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"But that can also be determined by what we are exposed to in infancy and in the womb too.
Also, UHT and skimmed/semi-skimmed milk may exacerbate the problem because it's too easy to digest and breaks down too quickly in the intestines. Just a hypothesis, but processed food and stress may be a large cause of IBS."
none of this has ANYTHING to do with the inability to produce lactase and thus the inability to metabolize lactose.
"but processed food and stress may be a large cause of IBS.""
it might cause the same symptoms, but it doesn't suddenly switch off a gene when lactose is present. really, you don't choose whether you switch on these genes, they just do in the presence of substrate. or did the gene expression mechanism of the Lac gene suddenly change while i was gone?
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Why would not being able to digest milk subject someone to natural selection? Or was it more of an ongoing process of exposure resulted in this mutation?
Those who live in a culture that drinks a lot of milk are going to benefit from being able to drink milk safely. This creates a selection pressure, and thus natural selection comes into play. Those who just so happen to be lactose tolerant are more likely to have kids, thus spreading their lactose tolerant genes.
Without the selection pressure, then lactose intolerant people would have kids just as often as the lactose tolerant people, so natural selection doesn't favour either.
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"Why would not being able to digest milk subject someone to natural selection?"
....because it's and entirely new substrate we can metabolize to glucose....and glucose=win in biology.
"Or was it more of an ongoing process of exposure resulted in this mutation?"
noo, it was a ongoing process of exposure that led to the SELECTION, mutations where happening all the time, they just weren't selected for. i mean....why select for lactose if you're not consuming it after your 3rd year anyway.
basic biology.
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It's a great pity that natural selection has been described by the phrases "survival of the fittest" and "nature is red in tooth and claw". These conjure up the idea of healthy specimens pushing out the weak and infirm. However, the testament that belies these exaggerated expressions is the way our bodies repair themselves and fight off infections etc. From an evolutionary point of view, countless reproductively successful individuals (the so-called 'fittest') will have suffered from disease, lost teeth, infected gums, missing limbs, scarred bodies and broken bones.
True, there is a struggle for existence, but much of this is to do with environmental factors that limit reproduction, rather than direct and aggressive competition. Natural selection is much better described in terms of long-term differential survival rates.
Originally Posted by catzrfluffy
Why would not being able to digest milk subject someone to natural selection?
I'll rephrase that, if you don't mind. Since the ancestral position was for digestive lactase to decline rapidly after weaning, the question you should be asking is why would retaining it be subject to natural selection.
If animals are being reared as beasts of burden and for their meat, it would make sense to keep them in milk production, which provides an on-going supply of highly nutritious protein, fat and minerals.
Milk is uncontaminated by parasites, unlike stream water, making it a safer drink. Also, if those that were intolerant of lactose tried to drink the milk, they would develop diarrhoea and vomiting – this could be lethal in difficult living conditions and they could therefore die of dehydration in the most extreme cases. Another suggestion is the benefit of having a continuous supply of milk as opposed to seasonal crops – cows will give milk all year round whereas crops can only thrive at certain times in the year. Also, milk has many nourishing properties – it is high in fat and calcium, amongst other nutrients. All in all, the ability to drink milk gave some early Europeans and East Africans a big survival advantage.
ht*p://darwinstudents.blogspot.com/2009/02/evolution-of-lactose-tolerance.html
Lactose tolerance is an example of a genetic change associated with a cultural practice.
Originally Posted by catzrfluffy
Or was it more of an ongoing process of exposure resulted in this mutation?
Good question. From the neo-Darwinian point of view, this would be considered very unlikely because that is not the mechanism by which evolution is thought to proceed. Also, mutations have been detected in the genes that regulate the activity of the lactase gene. However, without the mutations, you're right, it could be due to epigenetic effects. Evolutionary biologists don't have all the answers and indeed, it could be argued that these mutations came before any cattle were being milked and milk consumption simply followed as a consequence being able to drink it.
"Evolutionary biologists don't have all the answers and indeed, it could be argued that these mutations came before any cattle were being milked and milk consumption simply followed as a consequence being able to drink it."
mm nice insight.
but why then the distribution we observe? why is it that all milk drinking cultures have such a high percentage of tolerance and all the others have such a low percentage? surely that is the strongest piece of evidence for it to have evolved due to selective preassures caused by husbandry?
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"Evolutionary biologists don't have all the answers and indeed, it could be argued that these mutations came before any cattle were being milked and milk consumption simply followed as a consequence being able to drink it."
mm nice insight.
but why then the distribution we observe? why is it that all milk drinking cultures have such a high percentage of tolerance and all the others have such a low percentage? surely that is the strongest piece of evidence for it to have evolved due to selective preassures caused by husbandry?
I agree, but how did drinking milk from other mammals originate? One can only speculate, but one possibility is that non-human milk might have been used to feed babies where the mother was unable to produce sufficient quantities of her own. Maybe there were other adaptations taking place, before there were any mutations, that extended a baby's tolerance of lactose into childhood, but not into adulthood. Also, some cultures made cheese from their milk (the process of making cheese reduces the amount of lactose) - and that would have established milking as a cultural practice, as you suggest. Finally, I understand it's not just a single mutation responsible for the trait.
So I don't think these mutations arose before milk consumption, I think they simply extended an already established practice, which would therefore have been associated with animal husbandry.
I agree, but how did drinking milk from other mammals originate? One can only speculate, but one possibility is that non-human milk might have been used to feed babies where the mother was unable to produce sufficient quantities of her own. Maybe there were other adaptations taking place, before there were any mutations, that extended a baby's tolerance of lactose into childhood, but not into adulthood. Also, some cultures made cheese from their milk (the process of making cheese reduces the amount of lactose) - and that would have established milking as a cultural practice, as you suggest. Finally, I understand it's not just a single mutation responsible for the trait.
So I don't think these mutations arose before milk consumption, I think they simply extended an already established practice, which would therefore have been associated with animal husbandry.
Just to be pedantic for no good reason... the mutations arise when they arise, not when they're needed. They stay when they're useful, but they arise whenever they feel like it .
__________________
A scientific man ought to have no wishes, no affections, -- a mere heart of stone.
- Charles Darwin
"I am a scientist... when I find evidence that my theories are wrong, it is as exciting as if the evidence proved them right."
- Stargate: SG1
What can be asserted without reason, can be denied without reason.
- Anon
"A casual stroll through the lunatic asylum shows that faith does not prove anything."
Why would not being able to digest milk subject someone to natural selection? Or was it more of an ongoing process of exposure resulted in this mutation?
Because when the E. coli in the DM25 solution have used up all the citrate, they die... Unless of course they have the ability to use the huge amounts of citrate as an energy source.
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I agree, but how did drinking milk from other mammals originate? One can only speculate, but one possibility is that non-human milk might have been used to feed babies where the mother was unable to produce sufficient quantities of her own. Maybe there were other adaptations taking place, before there were any mutations, that extended a baby's tolerance of lactose into childhood, but not into adulthood. Also, some cultures made cheese from their milk (the process of making cheese reduces the amount of lactose) - and that would have established milking as a cultural practice, as you suggest. Finally, I understand it's not just a single mutation responsible for the trait.
So I don't think these mutations arose before milk consumption, I think they simply extended an already established practice, which would therefore have been associated with animal husbandry.
Just to be pedantic for no good reason... the mutations arise when they arise, not when they're needed. They stay when they're useful, but they arise whenever they feel like it .
I'm sorry you misunderstood me, I never suggested anything otherwise.
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