I think that before we jump directly to any conclusions regarding "what humans used to eat way back when", we should look at the common fallacy that states that what we used to do in the past is how we should do things now.
http://anthroslug.blogspot.com/2009/...n-fallacy.html
That's not to say that we can't go back and see what was eaten back then, and then test to see whether it works now. It's just that we can't use that argument as fact/proof that it is the be-all, end-all of nutritional guides.