Biologists claim humans are omnivores and the evidence offered is mostly about the size and shape of our teeth. But while we may have short canine teeth, that is more a consequence of having an enlarged head, ironically brought about after our ancestors started eating meat, causing an evolutionary reduction in the size of our jaws. However, Apes, who are herbivore, have much longer canine teeth than we do while chimpanzees, who are omnivore, have much shorter canines than their larger cousins. So canine length may not be as significant as it first seems.
Teeth are only the beginning of the story when it comes to our digestion and assimilation of food. Getting meat into our digestive system is one thing but processing it is a far more important and complex concern and when comparing the human digestive system to other animals, both herbivore and carnivore, a clearer, more significant picture begins to emerge.
According to this PDF published by the Journal of Dairy Science – the official publication of the Dairy Science Association – about intestine lengths in calves, it states the following…
“In carnivorous animals the small bowel is said to be only from four to eight times the body length, while in herbivorous animals it is from twenty-five to seventy-five times the body length.”
Cats are 100% carnivore and dogs while being scavengers are pretty much totally carnivore given the choice. A adult cat’s intestines are approximately 1 to 1.5 meters long which fits within the 4x-8x ratio to body length. With dogs the range is wider due to the variation in size between breeds, it’s between 1 – 5 meters but this too sits within the 4x-8x ratio to body length.
With herbivores we find the 25x-75x ratio in the ruminants we eat. Cows for example have intestines between 33-63 meters. In sheep, the total length is between 22-43 meters and in goats an average of around 33 meters… so a massive difference from the carnivore cat and dog.
Now let’s look at the human digestive system. Our small intestine is about 6 meters long while the average human height is approx 1.7 meters. This gives a ratio of 3.53 which is below the lowest end of the ratio so digestively speaking, we are as carnivore as cats and dogs!