David Reich

The reaction after the Second World War was to say, we don't know this.

In fact, when you see the arrival of new types of material culture, pots, for example, or tools or ways of organizing life, what you might be seeing is more the spread of culture.

You might be seeing, for example, something like people copying use of a cell phone or

Something like this, which can be used by people of very different backgrounds, and it's just, or a new religion spreading, and it's not actually movement of people.

And in fact, how could there be a big movement of people?

You're looking at densely settled Europe with well-developed agriculture.

How could it be that new people coming in from outside

will unseat these people, disrupt these people, especially after a period of stasis, after a period of, especially once, sorry, especially once when you have farmers who are densely settled and how could these be pastoralists coming from somewhere else?

They're not as dense on the ground.

In India today, the British were sort of in control, the Mughals were in control for hundreds of years, but made hardly any demographic impact.

How could people from outside with less density make much of a demographic impact?

But then you look at the genetic data, and there's a 50%, 70%, 90% population disruption.

You take the DNA from people after these events, and almost all their ancestors are from far Eastern Europe, right across most of Europe.

And so the DNA proved that that idea was wrong.

It was very disruptive.

So the question that you had is, what does it look like on the ground?

And so the DNA results was extremely disruptive to people in archaeology who had made these arguments that change wasn't possible in this very, that large-scale migration, large-scale disruption probably didn't occur in the past.

And so it was a real challenge.

It was a real challenge to our understanding of prehistory.

It was sort of a case example, a prime example that's been important for me in showing that we really don't know what the past was like until we actually