000 years ago the way of life of most people changed from obtaining their food by hunting and gathering to producing it by growing crops or herding animals. Historical records from the last few thousand years document migrations, wars and plagues. In the Indian subcontinent, the Palaeolithic archaeological record is sparse, but the Neolithic period left abundant traces in the Indus Valley from ~6,500 BC onwards, culminating in the Harappan Civilizatioñ 2,600-1,500 BC (Kenoyer 1998). Towards the end of this time, Indo-European speakers appeared and established the caste system that long dominated much of Indian society. The cultural importance of these transitions is undisputed, but did they involve large-scale replacement of the existing people by outsiders, bringing first Neolithic practices and perhaps Dravidian languages from the Fertile Crescent, and later Indo-European languages, iron and the horse from Central Asia? Or did the people already in India change their habits and languages? Studies of genes can now help to answer these questions, and the Y chromosome, which is passed from father to son, provides a particularly clear, although male-specific, perspective. The first such genetic investigations were interpreted as suggesting extensive movements into India (Quintana-Murci et al 2001), and, more specifically, a Central Asian origin for caste, but not tribal, groups (Bamshad et al 2001; Basu et al 2003; Cordaux et al 2004). Other studies, however, suggested that both tribal and caste populations could be derived largely from the earliest Palaeolithic settlers (Kivisild et al 2003). So do castes and tribes share a common origin? Where did the Dravidian language arise? Did the migration of Central Asians to India that had such a strong linguistic and social impact leave a genetic footprint as well? Sengupta et al (2006) have now reinvestigated these questions using a large new dataset. They analysed 728 Indian samples (17 tribes and 19 castes from different geographical regions and social/linguistic categories) with 71 slowly-evolving Y-chromosomal binary markers and 10 faster-evolvingY-microsatellites. For comparison, they also typed 176 Pakistani and 175 East Asian males with the same markers. They then used a phylogeographic approach that took into account both the geographical distribution of the main lineages and the variation within them to infer the direction and timing of their spread. They conclude that, while some lineages did move in from the outside, many of the major ones are likely to have arisen within India. Four lineages (J2a-M410, J2b-M12, O2a-M95 and O3e-M134) probably came from elsewhere, but five major ones (C5-M356, F*-M89, H-M69, L1-M76 and R2-M124) were likely to have originated within the subcontinent, and the origins of one common lineage (R1a1-M17) could not be determined. Furthermore, they calculated from the diversity within the lineages that most of them had been around for 9,000-20,000 years or so. The O lineages are largely restricted to a few tribal populations, and Sengupta et al. agree with previous suggestions that they probably came from East Asia; the J2 lineages may have come from West Asia. The indigenous lineages, however, are widespread and common in both tribal and caste populations, implying that tribes and castes have a shared origin, and that the genetic roots of most Indians must trace back to India some 9,000 years ago or more. Consequently, the Indo-European-speakers entering ~3,600 years ago can
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hal-03378456 , version 1 (14-10-2021)

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Tatiana Zerjal, Denise Carvalho-Silva, Chris Tyler-Smith. Ancient Indian roots?. Journal of Biosciences, 2006, 31 (1), pp.1-2. ⟨10.1007/BF02705228⟩. ⟨hal-03378456⟩
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