…we found that West Eurasian-related mixture in India ranges from as low as 20 percent to as high as 80 percent…
Groups of traditionally higher social status in the Indian caste system typically have a higher proportion of ANI [Ancestral North Indians] ancestry than those of traditionally lower social status, even within the same state of India where everyone speaks the same language. For example, Brahmins, the priestly caste, tend to have more ANI ancestry than the groups they live among, even those speaking the same language.
It also seems that a disproportionate share of the ANI genetic input came from males. Furthermore:
Around a third of Indian groups experienced population bottlenecks as strong or stronger than the ones that occurred among Finns or Ashkenazi Jews.
Many of the population bottlenecks in India were also exceedingly old. One of the most striking we discovered was in the Vysya of the souther Indian state of Andhra Pradesh, a middle caste group of approximately five million people whose population bottleneck we could date…to betweenthree thousand and two thousand years ago.
The observation of such a strong population bottleneck among the ancestors of the Vysya was shocking. It meant after the population bottleneck, the ancestors of the Vysya had maintained strict endogamy, allowing essentially no genetic mixing into their group for thousands of years.
And the Vysya were not unique. A third of the groups we analyzed gave similar signals, implying thousands of groups in India like this…long-term endogamy as embodied in India today in the institution of caste has been overwhelming important for millennia.
…The truth is that India is composed of a large number of small populations.
That is all from David Reich’s superb Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past. Here is my earlier post on the book.