Dwarkesh Patel: evaluation

Transcript context

…Maybe. One of the big takeaways for me from the paper was just that something weird happened in the Bronze Age. As you said, across trait after trait, the selection intensifies during the Bronze Age. This makes sense for some things. For example, why do we see lactase persistence, where adults can process milk, intensified during this period? This is the time when we start using cattle not just for the meat, but also for milk and wool and other secondary products. So it makes sense why lactase persistence would matter more. But then there are other things that seem like they should have been relevant since the dawn of agriculture. I forget the exact name of the allele, but was it FADS1, which helps convert plant fatty acids into long-chain fatty acids that your body needs? That’s obviously relevant when you move from a diet of meat as a hunter-gatherer to a diet of cereals. That is also one I think you found was under especially high selection 5,000 to 3,000 years ago. So what’s going on? Why is the Bronze Age so special across all these different traits that you’re observing? So this FADS1/2 variant is a vegetarian/meat-eating adaptation. Already in work prior to this, Ian Mathieson, who worked with me in 2015, identified this as a very strongly selected variant. It’s actually ancient. You see copies in archaic humans too. One of the findings of our paper is the ABO blood system. You get your blood typed as A, B, and O. The B variant has increased up to 10% at the expense of A, but previous work has shown that A and B were both already present in the ancestor of humans and gibbons and other apes. Some of these mutations have been going back and forth and fluctuating over different time periods. But we’re talking about changes in the Bronze Age. The TYK2 variant for tuberculosis risk, a multiple sclerosis risk variant, inflected and increased in frequency before the Bronze Age, and then 2,000 or 3,000 years ago reversed in that period. There are differences in Northern Europe where this process is super strong, very strong positive selection, very strong negative selection. And then in Southern Europe, only a little bit, and not even very strong negative selection. For haemochromatosis, which is pathogenic iron buildup that causes problems in Europe, that too has reversed around this period. In some of the complex traits that maybe we’ll talk about later, these traits too have periods of intensification of natural selection. For example, depigmentation: Europeans have gotten lighter skin over the last 10,000 years. You can see it in our data. The period of strongest depigmentation is between about 4,000 to 2,000 years ago, and then after that it’s much less. This seems to be a very impactful, eventful, important period where a lot of the processes we are seeing become very powerful. It’s surprising on first principles. You might think, before you walked into this genetic data, that the big change is going to be starting to grow plants and maybe farm animals. That happens in the Neolithic, beginning 10,000-12,000 years ago, and spreads into Europe after 8,500 years ago. But actually, the intensification happens 5,000 years ago, 4,000 years ago. It’s really interesting. This observation of that being an inflection point tells us something about when humans, at least in this part of the world, were wrenched into a way of living that was so different from how their hunter-gatherer ancestors lived that the organism had to adapt very strongly. It may be that the degree of that wrenching process moving into the Bronze Age was qualitatively greater than the degree of the wrenching process that happened from the initial transition to growing plants. That’s surprising, because our cartoon picture is that the big transition is farming. But the biological readout is saying our genome is reacting much more strongly to these events that happened 5,000 years ago.…

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