There is a question no one seems to be asking about the grain residue on paleolithic tools:
Was this residue really foodstuffs? Just because they find ground starch on a mortar and pestle, doesn't necessarily it was consumed as starch, or consumed at all. What is the first thing that happens when water is added to starch? It gets gooey and sticky.
Paste. They were making paste. Perhaps it was to seal the leaks in a shelter. Perhaps they were making dyes or facepaints. Perhaps they figured out how to make a paleolithic lecithin so the brontosaurus burgers wouldn't go bad on the way home to Wilma.
My point is: There are SOOOOOO many other uses for starch that don't involve eating. Why is everyone so scope-locked on the food part?
I particularly like Melissa McEwan's Drunk hypothesis, however.