Published online 17 December 2009 | Nature | doi:10.1038/news.2009.1147

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Stone Age sorghum found in African cave

Harvesting of wild grains may have begun more than 100,000 years ago.

GrainsSorghum granules have been found on ancient stone tools.Mercader, J. Science

Humans may have been baking bread 105,000 years ago, says a researcher who has discovered evidence of ground seeds from sorghum grass on stone tools in a Mozambique cave.

"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 study author Julio Mercader, an archaeologist at the University of Calgary in Alberta, Canada. Today, seeds from domesticated sorghum grass are used as flour for porridge, as a fermentation substrate for beer and as a dye for clothing.

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 ago1, so the latest findings could push that date back another 80,000 years.

Stone toolsGrinding and pounding implements from the Ngalue cave had starchy grains on their surfaces.Mercader, J. Science

Mercader first discovered the Ngalue cave, in the sparsely populated Niassa province of Mozambique, with the help of locals in 2005. After a drive to the end of a road at an old mine site, he and his team then had to hike for 45 minutes to reach the cave's mouth. In 2007, the team made this trip every day as they excavated in a dark chamber 20 metres from the cave entrance, identifying animal bones along with more than 500 quartz artefacts.

Mercader says that he has always taken precautions not to wash or touch the excavated tools to ensure that he leaves pollens, starches and other microfossils intact. After examining 70 stone tools, including scrapers and grinders, he found that 80% contained traces of starch granules, mainly from wild Sorghum species. Some of the grains appeared damaged, but none had been cooked. "These data imply that early Homo sapiens from southern Africa consumed not just underground plant staples, but above-ground resources too," he writes in this week's issue of Science.2

Half-baked?

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.

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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. "It's fascinating and suggestive, but the logic doesn't fall in place." He points out that there is no anvil rock with which to grind the grains as discovered in Israel, for instance, nor is there evidence that humans were cooking the grains.

But Mercader believes early human grain consumption is possible even if he has not yet fully demonstrated it. "If you think about the complexity of modern human behaviour, I'm not sure the early use of grains is unexpected: it's in line with other discoveries from the Middle Stone Age," he says. Early modern humans first emerged around 150,000 to 200,000 years ago, and scientists working in South Africa have found that humans 72,000 years ago were using shell beads and ochre pigments, in addition to making stone tools with the help of fire.3 "I understand healthy scepticism goes a long way," Mercader says, "but let us not overdo it." 

  • References

    1. Piperno, D. R., Weiss, E., Holst, I. & Nadel, D. Nature 430, 670-673 (2004). | Article | ChemPort |
    2. Mercader, J. Science 326, 1680-1683 (2009). | Article | ChemPort |
    3. Brown, K. S. et al Science 325, 859-862 (2009). | Article | ChemPort |
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