Kolkata, Feb 1 (IANS): Using genetic data, Indian scientists have traced the emergence of a rigid caste system to about 1,600 years ago during the Gupta period when a lot of social transformation occurred. It, they claim, eventually left its mark on people's DNA.

Researchers at the National Institute of Biomedical Genomics (NIBMG) in West Bengal have estimated that the "transition in India from free intermarriage to endogamy took place about 70 generations ago (about 1600 years ago)". 

Endogamy is the practice of marrying within a specific ethnic group, class, or social group.

"During this time, the Gupta empire founded by Maharaja Sri Gupta, covered much of the Indian sub-continent, with Pataliputra (near Patna) as the capital of the empire. A lot of social transformation took place during the Gupta period," Partha P. Majumder, director, NIBMG, who authored the study with researchers Analabha Basu and Neeta Sarkar-Roy, told IANS.

Majumder explained that "notable among these was the enforcement of social strictures against marriage between castes, as enshrined in the Dharmasastra".

"This reveals that some social norms leave imprints on the DNA of people, which can be reconstructed by careful genetic studies," he said.

The researchers said they "systematically explored DNA variation in about 400 unrelated Indians belonging to 20 ethnic groups".

In addition to historical links, the study also highlights the complex ancestries.

"The ancestry of Indian population is not unipolar. Multiple ancestral lineages -- four in mainland India -- have provided their genetic inputs into the population groups of India," said Majumder.

These four ancestral stocks are: Ancestral North Indians (ANI), Ancestral South Indians (ASI), Austro-Asiatic and Tibeto-Burman (north-east India).

"These differences among groups need to be taken into account in understanding casualties of genetic diseases, responses to drugs and vaccines, etc.," added Majumder on the possible applications of the findings.

The findings were published recently in the Proceedings of the National Academy of Sciences journal.