Paleolithic humans have long been considered predominantly carnivorous. However, grain residues on grinding stones recently discovered at three different archaeological sites suggests that starchy grains were already being processed around 30,000 years ago in Europe.
Revedin A, Aranguren B, Becattini R, Longo L, Marconi E, Lippi MM, Skakun N, Sinitsyn A, Spiridonova E, Svoboda J (2010). Thirty thousand-year-old evidence of plant food processing. Proceedings of the National Academy of Sciences USA. 107(44):18815-9