David Reich: observation

Transcript context

…Where did the most recent gene flow between Neanderthals and humans happen? I guess it’s not the most recent, because the most recent was 60,000 or whatever years ago. But the one you're referring to here, where physically did that happen? Even that's not clear. Probably such a thing would have occurred somewhere in the Near East or in western Eurasia somehow. It's not even clear where the modern human lineage was residing at that time. The modern human lineage, leading to the great majority of the ancestors of people today, was probably in sub-Saharan Africa for the last 500,000 years at least. It might be much more. Certainly our main lineage was in Africa, probably 3-7 million years ago. But in a period between about 2 million to 500,000 years ago, it's not at all clear where the main ancestors leading to modern humans were. There were humans throughout many parts of Eurasia and Africa with a parallel increase in brain size and not obviously closer ancestrality to modern humans in one place than in the other. It's not clear where the main lineages were. Maybe they were in both places and mixed to form the lineages that gave rise to people today. There's been an assumption where Africa's been at the center of everything for many millions of years. Certainly it's been absolutely central at many periods in human history. But in this key period when a lot of important changes happen—when modern humans develop from Homo habilis and Homo erectus all the way to Homo heidelbergensis and the shared ancestor of Neanderthals, modern humans, and Denisovans— that time period which is when a lot of the important change happened, it's not clear, based on the archaeology and genetics, where that occurred as I understand it. We're humans and you would think one of the things history would have figured out is how humans came to be. That's probably one of the biggest questions you could imagine asking of history, of archaeology, of anthropology, of genetics. The conventional model is the thing you're taught in the third grade. This is one of the first things you're taught about the world. The fact that many parts of it could be wrong… We're learning in greater detail what those parts look like, at the very least. We're doing that right now because of new technology that's being used by labs like yours. That's really wild. The audience might not be aware of how much of a change this is in our understanding of the human past. I just really want to emphasize that. The gene flow event you're talking about a few hundred thousand years ago happened between modern humans and Neanderthals. If it happened outside of Africa, then did that lineage go back to Africa and then come back out again? How should we think about that?…

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