David Reich

die and knowledge gets lost and there's not a critical mass of shared knowledge.

But once it goes above some kind of critical mass, the group can get larger, the amount of shared knowledge becomes greater, and then you have a runaway process where an increasing body of shared knowledge of how to make particular tools, how to innovate, patterns of innovation,

and so on, language, conceptual ideas run amok.

So an example that I've heard talked about in this context is what happened with, for example, indigenous Tasmanians.

You probably know this story, but

About 10,000 years ago, the ancestors of people in Tasmania, which is this large island south of Australia, were continuous with the aboriginal populations of Australia.

They had fire.

They lost it.

And they lost fire because it got forgotten somehow, and it's a cold place.

And they just forgot it.

The cultural knowledge lost it.

So what you actually have in the world is—50,000 years ago is tens or hundreds—

thousands or tens of thousands of different human groups, each of them possessing local knowledge, rarely exchanging with each other.

When we get lucky in ancient DNA and sample them, they're quite isolated from each other, and they have reduced diversity in the last tens of generations.

The great majority of them go extinct.

The great majority of them are wiped out by encounters with natural disasters or other groups of humans or other animals.

And so what you have is a vast experiment with an archipelago of these groups.

And

what might be happening is that you just have a process of accumulation of cultural knowledge and loss of cultural knowledge.

But since there's many of these experiments going on, maybe something takes off somewhere and maybe that's what happens 50 to 100,000 years ago.