David Reich: uncertainty

Transcript context

…What are other questions you are either investigating right now or want to investigate, these kinds of big picture questions of human history? I’m perplexed. I don’t know if we talked about it before, but I remain very confused about the relationships between archaic and modern humans. We have genome sequences now from archaic humans who lived in Europe, West Eurasia, and Central Eurasia, and the Neanderthals. We have archaic sequences from these enigmatic Denisovans, who we now have a skeleton for since we last talked. There’s now a skull that’s been shown to be a Denisovan. We have data from lots of modern humans, and there are really big mysteries about the relationships amongst these groups. Genetically, the Denisovans and the Neanderthals are sisters. They descend from a common ancestral population 500,000 or 600,000 years ago. That group descends 700,000 or 800,000 years ago from the common ancestors of modern humans. Genetically, the whole genome data says that Neanderthals and Denisovans are archaic humans from a common ancestral archaic population. But there are so many things shared between Neanderthals and modern humans that don’t seem to be shared with East Asians. They both share Middle Stone Age stone tools, Levallois technology, this cognitively unique way of making stone tools that wasn’t used in East Asia. They both have the same mitochondrial DNA and Y chromosome sequence. The Y chromosome sequence of Neanderthals and the mitochondrial DNA of Neanderthals, is actually modern human that came through interbreeding 200,000 or 300,000 years ago and then shot up to 100% frequency. Neanderthals and modern humans are both the product of mixture events that happened between archaic and modern humans 300,000 or 200,000 years ago, demonstrably through patterns of variation in ancient and modern DNA. It feels that there’s something shared between Neanderthals and modern humans that’s not shared with Denisovans, even though the vote of the whole genome says that Denisovans and Neanderthals are related. One wonders whether there’s something connecting Neanderthals and modern humans that’s different from Denisovans, even though genome-wide, Denisovans and Neanderthals cluster. I’m thinking about that all the time now. Connecting them would be interbreeding events or being in the same place at the same time that we missed?…

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