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Thread: Why we can't digest cellulose

  1. #1

    Default Why we can't digest cellulose

    Someone maybe knows why human cannot digest cellulose as any other herbivore?

  2. #2
    Ex-admin Korn's Avatar
    Join Date
    Apr 2004

    Default Re: Why we can't digest cellulose

    Hi someone235, there's lots of stuff which makes humans different from other animals... One of them is that we don't have the enzyme needed to digest cellulose, and we don't need to eat cellulose either. No big deal...
    I will not eat anything that walks, swims, flies, runs, skips, hops or crawls.

  3. #3
    Bad Buddhist Clueless Git's Avatar
    Join Date
    Sep 2010
    Milton Keynes

    Default Re: Why we can't digest cellulose

    Quote someone235 View Post
    Someone maybe knows why human cannot digest cellulose as any other herbivore?
    Without being racist at all I understand it to be fact that Asians cannot handle alchohol as well Europeans can.

    Reason being along the lines of this; European cultures learned to use alchohol to make water safe to drink whilst Asian cultures learned to boil water and turn it into tea.

    By natural selection Europeans not able to cope with alchohol did not fare as well as those who could with it well (permanent 'brewers droop' or something?). So the 'booze gene' prospered, as it were, amongst Europeans.

    To Asians the ability to cope with alchohol made no difference at all. Total non issue there so the 'booze gene' has not prospered there.

    Point being this: The human appendix (believed to have been a repository for cellusose digesting bacteria) indicates that we did once digest cellulose. It is probably because all human cultures learned to break down cellulose by cooking that whatever gene that governed the appendix function became irrelevant to survival and has now been completely filtered out.

    If you were fishing for 'are humans natural herbivores' then I think that the answer is no. Our nature is omnivorous with a strong leaning towards a heavily plant based diet.

    Thing being there that we are capable of surving and thriving on a totally plant based diet and all consistent morality and ethics dictate that we should do so.

    The ability to adjust what we do according to a code of morality and ethic is what makes us 'better' than animals and the more consistent the morality/ethics we live by then the more so. To follow our nature alone makes us no better than dogs.

    To choose to be no better than a dog whilst believing ourself to be better than a dog is a total nonsense so far as I can see.
    All done in the best possible taste ...

  4. #4

    Default Re: Why we can't digest cellulose

    So don't eat grass :P

  5. #5

    Default Re: Why we can't digest cellulose

    Because humans are frugivores. Grazers and leaf-eaters can digest cellulose. Frugivores cannot. Therefore cellulose digestion is NOT a hallmark of a "herbivore" since frugivores are herbivores too.

    We also DO need cellulose. Cellulose = fibre. Fibre is vital to help move food through the intestines.

    Actually, we are NOT designed to be omnivorous, in any way shape or form AT ALL.

    Facial Muscles

    CARNIVORE: Reduced to allow wide mouth gape
    HERBIVORE: Well-developed
    OMNIVORE: Reduced
    HUMAN: Well-developed

    Jaw Type

    CARNIVORE: Angle not expanded
    HERBIVORE: Expanded angle
    OMNIVORE: Angle not expanded
    HUMAN: Expanded angle

    Jaw Joint Location

    CARNIVORE: On same plane as molar teeth
    HERBIVORE: Above the plane of the molars
    OMNIVORE: On same plane as molar teeth
    HUMAN: Above the plane of the molars

    Jaw Motion

    CARNIVORE: Shearing; minimal side-to-side motion
    HERBIVORE: No shear; good side-to-side, front-to-back
    OMNIVORE: Shearing; minimal side-to-side
    HUMAN: No shear; good side-to-side, front-to-back

    Major Jaw Muscles

    CARNIVORE: Temporalis
    HERBIVORE: Masseter and pterygoids
    OMNIVORE: Temporalis
    HUMAN: Masseter and pterygoids

    Mouth Opening vs. Head Size


    Teeth: Incisors

    CARNIVORE: Short and pointed
    HERBIVORE: Broad, flattened and spade shaped
    OMNIVORE: Short and pointed
    HUMAN: Broad, flattened and spade shaped

    Teeth: Canines

    CARNIVORE: Long, sharp and curved
    HERBIVORE: Dull and short or long (for defense), or none
    OMNIVORE: Long, sharp and curved
    HUMAN: Short and blunted

    Teeth: Molars

    CARNIVORE: Sharp, jagged and blade shaped
    HERBIVORE: Flattened with cusps vs complex surface
    OMNIVORE: Sharp blades and/or flattened
    HUMAN: Flattened with nodular cusps


    CARNIVORE: None; swallows food whole
    HERBIVORE: Extensive chewing necessary
    OMNIVORE: Swallows food whole and/or simple crushing
    HUMAN: Extensive chewing necessary


    CARNIVORE: No digestive enzymes
    HERBIVORE: Carbohydrate digesting enzymes
    OMNIVORE: No digestive enzymes
    HUMAN: Carbohydrate digesting enzymes

    Stomach Type

    CARNIVORE: Simple
    HERBIVORE: Simple or multiple chambers
    OMNIVORE: Simple
    HUMAN: Simple

    Stomach Acidity

    CARNIVORE: Less than or equal to pH 1 with food in stomach
    HERBIVORE: pH 4 to 5 with food in stomach
    OMNIVORE: Less than or equal to pH 1 with food in stomach
    HUMAN: pH 4 to 5 with food in stomach

    Stomach Capacity

    CARNIVORE: 60% to 70% of total volume of digestive tract
    HERBIVORE: Less than 30% of total volume of digestive tract
    OMNIVORE: 60% to 70% of total volume of digestive tract
    HUMAN: 21% to 27% of total volume of digestive tract

    Length of Small Intestine

    CARNIVORE: 3 to 6 times body length
    HERBIVORE: 10 to more than 12 times body length
    OMNIVORE: 4 to 6 times body length
    HUMAN: 10 to 11 times body length


    CARNIVORE: Simple, short and smooth
    HERBIVORE: Long, complex; may be sacculated
    OMNIVORE: Simple, short and smooth
    HUMAN: Long, sacculated


    CARNIVORE: Can detoxify vitamin A
    HERBIVORE: Cannot detoxify vitamin A
    OMNIVORE: Can detoxify vitamin A
    HUMAN: Cannot detoxify vitamin A


    CARNIVORE: Extremely concentrated urine
    HERBIVORE: Moderately concentrated urine
    OMNIVORE: Extremely concentrated urine
    HUMAN: Moderately concentrated urine


    CARNIVORE: Sharp claws
    HERBIVORE: Flattened nails or blunt hooves
    OMNIVORE: Sharp claws
    HUMAN: Flattened nails

    In addition:

    Saliva: in omnivores and carnivores it's acidic, in herbivores it's alkaline. Human saliva is alkaline.

    Eyes: Much is made of our forward facing eyes. But sideways-pointing eyes indicate a prey animal, so herbivore animals that are not typically prey can have forward facing eyes, like hippos and many primates. Forward facing eyes are essential for animals, like primates, that climb trees, as it enables us to judge depth and work our way through branches and dense vegetation. In addition, the eyes of omnivores and carnivores cannot see colour well (dichromatic or monochromatic, referring to the how many types of rod there are in the eye), however we can see colour very well (trichromatic) and find it highly attractive - this corresponds with brightly coloured fruit being the tastiest and most nutritious, and is an evolutionary trait to find the best food. In mammals, only frugivores, or animals who eat a significant amount of fruit (like other primates) have good colour vision. Also, the eyes of many predators are able to track movement A LOT more easily than us, to enable them to accurately attack prey.

    Cooking food - we're the only animal that has to cook and process its meat perfectly to render it edible and safe, cut it with knives because we can't chew it, marinate it to make it more interesting, breed the farmed species and manipulate their life cycles and growth to produce less unsuitable meat, and kill the animal using tools because our own bodies are unable to.

    Other great apes have intestines that take up 50% of their digestive track whereas our takes up 20%. This is because other great apes are designed to eat more leaves than us. This is because leaves are high in protein, and since other great apes are multiple-times stronger than us, they need more protein.

    Male humans show colour preferences to blue and green, like other apes, whereas female humans prefer red. Perhaps this shows men's need for slightly more leaves in their diet, since they have proportionally more muscle than females. Red and dark pink fruit have the most of certain phytochemicals.

    Perphaps the genuine canines of non-human primates are used for their occasional attacks or slaughter of each other and other animals. Some primates, like male chimpanzees, occasionally kill and eat smaller monkeys for psychological reasons, to prove their strength.

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