Can Humans DIGEST Cellulose.. ??

Discussion in 'Biology & Genetics' started by srimukh, May 18, 2009.

  1. charles brough Registered Senior Member

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    fascinating . . . ! I am not disputing that, but it seems unlikely to me. Do you have any other information on this? What has the cecum to do with digesting cellulose? Are you saying that "cavemen" were "people" (homo sapiens)? How could we have evolved out of cellulose digestion in a hundred thousand years or so instead of millions of years? . . .just curious.

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    charles
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  3. Enmos Staff Member

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    It seems very likely to me. But I don't know about people (cavemen).. lol
    Humans evolved from leaf-eating primates, which in turn evolved from other plant-eating mammals.
    It's not just likely, it must be true that human's ancestors were able to digest cellulose.
     
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  5. srimukh Registered Senior Member

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    evolution

    but we are very much refined by millions of years of evolution from ancient primates... so, evolution should bring some beneficial characteristics and add more and more abilities to that organism.... even we are omnivorous... why we would lose that ability to digest cellulose.? in the previous replies, we read that cellulases are secreted by some bacteria present in the guts of herbivorous animals.. so did our ancestors eat some kind of food that would lead to formation of these bacteria???? did these bacteria come from the food they ate??

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  7. CharonZ Registered Senior Member

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    Evolution is not about adding abilities. If there is no selective pressure to maintain them, abilities are as easily lost.
    Generally, cellulose is digested with the help of bacteria and protozoa as mentioned above. While some may eventually come in with the food, much is of the flora is also inoculated by the mother.
     
  8. ElectricFetus Sanity going, going, gone Valued Senior Member

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    Very true take a look a predators, they actually have lost vitamin production capabilities because they don't need them anymore since they started eating meat.
     
  9. Fraggle Rocker Staff Member

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    When people say "cavemen" they loosely refer to all the ancestral genera and species of Homo sapiens after the family split off from the chimpanzee family, several million years ago. This includes, for example, Australopithecus.

    Presumably the very first hominids must have been grazers like their ancestors. The adaptation to become the apex predator of the entire global ecosystem happened slowly.
     
  10. srimukh Registered Senior Member

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    yes, so we cannot derive energy out of cellulose.right?
     
  11. Fraggle Rocker Staff Member

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    Not without cooking it and breaking down the cellular structure. This is why fire was a key technology. There would have been no point in inventing the subsequent technology of farming if we couldn't cook the grains.
     
  12. srimukh Registered Senior Member

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  13. DRZion Theoretical Experimentalist Valued Senior Member

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    I thought it would be cool to develop a pill that would contain cellulose degrading bacteria. You would dump a bunch of grass, leaves, whatever in a pot, throw in a pill, and after some (lots) stirring, it could be edible. Does anyone see why this couldn't be done?

    This could be a very handy tool for wilderness expeditions (as an emergency backup) or as a safeguard against natural disasters. At the same time, it would give people another incentive to tear down forests, so it would have to be controlled too.
     
  14. srimukh Registered Senior Member

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    good idea.

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    BUT...


    good idea DrZion..

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    but, do u think That bacteria will survive the harsh washout by HCL acid?
    I think HCL helps in destroying the bacteria and other microbes that enterering our digestive system......

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  15. Barbie Banned Banned

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    Not really, we can't extract calories from cellulose because we lack the acids and bacterial culture necessary, our stomach acid is really quite pathetic. We also don't have long enough intestines, so eating plants full of cellulose won't help us in desperate times. Eating raw plants will probably make you shit out forest green cinder blocks, your farts would be really loud and smell like spraypaint, and your colon would be irritated and swollen - so incredibly swollen.
     
  16. Fraggle Rocker Staff Member

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    It's a stonewall impediment. We can't digest enough of the nutrients embedded in uncooked cellulose to pay us back for the energy of chewing. As I mentioned earlier on this thread, fire is on the short list of nominees for the Breakthrough Technology that allowed H. sapiens to become us. One of the many things that cooking does is simply make food easier to eat. I recently saw a calculation that even if we didn't have to hunt our meat, it would take about four hours a day to eat a day's ration of it raw. That alone gives us a lot of time for other pursuits that advance civilization.
    Because we didn't need it any more. Grazing is an incredibly time-consuming activity. If you think spending four hours a day eating raw meat would be a bummer, try spending most of your waking life munching on raw plants. As we developed into hunters and adapted to a more carnivorous diet, we just didn't need to bother wasting our time chewing on roots, leaves and bark. A digestive system more compatible with a carnivorous diet would have been a favorable adaptation and evolution would have selected for it when it occurred. Herbivores have huge guts that would not make them nimble hunters.
    It's a stable bacterial culture that regenerates itself. Once it becomes established in the gut of a young animal a steady state exists in which the existing bacteria eat the cellulose and transform it into new bacteria, while at the same time the animal is digesting the protein-rich bacteria cells and keeping the population constant. I'm not sure how each species of herbivore establishes the initial culture, but baby rabbits, for example, eat the feces of adults in which there is inevitably some bacteria still alive.

    The digestive help of bacteria is not limited to herbivores. Dogs and other canids have such short guts that they maintain a bacterial culture to help digest their food. In the wild they eat the intestines of their prey (and the leftovers from the meals of more finicky carnivores) to keep that culture going. If you see your dog out in the yard eating the feces of other animals, it's probably because you feed him commercial food full of preservatives and it's killing off his intestinal culture. He might even eat his own poop if he's desperate, some bacteria will have survived the onslaught of preservatives.
    Because it's so much easier to simply apply a nice flame to that pot and accomplish the same result by cooking.

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    High heat breaks down cellulose into simpler molecules like starches that we can digest. That's where this whole discussion started!
     
  17. srimukh Registered Senior Member

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    Fraggle... that was a huge explanation. thank u

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  18. tommi123 Registered Member

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    No, we cannot digest cellulose. However, the microbes inside us can help us do it: they digest cellulose and we digest them.
     
  19. Fraggle Rocker Staff Member

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    Only herbivores can do that. They have extremely long intestines that host an extensive bacterial culture. Food takes quite a while to pass through them so it gives the bacteria plenty of time to work. Some of them, the ruminants, have stomachs with multiple chambers in which different specific digestive processes take place. Cattle even regurgitate their food and run it through the cycle a second time.

    Humans can't do any of those things. We do indeed host bacteria in our guts that help us digest our normal diet of protein, starch and sugar, but not cellulose. Even if we had cellulose-digesting bacteria, they could not stay in our relatively short digestive tract (compared to a sheep or a hippopotamus) long enough to do their job.
     
  20. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    I doubt that 100C (pot of boiling water at 1 atmosphere) can break down cellulose. A lot of money is trying to do that for second generation alcohol. AFAIK much higher temperatures and / or enzimes are required to break down cellulose. If I am wrong - please tell me.
     
  21. DRZion Theoretical Experimentalist Valued Senior Member

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    Crap, I keep getting lost all over these forums. Sorry for the delayed response.

    Your point is valid. However, there are probably ways to engineer bacteria that could live even in our stomachs (since there are already some living species there). A problem may be toxic metabolites and the rate at which the breakdown of cellulose happens. This is why I think the bacteria should be free-living and added to batches of chopped up trees.
     
    Last edited: Aug 23, 2009
  22. ZaccPF Registered Senior Member

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    Great discussions going on here
     
  23. Fraggle Rocker Staff Member

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    Sorry, I missed your post last year. Yes, you're right. Heat does not break cellulose molecules down into simpler compounds that we can digest. It merely softens cellulose so that our digestive juices (aided by water) can squeeze between the molecules and digest the protein, starch and sugar that is unavailable to us in its natural state.

    Almost no mammal has the enzymes to actually digest cellulose and use it as a source of calories. They require a bacterial culture to do that. (And when they say "almost no mammal," nobody every says who the exceptions are!)
     

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