David Reich

Well, maybe the arrival of the Beaker phenomenon, which happens about 4,500 years ago, maybe it's not an invasion, maybe it's a kind of peaceful event, maybe the previous people

The reason we're seeing such a disruption is the previous people, we know they cremated their dead and the Beaker people buried their dead.

So it looks like a much more abrupt change than it did.

Maybe what happens in Iberia when there's a 40% arrival of these foreigners from the East and 60% local people, but the Y chromosomes are completely replaced.

So the local men don't sort of contribute their DNA to local later populations.

It looks to you, it looks somehow like that must be extremely disruptive to the local male population.

But people are saying, well, maybe this is female mate choice.

Maybe this is somehow kind of not what you think it is.

Maybe it's not what happened 4,000 years later amongst the descendant of the Iberians in the Americas, where today in Colombia, 95% of the Y chromosomes are European, 95% of the mitochondrial DNAs are Native American.

We know what happened there.

It wasn't friendly.

It wasn't peaceful.

It wasn't nice.

But maybe what happened in Iberia 4,000 years ago amongst these ancestors of people was much more peaceful, was much more calm.

If you look at detail in Iberia, what you see is the period of this change is actually over 500 years.

But if you look at a microscale, now that we have better data, it's immediate each place.

So in southern Spain, it's very fast.

And then in central Spain, it's a little later, but very fast.

And so actually, there's these rapid changes occurring in one place or another.

People thought in Britain, maybe this was actually a slow process.