David Reich

And there's a big transformation in terms of the culture of humans 300, 400,000 years ago, this invention of level technology, the ability to make stone tools out of cores, the Middle Stone Age revolution or the Middle Paleolithic revolution, depending on what you call it in Africa or Eurasia.

And this is a

a new way of making stone tools that's shared by Neanderthals and by modern humans, but is not shared in East or South Asia.

And it's a big change, and it involves a cognitive change, presumably, in order to make this sort of technology.

And then there's a further change to the Upper Paleolithic, later Stone Age technology,

maybe 100,000 to 50,000 years ago when there's a second transition with a new type of toolmaking, but not as revolutionary as the earlier one.

So when the cognitive leap happens is unclear.

The diversification of the lineages leading to people living today, like Khoisan Southern Africans and rainforest hunter-gatherers, and that all occurs more on the timescale of 300,000 or 200,000 years.

And all of these people are capable of going to college,

and doing everything and so you know it's not obvious that all the toolkit the cognitive toolkit the behavioral toolkit the genetic abilities were not all in place two or three hundred thousand years ago and that even Neanderthals had them right so it's not obvious that this was not the case and so

Like, I just don't know.

You sort of distribute these people descended from this diversification that happens 200, 300,000 years ago to different parts of the world.

And then, bing, you know, after 12,000 years ago, you start having agriculture popping up in different places.

It's kind of an outstanding mystery of human history.

And, you know, I find it unbelievable that we live in a time period that climatologically is so unique on a scale of 2 million years.

But my colleagues tell me it's true.

It's very, very surprising.

And I think we accept it, but it's just like a crazy observation that most normal people don't realize.

The thing that basically everybody accepts is that the common ancestral population of almost everybody in the world, except for rainforest hunter-gatherers and Khoisan,

is like around 70,000 years ago.