Girish Menon, The Hindu, Nov 21, 2006
|Holds key to the origin of humans, say scientists|
IN FOCUS: Tribals of Andaman and Nicobar
Thiruvananthapuram: Scientists at the Centre for Cellular and Molecular Biology, Hyderabad, are analysing DNA samples of Andaman and Nicobar tribes to gain insight into the history and migration of human population.
The Centre has analysed the complete mitochondrial DNA (mtDNA) of five Onge, five Great Andamanese and Five Nicobarese to understand how humans were hundred thousand years ago when the first modern humans left Africa, Dr. Lalji Singh, director of the Centre, said here on Saturday.
Delivering the M.R. Das Memorial Lecture 2006, under the auspices of the Rajiv Gandhi Centre for Biotechnology here on `Mystery of Our Origins,' Dr. Lalji Singh said the analysis of mtDNA, a genetic element passed down through women, would give us a clear understanding of our origin.
The origin of Andaman `Negrito' and Nicobar `Mongoloid' populations has led to a wide range of speculation. "No one knows where they came from and how long they have been there.
"We have used the mtDNA sequence to trace the emigration of the Andamanese. Comparison of the complete mtDNA sequences of the Onge and the Great Andamanese with the mtDNA sequences of population known so far across the world has revealed that the mtDNA sequences of these two tribes do not match with any population in the world, including the 6,500 samples covering the entire Indian subcontinent. Therefore, these two populations are unique in their origins. Novel mutations found by us in the mtDNA of Onge and Great Andamanese have helped in placing them in two unique branches (defined as M31 and M32) in the human evolutionary tree," Dr. Lalji Singh said.
The Centre's study has suggested that two ancient maternal lineages have evolved in the Andaman Islands in genetic isolation independently. This may be due to the initial penetration of the northern coastal areas of the Indian Ocean by modern humans in the migration out of Africa about 50,000 to 70,000 years ago. "They are windows to look into the past and hence need to be preserved as it supports the `out of Africa' hypothesis," he said. There was only a single dispersal from Africa most likely via the southern coastal route. Similar analysis of Nicobarese revealed that they belonged to two lineages (B and F) that are commonly found in China, Malaysia, Myanmar and Thailand, suggesting their recent arrival from the east during the last 18,000 years.
Dr. Lalji Singh said modern humans arose about 1,50,000 years ago, possibly in East Africa and colonised the Kalahari Desert and the Central Africa rain forest within Africa.