David Reich: evaluation

Transcript context

…I still don't understand. Is the answer that we just don't know what happened 60,000 years ago? Before humans and other modern humans and other types of humans were interacting, but no one was in a dominant position at least in Eurasia. Now humans not only dominate, but in fact we drove them to extinction. Do we have any idea what changed between that time? This is really outside my expertise. There are ideas that have been floated, which I'll summarize possibly badly. In every group of human beings of hundreds of people—which is the size of a band—or sometimes a thousand people, they accumulate shared cultural knowledge about tools, life strategies, and build up shared knowledge more and more. But if you have a limited-sized group that's not interacting with a sufficiently large group of people, occasionally this group has an information loss. There's a natural disaster, key elders die, and knowledge gets lost. There's not a critical mass of shared knowledge. But once it goes above some kind of critical mass, the group can get larger. The amount of shared knowledge becomes greater. You have a runaway process where an increasing body of shared knowledge of how to make particular tools and patterns of innovation, language, conceptual ideas, run amok. An example I've heard talked about in this context is what happened with Indigenous Tasmanians. About 10,000 years ago, the ancestors of people in Tasmania—this large island south of Australia—were continuous with the aboriginal populations of Australia. They had fire, but they lost it because it got forgotten somehow. It's a cold place. They just forgot it. The cultural knowledge lost it. What you actually have in the world 50,000 years ago is tens, or hundreds, or thousands, or tens of thousands, of different human groups. They each possess local knowledge and rarely exchange with each other. When we get lucky in ancient DNA and sample them, they're quite isolated from each other and have reduced diversity in the last tens of generations. The great majority of them go extinct, wiped out by natural disasters or other groups of humans or animals. You have a vast experiment with an archipelago of these groups. What might be happening is that you just have a process of accumulation and loss of cultural knowledge. Since there are many of these experiments going on, maybe something takes off somewhere. Maybe that's what happened 50,000 to 100,000 years ago in people who all have the capacity to do these things. One thing I didn't realize until I read your book is how small the population that expanded out into Eurasia was, and how small even generally the human population was 50,000 to 100,000 years ago. I remember one of the papers you cited said that there might have been a population bottleneck around this time period. People talk about the Toba eruption. I don't know if that's the cause, but there's many potential causes. Anyways, I remember from somewhere that the ancestors of everybody in Eurasia was initially like 1000 to 10,000 people. How small was the human population that was the seed of this modern period?…

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