let’s see, our ancient ancestors the lemurs ate fruit almost exclusively!!!! (see; http://www.buzzle.com/articles/lemurs-diet.html ) ~ so what happened? Did fructose in vast quantities, our basic staple for millions of years, turn poisonous on us? Guys it ain’t always been porkchops and hominey!
We've been omnivores for quite a while. Those incisors, cuspids and bicuspids didn't happen for no reason. Check out the Lustig lecture in comments 3 or 4. (It was accidentally double posted.) The biochemistry is very compelling. Excess fructose is the best explanation for non-alcoholic fatty liver disease that I've seen.
What happened to rhesus monkeys? Didn't they evolve from the lemurs?