David Reich

you can break it up into a hundred or so deems, little areas.

And modern humans get introduced at the bottom right corner in the Middle East or something, and they spread into Europe.

And as this population spreads, there's a wave front of expansion and they're interacting with the local archaic humans.

And even if there's a small amount of interbreeding, the theory,

from lots of studies, simulations, and lots of studies of all these different species, like mammals and birds and so on, shows that there is, when there's even a little amount of interbreeding, as there's an invasion or a movement of expansion of one group into the territory occupied by the other, there's massive introgression of local genes.

There's that...

that these pioneers at the wavefront, they'll sometimes interbreed with the local population.

There's so many of them around that their DNA will get swamped by the local groups.

So by the time they make it to the other side, they're largely local.

And so maybe what we're seeing is that this is what's happened.

You have like a modern human population that's matrilineal, for example, where transmission of making stone tools this way is happening from your mother to the kid.

And...

That's why they're retaining their mitochondrial DNA.

But by the time they get to the other end of Europe, they're mostly archaic.

They're mostly local archaic.

So you'll end up with a 95% population replacement.

So this would explain why the mitochondrial DNA is shared between Neanderthals and modern humans.

And it would also explain why the mixture proportion is only 5%.

But like the really interesting thing is that actually there's other evidence from studies of modern humans that actually modern humans are too also admixed.

And that the right way to think about this