Scientists studying a primitive tribe in India have uncovered a genetic signature previously unknown in Indian genomes that traces back to early Dravidian-speaking people from the Iranian plateau, roughly 4,400 years ago.
The findings have deepened the understanding of South Asia’s complex population history, adding a sixth ancestral source to India’s population genetic makeup — alongside South Asian hunter-gatherers, Neolithic Iranian farmers, Caspian steppe pastoralists, and Tibeto-Burman and Austroasiatic groups.
Multiple studies over the past two decades, seeking to explore the roots of modern populations, have shown that nearly all present-day Indians carry highly mixed ancestry, with varying proportions of genetic material from at least five ancestral populations.
Now, geneticists studying the Koragas, a primitive and vulnerable tribe native mainly to coastal Karnataka and Kerala, have identified a sixth ancestral component. They call it the proto-Dravidian ancestry, which appears to have emerged around the dawn of the Indus Valley civilisation.
“The Koragas were the key to this discovery — we found the proto-Dravidian ancestral component in them first,” Ranajit Das, a population geneticist and associate professor at Yenepoya University, Mangalore, told The Telegraph.
“But subsequent analyses show that it is present in other Indian populations as well.”
The study by Das and his collaborators at Mangalore University and the University of Bern, Switzerland, found that the proto-Dravidian ancestry makes up around 20 per cent of the modern-day Indian genome.
The proto-Dravidian ancestry is “distinct” from all other known ancestral components, the researchers said in a paper describing their findings published in the European Journal of Human Genetics on Friday. Mohammed Mustak, Jason Jeevan Sequeira and Swati Krishna in Mangalore and George van Driem in Berne were coauthors on the paper.
Earlier genetic studies had revealed that present-day Indians derive their ancestry from multiple populations that entered the subcontinent over tens of thousands of years.
The earliest were the South Asian hunter-gatherers, descendants of modern humans who had migrated out of Africa roughly 60,000 to 70,000 years ago.
Several Indian tribes, including those in the Andaman and Nicobar Islands, retain large portions of this ancient heritage.
The later waves included Neolithic farmers from the Iranian plateau, who arrived between 8,000 and 6,000 years ago and mixed with the South Asian hunter-gatherers.
They were followed 3,000 to 4,000 years ago by Caspian steppe pastoralists from the northwest. Additional contributions came from the Northeast, where Tibeto-Burman groups entered the region, and from Southeast Asia, which brought the Austroasiatic component.
The Koragas are among the oldest tribes in Karnataka’s Udupi and Dakshina Kannada districts and Kasargod in Kerala. Social scientists have documented their traditional occupations as basket-weaving and drum-beating.
Researchers believe that endogamy may explain the unusually high prevalence of multiple genetic diseases — congenital deafness, congenital retinal disease, congenital anaemia and several genetic neurological disorders — among members of the Koragas.
The discovery of the proto-Dravidian ancestral signature provides fresh evidence for the theory that the region between the Iranian plateau and the Indus Valley was a Dravidian heartland before the arrival of the Indo-European languages into thesubcontinent.
The Koragas speak a Dravidian language that, the researchers believe, is related to a set of north Dravidian languages. Brahui, spoken in Balochistan, is the only surviving north Dravidian language.
The results illustrate how studies on isolated population groups can show hidden ancestral signatures,” said Kumaraswamy Thangaraj, a scientist at the Centre for Cellular and Molecular Biology, Hyderabad, who was not associated with the study. Two decades ago, his CCMB team had shown that the Andaman and Nicobar tribes were descendants of the earliest modern humans to arrive in India from Africa — a finding that underscored the same principle