An Evolutionary Whodunit: How Did Humans Develop Lactose Tolerance?

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Got milk? Ancient European farmers who made cheese thousands of years ago certainly had it. But at that time, they lacked a genetic mutation that would have allowed them to digest raw milk’s dominant sugar, lactose, after childhood.


Today, however, 35 percent of the global population — mostly people with European ancestry — can digest lactose in adulthood without a hitch.

So, how we did we transition from milk-a-phobics to milk-a-holics? “The first and most correct answer is, we don’t know,” says Mark Thomas, an evolutionary geneticist at University College London in the UK.

Most babies can digest milk without getting an upset stomach thanks to an enzyme called lactase. Up until several thousand years ago, that enzyme turned off once a person grew into adulthood — meaning most adults were lactose intolerant (or “lactase non-persistent” as scientists call it).

But now that doesn’t happen for most people of Northern and Central European descent and in certain African and Middle Eastern populations. This development of lactose tolerance took only about 20,000 years – the evolutionary equivalent of a hot minute – but it would have required extremely strong selective pressure.

“Something happened when we started drinking milk that reduced mortality,” saysLoren Cordain, an exercise physiologist at Colorado State University and an expert on Paleolithic nutrition. That something, though, is a bit of a mystery.

Written By: Helen Thompson
continue to source article at npr.org

18 COMMENTS

  1. Why is there programmed lactose intolerance in the first place? Was it a way to safeguard an exclusive food source for the younger generation? If so, it may have just become obsolete, the selection pressure maintaining it removed.

    I mean, as long as we’re just making stuff up….

  2. Perhaps not having to kill the animal to get our protein gave small groups the advantage of having access to a quickly renewable resource. Perhaps drought, ice ages and other pressures forced us to take advantage of animal milk instead of butchering what little meat we could find. Is there not an African tribe who mix the cow milk with its blood leaving the animal intact for a later meal?

    Those that could drink milk, survived; those that could not, starved from lack of meat.

    Just a wild guess.

  3. In reply to #1 by This Is Not A Meme:

    Why is there programmed lactose intolerance in the first place? Was it a way to safeguard an exclusive food source for the younger generation? If so, it may have just become obsolete, the selection pressure maintaining it removed.

    I mean, as long as we’re just making stuff up….
    Aren’t you stating that the wrong way round? It wasn’t intolerance programmed, it was tolerance NOT programmed. It was the latter that had to wait for the right mutation.

  4. In reply to #1 by This Is Not A Meme:

    Why is there programmed lactose intolerance in the first place? Was it a way to safeguard an exclusive food source for the younger generation? If so, it may have just become obsolete, the selection pressure maintaining it removed.

    I mean, as long as we’re just making stuff up….

    The body has to manufacture the enzyme necessary to digest lactose which has a material cost and therefore shuts down its production when it is no longer needed, which for most mammals is after weaning. This particular adaptation in humans is a lack of the inhibiting protein that would normally prevent the enzyme production.
    This a good example of evolution in action within the human gene population and its not too hard to see how this would have provided a survival advantage in Northern Europe during the long cold winters from the vitamins and proteins in milk.

  5. Here in fatso-land, lard-ass America, we need to have a clinic on every street corner that could induce lactose intolerance. Once upon a time in our evolutionary past, the ability to process this particular food source may have saved our lives, but now dairy products are adding much fat to our diet and it’s killing us!

    Help!

    Save us from death by lipid overdose!

  6. But now that doesn’t happen for most people of Northern and Central European descent and in certain African and Middle Eastern populations. This development of lactose tolerance took only about 20,000 years – the evolutionary equivalent of a hot minute – but it would have required extremely strong selective pressure.

    I would suspect that evolving a “broken genetic off switch”, that turned the enzyme off, should not take a lot of evolutionary time.
    There are, (and were), numerous pastoral herders who live on the milk of their, cattle, horses, yacks, goats, llamas etc. with the failure to use these resources likely to be fatal, or reducing reproduction, in environmentally stressful times.

  7. In reply to #6 by LaurieB:

    Here in fatso-land, lard-ass America, we need to have a clinic on every street corner that could induce lactose intolerance. Once upon a time in our evolutionary past, the ability to process this particular food source may have saved our lives, but now dairy products are adding much fat to our diet and it’s killing us!

    Help!

    Save us from death by lipid overdose!

    It’s not the fat in the milk that is the problem, but the opioid peptides that are in it that stimulate babies to drink it. (There are also non-opioid peptides that stimulate appetite btw.) It’s good for babies to drink mother’s milk of course, but cow milk for adults seem to be a bit of a misfire. :-) There are also opioid peptides in wheat. That’s why for example bakery / bread smells are spread via the airconditioning through the supermarket.

  8. In reply to #10 by Wokkie:

    Where is the edit button?

    The edit button atrophied when the forum developed the preview feature.  Now instead of a ten minute grace period, we just need to get it rite thirst thyme.

  9. In reply to #5 by mr_DNA:

    The body has to manufacture the enzyme necessary to digest lactose which has a material cost and therefore shuts down its production when it is no longer needed, which for most mammals is after weaning.

    Thank you. So losing the enzymes is a matter of optimum efficiency… that makes sense. This kind of economy is a known driving force, and very insightful. I imagine the enzyme has an energetic cost as well.

  10. A related issue/question is the tolerance for alcohol among Europeans, compared to that among North American Aboriginals. Did the consumption of alcoholic beverages drop off as the population of humans migrated north-east into Siberia, then across the Bering Strait ? Perhaps the climate of that time & place was not supportive of the grains used to make beer, etc. But I don’t recall reading that Central American populations were subject to the same reaction. Maybe by then & there (migration-wise) they could resume growing and fermenting grains.

  11. I’m just reading one of Loren Cordain’s books now. He’s got a short overview of paleolithic food on YouTube:

    http://www.youtube.com/watch?v=52A3ayfxfTs

    When I grew up in NZ we were in the midst of a govt education department national compulsory experiment where milk was supplied to kids in all primary schools. Milk would be delivered in bulk each school day morning to special racks, carefully designed by Ministry of Works engineers and situated where the milk crates would be exposed to maximum solar irradiation.

    To minimise transportation costs the milk was not refrigerated. After solar heating crates would be distributed to each classroom and allowed several hours to settle to reach optimum bacterial reproduction potential. Normally to the point where the tin foil caps on the milk bottles would bulge with the internal gas pressure.

    Shortly after consumption the sawdust man would visit each classroom with his bucket.
    Kids who became frequent customers of the sawdust man were deemed to be lactose intolerant.
    It truly is amazing how lactose tolerance could ever have developed in pre-refrigeration Neolithic times, let alone in modern unrefrigerated NZ schools.

    One unquantifiable aspect might be the impact of bovine growth hormone on human children. I was a heavy milk consumer throughout childhood and teens. I’m reasonably sure that I was never a customer of the sawdust man. And I grew to 195 cm and 93 kg before age 16. I wasn’t overweight and I wasn’t considered particularly large compared to many kids of similar age. Oddly enough I’m pretty much the same dimensions now, 4 decades on, yet I am a few kg overweight. (And addicted to cheese.)

    Given that grain consumption, introduced in Neolithic times, especially wheat farming, is quite harmful to human stature, strength, and overall health. (Check the book ‘Wheat Belly’ or various YouTube presentations by the author.) Then it might be that consumption of dairy products could have partially compensated for the negative impact of wheat on youthful growth. Which may have led to military or other physical advantages over competing tribes or cities during the initial stages of agriculture and early civilisation.

    So lactose tolerance may not have been so much lifesaving during famines for those who became lactose tolerant, but instead enabled some form of deathspending to be inflicted upon rival tribes that remained lactose intolerant.

    It might be a combination of wheat intolerance plus lactose tolerance that may be the key.

  12. As I understand it lactase persistence may have evolved on three occasions at three locations. Amongst the cattle farming Tutsi, camel driving Arabs and the un-sunny climes of northern European sheep herders. The latter being the big one.

    Whatever arguments are put forward for evolving lactase persistance we might imagine that the fundemental energy cost argument for the first two (free energy from free milk paying for the lactase production energy cost) may be Vitamin D supplemented in the gloomy north.

  13. In reply to #16 by Wokkie:

    See: http://www.4.waisays.com/ExcessiveCalcium.htm with good references.

    Cracking link Wokkie. Thanks. Really educational.

    This thesis for the bone loss mechanism I find also persuasive. (The skeleton acts as a pH buffer against acidosis at the cost of bone loss. Employing dietary means to alternately regulate pH can reduce the rates of bone loss without the mechanism of adding compensatory calcium, with all its negative consequences.)

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