A nationwide consortium of scientists has traced the ancestry of present-day Nicobarese islanders to Austroasiatic populations in Southeast Asia and estimated their arrival on the islands to have taken place about 5,000 years ago.

The researchers have found through a genome study that the Nicobarese have the most Austroasiatic genetic markers among modern populations and are closest to the Htin Mal, a Mon-Khmer-speaking group from present-day Laos.

Anthropologists had first suggested in the late 19th century that the Nicobarese had Southeast Asian roots, noting their linguistic ties to Austroasiatic speakers. But a more precise ancestry and the timing of their arrival on the islands had been under debate.

Now, Gyaneshwer Chaubey, a population geneticist at Banaras Hindu University, and his collaborators have analysed the genomes of five Nicobarese individuals alongside over 1,500 genomes from members of other Asian population groups to explore their ancestry.

Their study, published on Friday in the European Journal of Human Genetics, has found that the Nicobarese have retained 76 per cent of the genetic markers associated with ancestral Austroasiatic populations and the Htin Mal have retained 69 per cent.

"The Nicobarese and the Htin Mal are the closest cousins among the many populations in Southeast Asia that have ancestral Austroasiatic roots," Chaubey said.

"But because the Nicobarese have remained isolated on the islands without contact with other populations, they retain the highest proportion of the ancestral markers."

Scientists had known for decades that the Mundas — an Austroasiatic-speaking group found in eastern and central India — too had Southeast Asian roots.

Linguistics researchers Felix Rao from the University of Cologne and Paul Sidwell from Sydney University had said in a 2019 paper that the available archaeological and genetic evidence supported the hypothesis that a small founder population of Austroasiatic speakers had arrived in Odisha between 3,500 and 4,000 years ago.

The new study has found that the Munda have only 28 per cent of the genetic markers associated with ancestral Austroasiatic groups. The Mundas’ Austroasiatic ancestry has been diluted through admixture with other populations on the subcontinent over the centuries, said Kumarasamy Thangaraj, a scientist and study team member from the Centre for Cellular and Molecular Biology, Hyderabad.

Earlier genetic studies had suggested that the ancestors of the Nicobarese may have arrived on the islands as early as 11,000 years ago. “But our data shows that the migration took place much later, around 5,000 years ago,” Thangaraj said.

The Nicobar archipelago in the eastern Bay of Bengal has seven large islands — including Car Nicobar and Great Nicobar — and dozens of smaller islands, all marked by flat topography, coral reefs and sandy beaches. Government authorities have estimated the population of Nicobarese to be around 27,000.

Scientists at the CCMB had through pioneering genetic studies nearly two decades ago shown that the Andamanese and Onges on the Andaman islands are the direct descendants of the earliest modern humans who trudged out of Africa 70,000 years ago.

While both the Mundas and the Nicobarese have Austroasiatic ancestry, the study has shown different migratory histories. “We find that the migration of the Mundas’ ancestors was dominated by men who assimilated with women in the subcontinent,” Chaubey said.