Why we can't digest cellulose

[someone235]

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

[Korn]

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...

[Clueless Git]

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.

[fresherthanlife]

So don't eat grass :P

[splodge]

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.

http://www.veganforum.com/forums/sho...o+be+herbivore

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

CARNIVORE: Large HERBIVORE: Small OMNIVORE: Large HUMAN:
Small

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

Chewing

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

Saliva

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

Colon

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

Liver

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

Kidney

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

Nails

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.