The consumption of wild cereals among prehistoric hunters and gatherers appears to be far more ancient than previously thought, according to a University of Calgary archaeologist who has found the oldest example of extensive reliance on cereal and root staples in the diet of early Homo sapiens more than 100,000 years ago.
     Julio Mercader, holder of the Canada Research Chair in Tropical Archaeology in the University of Calgary's Department of Archaeology, recovered dozens of stone tools from a deep cave in Mozambique showing that wild sorghum, the ancestor of the chief cereal consumed today in sub-Saharan Africa, was in Homo sapiens' pantry along with the African wine palm, the false banana, pigeon peas, wild oranges and the African 'potato.' This is the earliest direct evidence of humans using pre-domesticated cereals anywhere in the world. "This broadens the timeline for the use of grass seeds by our species, and is proof of an expanded and sophisticated diet much earlier than we believed," Mercader said. "This happened during the Middle Stone Age, a time when the collecting of wild grains has conventionally been perceived as an irrelevant activity and not as important as that of roots, fruits and nuts."
     In 2007, Mercader and colleagues from Mozambique's University of Eduardo Mondlane excavated a limestone cave near Lake Niassa that was used intermittently by ancient foragers over the course of more than 60,000 years. Deep in this cave, they uncovered dozens of stone tools, animal bones and plant remains indicative of prehistoric dietary practices. The discovery of several thousand starch grains on the excavated plant grinders and scrapers showed that wild sorghum was being brought to the cave and processed systematically. "Whether they were eating it or not, we cannot be sure, but I cannot see how sorghum gets into the cave unless humans bring it in," says Mercader.
     Most researchers think that humans in the Middle Stone Age - which began around 300,000 years ago and ended around 50,000 years ago - depended on foodstuffs such as underground tubers and meat. Grains require a complex preparation process of grinding and charring before they can be digested by humans. Mercader says that sorghum flours could have been used to make culinary preparations such as bread. The first confirmed use of grains in the human diet comes from charred barley and wheat from Israel dating to about 23,000 years ago, so the latest findings could push that date back another 80,000 years. "The inclusion of cereals in our diet is considered an important step in human evolution because of the technical complexity and the culinary manipulation that are required to turn grains into staples," Mercader said.
     Other scientists, however, are sceptical. Archaeologist Lyn Wadley, an honorary professor at the University of the Witwatersrand in Johannesburg, South Africa, points out that starch grains are notoriously difficult to identify, varying not only among species but also between different parts of a plant. "Even if sorghum is truly present at the site," she says, "there could be a reason for this presence other than eating of grains." At the Sibudu cave in the KwaZulu-Natal province of South Africa, her group has found that grasses similar to sorghum were used for bedding and as tinder for fireplaces. Loren Cordain, an exercise physiologist at Colorado State University in Fort Collins and an expert on the Palaeolithic diet, agrees that the evidence is too thin to support the consumption of grains as food. "I don't think they've really built a strong case for the notion that cereal grains were exploited on a real basis and were part of the diet of our ancestors," he says.

Sources: EurekAlert!, Red Orbit, Nature News (17 December 2009)