Among the world's oldest indigenous populations, too
indian scientists have uncovered a missing link in the prehistoric human migration jigsaw puzzle by revealing that two reclusive tribes in the Andaman and Nicobar Islands are among the world's oldest surviving indigenous groups.
The researchers from the Centre for Cellular and Molecular Biology (ccmb), in Hyderabad, have gathered enough genetic clues to prove that the Great Andamanese and the Onge, whose numbers are shrinking day by day, are the direct descendants of modern humans who evolved in east Africa some 150,000 years ago (Science, May 13, Vol 308, No 5724). "Ancient genetic mutations found in these groups make them closer to Africans than any other populations that survive today," Lalji Singh, ccmb director and a co-author of the study, told Down To Earth.
The study looked at the mitochondrial dna (mdna), which is ideal to trace maternal lineage. Led by K Thangaraj, the scientists analysed m dna of three tribes living in the Andaman and Nicobar Islands -- the Great Andamanese, the Onges and the Nicobarese -- and compared them with mutations in 6,500 mdna samples of different populations on mainland India. Explaining the method, the scientists said any population slowly accumulates mutations in certain parts of m dna. For instance, after a population splits, the people going east will gain a set of mutations different from those heading west. The mutation patterns help scientists reconstruct family trees and even work out rough dates of each branching off. While the Great Andamanese and the Onges are Negritos (similar to African pygmies), the Nicobarese are Mongloid (similar to Chinese and Malays).
The study revealed both the Great Andamanese and the Onges carry certain genetic mutations not reported elsewhere. "Our data indicate that two ancient maternal lineages, m 31 and m 32 in the Onges and the Great Andamanese respectively, have evolved in the Andaman Islands independently from South and Southeast Asian populations (that are Mongloid)," the team said.
It also conclusively proved that Nicobarese tribals have genetic resemblance to populations in Southeast Asia and probably arrived in the islands some 18,000 years ago. On the contrary, the Andaman tribes reached there much earlier -- about 65,000 years back. The modern humans are believed to have started moving out of Africa about 70,000 years ago.
The study has put a question mark on prevailing understanding on probable routes taken by the first Eurasians out of Africa. As per the reigning theory, they moved north along the Nile river, across the Sinai Peninsula, into central Asia before travelling east towards India. "But our findings suggest they also traced a coastal route along east Africa and the Arabian Peninsula into South Asia," said Thangaraj. If this is true, they would likely have traced a route through Pakistan and west coast of India to the Andamans.
According to Peter Forster and Shuichi Matsumura of Cambridge University, who wrote an accompanying commentary on the ccmb study, this inference can partly explain why distant Australia was settled thousands of years before Europe, which is close to Africa. It is believed that Neanderthals were replaced in Europe only 30,000-40,000 years ago, whereas southern Australia was inhabited 46,000 years ago and northern Australia and Southeast Asia even earlier.
But a convincing proof is yet to be found. Singh said ccmb plans to look for genetic clues among tribes living in the western parts of the country to substantiate their hypothesis.
The same issue of Science carries a study on a primitive tribe called Orang Asli in Malaysia by Vincent Macaulay and others at Glasgow University in the uk . Their analysis, also based on m dna, revealed these aborigines had branched off 60,000 years ago. Interestingly, the Glasgow team also calculated the likely speed of the prehistoric migration. Comparing the possible dates of arrival at their respective locations by Indian and Australian tribes, they concluded the first Eurasian covered the 12,000-kilometre trek along the Indian Ocean coastline at a speed of 0.7-4 km per year.
Says P P Majumder, head of Human Genetics Unit at the Indian Statistical Institute in Kolkata, "If modern humans had indeed used the southern exit route as they moved to populate Australia, then the Andaman Islands and Southeast Asia could have lain on their trail."
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