David Reich: uncertainty

Transcript context

…What is it you need to get those samples? We need to identify those skeletal remains, or the sediments in old caves that are well preserved or rock shelters that contain enough DNA to extract. We need extraction techniques that will allow us to get at that material. Maybe we even already have them. We just need to wait until that begins to happen. It would be revolutionary. The experience in Eurasia has been when we get DNA from old sites or new sites for which there's been nothing, we find Denisovans. We find people we completely didn't expect to see before, that breaks our understanding of the past. The other area where I am super excited, and a thing to reward and incentivize, would be to try to crack this body of information, to try to understand how biological adaptation happened in the last hundreds of thousands of years. We simply don't know the answer to your question, from a genetic point of view. How did modern humanity, in cognitive and other types of propensities, develop? We don’t know the biological underpinning of the differences that modern humans have from our closest living relatives. We just don't know how they evolved. It's not even clear how biological they were. We just don't know how to interpret the genome in terms of how these changes occurred. I was at a talk a few years ago that was really shocking to me. There was a researcher at Caltech. She was talking about being able to directly read the brains of macaque monkeys. Monkey would be shown 2000 photographs. Her student would be recording from different neurons in its visual cortex and learning the neurons' response to different images. What they would do is they would decompose the images of faces, human faces, into eigenvectors with the principal component analysis. Specific neurons were responding to particular eigenvectors. They learned the language of how the photographs and the decomposition of them computationally mapped on to the neurons. They actually learned a language for how that's the case. What they did then is they showed a 2001st photograph to the monkey. They recorded from its neurons. Then they tried to use the neurons to reassemble a photograph. It was a perfect reassembly of the photograph. They had actually completely learned how this macaque's brain represents the photograph going through the brain representation. In that case, they were able to completely figure out the language of appreciation of a photograph through the biological representation of it. If you look at the parallel problem of the genome, how does the genome code for development? How did we get to how we are today? How do we have our capacities and so on? At first principles, let’s say you asked me, “What's a simpler problem, figuring out how to represent the natural world in our brain or figuring out how to code for development?” My cognitive bias would be to say that if you were presented with this problem ab initio, it's easier to code for development than to represent the outside world in a brain. to code for development?” My cognitive bias would be to say that if you were presented with this problem ab initio, it's easier to code for development than to represent the outside world in a brain. But this group and other groups are figuring out how to do this nearly perfectly with a readout from the brain. We really can't read a genome and tell you how a person looks or how a person develops. We can begin to say what terrible diseases they have, but not even predict that so well. It's very depressing that we can't actually read the genome enough to actually see how that occurs. We actually don't even know how evolution happens. For example, does evolution happen by lots of little changes pushing in some direction? For example, if we want to move toward a different positive set point for height or for some cognitive capacity or propensity? Is this by infinitesimal change of polygenicity, many genetic variants pushing in the same direction? That's the mathematician's bias. Or is it like the example I told you about before with David Gokhman and Liran Carmel, with the voice box where everything pushes in the same direction and goes up to 100% and shifts all in the same direction in an incredibly simple and simplistic way. If you talk to neuroscientists and molecular biologists, their brain tends toward the latter. These few examples suggest that maybe that's occurred. This polygenic paradigm of adaptation, when adaptation really matters, is that really what happens when important adaptation happens? Or is it instead something simple and simplistic and reliant on a small number of genes? So what I would really like to know is if we can mine the genetic data we have from modern genomes and archaic genomes. We now have Neanderthals and Denisovans. We now have some early modern humans who are far enough back in time that appreciable change may have occurred. Can we actually learn the patterns of biological adaptation well enough to actually read the code of how we change and how we adapt to new pressures? That's something that's not impossible to imagine we learn how to do, but it takes a different way of thinking.…

Stored transcript either side of the excerpt. The highlighted words are the published quote; the surrounding text is unedited source, never generated.