Italian researchers found evidence that mankind 32,000 years ago was using mortar and pestle to grind oats. Other grindstones from the era have been found leading researchers to believe that the activity was widespread. Here's a link to the article published in Archaeology.
Current fad-diet concepts of "Paleo" have been proven wrong. Every fad-diet I've seen is less successful than this simple advice: eat a varied diet of whole foods that is plant-based (meaning a significant portion of each meal is from plants). Have some of your veggies be raw, some cooked, have your meat and dairy from free-range, drug and hormone free animals, and enjoy it all! Then, forget about it and focus on something else.