Origins of Indian Endogamy
One of India's most characteristic institutions is its division into endogamous clans, or jatis - somewhat misleading referred to as the caste system. A group of genetics researchers from Hyderabad and Boston now claim to have evidence that the endogamic system originated, or at least took shape, about 1900 years ago.
Indian ancestry is complex, but there are two major strands, the so-called Ancestral North Indians, who are related to central Asians, Middle Easterners, and Europeans one the one hand and Ancestral South Indians, who don't appear to be closely related to any outside groups. The claim is that the genetic evidence indicates that mixing between the groups began about 4200 years ago - plausibly at the time Indo-European languages arrived in India - and stopped 1900 years ago, when the Jati system took hold.
Naturally I would be interested in Arun's opinion, fortified as it is by his vast knowledge of Indian history and deep skepticism about conventional interpretations.