4 ms·

I'm not seeing the issue here. As you say, let's talk about this at the individual level: picture yourself as a prehistoric pastoralist raising cattle. They eat

I'm not seeing the issue here. As you say, let's talk about this at the individual level: picture yourself as a prehistoric pastoralist raising cattle. They eat plants you can't digest, and from them you get milk and meat. Everybody knows that you can't just drink the milk raw -- the lactose in there will really do a number on your digestive system -- but processed milk products like cheese make up a major part of your diet. ... Except that you can digest the lactose. You don't feel sick after drinking milk, because you have a mutation that breaks the normal mammalian mechanism for reducing lactase production in adulthood. Sounds nice, right? But maybe not something that'll bring a huge reproductive advantage to you and yours; more of a cool party trick to show off to your neighbors. And then one year there's not nearly enough rain. Famines have always been pretty common, alas, and here's another one. Now consider this: processing the milk so lactose-intolerant people can digest it loses about 40% of the calories. You can drink it straight because of your freaky mutant milk-drinking powers, and your neighbors can't. You get a lot more food at a time when people are dying from lack of food. Is this sounding like an evolutionary advantage? The sort of thing you might pass on to the kids you'll have because you didn't starve? The ability to digest lactose as an adult is potentially a really big deal if you happen to live in a culture that already uses processed milk products as a major source of calories.

TangoTrotFox 8y ago
Dairy products would not have made up a substantial portion of a regions diet until lactose tolerance had emerged. Lactose intolerance extends to all dairy products, not just milk. And again, you need lactating animals to produce consistent dairy products. Animals do not naturally lactate unless they're feeding their young. And animals also do not naturally produce the freakish amount of milk that we're able to extract now a days from millennia of artificial selection and, in the US at least, using a lifelong cocktail of all sorts of different drugs. To be clear, I do agree with you that in certain uncommon scenarios lactose tolerance could provide a tangible, though not enormous, advantage. And that's the problem. A different shaped beak for a bird entails a never-ending constant, and enormous, advantage. Lactose tolerance is something that's pretty irrelevant by comparison, yet it would become ubiquitous.

TangoTrotFox 8y ago

Dairy products would not have made up a substantial portion of a regions diet until lactose tolerance had emerged. Lactose intolerance extends to all dairy products, not just milk. And again, you need lactating animals to produce consistent dairy products. Animals do not naturally lactate unless they're feeding their young. And animals also do not naturally produce the freakish amount of milk that we're able to extract now a days from millennia of artificial selection and, in the US at least, using a lifelong cocktail of all sorts of different drugs. To be clear, I do agree with you that in certain uncommon scenarios lactose tolerance could provide a tangible, though not enormous, advantage. And that's the problem. A different shaped beak for a bird entails a never-ending constant, and enormous, advantage. Lactose tolerance is something that's pretty irrelevant by comparison, yet it would become ubiquitous.