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‘Few thousand years ago, Indian population structure was vastly different from today’

M. Somasekhar Hyderabad | Updated on August 12, 2013 Published on August 12, 2013




In the beginning there were the c. Then came a phase of random mix of populations. After that came the caste system, with its typical marriages within communities, and finally the present, evolving modern India with its characteristic diversity in population groups.

This journey of India where mixture between different populations was rampant (1,900-4,200 years) to one where endogamy (marrying within local community), a key attribute of the caste system, emerged as the norm, has been established using genetic studies by an Indo-US scientific study.

But once established, the caste system became genetically effective, the researchers observed in the study. Inter-caste marriages became very rare.

An important consequence of these results is that the high incidence of genetic and population-specific diseases that is characteristic of present-day India is likely to have increased only in the last few thousand years when groups in India started following strict endogamous marriage says Kumarasamy Thangaraj of the Centre for Cellular and Molecular Biology (CCMB), Hyderabad.

He told Business Line that in addition to insights into congenital diseases, questions like why certain communities find it difficult to tolerate anaesthesia to some who suffer rare physical problems like stunted growth, can now be focussed in further genetic studies.

“Only a few thousand years ago, the Indian population structure was vastly different from today,” says David Reich, professor of genetics at Harvard Medical School. “The caste system has been around for a long time, but not forever.”

Genetic evidence suggests that most groups in India descended from two divergent ancestral populations. The Ancestral North Indians (ANI) related to West Eurasians (people of Central Asia, Middle East, Caucasus and Europe) and the Ancestral South Indians (ASI), related to indigenous Andaman Islanders.

By measuring the lengths of the chromosome segments of ANI and ASI ancestry in Indian genomes, the researchers were able to obtain precise estimates of the age of population mixture, which they infer varied about 1,900 to 4,200 years, depending on the population analyzed.

“We have studied about one million genetic markers in nearly 100 Indian population groups, predominantly represented by Dravidian and Indo-European speakers” said Thangaraj.

“The fact that every population in India evolved from randomly mixed populations suggests that social classifications like the caste system are not likely to have existed in the same way before the mixture,” said Lalji Singh, currently, Vice-Chancellor of Banaras Hindu University, in Varanasi, India, and formerly of the CCMB.

In terms of dating of the mixing of populations, “Groups in the north tend to have more recent dates and southern groups have older dates,” said Priya Moorjani, a researcher from the Harvard Medical School. “This is likely because the northern groups have multiple mixtures.”

somasekhar.m@thehindu.co.in

Published on August 12, 2013
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