Article Excerpt:Research published in the American Journal of Human Genetics shows that the mixing of different cultural groups in India occurred between 4,200 and 1,900 years ago but started to decline as people began marrying only within their social castes, a much more recent development. Still, this means modern-day Indians share connections to all the groups that intermarried in the distant past.
“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 study co-senior author Dr. Lalji Singh of Banaras Hindu University in Varanasi, India in a press release. “Thus, the present-day structure of the caste system came into being only relatively recently in Indian history.”
Abstract: Most Indian groups descend from a mixture of two genetically divergent populations: Ancestral North Indians (ANI) related to Central Asians, Middle Easterners, Caucasians, and Europeans; and Ancestral South Indians (ASI) not closely related to groups outside the subcontinent. The date of mixture is unknown but has implications for understanding Indian history. We report genome-wide data from 73 groups from the Indian subcontinent and analyze linkage disequilibrium to estimate ANI-ASI mixture dates ranging from about 1,900 to 4,200 years ago. In a subset of groups, 100% of the mixture is consistent with having occurred during this period. 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.