Everything I learned about this I learned out of my dental school texts. But this is a bit of an explanation, althought I'm sure it won't suffice.
And yet despite all these eons of evolution, we still desire to and are able to eat the fruits of the trees and the grains of the fields in their natural state.
Did you ever look at the human dentition compared to a cow's or a dog's? It represents a convergence of both. The anterior incisors and canines are closely related to carnivores, for tearing and ripping meat, while the posterior molars are better suited to grinding and mashing fruits and grains. We have developed to eat both. Of that there can be no doubt.
Hey man, all I know is that I saw "Dances with Wolves", and those Indians sure seemed to enjoy taking a big bite out of a freshly killed buffalo's liver. Thank God that's not part of my "conditioning" :) I'll take my meat cooked thanks.
This is in conflict with the article you linked above.
The article claims that man originally was a plant-eater, but then a couple of million years ago 'switched' and added meat to his diet and as a result the teeth adapted to the new chewing requirements.
Which is to say, that we originally weren't designed as carnivores, but herbivores.