DNA polymorphism provides new insights into the origin and history of human populations, Lalji Singh, Bhatnagar Fellow in CSIR and the Centre for Cellular and Molecular Biology, Hyderabad, has said.
Delivering a lecture on “Mystery of our origins” during an open house and exhibition organised at the Yogi Vemana University on International Science Day, Dr. Singh said modern humans arose about 1.50-lakh years ago, possibly in East Africa and colonised the Kalahari desert and Central African rain forest in Africa. Oazeh fossils and a skull dating back to 90,000 years found in Israel indicated that early humans ventured out of Africa briefly. Immigration of people can be tracked based on errors (mutations) during copying of DNA and the mutations slowly accumulate in certain regions of the DNA, he stated.
Whenever a population splits and there is no intermingling of the splits, different populations accumulate different sets of mutations depending on the geographical location and the environment around them, he said. Based on them, family trees of different lineages and shared genealogy of humankind can be constructed and dates to the branch points approximately assigned.
Mitochondrial DNA (mtDNA) is a genetic element passed down only through women, while the DNA of Y-chromosome is passed on to next generations only through men, Dr. Singh said. Based on the mutations, various sections known as ‘haplogroups' have been identified and several of those groups were specific to African populations (L2 and L3 mtDNA signature) about 85,000 years ago, which now represent more than two-thirds of female lineages throughout most of Africa.
The origin of the Andaman “Negrito” and Nicobar “Mongoloid” populations stimulated a wide range of speculation, but their origins were still a mystery, he remarked. He wondered if the islanders could serve as a window to the past showing how humans were hundred thousand years ago when the first modern humans left Africa. To address these questions, the complete mitochondrial DNA (16,569 pairs) of five Onge, five Great Andamanese and five Nicobarese were analysed, he said.
The Onge and Great Andamanese are unique in their origin and novel mutations found in mtDNA of the tribes helped into two unique branches in the human evolutionary tree, he said.
Dr. Singh, who established the Centre for DNA Fingerprinting and Diagnostics (CDFD), Laboratory for Conservation of Endangered Species (LaCONES) and Clinical Research Facility at Hyderabad, said their study suggested that two ancient maternal lineages had evolved in Andaman Islands in genetic isolation independently, possibly due to initial penetration of the northern coastal areas of the Indian Ocean by modern humans in their out-of-Africa migration about 50,000 to 70,000 years ago.
They provide an insight into the past and hence need to be preserved and support the existing out-of-Africa hypothesis. There was only a single dispersal from Africa, most likely through southern coastal route, through India and onward into South-East India and Australia, Dr. Singh observed. Similar analysis of Nicobarese revealed that they belonged to two lineages (B and F), commonly found in China, Malaysia, Myanmar and Thailand, suggesting their recent arrival from the east during the past 18,000 years, he said.