David Reich

So today in South Asia, almost everybody is on a gradient of ancestry with two poles, what we call the ancestral North Indians and the ancestral South Indians, with very few exceptions.

The exceptions are people with your last name, Patel.

Oh, yeah?

And as a minor exception, but it's interesting that that's your last name.

But also people from Munda speak Austroasiatic languages or are unmixed with them or people who are Tibeto-Burman speakers.

But most people are on a mixture between two poles, ancestral North Indians and ancestral South Indians.

And when you look at genetic data from India, it looks like what you see today in African-Americans with people with relatively higher or lower proportions of, say, European and West African ancestry.

And so it looks like a population in the process of mixture like African-Americans who are the result of mixture in the last 10 or so generations between two, mostly two very different populations mixing in different proportions.

But what happened in India is it froze.

So the mixing started and then it froze.

And the freezing happened 2,000 to 3,000 years ago, and it froze because of cultural change.

So what happens in India is you have a three-part change.

You have an arrival of three source populations, essentially parallel to what you see in Europe.

There's a local hunter-gatherer population.

There's what's probably a farming population, maybe also a hunter-gatherer population initially.

And then there are these people descended at some level from steppe pastoralists.

These are the three primary ancestral populations.

They come together at the end of the decline of the Harappan civilization, which ends about 3,800 years ago.

Groups from this Harappan group, which we actually have sampled, and they're all on a different gradient, they mix with the steppe groups and with the local hunter-gatherer groups to form and coalesce to these two later groups, which we call the ancestral North Indians and ancestral South Indians.

And then mixtures of these two mixed populations form in the gangetic plane, form people all along this gradient, and it's really a very simple mixture of two sources.