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Explain to me how childhood exposure to milk (the period when humans tolerate lactose) selects against lactose intolerance in adulthood? People who are lactose

by MaysonL 12y ago

Explain to me how childhood exposure to milk (the period when humans tolerate lactose) selects against lactose intolerance in adulthood? People who are lactose tolerant will be able to continue drinking milk well after those in their birth cohort who are lactose intolerant will have to stop. They will thus be likely to be substantially better fed with subsequent better health. People who are lactose tolerant will be able to survive famines where lactose intolerant people will starve.

galacticLactic 12y ago
Sure, I get the general concept that we assume must exist because it sounds like it's probably reasonable, but there's no concrete smoking gun evidence of that particular mechanism at work anywhere in the world. Not even in folklore. Where in history is the famine in which plenty of farm animals were thriving and impregnating and lactating amongst one another, but all the humans had to live on was milk?
- mc32 12y ago
  Maybe it was more like among a small tribe/civilization there were those who specialized in herding cows and could take them to green pastures when a drought hit the tribe's normal crops. Herders could bring their cows down from the unfarmable hillsides to sustain the other townies with their cow byproducts. They could have milked and produced cheese while holed up along caves etc. during their season "away". (think how trappers live away from their town for most of the year and come in to town, only in the off season.
- azakai 12y ago
  There wouldn't necessarily be an extreme event like a famine in which only consuming milk would save you. It could well be that consuming milk gave you even just 1% more calories on average (not skipping a meal every so often, when all there is is milk to be eaten right at that moment, because other food spoiled or was unavailable). Even a 1% fitness increase compounds itself over multiple generations into a large effect, even if in each generation it is so small it is hardly noticeable (and so not written into legend).
- ansible 12y ago
  Producing the lactase enzyme also has a biologic energy cost. If the is no regular milk in your diet, then it is a waste of energy. That's why it is selected against in many situations.
- baddox 12y ago
  That's like asking when in history was there some catastrophic era where particles were flying into some organisms' eyes and the only individuals that survived were those who (through genetic mutations) had small hairs around their eyes that managed to catch some of the particles.
  - digi_owl 12y ago
    I guess it is hard for most to come to terms with just how long time scales evolution works on.

by MaysonL 12y ago

galacticLactic 12y ago

Sure, I get the general concept that we assume must exist because it sounds like it's probably reasonable, but there's no concrete smoking gun evidence of that particular mechanism at work anywhere in the world. Not even in folklore. Where in history is the famine in which plenty of farm animals were thriving and impregnating and lactating amongst one another, but all the humans had to live on was milk?

mc32 12y ago
Maybe it was more like among a small tribe/civilization there were those who specialized in herding cows and could take them to green pastures when a drought hit the tribe's normal crops. Herders could bring their cows down from the unfarmable hillsides to sustain the other townies with their cow byproducts. They could have milked and produced cheese while holed up along caves etc. during their season "away". (think how trappers live away from their town for most of the year and come in to town, only in the off season.
azakai 12y ago
There wouldn't necessarily be an extreme event like a famine in which only consuming milk would save you. It could well be that consuming milk gave you even just 1% more calories on average (not skipping a meal every so often, when all there is is milk to be eaten right at that moment, because other food spoiled or was unavailable). Even a 1% fitness increase compounds itself over multiple generations into a large effect, even if in each generation it is so small it is hardly noticeable (and so not written into legend).
ansible 12y ago
Producing the lactase enzyme also has a biologic energy cost. If the is no regular milk in your diet, then it is a waste of energy. That's why it is selected against in many situations.
baddox 12y ago
That's like asking when in history was there some catastrophic era where particles were flying into some organisms' eyes and the only individuals that survived were those who (through genetic mutations) had small hairs around their eyes that managed to catch some of the particles.
- digi_owl 12y ago
  I guess it is hard for most to come to terms with just how long time scales evolution works on.