Population admixture happened in India for 2,300 years

Genetic evidence provides sufficient proof that modern day Indian population that was derived from two major ancestral populations — ancestral north Indians (ANI) and ancestral south Indians (ASI) — does not have major genetic differences.

Till 4,200 years ago, the two populations grew independently and produced many more groups but there was no admixture between them. But during the long time period between 1,900 years and 4,200 years, the ANI-derived populations and ASI-derived populations mixed together to form the modern day population.

The ANI population is related to West Eurasians (people of Central Asia, the Middle East, the Caucasus and Europe); the ASI population is distinctly related to the indigenous Andaman Islanders.

In a paper published on Thursday, in The American Journal of Human Genetics , scientists from the Hyderabad-based Centre for Cellular and Molecular Biology (CCMB) and Harvard Medical School state that the admixture of the populations between the two respective ancestral groups was rather rampant for an extended period before endogamy became the norm.

The rampant period of admixture coincides with “increasing population density in the central and downstream portions of the Gangetic system, and deurbanisation of the Indus civilisation.”

Even though endogamy has been largely practised for the last 1,900 years, Indians as a whole do not have major genetic differences. “There is no distinct difference between groups across the Indian population,” said Dr. Kumarasamy Thangaraj from CCMB and one of the co-authors of the paper. “When you look at the recently evolved genetic markers, there is a difference, but on a larger scale, Indians do have a close affinity to one another.”

Such was the extent of admixture between groups that almost every group, including the isolated tribes like the Paliyar that live in Kodaikanal Hills and Bhil that are primarily located in Rajasthan, had some population mixing. But some populations like the Vysya from Andhra Pradesh have experienced “negligible gene flow from neighbouring groups in India for an estimated 3,000 years.”

But the endogamy in the respective admixtured populations ensured that no further gene mixture happened between groups for the last 1,900 years.

Published in The Hindu on August 9, 2013