3 ms·
Lots of "likelihood," "probablilities" and "maybes" floating around in that article, and not a lot of certainty. I find the article scant on proof, and speclati
by galacticLactic 12y ago
Lots of "likelihood," "probablilities" and "maybes" floating around in that article, and not a lot of certainty. I find the article scant on proof, and speclative at best.
In particular, there's this:
What this meant, says Kindstedt, is that “children
and newborns would be exposed to milk frequently,
which ultimately through random mutations selected
for children who could tolerate lactose later into
adulthood.”
Explain to me how childhood exposure to milk (the period when humans tolerate lactose) selects against lactose intolerance in adulthood?
For example, so let's say you have a mixed population of families, where initially there's a prevaling majority of hereditary lactose intolerance, but with a minority of the new mutants present, who decades later will comfortably continue to consume dairy.
Mutations are typically recessive so you might have households where one parent is lactose tolerant, and none of the children are, due to the lottery of gene expression in sexual reproduction. Maybe some intolerant children are carriers and some aren't, but it's still a roll of the dice.
How does consuming dairy products as a child select for this trait which will not be expressed until years later? What obvious mechanism of selection am I failing to understand here?
Are medieval societies filled with stories of the lactose intolerant humilating themselves with dairrhea on prom night and reducing themselves to social pariahs, doomed to die childless and alone? I mean really.
- defen 12y agoI don't think anyone knows how exactly lactase persistence arose in Europe. Here is a brand new paper describing a DNA analysis of 83 ancient European individuals: http://biorxiv.org/content/early/2015/03/13/016477.article-info http://biorxiv.org/content/early/2015/03/13/016477.article-i... The relatively late appearance (earliest known example of lactase persistence gene is from 4,300 years ago) and relatively small selective advantage (1.5%) are surprising. > Mutations are typically recessive so you might have households where one parent is lactose tolerant, and none of the children are, due to the lottery of gene expression in sexual reproduction. Maybe some intolerant children are carriers and some aren't, but it's still a roll of the dice. Lactase persistence is a dominant mutation. If you only have one copy of the gene you still produce enough lactase to fully digest milk.
- MaysonL 12y agoExplain 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 agoSure, 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 agoMaybe 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 agoThere 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).
- 12y ago
- vanderZwan 12y agoThe phrasing is wrong, but being lactose tolerant in adulthood would have meant having an extra possible food source compared to those who are not lactose tolerant. That is a pretty major advantage. Also, 5500 BC is not medieval society...
- galacticLactic 12y ago...and medieval society also didn't have high schol proms.
- autokad 12y agoI think the idea that natural selection and sexual selection as the only players in gene manipulation is probably wrong. genes are somewhat dynamic and pressures and exposures to a parent will result in offspring more likely to have mutations to deal with them
- autokad 12y agoThose who downvoted me, #1 I dont think comments should be down voted just because you do not 'agree' with them. I am just contributing to the conversation. #2, you probably have a grade school view of the world with regards to genetics. I admit that I have only a laymen / rudimentary understanding of genes. However, if you look up Epigenetics, you will find things are a bit more complicated. http://dukemagazine.duke.edu/article/big-question-can-your-environment-change-your-dna http://dukemagazine.duke.edu/article/big-question-can-your-e...