David Reich

And so what seems to be happening is that the whole continent of Sub-Saharan Africa, and probably Eurasia at this time, is full of hundreds, thousands, tens of thousands of little groups that are communicating hardly at all with each other, are in very small sizes, are losing diversity.

And when we sample them, this is a group that leaves hardly any descendants at all, maybe none, amongst modern people.

And what's actually happening is occasionally these groups merge together and recharge their diversity.

So the diversity is maintained in the ensemble of rarely mixing groups.

And you can't really appreciate the diversity by studying any one group, but rather you actually have to think about the whole ensemble of hundreds or thousands of tens of thousands of them as preserving the diversity.

So there's some question about the migration rate amongst these groups, which are archipelago of little groups losing diversity, going extinct at some level.

But together, there is enough recontact to recharge the diversity and then create the incredibly diverse populations you see today, for example, in Southern Africa or Western Africa or Central Africa.

So that's super interesting question.

And I think there's a lot of insight and ideas about this topic.

And I think it's an area to which genetics right now has contributed almost nothing.

So I think, you know, in the book that I have, this book that I wrote

who we are and how we got here, ancient DNA and the new science of the human past.

And it's a bit of a misleading title or a kind of bait and switch title.

And the way in which it's a bait and switch title is you might read it thinking you're going to learn something about how we became whatever we think is distinctive about us relative to other animals.

And so I try very early in the book to say that, unfortunately, with the genetic data available up to this point, we don't really have very meaningful evidence

insights about what makes us distinct how we became to be distinct from other animals but what i'm going to tell you about is how we came to be how we are from another perspective that through mixture and migration so it's very surprising how we came to be uh how we are through migrations and mixtures a lot of people used to think that we were not mixed but in fact it's been mixture again and again in the past and many populations we didn't anticipate but with regard to your question which is how it is

That humans evolved into a distinctive niche, which includes having a strong reliance on a large brain, putting a large amount of metabolic energy into the brain, brain relative to body size much bigger than it is in the past.

I have two things that are striking to me about that.

One of them is that

I think genomics actually has promised to learn about those things, and I think we are potentially on the verge of learning a lot about those things.