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Thread: evolution and lactose-tolerance

  1. #1 evolution and lactose-tolerance 
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    First off, please excuse me if I show a complete lack of understanding in regards to evolution, I've only taken one high school bio class...

    I've read that most humans are lactose-intolerant, but that a few populations are lactose-tolerant. I guess my question is, did the lactose-tolerance come before or after they began consumption of milk? In other words, is the fact that some populations are tolerant completely random?

    I know that many changes in life come from the fact that some animals with a mutation are better suited to survive, so those with it survive, and pass it on to their offspring, but I fail to see how something like a mutation for lactose-tolerance could lead to an entire population becoming tolerant. It seems relatively trivial, I mean it's hard to imagine a scenario where someone's survival is based on whether or not they are lactose-tolerant.

    Might be a stupid question, but give me a break, I'm still going to take a college bio class or two


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  3. #2  
    Forum Isotope Zelos's Avatar
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    I mean it's hard to imagine a scenario where someone's survival is based on whether or not they are lactose-tolerant.
    not really, when its a lack of food and such lactose tolerance give you an extra source of energy. I for my part is lactose tolerant.

    The mutation came about at the time when needed milk and such. simple evollutionary basics


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    Forum Freshman Draculogenes's Avatar
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    babies aren't usually lactose intolerant, jsut adults. Adults weren't supposed to drink milk, so they'd have no reason to produce lactase. However if babies couldn't digest lactose, they'd probably die. Since i'm not sure if lactose-intolerance has anything to do with age, i can't make a call here. But i figure if it wasn't all lactose-intolerant people would have died off in infancy, therefore no propagation of genes.
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  5. #4  
    Forum Professor captaincaveman's Avatar
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    The fact that drinking cows milk is quite a modern thing in the evolution of man and maybe our digestive system hasn't caught up with our diets

    Just a thought :-D
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    Forum Professor Zwolver's Avatar
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    no, humans have been milking animals for centuries. It is just that the entire shift of human life brings the "lactose intollerant" towards those who drink milk.

    Adoption, migration all add to the point that people who's ancestors never drank milk get to those who have done it for centuries. And so they havent lost the gene that digestes lactose.
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    Forum Freshman electricant's Avatar
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    Lactase is the gene that breaks down lactose, the principal sugar present in milk. All mammals can produce this enzyme as infants but as they grow up expression is stopped. This correlates with being weened from breast milk (and makes sense because it is a waste of resources to continue to make enzymes which are no longer needed).

    At various times in history groups of humans have changed from a nomadic, hunter-gatherer type lifestyle to a more reliable crops/animal-farming way of life. Around this time sheep/goat/cow milk became available as an alternative source of fluid, but was not ideal as it lead to gas and diarrhea in most people. Nutrition was still poor in those times so humans who acquired a mutation that lead to life-long expression of lactase were at a significant selective advantage. This is why lactose-tolerance (ie adult lactase expression) has spread throughout the majority of european and north american population. Cultures which have never traditionally drank milk as adults remain lactose intolerant, indeed lactose intolerance is far more common in world population than tolerance.

    So to answer your question: lactose tolerance can occur through a mutation in the regulatory regions of the lactase gene. After we started farming cattle, people who acquired this random mutation had a huge selective advantage because they could use milk as an extra fluid/food source. This is the reason that lactose tolerance spread among farming populations.

    Lactase tolerance is really interesting as its preponderance in certain parts of the world identifies populations who took to cattle farming. Another gene that identifies regional changes in human culture is alcohol dehydrogenase.
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  8. #7  
    Forum Professor captaincaveman's Avatar
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    Quote Originally Posted by Zwolver
    no, humans have been milking animals for centuries. It is just that the entire shift of human life brings the "lactose intollerant" towards those who drink milk.

    Adoption, migration all add to the point that people who's ancestors never drank milk get to those who have done it for centuries. And so they havent lost the gene that digestes lactose.


    but centuries is a short time in evolution history :wink:
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  9. #8  
    Forum Freshman electricant's Avatar
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    Quote Originally Posted by captaincaveman
    but centuries is a short time in evolution history :wink:
    Its probably closer to a few millenia since we started farming animals. This is still a short amount of time in evolutionary terms but we are talking about a single specific mutation that affects lactase expression, not the evolution of the eye or anything else of such complexity!
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  10. #9  
    Cooking Something Good MacGyver1968's Avatar
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    Quote Originally Posted by electricant
    indeed lactose intolerance is far more common in world population than tolerance.
    Holy cow! (pun intended). That's why I come to this forum, I learn new things every day. I thought the exact opposite was true.
    Fixin' shit that ain't broke.
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  11. #10  
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    Quote Originally Posted by Draculogenes
    babies aren't usually lactose intolerant, jsut adults. Adults weren't supposed to drink milk, so they'd have no reason to produce lactase. However if babies couldn't digest lactose, they'd probably die. Since i'm not sure if lactose-intolerance has anything to do with age, i can't make a call here. But i figure if it wasn't all lactose-intolerant people would have died off in infancy, therefore no propagation of genes.
    I wasn't clear in my original post, but I was actually referring to lactose-tolerance in adults.
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  12. #11  
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    Quote Originally Posted by electricant
    Lactase is the gene that breaks down lactose, the principal sugar present in milk. All mammals can produce this enzyme as infants but as they grow up expression is stopped. This correlates with being weened from breast milk (and makes sense because it is a waste of resources to continue to make enzymes which are no longer needed).

    At various times in history groups of humans have changed from a nomadic, hunter-gatherer type lifestyle to a more reliable crops/animal-farming way of life. Around this time sheep/goat/cow milk became available as an alternative source of fluid, but was not ideal as it lead to gas and diarrhea in most people. Nutrition was still poor in those times so humans who acquired a mutation that lead to life-long expression of lactase were at a significant selective advantage. This is why lactose-tolerance (ie adult lactase expression) has spread throughout the majority of european and north american population. Cultures which have never traditionally drank milk as adults remain lactose intolerant, indeed lactose intolerance is far more common in world population than tolerance.

    So to answer your question: lactose tolerance can occur through a mutation in the regulatory regions of the lactase gene. After we started farming cattle, people who acquired this random mutation had a huge selective advantage because they could use milk as an extra fluid/food source. This is the reason that lactose tolerance spread among farming populations.

    Lactase tolerance is really interesting as its preponderance in certain parts of the world identifies populations who took to cattle farming. Another gene that identifies regional changes in human culture is alcohol dehydrogenase.
    Ok, thanks for the depth you went to. You said that those who have the random mutation are at an advantage, which makes perfect sense, but also highlights what confused me.

    Let me try to explain, say you have a population whose adults can't digest lactose, but a few of them get this mutation that allows them to do so. What's confusing about this situation to me, is that I don't see how it would lead to the population becoming primarily lactose-tolerant, because (as far as I know) lactose-intolerance isn't going to cause problems that will remove you from the gene pool.

    Maybe someone with intolerance who consumes dairy causes more problems than I realize? (I'm lactose-tolerant myself). I can see the advantage tolerance gives in a society with dairy, but I would think that someone would put up with gas or some diarreah if the alternative is starvation (unless, like I said, the symptoms are worse than I realize).

    Thanks again
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  13. #12  
    Forum Masters Degree invert_nexus's Avatar
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    In modern society, you can handle diarhea quite well with minimal loss of life and health.

    This is not the case in more primitive socities which are on the edge of existence.

    A good case of the squirts could be a death sentence.
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