The concept of grains as a staple has become standard only in the last few thousand years, while man had evolved for a couple of million years. It became standard as Man moved north into less hospitable climes, where incidentally, there were fewer dangerous predators: Apart from Man. Homo Sapiens had to form collectives to store grain for winter, and to protect themselves and the grain store from marauders.
A true Paleo would have us eating grubs, animals we have run down [early man could run down faster animals because we became hairless and could sweat, thus had more endurance during the heat of the day than they did, and work collectively] and the eternal fruits, berries and eggs.
