New Delhi, May 12: Two tribes in the Andamans may be the direct descendants of the earliest modern humans who trudged out of Africa over 70,000 years ago, scientists will announce tomorrow.
A study by Indian scientists has revealed the African origins of the Great Andamanese and the Onge tribes and may force researchers to revise current theories about prehistoric human migration.
The Great Andamanese and the Onge are both Negrito tribes and scientists have suspected that their roots lie in Africa. But previous studies had hinted that they are closer to Asians than to Africans.
Now, scientists at the Centre for Cellular and Molecular Biology (CCMB) in Hyderabad have reported that the two tribes have remained isolated on the islands for tens of thousands of years.
“Ancient genetic mutations in these tribes make them closer to Africans than any other populations in the world,” said Dr Lalji Singh, CCMB director.
Scientists believe that all people alive today are descendants of modern humans who migrated out of east Africa about 70,000 years ago to replace ‘early humans’ elsewhere.
The reigning theory is that modern humans first moved north along the Nile, across the Sinai peninsula, into central Asia before heading east towards India.
“But our findings suggest that they also traced a coastal route along east Africa and the Arabian peninsula into south Asia,” said Kumarasami Thangaraj, a senior scientist at the CCMB.
Thangaraj studied genetic mutations to construct a human family tree spanning 70,000 years with the migrants from Africa at the top, and their descendants branching off into populations across Asia. Mutations in genetic material called mitochondrial DNA, which is inherited only from mothers, can help scientists determine the proximity between different populations.
The CCMB analysed complete mitochondrial DNA sequences from five Great Andamanese, five Onges and five Nicobarese ' and compared them with mutations in other populations.
The analysis revealed that the genetic branches M31 and M32 in the Great Andamanese and the Onges emerged directly from a “founder population” about 65,000 years ago. “And they have remained trapped there since then,” said Singh.
An independent investigation by British and Malaysian scientists has corroborated the CCMB findings. Both studies appear in Friday’s issue of the US journal Science.
Glasgow University’s Vincent Macaulay and his colleagues found that an aboriginal tribe named Orang Asli in Malaysia had branched off 60,000 years ago. Macaulay’s team also calculated that the 12,000-km trek along the coast from India to Australia was made at speeds between 0.7 km to 4 km per year.
Thangaraj said the move from coastal India to the islands may have been made on primitive boats fashioned out of tree trunks. The CCMB scientists have observed that even today, the Onges build boats from trees.
“We hope these findings inspire archaeological exploration between the Arabian peninsula and Southeast Asia in search of the remains of the first Eurasians,” Peter Forster, an anthropologist from Cambridge University, said.
The CCMB study has also thrown up a surprise.
Genetic analysis of 6,500 people on mainland India showed that no one had the M31 or M32 mutations. “If the tribes had moved from India, we would have expected to find the mutations in some people on the mainland, too,” said Thangaraj.