Dwarkesh Patel: evaluation

Transcript context

…What you see is a reduction in the combination of genetic mutations that make you at risk for obesity, body mass index, and similarly very correlated to it, higher fat mass, higher waist-to-hip ratio, and higher type 2 diabetes risk. There is clear selection, by about a standard deviation on the scale of modern variation for these traits, reducing over the last 10,000 years in this part of the world. What can be going on there? Why wasn’t there selection for this combination of traits before? There’s a longstanding idea known as the thrifty gene hypothesis. The idea is that once you have hunter-gatherer populations that move into a farming environment where there’s plentiful food, there is no longer a need to the same extent to be able to build up body fat to survive in times of stress, because there are more constant stores of food. As a result, there will be natural selection against body fat once you move into an agricultural environment and into periods of food plenty. Maybe what you’re seeing is that this group of people in Europe and the Middle East over the last 10,000 years has moved into a period of relatively more stable food, where building up stores of fat is not as advantageous, and there’s been selection against this combination of traits. Europeans are actually relatively better protected genetically against type 2 diabetes than some other populations around the world, like African Americans and Native Americans, that have perhaps not been exposed to agriculture for as much time. So you may be seeing the effect of more exposure to more stable food accessibility. This is also another way in which the data go against a common story. The common story is that hunter-gatherers actually had much more stable diets because they were more varied, and they weren’t reliant on a single cereal or crop for their calories. If one game went away, they had other things they could scout for. They could move locations more easily because they weren’t tied down to the land. So they were more food-stable. But if there’s been selection against storage of body fat, that suggests that as unstable and as common as famines might have been in agricultural societies, it’s at least more stable than what the hunter-gatherers had. There’s a timescale issue. You’re absolutely right. As I understand it, I’m no anthropologist, when there’s a hunt in traditional societies or communities that hunt, people will often gorge themselves, eat a huge amount, build up a temporary store of fat, and then go multiple days without eating meat until the next hunt. There is this boom-and-bust access to high-value nutrition that is not true to the same extent in farming communities. On the flip side, famines are something that occurs more commonly in agricultural societies, but the timescale and the tempo of them is very different from the hunting tempo. Maybe there’s a famine every three years. Indeed, if you look at the bones of farmers, at least in some communities, there’s more stress in them, maybe due to a famine every three years or every five years. But selection might not be acting on that three-year time period. Your fat store from the latest hunt is not going to carry you through to the famine three years later. Survival of famines is a different thing than building up body fat to be able to survive two weeks later.…

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