From CK Nayak
NEW DELHI, March 23: In a landmark scientific reversal, a new whole-genome study has debunked the long-held theory that Northeast India was a “genetic barrier,” revealing that the Khasi and Ahom populations share a much deeper biological link with the Indo-Gangetic plains than with their immediate neighbours in Bengal or Arunachal Pradesh.
Scientists analysing whole-genome sequences from 1,120 individuals found that Indo-Aryan speakers in Assam carry 76 per cent of their ancestry from the Indian subcontinent and 24 per cent from East and Southeast Asia.
The findings indicate that groups such as the Ahoms and Khasis are genetically closer to populations in the central Indo-Gangetic plains than to geographically closer groups like the Nyishis.
The study, to be published in the American Journal of Human Biology, contradicts a 2004 report by the Max Planck Institute for Evolutionary Anthropology.
That earlier research, based on limited Y-chromosome and mitochondrial DNA, suggested the region was a barrier with little genetic mixing between North East Indians and the rest of the subcontinent.
“The new study, based on a more widespread number of markers on the genome, points to bidirectional gene flow,” said Chandana Basu, a research team member at Banaras Hindu University (BHU).
“Had the Northeast been a barrier, we would not expect to see such a large proportion of 76 per cent genetic ancestry in the Indo-Aryan speakers in Assam,” she told this newspaper.
Gyaneswer Chaubey, a professor of genetics at BHU who led the study, explained that while the 2004 research relied only on uniparental markers inherited from single parents, the new analysis used entire genomes to provide a more comprehensive ancestry profile.
“Our results compel us to rethink the role of Northeast India in human history,” said Arup Kumar Bandopadhyay, a professor of anthropology at the University of Calcutta. “It was not a wall, but a thriving melting pot.”
The analysis suggests the most significant genetic mixing in this corridor occurred between 55 and 61 generations ago, roughly between 196 AD and 376 AD, during the period of the Kushan Empire.
The researchers also noted that the Ahom people, traditionally known as descendants of migrants from Thailand, have seen their original Southeast Asian genetic signatures diminish over centuries due to extensive mixing with other South Asian populations. Similarly, the Khasi—an Austroasiatic group—and the Kusunda of Nepal share mixed South and Southeast Asian ancestry, further illustrating the region’s history as a transit point for ancient migrations.
