David Reich

A model that might explain the data is that you have sparks coming out of a kind of forest fire in the Middle East or the Near East of humans expanding.

They come in and they start going to places like Western Siberia or parts of South Asia or parts of Europe.

They mix with the Neanderthals and they produce these mixed populations like these initial upper Paleolithic groups we sample in the record, and they all go extinct.

including the modern human ones.

There's just extinction after extinction after extinction of the Neanderthal groups, of the Denisovan groups, and of the modern human groups.

But the last one standing is one of the modern human groups, and that's what we happen to see.

And so the interbreeding event that we see, the great majority of the ancestors of modern humans, for example, in Eurasia, are not from the initial upper Paleolithic ones, but from a later wave from the core in the Near East after 39,000 years ago that re-people a place that's been

sort of affected by these sparks coming out of the same region.

And those groups too disappear.

I don't know if that model- I think that that's probably right at some important level.

I think it's not a triumphal march of superiority and inferiority with the group that now comes in having

advantages somehow establishing itself permanently.

I think that what you have is a very complicated situation of many people coming together and natural disasters or encounter with animals or encounter with other human groups resulting in an almost random process of who

Or who ends up on top and other groups coming in afterward.

And so it may be that from a big picture perspective, you end up having African lineages spreading into these different parts of groups, different parts of Eurasia.

That's certainly what happened.

But at a local level, I think it would be very difficult to understand what's going on.

I think that's right.

And there's lots of analogies that you have later.

There's European farmers encountering step migrations.