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Interesting. As a Chinese I have always wondered why lactose intolerance is so common in China but not in the west. Turns out I asked the wrong question :)

by xiaq 12y ago

raldi 12y ago
Before cows and sheep and goats were domesticated, it made sense for humans to be lactose-intolerant as adults. Otherwise, during a time of scarcity and near-starvation, the strongest members of the group could forcefully take all the available breast milk, or the older siblings would demand it, and the babies and infants would die. Nature's solution was to make sure that anyone old enough to eat real food would suffer greatly if they refused to wean themselves. But once people had animal milk available, it was a gigantic natural advantage to be able to drink it as adults -- not just for nutrients and calories, but much more significantly, to avoid dehydration, which was a major killer back then.
- irishcoffee 12y ago
  >during a time of scarcity and near-starvation You may not know much about lactation, but nutrition is a big part of it. If there is a famine/drought, there is no milk to be had, doesn't matter how strong you may be.
  - raldi 12y ago
    Why do you think lactose intolerance came about, if not as evolution's way to ensure that the available milk went to those who needed it because they were not yet old enough to eat normal food?
    - samatman 12y ago
      Producing lactase is costly, those proteins could be doing other things. What's the evolutionary selection pressure to continue digesting a food source that's only present in the infant diet? None.
      - raldi 12y ago
        That's circular reasoning. The only reason it was "only present in the infant diet" is because of the evolution of lactose intolerance. Without that development, children would keep drinking milk for as long as they could get away with it. But don't take my word for it; here's what Slate has to say: "With Cain weaned, Abel could claim more of his mother's attention and all of her milk. This kept a lid on sibling rivalry [...] while allowing women to bear more young." http://www.slate.com/articles/health_and_science/human_evolution/2012/10/evolution_of_lactose_tolerance_why_do_humans_keep_drinking_milk.html http://www.slate.com/articles/health_and_science/human_evolu...
  - raldi 12y ago
    That doesn't appear to be correct; e.g.: "There is a common misconception that malnutrition greatly reduces the amount of milk a mother produces. Although malnutrition may affect the quality of milk, studies show that the amount of breastmilk produced depends mainly on how often and how effectively the baby sucks on the breast. If a mother temporarily produces less milk than the infant needs, the infant responds by suckling more vigorously, more frequently, or longer at each feeding. This stimulates greater milk production." http://rehydrate.org/breastfeed/faq-maternal-nutrition.htm http://rehydrate.org/breastfeed/faq-maternal-nutrition.htm Do you have a citation saying otherwise?
    - irishcoffee 12y ago
      No I don't. Perhaps I should do more homework. I was appealing to common sense. If there is a famine or drought, people are starving and thirsty. Making milk is a lot of work and requires at least marginally decent nutrition. If someone is only eating one "meal" a day and drinking 2-4 cups of water a day, there's just not much with which to make milk. N=1 anecdote, my daughters mother was very easily able to tell how her diet affected breastfeeding. A lot of it had to do with water intake.
- a3n 12y ago
  Maybe I don't understand cows. If you had milk to drink, then why couldn't you just drink the water that the cows and other animals drank?
  - eru 12y ago
    Milk has calories. Cows make milk calories out of grass. Grass is useless for humans otherwise.
  - raldi 12y ago
    "Other researchers have suggested that fresh milk provided a more pure fluid alternative to contaminated water sources in arid environments" http://www.npr.org/blogs/thesalt/2012/12/27/168144785/an-evolutionary-whodunit-how-did-humans-develop-lactose-tolerance http://www.npr.org/blogs/thesalt/2012/12/27/168144785/an-evo... "Milk is uncontaminated by parasites, unlike stream water, making it a safer drink." http://darwinstudents.blogspot.com/2009/02/evolution-of-lactose-tolerance.html http://darwinstudents.blogspot.com/2009/02/evolution-of-lact...
  - bane 12y ago
    Cows convert grass and water into meat and milk. Humans convert grass and water into starvation.
- pascal_cuoq 12y ago
  > … it made sense for humans to be lactose-intolerant as adults > Nature's solution was … What made sense for an individual human is for everyone to be lactose-intolerant except them. This is what gives the best results for the individual in the near-starvation scenario. Your suggestion sounds very much like “group selection”, an idea with many high-profile detractors (http://en.wikipedia.org/wiki/Group_selection http://en.wikipedia.org/wiki/Group_selection ). The only argument I read against it was in “The Selfish Gene”, but according to the Wikipedia page, I could have picked from other high-profile scientists. Something looking like group selection may work in some cases (“The Selfish Gene” itself describes John Maynard Smith's counter-proposal of Evolutionary Stable Strategies), but offering such an explanation as obvious amounts to ignoring a lot of debunking by many bright people.
douche 12y ago
That is something that I also, as an American of mostly English/French/German descent, have wondered about. It was, quite frankly, a revelation to me when I first encountered people who were lactose intolerant in college. It seems even more unlikely, given that China has had so much interaction with the nomad peoples from Mongolia, Manchuria, and central Asia, who lived mostly off of their herds and milk-products.
- xiaq 12y ago
  > It seems even more unlikely, given that China has had so much interaction with the nomad peoples from Mongolia, Manchuria, and central Asia, who lived mostly off of their herds and milk-products. Dairy products never really made it into Chinese diet. The next question to ask is why diary products didn't make it into Chinese diet despite the interactions with the nomad peoples :)
  - douche 12y ago
    That is a very interesting question. The most obvious answer is that most of south-central China is just more suited to rice production than cattle/sheep/goats. I still find it interesting, since many of the more successful Chinese ruling dynasties have central/north asian roots (Tang, Yuan, Qing). Considering that Genghis Khan is probably an ancestor to most of the eastern half of eurasia, once might expect those lactose-tolerant genes to be more prevalent.
    - xiaq 12y ago
      > Considering that Genghis Khan is probably an ancestor to most of the eastern half of eurasia, This is simply wrong. Maybe some 16 million. But that has also been more of a hypothesis. See http://clubtroppo.com.au/2012/10/15/why-genghis-khan-wont-have-had-16-million-descendants/ http://clubtroppo.com.au/2012/10/15/why-genghis-khan-wont-ha... for one of the refutations for instance.
      - jobposter1234 12y ago

Interesting. As a Chinese I have always wondered why lactose intolerance is so common in China but not in the west. Turns out I asked the wrong question :)

by xiaq 12y ago

Interesting. As a Chinese I have always wondered why lactose intolerance is so common in China but not in the west. Turns out I asked the wrong question :)

raldi 12y ago

Before cows and sheep and goats were domesticated, it made sense for humans to be lactose-intolerant as adults. Otherwise, during a time of scarcity and near-starvation, the strongest members of the group could forcefully take all the available breast milk, or the older siblings would demand it, and the babies and infants would die. Nature's solution was to make sure that anyone old enough to eat real food would suffer greatly if they refused to wean themselves. But once people had animal milk available, it was a gigantic natural advantage to be able to drink it as adults -- not just for nutrients and calories, but much more significantly, to avoid dehydration, which was a major killer back then.

irishcoffee 12y ago
>during a time of scarcity and near-starvation You may not know much about lactation, but nutrition is a big part of it. If there is a famine/drought, there is no milk to be had, doesn't matter how strong you may be.
- raldi 12y ago
  Why do you think lactose intolerance came about, if not as evolution's way to ensure that the available milk went to those who needed it because they were not yet old enough to eat normal food?
  - samatman 12y ago
    Producing lactase is costly, those proteins could be doing other things. What's the evolutionary selection pressure to continue digesting a food source that's only present in the infant diet? None.
    - raldi 12y ago
      That's circular reasoning. The only reason it was "only present in the infant diet" is because of the evolution of lactose intolerance. Without that development, children would keep drinking milk for as long as they could get away with it. But don't take my word for it; here's what Slate has to say: "With Cain weaned, Abel could claim more of his mother's attention and all of her milk. This kept a lid on sibling rivalry [...] while allowing women to bear more young." http://www.slate.com/articles/health_and_science/human_evolution/2012/10/evolution_of_lactose_tolerance_why_do_humans_keep_drinking_milk.html http://www.slate.com/articles/health_and_science/human_evolu...
- raldi 12y ago
  That doesn't appear to be correct; e.g.: "There is a common misconception that malnutrition greatly reduces the amount of milk a mother produces. Although malnutrition may affect the quality of milk, studies show that the amount of breastmilk produced depends mainly on how often and how effectively the baby sucks on the breast. If a mother temporarily produces less milk than the infant needs, the infant responds by suckling more vigorously, more frequently, or longer at each feeding. This stimulates greater milk production." http://rehydrate.org/breastfeed/faq-maternal-nutrition.htm http://rehydrate.org/breastfeed/faq-maternal-nutrition.htm Do you have a citation saying otherwise?
  - irishcoffee 12y ago
    No I don't. Perhaps I should do more homework. I was appealing to common sense. If there is a famine or drought, people are starving and thirsty. Making milk is a lot of work and requires at least marginally decent nutrition. If someone is only eating one "meal" a day and drinking 2-4 cups of water a day, there's just not much with which to make milk. N=1 anecdote, my daughters mother was very easily able to tell how her diet affected breastfeeding. A lot of it had to do with water intake.
a3n 12y ago
Maybe I don't understand cows. If you had milk to drink, then why couldn't you just drink the water that the cows and other animals drank?
- eru 12y ago
  Milk has calories. Cows make milk calories out of grass. Grass is useless for humans otherwise.
- raldi 12y ago
  "Other researchers have suggested that fresh milk provided a more pure fluid alternative to contaminated water sources in arid environments" http://www.npr.org/blogs/thesalt/2012/12/27/168144785/an-evolutionary-whodunit-how-did-humans-develop-lactose-tolerance http://www.npr.org/blogs/thesalt/2012/12/27/168144785/an-evo... "Milk is uncontaminated by parasites, unlike stream water, making it a safer drink." http://darwinstudents.blogspot.com/2009/02/evolution-of-lactose-tolerance.html http://darwinstudents.blogspot.com/2009/02/evolution-of-lact...
- bane 12y ago
  Cows convert grass and water into meat and milk. Humans convert grass and water into starvation.
pascal_cuoq 12y ago
> … it made sense for humans to be lactose-intolerant as adults > Nature's solution was … What made sense for an individual human is for everyone to be lactose-intolerant except them. This is what gives the best results for the individual in the near-starvation scenario. Your suggestion sounds very much like “group selection”, an idea with many high-profile detractors (http://en.wikipedia.org/wiki/Group_selection http://en.wikipedia.org/wiki/Group_selection ). The only argument I read against it was in “The Selfish Gene”, but according to the Wikipedia page, I could have picked from other high-profile scientists. Something looking like group selection may work in some cases (“The Selfish Gene” itself describes John Maynard Smith's counter-proposal of Evolutionary Stable Strategies), but offering such an explanation as obvious amounts to ignoring a lot of debunking by many bright people.

douche 12y ago

That is something that I also, as an American of mostly English/French/German descent, have wondered about. It was, quite frankly, a revelation to me when I first encountered people who were lactose intolerant in college. It seems even more unlikely, given that China has had so much interaction with the nomad peoples from Mongolia, Manchuria, and central Asia, who lived mostly off of their herds and milk-products.

xiaq 12y ago
> It seems even more unlikely, given that China has had so much interaction with the nomad peoples from Mongolia, Manchuria, and central Asia, who lived mostly off of their herds and milk-products. Dairy products never really made it into Chinese diet. The next question to ask is why diary products didn't make it into Chinese diet despite the interactions with the nomad peoples :)
- douche 12y ago
  That is a very interesting question. The most obvious answer is that most of south-central China is just more suited to rice production than cattle/sheep/goats. I still find it interesting, since many of the more successful Chinese ruling dynasties have central/north asian roots (Tang, Yuan, Qing). Considering that Genghis Khan is probably an ancestor to most of the eastern half of eurasia, once might expect those lactose-tolerant genes to be more prevalent.
  - xiaq 12y ago
    > Considering that Genghis Khan is probably an ancestor to most of the eastern half of eurasia, This is simply wrong. Maybe some 16 million. But that has also been more of a hypothesis. See http://clubtroppo.com.au/2012/10/15/why-genghis-khan-wont-have-had-16-million-descendants/ http://clubtroppo.com.au/2012/10/15/why-genghis-khan-wont-ha... for one of the refutations for instance.
    - jobposter1234 12y ago