Carnies and omnis are always blabbing about human teeth and guts, claiming they are unique or specific adaptations to meat-eating. Of course, this is a misunderstanding of evolution, since not all traits are adaptations to their current use.
Our teeth are simply variations on the basic mammalian tooth plan, and our guts are variations of the basic primate gut morphology. In other words, they're just hand-me-downs; the fact that cavemen had them doesn't mean cavemen got them specifically for the uses they put them to.
More succinctly: cavemen may have found new uses for old things, but that doesn't mean the old things were "meant" for the new uses.
I'm working on a longer post right now that goes into detail about classification and taxonomy as it relates to vegan issues, including a fable about the checkered history of the word "omnivore." Many anti-vegans throw this word around in a most pseudo-scientific way. Hopefully, this will set some of them straight.