David Reich: belief

Transcript context

…Do you want to recapitulate the thing you were saying about the analogy to Ptolemy and the epicycles? I thought that was quite interesting. I think the model that we’ve put together collectively about the relationships between archaic and modern humans has accreted over time. There was this idea that modern humans are distinct and that Neanderthals and Denisovans are sisters of each other. Over time, we detected additional mixture events, like this modern human into Neanderthal, and then these other ones I didn’t even talk about, like a super-divergent lineage going into Denisovans and all this other stuff. We still say, “Oh, the whole genome says Neanderthals and Denisovans are sisters, so that’s the truth.” We’ve patched it all together and gotten it all to work. You look at the mitochondrial DNA and the Y chromosome, and they have this odd pattern, and it’s improbable, but we can get that to work if we invoke natural selection, things like this. You patch it all together. It reminds one of what happened in the ancient world, where there was this idea that the sun revolves around the Earth, but it doesn’t quite explain the movements of the planets properly. In order to get the movements of the planets to work right, Ptolemy and the astronomers made up these epicycles, these special extra rotations and movements to make everything work about right. It was such a convoluted model. When Copernicus and colleagues suggested instead that everything is revolving around the sun, it simplified things ever so much. What was happening is that as astronomical information accumulated, it kept being contradictory to the standard model, but it could be made to work by proposing another complication and another complication and another complication. This is not as fantastic as proposing that everything revolves around the sun rather than the Earth, but it is much simpler. And it actually explains many things. What is counterintuitive or unexpected or hard to accept about this alternative model? What is the hesitation that people have for adopting this?…

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