This article discusses a series of new archaeological finds; stones used for grinding grain that date back to the Stone Age. The archaeologists know that the stones were used for grinding grain not simply because of the shape, but because the stones are still coated with a microscopic layer of grain. Such stones have been found in Italy, southern Moravia in the Czech Republic and the Pokrovsky Valley in Russia as well.
Yes, the grains are wild grains, not cultivated; microscopic analysis identifies them as belonging to cattail, a fern, and a type of grass. Not nearly as nourishing as barley, or wheat, or rye would become. But at least a sign that humanity was looking to eat things other than meat or berries earlier than had formerly been thought.