To ascertain about when the two ancestral populations of modern-day Indians — Ancestral North Indians, related to West Eurasians, and Ancestral South Indians, distantly related to Andaman Islanders — mixed, researchers from the US and India gathered genome-wide genotype data from 571 people belonging to 73 different ethno-linguistic groups from the Indian subcontinent. The researchers add that knowing the timing of mixture "has implications for understanding Indian history."
As they report in the American Journal of Human Genetics, they traced the ANI-ASI mixture date to between about 1,900 years to 4,200 years ago — the mixture was thorough as it even affected isolated groups. This time, the researchers note, was also a period of change for the subcontinent.
Indeed, the researchers write that their findings indicate that India underwent a demographic shift about 2,000 years ago as mixture between populations changed from being common to being rare. This, they note, coincides with historical texts that date evolution of the caste system to about that timeframe.
"These results show that India experienced a demographic transformation several thousand years ago, from a region in which major population mixture was common to one in which mixture even between closely related groups became rare because of a shift to endogamy," the investigators write.
The researchers caution, though, that their results do not resolve the timing of when West Eurasians migrated to India.
GenomeWeb Daily News has more on this study here.