David Reich

epicycles, ideas like natural selection, to kind of make it work.

It's not impossible.

It may be the case.

But one wonders whether profoundly different models might actually explain the data.

And so that's something that we and others have been thinking about.

Can there be other models?

An example of another model that might be able to explain the data that we've been playing with is one where there's much more DNA in Neanderthals from modern humans than the three or 5% that's been estimated.

And we can get such models to fit, but here it's 30% or 50% or 70%.

So in that view, Neanderthals and Denisovans are not sisters.

In fact, modern humans and Neanderthals are just as qualified to be sisters as Neanderthals and Denisovans.

And in that case, maybe it's not clear what's modern and what's archaic.

Are modern humans archaic?

Are modern humans modern?

Are Neanderthals archaic?

Neanderthals are modern.

What's also become clear in the last few years in a separate thread of research, not based on ancient DNA, but based on using more and more powerful and sophisticated ways of pattern finding in modern data, is that modern humans are also highly substructured.

We can see that even without having ancient DNA yet.

Of course, once one has ancient DNA, it's so much clearer.

But it's very clear that you can't explain, for example, modern African DNA without invoking very extreme substructure as deep as the mixtures that contributed and mixed between Neanderthals and modern humans.

And so that mixture, which of those groups were archaic?