An archaeological dig of a cave in South Africa provides evidence of "burning events" 600,000 years older than other conclusive sites.



In 2009 Harvard anthropologist Richard Wrangham offered a novel theory on the evolution of humans: Homo erectus could not have evolved nearly two million years ago without consuming cooked food. No way, he argued, could raw food have provided the calories necessary for the development of the human brain. Its digestion alone requires too much energy. But cooked food changed everything. It's much easier to digest, freeing up energy to fuel our brains, not our guts. "The extra energy gave the first cooks biological advantages," he wrote. "They survived and reproduced better than before. Their genes spread. Their bodies responded by biologically adapting to cooked food, shaped by natural selection to take maximum advantage of the new diet. There were changes in anatomy, physiology, ecology, life history, psychology and society."

But there was one small problem with Wrangham's theory: Cooking food requires fire, and the oldest unequivocal evidence for human control of fire only ("only") dates to 400,000 years ago. No fire, no cooking. The few archaeological sites in Africa, Asia, and Europe with trace fire evidence dating back to 700,000 to 1.5 million years ago are open air, meaning wildfires cannot be ruled out, or are inconclusive for other reasons.

Now a new paper published this week provides what the authors call "unambiguous evidence in the form of burned bone and ashed plant remains" that "burning events" occurred in Wonderwerk Cave, an archaeological site in South Africa, one million years ago. The archaeologists -- led by Francsco Berna of Boston University -- have been working in the cave, "an approximately 140-m-long phreatic tube," since 2004. Kate Wong explains at Scientific American:

Berna's team obtained blocks of sediment from a layer in the cave that contains stone tools made in the so-called Acheulean tradition, which is believed to have originated with the early human ancestor Homo erectus. Studying thin sections of the sediment blocks under a microscope, the scientists observed lots of ashed plant remains and tiny fragments of burned bone. Further analysis of the thin sections using Fourier transform infrared microspectroscopy, which reveals molecular structure, showed that some of the bones had been heated to temperatures of around 500 degrees Celsius. Preliminary data suggest that leaves and grasses, rather than wood, fueled these ancient fires. All told, the burned remains appear to have been the products of repeated, local combustion episodes that occurred in the vicinity of where the remains were discovered, 30 meters in from mouth of the cave.

Additionally, the team did not find traces of berlinite and hydroxylellestadite, two minerals that "characteristically form during spontaneous combustion of bat guano -- a rare event but one documented inside caves" (a very wonderful phrase if there ever was).

Evidence for the earliest stone tools still predates the control of fire, by hundreds of thousands of years, but the authors of the paper believe that the techniques they used to study the Wonderwerk sediments may result in discoveries of even earlier "burning events."

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