David Reich

I think that we have to assume that there's a linkage between the cultural transformations in Africa and Eurasia at this time, and that's sort of not something that the community has really put together with the genetic data.

So I think that there's this thread in the genetics about substructure in Africans, and then there's this whole world based on ancient DNA, and they've never been put together.

So nobody's put together the...

extensive now extensive work on modern human substructure with the now extensive work based on ancient dna of archaic human relationships to modern humans and if you put them together you realize they line up in terms of their time uh of substructuring so i think that i don't know if that's improbable it seems actually parsimonious to me but yeah

Well, who knows?

I mean, it could be that actually this was genetically driven, right?

We talked before about the time to the common ancestor of human genes.

There's nothing at 100,000 years or 150,000 years, but there's a lot at 400 or 500,000 years.

So if that's what happens and you have a mutation that occurs in the Caucasus or somewhere in the Middle East or Northeast Africa, and there's key genetic mutations that make people able to do this, and then this population expands,

When it moves into Europe, it's swamped by local genes, but there could be retention of those genes through selection as it expands.

So maybe what you're actually seeing is that actually there are genetic developments.

Most of the discussion on this, I point, has been focused on the 50 to 100,000 year event.

And this is like anatomically modern human behavior.

But this is like a lot of my archaeologists think this is an equally, if not more profoundly significant event in many ways.

And why is that not the event that we should be talking about?

I think that this is what we're talking about, which is like, if you look at the genetic variation going back three or 400,000 years, then there do begin to be places where all modern humans share common ancestry three or 400,000 years ago.

And that's another way of saying there begin to be fixed differences at that time depth.

So that is where you start seeing evidence for possible fixed differences.

What's basically happening if everybody shares a common ancestor 400,000, 500,000 years ago, is there's a single ancestor at that time, and if you compared it to another population, like these guys, they would descend from a different lineage, so any mutation that occurred ancestral to that single ancestor would be a fixed difference.

So this is the time at which you can begin to see fixed differences.