Yes, it has, and a blog post linking to a paper about neanderthals does not count as proof of your assertion. I don't know about you, but I haven't seen any neanderthals walking around lately, so the fact that they may have subsisted on plants doesn't say much about homo sapiens.
The evidence of human diets spans millennia, including pre-humans and early human populations. There are a very few bits of evidence of isolated populations eating what could be called a "paleo diet" by modern definitions (with a lot more bugs and grubs and nasty stuff like brains and organs from rats), but on the whole, humans have always been omnivores, eating anything remotely edible within their grasp, including mammals, reptiles, plants, fish, insects, fungus...if an alien landed during early human times, they'd have probably tried to eat it, too. But, most populations in most places were eating plenty of plant matter, including grains, and some of the oldest food evidence we have includes grains.
The idea that the early human diet was nearly all meat is a highly selective reading of the evidence; picking and choosing from only those populations in those locations where meat was the only available food source. I don't want to attack your deeply felt beliefs, as you seem to have a personal investment in the paleo cult, but it's simply not borne out by science.
Also, I strongly recommend not taking ones anthropology lessons from fad diet book authors.
Note that I'm not arguing that people should be consuming a bunch of white bread and refined sugar. Knowing the paleo diet is based on junk science doesn't mean I think the modern first world diet is sane.
