David Reich

is that modern humans are a mixture of two groups, maybe like 1.5 million years ago, and that they come together two to 300,000 years ago with like 20%, 200 to 300,000 years ago, with maybe 20% ancestry from this archaic world.

African group and 80% ancestry from this early modern lineage.

And that the same group then mixes with Neanderthals in this 5% modern here and 95% local here.

And so you actually have this key population that makes the Middle Stone Age.

or Levawatt technology, this one that appears here.

And it expands in all directions into Europe here, into Africa here, two to 300,000 years ago, bringing this technology, bringing these new ideas, bringing perhaps some genetic adaptations.

It expands into archaic humans in Europe.

It mixes with the local population.

It gets 95% replaced, but still retains its cultural identity.

features and maybe some genetic features.

And it expands in Africa too.

And here it's not 95% replaced, it's only 20% replaced.

And probably the reason that happens is that this group is much, much more diverged.

It's much more archaic.

It's 1.5 million years diverged rather than seven to 800,000 years diverged.

And as a result, there's many more incompatibilities genetically, and there's much more barriers to gene flow, but there's still a lot, maybe 20%.

And we have evidence that this is a big mixture that happens.

And so what you're actually seeing is a modern human expansion, both into Europe and into Africa,

In one place is it forms Neanderthals, in one place is it forms the ancestors of everybody living today.

But all of these groups are descended from this key sort of revolutionary event that happens here.