lvysaur
Member
- Joined
- Mar 15, 2014
- Messages
- 2,287
70% of the world's population (and 100% of other mammals) are lactose "intolerant", meaning they can't digest lactose
lactose "tolerance" (the trait of digesting lactose) only started evolving 5000 years ago. This is despite pastoralism being over 10,000 years old.
I use quotes because the term "intolerance" and "tolerance" are factually wrong; most so-called "lactose intolerant" people (81% to be precise) can drink 3 glasses of milk a day without issue. The remaining 19% probably just have microbiome issues.
The reason that lactose digestion (AKA "tolerance") evolved is due to starvation and living on poor agricultural soils. Lactose makes up 1/3 of milk's calories.
But why did lactose indigestion (lactose "intolerance", the ancestral state in all mammals) evolve in the first place? Why don't infants just stay digesting lactose throughout their whole lives, instead of shutting it off at age 3 (in human years)?
Mechanistic biologists say that it evolved to conserve energy. Making lactase takes energy, and milk isn't available regularly for most mammals. However, the amount of energy this saves is so miniscule that I have trouble believing it was important.
I think it's deeper than that. We know lactose fosters growth of gram-positive bacteria, so much so that an entire probiotic industry is based around yogurt. There is a problem with yogurt though, which is that stomach acid can kill bacteria. The only way to turn your intestines into a yogurt chamber is to be "lactose intolerant"
I think that as the infant mammal weaned off of milk, a gradually decreasing lactose digestion would allow more of the sugar into the large intestine, growing more lactobacillus species and setting the mammal up for good health in the future. This is probably one reason why mammals evolved to be lactose "intolerant".
lactose "tolerance" (the trait of digesting lactose) only started evolving 5000 years ago. This is despite pastoralism being over 10,000 years old.
I use quotes because the term "intolerance" and "tolerance" are factually wrong; most so-called "lactose intolerant" people (81% to be precise) can drink 3 glasses of milk a day without issue. The remaining 19% probably just have microbiome issues.
The reason that lactose digestion (AKA "tolerance") evolved is due to starvation and living on poor agricultural soils. Lactose makes up 1/3 of milk's calories.
But why did lactose indigestion (lactose "intolerance", the ancestral state in all mammals) evolve in the first place? Why don't infants just stay digesting lactose throughout their whole lives, instead of shutting it off at age 3 (in human years)?
Mechanistic biologists say that it evolved to conserve energy. Making lactase takes energy, and milk isn't available regularly for most mammals. However, the amount of energy this saves is so miniscule that I have trouble believing it was important.
I think it's deeper than that. We know lactose fosters growth of gram-positive bacteria, so much so that an entire probiotic industry is based around yogurt. There is a problem with yogurt though, which is that stomach acid can kill bacteria. The only way to turn your intestines into a yogurt chamber is to be "lactose intolerant"
I think that as the infant mammal weaned off of milk, a gradually decreasing lactose digestion would allow more of the sugar into the large intestine, growing more lactobacillus species and setting the mammal up for good health in the future. This is probably one reason why mammals evolved to be lactose "intolerant".
