David Reich: uncertainty

Transcript context

…Oh, so you increased the range there. You said 100,000, 200,000, 300,000 years ago. Based on the genetic differences between modern people and people from 300,000 years ago. Do you basically think they’re modern 300,000 years ago? I don’t know. This is actively what I’m thinking about all the time right now. There’s a big transformation in terms of the culture of humans 300,000 or 400,000 years ago: this invention of Levallois 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, is 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. It’s a big change, and it presumably involves a cognitive change in order to make this sort of technology. Then there’s a further change to the Upper Paleolithic Later Stone Age, maybe 100,000 to 50,000 years ago, when there’s a second transition with a new type of tool making, but it’s 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, all occurs more on the timescale of 300,000 or 200,000 years. All of these people are capable of going to college and doing everything. So it’s not obvious that the cognitive toolkit, the behavioral toolkit, and the genetic abilities were not all in place 200,000 or 300,000 years ago, and that even Neanderthals had them. It’s not obvious that this was not the case. I just don’t know. You distribute these people descended from this diversification that happened 200,000 or 300,000 years ago to different parts of the world, and then after 12,000 years ago, you start having agriculture popping up in different places. It’s an outstanding mystery of human history. I find it unbelievable that we live in a time period that climatologically is so unique on a scale of two million years, but my colleagues tell me it’s true. The climate thing seems surprising given there are so many different environments in which agriculture was independently developed. I understand that across environments the variance could have gone down. If it had only happened in one place at one time, I could have bought that explanation. But the fact that they’re making maize in the New World and they’ve got cereals in the Old World in very different environments makes it surprising.…

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