Humans: Carnivore, Herbivore, or Omnivore?

[WingedWolfPsion]

Since one of our fellow BPers has made the statement that humans are herbivores, and I refuted that with references to a great deal of evidence to the contrary, rather than hijacking the Bullfighting thread, I figured I would go ahead and give it its own arena.

So:
Evidence for omnivory in humans:

Dentition: Cutting surfaces and grinding surfaces evenly arranged. Molars are weak, not up to the task of grinding large amounts of plant matter. Canines are small, but canines are used for grasping prey, not for cutting meat, so are not necessary for an animal that does not kill using its teeth. Number of teeth reduced in modern humans. Jaw size also reduced, indicating a diet that is not high in fibrous or tough materials. Jaw PRESSURE in modern humans is quite impressive, however. We can crack a nut (or a bone) if we have to. In a fossil record, modern humans would be easily identified as omnivores.

Intestinal length: Herbivores use one of two strategies to enable them to digest plant matter--either an extremely long and elaborate digestive system (such as in a cow), or a shorter system that food is passed through more than one time (such as in a rabbit). Carnivores have a short digestive tract, because meat is high in nutrients and extremely simple to digest. Omnivores have a digestive tract that is intermediate between the two. In fact, the human digestive tract is closely comparable in length and structure to that of a pig--a devout omnivore.

Tools: Hominids and great apes are devout tool users. Tool use itself is an interesting adaptation that allows a species to take advantage of a variety of food resources. Some species rely on tool use almost exclusively in order to procure food, such as woodpecker finches. Great apes regularly use tools to procure their food--to crack nuts, for example, to fish for termites, and to kill small animal prey. Our closest living relatives, bonobos and chimpanzees, both kill and eat monkeys fairly regularly to supplement their diets. Female orangutans have also been observed catching and eating small animal prey, and fish. The oldest stone tools we have found created by homonids were clearly designed for pounding, cutting, and scraping. Cutting and scraping are needed for preparing meat, and not for much else. Throughout the progression of homonid tool development, we find increasingly sophisticated tools for preparing meat and hides, and for hunting (such as spearheads).

Behavior: Humans hunt. Even children, left to their own devices, will stalk small animals. Catching butterflies isn't just about the 'pretty'. We have all the instinctive equipment necessary to wait patiently for long periods, to track, and to persist. We enjoy the process of hunting, like all predators.

Physical fitness: Although you wouldn't know it by looking at the average cubicle-dweller, humans are incredible athletes. We are not particularly fast, but we don't have to be fast--we have tremendous endurance, and we can run for miles. Many prey species cannot. As a result, one of the oldest methods of hunting is known as persistance hunting. It involves selecting a large, fit male of a horned animal species, and following it until it drops dead of heat prostration and exhaustion. (The heavy horns tax the animal's strength faster). This is not a rare occurrence, or luck--it is a regular hunting style still practiced by the San people in Africa today. The San are our genetic ancestors, according to gene mapping...they are the oldest surviving lineage of humans on the planet. Humans can climb, dig, swim, jump, and run for miles without stopping. We are superb predators and are capable of grasping any opportunity presented to us.

Culture: The oldest existing human cultures on Earth are omnivorous. In fact, there are no primitive herbivorous cultures. There are primitive carnivorous cultures, however (the Inuit, for example).

Nutrition: Humans require vitamin B-12 in their diet, which is a vitamin that herbivores manufacture in their own gut. B-12 is found primarily in meat. B-12 is a very important vitamin for human health. Non-animal sources of B-12 are few and far between, and were largely or entirely unavailable to primitive peoples (such as yeast). No successful herbivore is unable to manufacture vitamin B-12 for itself.

Other various adaptation (such as digestive fluids and saliva):
As has been pointed out, meat is easy to digest. Vegetable food sources are difficult to digest, so most herbivores will concentrate their efforts on making the vegetation they find palatable actually digestible. It's much harder to digest a leaf than it is to digest a mouse, so more changes are needed to enable the digestion of plant matter. This is the flaw of omnivory:
You can eat many things, but you will not be perfect at eating any of them. Humans are poorly adapted to eating both meat AND plant matter, but they are supremely adaptable because they can derive proper nutrition from eating both.

Evidence for herbivory in humans: ? (I don't know of any).