David Reich

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.

There's Native Americans encountering Africans and Europeans as they come from the old world.

There's various other groups encountering other groups.

And you have people who have cognitively or...

culturally all the capacity to thrive in other contexts but just because of the nature of the interaction that happens one group declines demographically and one group doesn't and it's just complicated so I don't think you should conclude necessarily it's very tempting to think

that at some level it's innate, biological.

I'm not trying to be politically correct, that it's innate, some better biological hardware that makes it possible for these African lineages to spread into Eurasia.

I have no good insight into that topic.

I don't think there's very good genetic evidence or any other kind of evidence to say that that contributed in a very strong way.

I think that it's just complicated, and we certainly have many modern examples where people with better or more competitive cultural complexes encountering each other, and the ones that are more organized in a certain way sort of thrive somehow demographically more.

There's an amazing book by Kyle Harper called, I think it's called The Fate of Rome.

And it's an argument about the history.

He's a historian, a Roman historian.

And it's a history of three major plagues in the Roman period, two of which are really not even very well known, and argues that the decline of the Roman Empire is due to just weakening as the result of plagues and other climatic, biological, climatological worsening events.