Welcome to Quantum Magazine's podcast.

Each episode, we bring you stories about developments in science and mathematics.

I'm Susan Vallett.

Humans today are mosaics.

Our genomes are rich tapestries of interwoven ancestries.

And with every fossil discovered and every DNA analysis performed, the story gets more complex.

We're the sole survivors of the genus Homo.

We harbor genetic fragments from other closely related but long extinct lineages.

Modern humans are the products of a sprawling history of shifts and dispersals, separations, and reunions.

It's a history characterized by far more diversity,

movement, and mixture than seemed imaginable a mere decade ago. But it's one thing to say that

Neanderthals interbred with the ancestors of modern Europeans, or that the recently discovered

Denisovans interbred with some older mystery group,

or that they all interbred with each other.

It's another to provide concrete details about when and where those couplings occurred.

Ailwyn Scali is an evolutionary geneticist at the University of Cambridge.

We've got this picture where these events are happening

all over the place. So we've got lots and lots of different structured human populations in various

parts of the world, most of whose descendants no longer exist today. They're extinct in some

formal sense. It's kind of funny. We're building up this story about

lots of subpopulations around the world and lots of integration and lots of gene flow,

and that seems to be quite persuasive, but it's very hard for us to pin down any particular

...