David Reich

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.

I just think we don't have important new qualitative insights about that topic right now.

The other is that the large brain was already in place prior to the separation of Neanderthals and modern humans, and maybe Denisovans as well.

So already the common ancestors of Neanderthals and modern humans probably had a brain as large as ours.

It's not obvious that there's parallel evolution in multiple parts of the world.

It may be that it's a sufficiently interconnected group that it's not a parallel evolution event, but a single process.

I think that's almost certainly true.

We don't yet know the frequency of exchange between Africa and Eurasia, but this is two million years.

It's a lot of time.

You know, Paul Salopek is like walking around the planet in like seven or...

years or something like this.

People move incredibly quickly.

And Africa and Eurasia are not really separated by barriers that mean anything very important to a species like ours over periods of even dozens or hundreds or thousands of years.

So the idea that being in Eurasia or Africa is such a profound barrier that you would not expect people to move from one region to the other in periods of tens of thousands of years or hundreds of thousands of years, that's a strange idea.