David Reich

And then the cultural change happens, which locks in the caste system, and people freeze, and they stop mixing very much.

And so what you see is instead of people collapsing to a point, which is what you see in Europe after this type of mixing process of these three sources happen in any one region, you see this gradient forming and it's stable.

And because of the...

enduringness of the caste system, you actually have a snapshot going back a couple of thousand years and without this continuing change.

And so it's kind of an amazing system genetically to look at because of people's reluctance to mix with people from very different groups in traditional communities.

And so the three steps are

coming together of very different populations, and then convulsive profound mixing of groups that had previously not mixed, and then locking into this static system as the caste system sets in, which is documented in the early texts like the Rig Veda.

And you can actually see the change in that discussion during the course of the Rig Veda.

So the first good genomic data from South Asians is embarrassingly from Houston, Texas.

So in the human haplotype map project, there was a sample from Houston, Texas of Gujaratis in Houston, Texas.

G-I-H.

And if you look at them, people are actually not on this gradient, but they're in a few different places.

They're clustered into groups, and there's the main gradient and there's an off-gradient group.

And I forgot how we figured this out, but someone figured out that these people are all Patels.

And Patels have their own distinctive history with different relationships to people in Central Asia.

And it's probably some additional ancestry from Central Asia pushing them off the main gradient.

It's very unstable life.

So I think that in some areas, like in archaeology, a lot of my colleagues who I respect tremendously, the career trajectory is you learn to become an archaeologist, you dig, and you have a set of digs that you're doing for dozens and dozens of years with similar or slowly evolving techniques.

And my work has just changed so radically.

When I started doing this work, one could not sequence a whole genome.