"What about these?" says the mighty Homo sapien, pointing triumphantly to the tiny canine teeth inside his mouth, “Don't these prove that humans are supposed to eat meat?” I call this the Argument Ad Caninum, a defense of meat-eating that is as tiresome as it is irrelevant. The logic implicit in this assertion seems to be the following: Animals who are unambiguously carnivorous, such as lions, wolves, and cheetahs, have canine teeth and they eat meat. The mouth of the Homo sapien is also equipped with canine teeth. Therefore, humans should eat meat!
The Ad Caninum argument is a logical fallacy based on a fundamental misunderstanding of both physiology and evolution. For starters, the canine teeth of lions and other carnivores are nothing like the so-called canine teeth of humans. I say "so-called" because the canine teeth of Homo sapiens are so unlike the true canine teeth of carnivores that ours are Canines In Name Only (CINOs).
“Our CINOs render us no more equipped for hunting, killing, and eating prey than our equally unimpressive fingernails, our comparatively weak jaw muscles, and our broad, flat incisors, all of which reflect our anatomical kinship to other frugivores.”
The canine teeth of true carnivores are long, sharp, and curved. They are formidable blades inside the mouth exquisitely evolved for killing and eating prey. The CINOs of humans, on the other hand, are short, blunted, and are thoroughly unimpressive as evolutionary adaptations for killing and eating animals, but are remarkably well-adapted for breaking apart and eating all manner of fruits, nuts, seeds, roots, tubers, and the like. Our CINOs render us no more equipped for hunting, killing, and eating prey than our equally unimpressive fingernails, our comparatively weak jaw muscles, and our broad, flat incisors, all of which reflect our anatomical kinship to other frugivores.
Remember that time that a group of human hunters, unaided by weapons, stalked and killed a wild animal, used their canine teeth to pierce the animal's thick hide, and then devoured the corpse without cooking or seasoning it? Neither do we.
And even if our CINOs were identical to those of true carnivores, it would not necessarily imply that we should eat animals, as the same anatomical trait can evolve in different species as an adaptation to different conditions. Our fellow frugivore, the Silverback gorilla, for instance, has evolved an impressive set of canine teeth which are used as a threat display to intimidate competitors and enemies, rather than as an aid to killing prey. Similarly, a bird's feathers can serve as either an aid to flying (as in the case of the eagle, heron, and other birds who fly), or as thermo-regulating devises among flightless birds, such as penguins.
The best response I have yet read to the Argument Ad Caninum is from the American physician and author John A. McDougal, M.D., who sums up the matter thus:
Our dentition evolved for processing starches, fruits, and vegetables, not tearing and masticating flesh. Our oft-cited "canine" teeth are not at all comparable to the sharp teeth of true carnivores. I lecture to over 10,000 dentists, dental hygienists, and oral specialists every year, and I always ask them to show me the "canine" teeth in a person’s mouth – those that resemble a cat’s or dog’s teeth – I am still waiting to be shown the first example of a sharply pointed canine tooth.
Your argument is invalid.
Sources:
http://www.scribd.com/doc/94656/The-Comparative-Anatomy-of-Eating
http://www.nealhendrickson.com/mcdougall/030700pumeatinthehumandiet.htm
http://michaelbluejay.com/veg/natural.html
https://en.wikipedia.org/wiki/Canine_tooth
https://en.wikipedia.org/wiki/Flightless_bird