Link: The Natural Human Diet
A short excerpt:
When you see dead animals on the side of the road, are you tempted to stop and snack on them? Does the sight of a dead bird make you salivate? Do you daydream about killing cows with your bare hands and eating them raw? If you answered "no" to these questions, congratulations—like it or not, you're an herbivore.
According to biologists and anthropologists who study our anatomy and our evolutionary history, humans are herbivores who are not well suited to eating meat. Humans lack both the physical characteristics of carnivores and the instinct that drives them to kill animals and devour their raw carcasses.
Although many humans choose to eat a wide variety of plant and animal foods, earning us the dubious title of "omnivore," we are anatomically herbivorous.
TEETH, JAWS, AND NAILS
Humans have short, soft fingernails and pathetically small "canine" teeth. In contrast, carnivores all have sharp claws and large canine teeth capable of tearing flesh.
Carnivores' jaws move only up and down, requiring them to tear chunks of flesh from their prey and swallow them whole. Humans and other herbivores can move their jaws up and down and from side to side, allowing them to grind up fruit and vegetables with their back teeth. Like other herbivores' teeth, human back molars are flat for grinding fibrous plant foods. Carnivores lack these flat molars.
Dr. Richard Leakey, a renowned anthropologist, summarizes, "You can't tear flesh by hand, you can't tear hide by hand. Our anterior teeth are not suited for tearing flesh or hide. We don't have large canine teeth, and we wouldn't have been able to deal with food sources that require those large canines."