Northeast India, particularly Assam, served as a corridor for ancient people moving between the Indian subcontinent and eastern and Southeast Asia, a study has found, challenging a long-held view that the region was a barrier to gene flow.
Scientists, who analysed whole-genome sequences from 1,120 individuals across India and Asia, have found that Indo-Aryans in Assam carry 76 per cent ancestry from the Indian subcontinent and 24 per cent from East and Southeast Asia.
The researchers also found that this Assamese population group is genetically closer to populations in the central Indo-Gangetic plains than to geographically nearer groups such as Bengalis or Nyishis. The study is to be published in the American Journal of Human Biology.
“Our results compel us to rethink the role of northeast India in human history,” Arup Kumar Bandopadhyay, professor of anthropology at the University of Calcutta and study team member, told The Telegraph. “It was not a wall, but a thriving melting pot.”
In 2004, scientists at the Max Planck Institute for Evolutionary Anthropology in Germany found little genetic mixing between Northeast Indian populations and other Indians, based on Y-chromosome and mitochondrial DNA, and a closer affinity with East Asian populations.
Mark Stoneking and his colleagues at the Max Planck Institute had proposed that the region acted more as a barrier than a corridor for human migrations between the
Indian subcontinent and East and Southeast Asia.
“But our evidence based on a more widespread number of markers on the genome now points to bidirectional gene flow,” said Chandana Basu, a research team member at the 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.
“Our study illustrates how high-resolution genetic data can profoundly reshape the scientific narrative of ancient human migration patterns,” said Gyaneswer Chaubey, a professor of genetics at the BHU who led the study.
The earlier 2004 study had relied only on Y-chromosomes inherited from fathers and mitochondrial DNA inherited from mothers. The new study analysed entire genomes, offering a more comprehensive picture of ancestry, Chaubey said.
The analysis also suggests that the most significant admixture events in the Northeast corridor occurred between 55 and 61 generations ago, roughly corresponding to 196 AD to 376 AD, during the Kushan Empire.
Two years ago, Chaubey and his colleagues had shown that Assam’s Ahom people, long known to be descendants of migrants from Thailand, have nearly lost their ancestral southeast Asian genetic signatures through excessive mixing with populations from elsewhere in the Indian subcontinent.
That study had found that the Ahoms’ closest-related populations are Khasi, Kusunda, and Nyishi. The Khasi are an Australoasiatic population group with south Asian and southeast Asian genetic ancestry; the Kusunda have the same genetic ancestry as the Khasi but are linguistically linked to Nepal, while the Nyishi is an ethnic Tibeto-Burman group with south Asian ancestry.