By Heather Pringle, Science Now, April 2, 2012
For millions of years, our ancestors were spread thinly
across the African continent. They dined on raw meat, huddled in the cold, and
slept fitfully in the dark, fearing the approach of large predators. But
eventually, early humans reached a crucial turning point: They learned to make
fire. Kindling and controlling a small blaze, they cooked their dinners,
socialized around warm hearths, and frightened off large, menacing carnivores.
Now, a new study suggests that humankind tamed the flame at least 200,000 years
earlier than previously thought.
"I think this research establishes as well as
possible that by 1 million years ago, early humans were able to control
fire," says one of the paper's authors, archaeologist Michael Chazan of
the University of Toronto in Canada.
The new evidence comes from a site known as Wonderwerk
Cave in South Africa. Back in the 1980s, a now-retired South African
archaeologist, Peter Beaumont, found what appeared to be wood ash and charcoal
in a layer of sediment dated to 1.7 million years ago. But early claims for
fire are often controversial because it is difficult to distinguish between
natural fires and those set by humans. The most widely accepted previous claim
came from the site of Gesher Benot Ya'aqov in Israel, where archaeologists found traces of what
appeared to be fire dating to 790,000 ago.
Other researchers challenged Beaumont's finding. The ash
and burnt bits, critics suggested, could have blown into the cave from a forest
fire or resulted from the spontaneous combustion of bat guano--an event that is
rare but has been documented elsewhere. So when Chazan and his team began
working at Wonderwerk Cave, they took a new look at the evidence.
The hearthlike feature that Beaumont spotted turned out
to be the product of natural geologic processes. But Chazan and his team found other visible signs of burning in a
younger layer they dated by geological methods to 1 million years ago. Then team member Francesco Berna
examined thin sections from the layer microscopically and analyzed their
molecular composition by passing an infrared beam through the samples and
studying the resulting spectrum. The presence of angular, sharp-edged bone
fragments and well-preserved plant ashes, he says, indicates that neither wind
nor water had buffeted and transported the particles; the burning took place in
the cave. Moreover, Berna detected no trace of guano or any sign of the
high-temperature combustion that phosphate-rich guano would produce. Instead,
his studies showed that the bone mineral had been heated to between 450 and 700
degrees Celsius, the temperature of a small campfire. "Before this, I
didn't believe that humans used fire so early," Berna says. "But
there's no other explanation."
Such a small, low-temperature fire would be ideal for
cooking. And the new finding, published online today in Proceedings of the
National Academy of Sciences, fits well with earlier research conducted by
Harvard University primatologist Richard Wrangham on the anatomy and behavior
of Homo erectus, an extinct human ancestor who roamed Africa as early as 1.9
million years ago. The relatively small molars of Homo erectus and its reconstructed small gut
suggest that it dined regularly on soft, nutrient-packed cooked food. And the fact that Homo erectus
slept on the ground suggests that it had already begun building campfires to
deter predators.
Still, the new Wonderwerk Cave study is likely to stir
controversy. Wil Roebroeks, an archaeologist at Leiden University in the
Netherlands, says that Berna and his colleagues failed to report any signs that
the sediments in the thin sections had been heated or burned. And this,
Roebroeks notes by e-mail, "suggests that the fire did not burn on the
sample spot, and that the charred material indeed underwent some transport from
a nearby fire."
But Wrangham thinks that the new microscopic way of looking for
fire holds great promise, particularly for turning up data that may have been
overlooked by previous archaeologists in several key early sites in Africa. The
new study at Wonderwerk, Wrangham concludes, "is an exciting
breakthrough."
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