David Reich: uncertainty

Transcript context

…We were talking earlier about how small the initial population that populated all of Eurasia was, a couple thousand people. We were also talking about how random and contingent the whole history of humanity has been. Was there some chance, if a couple of variables were different, that “modern,” civilization—greater population density, greater development, technology and so forth—would not have happened except for some really lucky chances? Or was it the case that even if that one tribe didn't do it, some other tribe of humans would have done it? Even if some other tribe of humans from Africa hadn't done it, then Neanderthals had enough cognitive sophistication that they would have done it? I know this is a very speculative question, but how random does “primate to civilization” feel? Does it feel like we had to go down the exact right path? Or was it the trend across many different branches of the family that leads to humans? I don't know. It's very speculative. I'm very tempted to think that there's so many of these groups that some of them would eventually have gone down this route. One example of this that's interesting to think about is the parallel development of agriculture in the Holocene in different parts of the world. You have in the Americas what's almost certainly a completely independent development of agriculture 9000-8000 years ago from that in Eurasia. You can argue whether the East Asian and Near Eastern developments are different. They probably are, but maybe you could argue they knew about each other somehow. Or with the Papuan one, maybe you could argue they somehow knew about what was going on in other parts of the world. They probably didn't. Certainly the Americas one was isolated. Suddenly for the first time, you have these independent evolutions of full-blown agriculture at the same time in many places in the world after the ice age. This makes you think that it's somehow deterministic. Somehow some kind of setup of characteristics at this time causes this to happen. Why doesn't it happen in the previous period of stable climate before the last ice age? Some people say, “Maybe it was actually not as good as the last 10,000 years.” I find that confusing as a statement. It's tempting to think that some sort of cultural or biological, more likely cultural, characteristics are in place and seeded already at the time of the last ice age, such that when the reemergence happens it happens in multiple places simultaneously. Because it happens so fast. It's not like you had to wait for tens of thousands of years after the ice age. It’s literally 2000 years after the ice age.…

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