From a dental standpoint, humans' teeth are equally suitable for eating meat
and plants. We have incisors, capable of cutting into meat and vegetable
matter, canines (not present in herbivores) suitable for tearing meat, bicuspids
suitable for grinding and tearing meat and vegetables, and molars suitable for
grinding both again. Our saliva contains enzymes such as lipase and
amylase, fat- and protein-reducing enzymes suited more to a carnivorous
diet. Yet, as Erenteta quite rightly pointed out, our digestive tract is more
suitable for a herbivorous diet. Our jaws also move horizontally as well as
vertically, a feature in many herbivorous (and omnivorous) animals and relatively few
carnivores. All in all, we're a bit of a mixed bag of a species.
Consider the following point, however. Mammalian herbivores have evolved
with their eyes on either side of their heads, providing almost a 360-degree
field of vision. Herbivores tend to be docile (in general), and are therefore
likely prey for their carnivorous predators. Their wide field of vision
enables them to eat and to keep a constant watch-out for predators. Witness the
antelope, mouse and even the rhinoceros for proof.
Carnivores and omnivores, on the other hand, have evolved with eyes at
the front of the head, with an overlapping field of vision. This provides
stereoscopic vision with depth-perception, essential when chasing down prey or
sizing up a potential kill. And guess what? Humans fall into this category,
along with tigers, wolves and countless other heartless killing machines.
We have evolved as hunters. Over the millennia, our intelligence has enabled
us to create weaponry and clothing, changing us from apish, feral, hairy
primates to the weak, relatively defenceless species we are today. Surely that
is evolution? Some birds started to build nests, so they evolved to be dependent
upon nests. We don't accuse them of assuming control of their own destiny. An
interesting effect of our intelligence is that we are able to design new
diets capable of supporting us without the consumption of meat, even though we
as a species have been eating meat since time immemorial.
The Romans ate meat, as did the Abyssinians, the Ancient Egyptians, the
Ancient Greeks and countless other civilizations. Humans ate meat then and we
are eating meat now, so the "suggestions" made by our physiology are
nothing more than that. Suggestions towards a situation (humans as herbivores)
proven patently incorrect by human history.
To sum up, primitive humans evolved to hunt, ergo to eat meat (in addition to
plants). Our intelligence has hastened our evolution, weakening our bodies while
sharpening our minds. And this rapid evolution has resulted in our ability to
choose to be vegetarians (apologies to sufferers of animal protein intolerance
who clearly have no such option). To me, the option to be vegetarian is little
different to the option to use recycled products - it is an option, some
people feel compelled - for a variety of perfectly good reasons - to take it,
and no-one should be criticized for it.