Long before early humans in North America grew corn and beans, they were harvesting and cooking the bulbs of lilies, wild onions and other plants, roasting them for days over hot rocks, according to a Texas archaeologist.
The evidence for this practice has long been known of in fire-cracked rock piles found throughout the continent, but archaeologists have tended to ignore it "because a new pyramid or a Clovis arrow point is much sexier," said archaeologist Alston V. Thoms of Texas A&M University.
In two reports published online this week in the Journal of Anthropological Archaeology and the Journal of Archaeological Science, Thoms reported that cooking on hot rocks first became a substitute for cooking on hot coals about 9,000 to 10,500 years ago, then had a sudden jump in popularity about 4,000 years ago.
The reason for the changes: population growth that required the exploitation of new food resources.
"Whatever they were eating before did not require prolonged cooking," Thoms said. But beginning about 10,000 years ago, "people couldn't live off the cream of the land anymore." The megafauna that had been a prime food source -- such as the woolly mammoth -- were becoming extinct, and other mammals were becoming harder to find. People had to turn to plants.
Meadowlands and forest edges were filled with lilies, wild onions and perhaps two dozen other wild plants ready for the harvesting. The bulbs of these plants are about as nutritious as sweet potatoes, but their energy is locked up in a dense, indigestible carbohydrate called inulin. The only way to make the bulbs digestible is to roast them for two days or longer.
Cooking over a hot fire, as people had done in the past, meant tending a fire pit. But adding large rocks, some weighing more than 2,000 pounds, changed the situation. If the rocks were heated red-hot, they would hold heat for 48 hours or longer, conserving both fuel and human energy.
The remains of these earth ovens have been excavated by archaeologists since 1900, "but people haven't recognized at a broad level that the earliest ones in Canada are about the same age as those in the Pacific Northwest and in Texas," Thoms said.
In other words, "this was a punctuated change, all at once, over a big part of the country."
Evidence suggests that a similar change occurred in Russia, Japan and perhaps Britain, he said. "There are lilies in northern environments around the world, and they were used as staples in the same way people today use wheat, grains or rice."