You want the long comparative anatomy lecture or the short one? 
Ok, to keep this "short" I won't get into tooth adaptation or variations in predator feeding strategies, which could take several pages. I'll also limit things to the placental mammals (that's us) and leave the marsupials (Koalas and Roos) out of it.
Pandas have a digestive system that is very poorly adapted to their diet. They have to make up for it by eating rather a lot of bamboo in order to get the required calories.
Horses and rabbits both have large caeca (blind sacs). They are hindgut fermenters (yet another good reason not to stand to close to a horse's *** - fermentation produces some interesting odours and rather a lot of gas).
The plant material roughage that is fermented in the foregut of a ruminant (cow, deer, etc.) and converted very efficiently to protein BEFORE the proteolytic stomach gets fermented in the hindgut of many other animals, including horses and rabbits. This releases volatile fatty acids, which can be absorbed through the caecum wall. The fecal material tends to be rather high in protein generated by the protozoans and bacteria that do the fermenting (again, in a cow these get digested later - very efficient).
Horses end up losing out on this protein but they do benefit from the fatty acids (this is not as efficient as the ruminant "four stomach" system). A horse that's working needs a higher protein diet (grain mash) than a cow - and a goat can live on stuff that would starve most other animals.
Now for the disgusting bit. Rabbits have a system for taking advantage of the protein produced in their hindguts. It's called coprophagy. They produce two kinds of fecal pellets - a soft, high protien one that they reingest, and a drier "twice digested" one that has a much lower protein content.
Humans have no caecum left - the remnants are known as the appendix. Make of this what you will.
Most other primates, including the mountain gorilla (which has a caecum), do derive some of their protein from animal sources - bugs, slugs, small birds. An awful lot of supposedly "vegetarian" animals (including squirrels) will snag animal protein when it comes along, often in the form of insect larvae and eggs.
The colon's main function in humans is to reabsorb *water* (and a few electrolytes, etc) and to store undigested food temporarily. And ours is pretty unimpressive compared to those of the other great apes (who have fermentation chambers right before the colon). Absorption of nutrients is the primary function of the *small* intestine. Comparing gut anatomy of the other great apes leads to some interesting results (we have less total gut for our body mass and what we do have is more heavily weighted to the small intestine than that of other great apes). There's more on this if you want detail.
Not all vegetarian diets are alike - fruit requires a different digestive setup than grains, while a diet of grasses and other low-nutrient/high cellulose foods really requires some form of fermentation mechanism. Top of the vegetarian heap are foods like nuts which are high in both protein and fat.
I could go on, but the audience is probably asleep already. Just want to add a couple of things to think about:
1. the preferred diet of many great apes tends to be mighty high in low pH foods (fruit) - might want to compare this to the "alkaline" fad that's big right now (acid in the stomach helps protect against invading bacteria as well as activiating the enzymes needed for proper digestion of protiens)
2. before deciding to eat *just* like your ancestors did, you might want to consider how long they tended to live (and whether you like the idea of dining on insects).
Happy termite-munching! Cat (who apologizes to the other posters for the temporary dietary hijacking)
PS: whatever you do, don't eat like an orangutan - in the wild they consume (among other things) fruit from the genus Strychnos - the source for strychnine poison. (add your own Kool-Aid joke here)
Ok, to keep this "short" I won't get into tooth adaptation or variations in predator feeding strategies, which could take several pages. I'll also limit things to the placental mammals (that's us) and leave the marsupials (Koalas and Roos) out of it.
Pandas have a digestive system that is very poorly adapted to their diet. They have to make up for it by eating rather a lot of bamboo in order to get the required calories.
Horses and rabbits both have large caeca (blind sacs). They are hindgut fermenters (yet another good reason not to stand to close to a horse's *** - fermentation produces some interesting odours and rather a lot of gas).
The plant material roughage that is fermented in the foregut of a ruminant (cow, deer, etc.) and converted very efficiently to protein BEFORE the proteolytic stomach gets fermented in the hindgut of many other animals, including horses and rabbits. This releases volatile fatty acids, which can be absorbed through the caecum wall. The fecal material tends to be rather high in protein generated by the protozoans and bacteria that do the fermenting (again, in a cow these get digested later - very efficient).
Horses end up losing out on this protein but they do benefit from the fatty acids (this is not as efficient as the ruminant "four stomach" system). A horse that's working needs a higher protein diet (grain mash) than a cow - and a goat can live on stuff that would starve most other animals.
Now for the disgusting bit. Rabbits have a system for taking advantage of the protein produced in their hindguts. It's called coprophagy. They produce two kinds of fecal pellets - a soft, high protien one that they reingest, and a drier "twice digested" one that has a much lower protein content.
Humans have no caecum left - the remnants are known as the appendix. Make of this what you will.
Most other primates, including the mountain gorilla (which has a caecum), do derive some of their protein from animal sources - bugs, slugs, small birds. An awful lot of supposedly "vegetarian" animals (including squirrels) will snag animal protein when it comes along, often in the form of insect larvae and eggs.
The colon's main function in humans is to reabsorb *water* (and a few electrolytes, etc) and to store undigested food temporarily. And ours is pretty unimpressive compared to those of the other great apes (who have fermentation chambers right before the colon). Absorption of nutrients is the primary function of the *small* intestine. Comparing gut anatomy of the other great apes leads to some interesting results (we have less total gut for our body mass and what we do have is more heavily weighted to the small intestine than that of other great apes). There's more on this if you want detail.
Not all vegetarian diets are alike - fruit requires a different digestive setup than grains, while a diet of grasses and other low-nutrient/high cellulose foods really requires some form of fermentation mechanism. Top of the vegetarian heap are foods like nuts which are high in both protein and fat.
I could go on, but the audience is probably asleep already. Just want to add a couple of things to think about:
1. the preferred diet of many great apes tends to be mighty high in low pH foods (fruit) - might want to compare this to the "alkaline" fad that's big right now (acid in the stomach helps protect against invading bacteria as well as activiating the enzymes needed for proper digestion of protiens)
2. before deciding to eat *just* like your ancestors did, you might want to consider how long they tended to live (and whether you like the idea of dining on insects).
Happy termite-munching!
Cat (who apologizes to the other posters for the temporary dietary hijacking)PS: whatever you do, don't eat like an orangutan - in the wild they consume (among other things) fruit from the genus Strychnos - the source for strychnine poison. (add your own Kool-Aid joke here)
