The chart below shows the relative sizes of 4 digestive compartments for some closely-related primate species:
Click to enlarge.
Our closest living relative in the animal kingdom, the chimpanzee (a great ape), and our next closest relative, the gorilla (also a great ape), have much smaller small intestines, and much larger large intestines (colons) than we do.
According to Katharine Milton, an expert in primate physiology:
"In humans, more than half (>56%) of total gut volume is found in the small intestine, whereas all apes have by far the greatest total gut volume (>45%) in the colon."So apes have more total intestine, and a larger relative colon. Considering that:
"In addition, the size of the total human GI tract in relation to body size is small in comparison to those of apes."
- Katharine Milton, Nutritional Characteristics of Wild Primate Foods: Do The Diets Of Our Closest Living Relatives Have Lessons For Us?
- The small intestine is the place where most chemical digestion and absorption take place.
- The large intestine is the place where undigested material is fed upon by bacteria, and where water is absorbed prior to feces exit.
"The proportions of the modern human gut appear to reflect the fact that many foods are "predigested" by technology in one way or another before they even enter the human digestive tract."One more thought. No digestion takes place in the colon, however, we do absorb nutrients (vitamins, fatty acids) produced by bacteria there. So, the nutrients an ape absorbs, and the nutrients we absorb, from the same foods, are different. They are different in amount, and in type. (These differences also exist among humans although to a lesser degree.)
- Katharine Milton, Hunter-Gatherer Diets - A Different Perspective