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Lactase Persistence: A Scientific Question

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  • Lactase Persistence: A Scientific Question

    Lactase persistence, which is the retention of the ability to digest lactose into adulthood, is a textbook example of human adaptation that occurred in the not so distant (on a geologic time scale) past. The story goes that those people who domesticated cattle and consumed their milk (most notably, northern Europeans) developed lactose persistence, while those people who did not (mostly Africans and Asians, though, importantly, NOT Africans who also happened to domesticate cattle, suggesting this is an issue of environmental context, not race) became lactose intolerant in adulthood.

    I have two big questions about this.

    First, how could have this evolved, especially so rapidly? An adaption will not evolve unless it confers increased fitness--a reproductive advantage. Was lactose intolerance so detrimental to fitness that the difference between it and lactase persistence was the difference between passing on one's genes or not? The evidence suggests yes, but I guess it's hard for me to fathom . . .

    (On an unrelated, but somewhat similar topic, I've heard some people argue that Type I diabetes is more common in northern Europeans because it conferred an advantage in a cold environment, which makes absolutely NO sense to me given what a huge fitness disadvantage Type 1 diabetes is, particularly pre-Insulin injection days.)

    Secondly, does this pose a challenge to the evolutionary rationale for avoiding grains? I am not trying to be hostile to the philosophy of grain abstinence as there seem to be plenty of nutritional/biochemical reasons for avoid them (as Mark says, there is no good reason to eat grains except as a cheap source of calories that quickly convert to glucose). This is more of a philosophic/scientific question.
    Last edited by Bill_89; 04-29-2011, 09:54 AM.

  • #2
    Yep.
    In all of the universe there is only one person with your exact charateristics. Just like there is only one person with everybody else's characteristics. Effectively, your uniqueness makes you pretty average.

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    • #3
      Lactase persistance did not develop *because* of animal husbandry. It is a genetic mutation. It did, just by chance, confer a reproductive advantage on those who had it when living in Northern Europe where it is bloody cold and you need every last calorie you can find to make it through the winter. Being able to eat milk and preserve milk products such as cheese became an advantage *under those climate conditions*, as opposed to the African people you mentioned.

      The T1 Diabetes argument is simply rubbish.

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      • #4
        Persistence into adulthood of childhood traits is a supreme boon for expedient adaptation. In any given generation you will have a degree of persistence of any particular childhood trait will persist into adulthood to a particular potency and frequency and what will will statistically add up in survival benefit over the generations. Perhaps someone has enough lactase persistence to increase their lifespan by 2 years and be somewhat stronger as a worker, then that could mean the difference between 3 children and 5, and then those genes will be passed on and will tend to flourish so long as there is selection pressure.

        Source: Richard Dawkins - The Greatest Show On Earth (wasn't about lactase in general but he used some of the physical traits of chimps to compare to humans as examples)

        There is however no such thing as childhood grain-tolerance traits. I'm not saying we don't have some adaptation, and some useful memes like cooking and soaking, but some of us are clearly better adapted to lactose than grain toxins.
        Stabbing conventional wisdom in its face.

        Anyone who wants to talk nutrition should PM me!

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        • #5
          Secondly, does this pose a challenge to the evolutionary rationale for avoiding grains? I am not trying to be hostile to the philosophy of grain abstinence as there seem to be plenty of nutritional/biochemical reasons for avoid them (as Mark says, there is no good reason to eat grains except as a cheap source of calories that quickly convert to glucose). This is more of a philosophic/scientific question.
          No... Mark points out in the PB that lactose persistence is probably the only genetic mutation/adaptation in the last 10,000 years that affects what some humans can eat, and differs by ancestry/genetics. Otherwise what is evolutionarily appropriate for humans to eat is pretty much the same, i.e. not grains, especially not wheat, because we haven't really faced selection pressures in recent times that would make eating grains somehow a genetic advantage.

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          • #6
            Originally posted by Stabby View Post
            There is however no such thing as childhood grain-tolerance traits. I'm not saying we don't have some adaptation, and some useful memes like cooking and soaking, but some of us are clearly better adapted to lactose than grain toxins.
            While there aren't specific childhood grain-tolerance traits, I think it's worth mentioning that humans did develop an adaptation for breaking down starches:

            Starch consumption is a prominent characteristic of agricultural societies and hunter-gatherers in arid environments. In contrast, rainforest and circum-arctic hunter-gatherers and some pastoralists consume much less starch1, 2, 3. This behavioral variation raises the possibility that different selective pressures have acted on amylase, the enzyme responsible for starch hydrolysis4. We found that copy number of the salivary amylase gene (AMY1) is correlated positively with salivary amylase protein level and that individuals from populations with high-starch diets have, on average, more AMY1 copies than those with traditionally low-starch diets. Comparisons with other loci in a subset of these populations suggest that the extent of AMY1 copy number differentiation is highly unusual. This example of positive selection on a copy number–variable gene is, to our knowledge, one of the first discovered in the human genome. Higher AMY1 copy numbers and protein levels probably improve the digestion of starchy foods and may buffer against the fitness-reducing effects of intestinal disease.
            Perry, GH, et al. Diet and evolution of human amylase gene copy number variation, Nature Genetics 39:1256-1260 (2007)

            This has no impact whatsoever on lectins or gluten, so there's still a great rationale for avoiding grains, but it does suggest that humans have evolved to eat starches.
            The Primal Holla! Eating fat. Getting lean. Being awesome.

            You were sick, but now you're well, and there's work to do. - Kilgore Trout

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            • #7
              mysterious double post!
              Last edited by theholla; 04-29-2011, 01:36 PM.
              The Primal Holla! Eating fat. Getting lean. Being awesome.

              You were sick, but now you're well, and there's work to do. - Kilgore Trout

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              • #8
                Yeah I'm not against starch in moderation. We were consuming starchy roots long ago and I can't really find evidence for tubers being unhealthy except perhaps less healthy if you base your diet on them then if you based it on fat.
                Stabbing conventional wisdom in its face.

                Anyone who wants to talk nutrition should PM me!

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                • #9
                  Probably less healthy. Definitely less fun. Mmmmm...fatty fat fat.
                  The Primal Holla! Eating fat. Getting lean. Being awesome.

                  You were sick, but now you're well, and there's work to do. - Kilgore Trout

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                  • #10
                    So is lactase persistance not an example of use-it-or-lose-it? would not a person who continues to consume milk after weaning retain the ability to digest it? while a person who stops consuming milk after weaning would lose that ability?

                    at least, in individuals who are not strongly genetically inclined one way or the other.

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                    • #11
                      Originally posted by Paleobird View Post
                      Lactase persistance did not develop *because* of animal husbandry. It is a genetic mutation. It did, just by chance, confer a reproductive advantage on those who had it when living in Northern Europe where it is bloody cold and you need every last calorie you can find to make it through the winter. Being able to eat milk and preserve milk products such as cheese became an advantage *under those climate conditions*, as opposed to the African people you mentioned.
                      I realize that evolution (specifically, mutation) does not directly respond to environmental need. However, the environment or context does indeed influence what genetic mutations are preserved. Hence, why we see lactase persistence in those of northern european descent and a higher rate of sickle cell anemia in people who descend from populations living in malaria environments.

                      There is however no such thing as childhood grain-tolerance traits. I'm not saying we don't have some adaptation, and some useful memes like cooking and soaking, but some of us are clearly better adapted to lactose than grain toxins.
                      I see what you mean about there being no childhood grain-tolerance traits . . . children do not (and never have) tolerated grains any better than adults.

                      However (not to be a pest), I still see how we can rule out an adaption to grain consumption in the last 10,000 years. The evolutionary rationale for the a paleo diet is that our genes have not adapted to a modern diet (particularly, grain consumption). Yet here we see lactase persistence evolved in 10,000 years. What makes grains different?

                      (I will say that one thing that makes grains different is that they too are actively evolving--and unlike milk, they don't "want" to be eaten. Cow milk is meant to be consumed, albeit not by humans, while grains are independent "self-interested" organisms).

                      No... Mark points out in the PB that lactose persistence is probably the only genetic mutation/adaptation in the last 10,000 years that affects what some humans can eat, and differs by ancestry/genetics. Otherwise what is evolutionarily appropriate for humans to eat is pretty much the same, i.e. not grains, especially not wheat, because we haven't really faced selection pressures in recent times that would make eating grains somehow a genetic advantage
                      Haven't faced selection pressures? I think most cultures (except maybe those at extreme latitudes) have eaten at least some grains over the last 10,000 years. Probably more cultures than consume dairy, though don't quote me on that. It would be reasonable to assume that 10,000 years is insufficient time to adapt (it is a blink of the eye on an evolutionary time scale), but then the dairy thing is hard to explain.
                      Last edited by Bill_89; 04-29-2011, 06:31 PM.

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                      • #12
                        Originally posted by elwyne View Post
                        So is lactase persistance not an example of use-it-or-lose-it? would not a person who continues to consume milk after weaning retain the ability to digest it? while a person who stops consuming milk after weaning would lose that ability?

                        at least, in individuals who are not strongly genetically inclined one way or the other.
                        Two years vegan and voila I'm lactose intolerant to a degree I never was before. I think it's gut flora, I don't buy the genetic argument on this one.
                        Wheat is the new tobacco. Spread the word.

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                        • #13
                          though, importantly, NOT Africans who also happened to domesticate cattle,
                          Rem: Africa temperature. Hot. Milk starts fermenting quickly as soon as expressed. No lactose left in the rapidly fermented milk. So no advantage in lactase persistence in these hot areas. Different matter in sh*tty cold natural 'fridge England!
                          Last edited by localad; 04-30-2011, 01:35 PM.
                          activate the rhythm, the rhythm that has always been within

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