Agriculture: African origins may go south.

Carbonized seeds discovered at an archaeological site in the Sahara Desert provide preliminary evidence that prehistoric inhabitants of the African savanna cultivated plants 8,000 years ago, much earlier than previously thought.

The finding, published in the Oct. 22 NATURE, challenges a long-standing theory that African agriculture first sprouted in Egypt about 6,400 years ago with the domestication of wheat and barley, then spread southward.

By contrast, investigators suspect plant cultivation first arose in southwestern Asia around 12,000 years ago (SN: 2/18/89, p.101).

"We have evidence for the intensive use of wild plants at an African site where they were undoubtedly harvested in great quantity," says archaeologist Fred Wendorf of Southern Methodist University in Dallas, who directed the excavation. "But it's premature to suggest that the domestication of wild plants definitely took place."

Even in the absence of domestication, massive seasonal harvesting represents an immediate precursor of planting and protecting crops, Wendorf asserts.

His team investigated a site in southernmost Egypt, just north of Sudan, that attracted initial excavations in the mid-1970s. At the time of its occupation, the desert site was located in a savanna and experienced seasonally heavy rains.

Further excavation of the site in 1990 and 1991 by Wendorf's group uncovered four houses and 12 large storage pits. The floors of the structures contained traces of 15 hearths, as well as 122 shallow depressions, or "cooking holes."

In ashy sediment piled up around some of the cooking holes, the researchers found several thousand carbonized seeds from more than 40 different plants, including sorghum, millets, legumes, fruits, nuts, and tubers. Prehistoric residents apparently placed food containers in the cooking holes and spread hot ashes around the vessels to heat their contents, Wendorf says. The contents sometimes boiled over or fell into the ash, contributing seeds for preservation, he maintains.

Radiocarbon dates for the seeds cluster around 8,000 years ago.

Although the ancient sorghum remains look much like modern wild sorghum, the chemical makeup of fats encased in the carbonized seeds more closely resembles that of modern domestic sorghum, the scientists contend.

Their chemical analysis relied on a recently developed technique in which researchers deliver a dose of infrared light to a seed and obtain data on its fat composition through a light-sensitive spectroscope. Other scientists have found that the technique distinguishes between wild and domestic forms of wheat and barley, Wendorf says.

His team compared the fat chemistry of five carbonized sorghum seeds to that of seeds from three cultivated forms of sorghum and four wild sorghum species. They plan to conduct the same analysis on hundreds of additional ancient seeds.

"We've got a long way to go before we understand the process of plant domestication in Africa," Wendorf says. "But I'd bet we eventually find a pattern of intensive plant use at many Saharan sites from the same time period."