I've wondered the same thing, I read a paper about it not too long ago, more related to chimps though-that being that they are more omnivorous than most people think-eating rodents, insects...etc. But gorillas, I read, are almost totally non meat eating. What I don't understand is their ability to digest so much cellulose-they must come equipped with cellulase but usually animals that are meant to eat that much fiber have more than one stomach and as far as I know, they don't.
Our closest genetic relatives are the bonobo chimps. The more I read and the more I experiment with my own diet, the more vegan I become. Right now I am down to one meat meal a day and the rest fruit, in mono meals.