Starch grains from cattail, grasses and fern plants have been found on grinding stones dating to 28,000 years BCE. The stones have been found across Europe in locations ranging from Italy to the Czech Republic to Russia. The flour residue gives a hint that the diet of early humans may have included a pita-like bread made from four and baked on hot stones. It has long been held that our human ancestors subsisted only on meat. Several discoveries made recently in Near East Paleolithic sites have also provided evidence of plant based foods. "It's another nail in the coffin of the idea that hunterñgatherers didn't use plants for food," says Ofer Bar-Yosef, an archaeologist at Harvard University (US). "I'm pretty sure that you're going to have many more cases where there is evidence for the use of plants by humans." Bar-Yosef was not on the research team who published the paper in the Proceedings of the National Academy of Sciences.
     The consumption of meat is easier to observe at ancient sites, as the butchering of animals leaves marks on bones that can be observed by archaeologists, according to Laura Longo from the University of Siena (Italy), one of the authors on the study. Plant residues are more short-lived and are sometimes lost when excavators wash grinding tools to remove sediments.
     Longo's group first began studying unwashed stone tools from Bilancino, a 28,000 year-old hunter-gatherer site in Italy. They found sandstone grinding implements that contained starch grains from cattail and Brachypodium, a species of grass. Cattail and fern was found on the tools in southern Moravia (Czech Republic) and in Russia. All of the residues at the Paleolithic sites have been from wild plants. Even so, they offered substantial nutrition and were so widely distributed across Europe as to provide a reliable food source. Evidence for farming and the intentional cultivation of food is not found until the Neolithic, and is what defines the Paleolithic to Neolithic transition.
     Since humans cannot get complete nutrition from meat alone, some scientists feel that evidence for flour-making may be be found at even older sites. "This is not isolated to a small group of people. It's a regular part of subsistence for humans," said Bruce Hardy, a paleoanthropologist from Kenyon College in Ohio. (US) "If you get that much meat in your diet not balanced out with other nutrients, you get protein poisoning," says Hardy.

Edited from The New York Times, Discovery News (18 October 2010), Nature News (19 October 2010)