Genetic evidence reveals origin of India's caste system

Washington, Aug. 9 : A recent study has revealed that the present caste system persisting in the Indian population is the result of a recent population mixture among divergent demographic groups.

Scientists from Harvard Medical School and the CSIR-Centre for Cellular and Molecular Biology (CCMB) in Hyderabad have provided evidence that modern-day India is an admixture of various groups.

India has transformed from a country where mixture between different populations was rampant to one where endogamy, marrying within the local community, became the norm.

David Reich, professor of genetics at Harvard Medical School, said that the caste system in India has been around for a long time, but it was not there since its inception.

Reich's 2009 study, based on an analysis of 25 different Indian population groups, found out that how all populations in India showed evidence of a genetic mixture of two ancestral groups, Ancestral North Indians , related to Central Asians, Middle Easterners, Caucasians, and Europeans; and Ancestral South Indians (ASI), primarily from the subcontinent.

Originally when the ANI and ASI populations mixed, the chromosomal segments would have been extremely long.

However, after mixture these segments would have broken up at one or two places per chromosome, per generation, recombining the maternal and paternal genetic material that occurs during the production of egg and sperm.

The authors were thus able to obtain precise estimates of the age of population mixture by measuring the lengths of the segments of ANI and ASI ancestry in Indian genomes.

They concluded that major ANI-ASI mixture occurred about 1,900-4,200 years ago.

The most remarkable aspect of the ANI-ASI mixture is how pervasive it was because it affected not just traditionally upper-caste groups, but also traditionally lower-caste and isolated tribal groups, all of whom seem to be united in their history of mixture in the past few thousand years.

Lalji Singh, former researcher in the CSIR- CCMB, said: "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 happened."

The researchers also observed that once established, the caste system became genetically effective, and mixture across groups became very rare.

Kumarasamy Thangaraj, of the CSIR-CCMB, said: "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."

--ANI (Posted on 10-08-2013)

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