This is a pretty dumb paper...meat eating is one of the very things that made us human! Our digestive tracts shortened because we started eating meat, providing room for our brains. We diverged from gorillas/chimps for a reason......
How does it make sense that a single diet is prescribed for an entire suborder of species? Gorillas are herbivores, although frugivorous at times: completely distinct from gibbons which are strictly frugivorous: these species differ only at the family level. Even old world monkeys (cercopithecoidea, members of the same super family) have different diets: Ceboids have rumen-like stomachs and eat only grasses, have slicing molars, and cercopithecines have crushing molars and eat only fruit. Prescribing a single diet to all of these animals would be a HORRIBLE idea. Not to mention, even chimps are also distinct from humans, although we only differ at the , as their diet typically consists of much less meat.