David Reich

Right.

And it interacts with the local people.

So, for example, if you look at the first modern humans of African and Near Eastern origin who get to, for example, Europe, where we have the best data, we have a number in Western Siberia where we have the best data so far.

We have a number of these very early ones from about 45,000 to 40,000 years ago, which are called initial Upper Paleolithic humans.

And a good fraction of them have had Neanderthal ancestors in their last two to four to eight generations.

So that's a kind of crazy result.

So we have only a couple of dozen or a dozen or so of these very early humans and a very large fraction of them recently mixed with Neanderthals in their ancestry.

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