A 6-centimetre long flint tool from the Evron Quarry archaeological site in Israel was found to be altered by past heating to a temperature of around 300 to 500 degrees Celsius. Researchers say the molecular change, which is invisible to the eye, is evidence that early human ancestors at the site may have been using fire as early as 800,000 to 1 million years ago.Michael Chazan
Archeologists in Israel and Canada have used artificial intelligence to uncover traces of the use of fire from a time that predates all but a handful of similar discoveries, in a place where no such evidence has previously been found.
By harnessing one of humanity’s newest technologies to study one of its oldest, the researchers were able to discern subtle signs of heating by fire in stone tools that date from about one million years ago. The results bring new evidence to bear on the long-standing question of how fire influenced the ancestors of modern Homo sapiens.
“It doesn’t tell us how they were using the fire or if they were making the fire, but it raises that association more tightly,” said Michael Chazan, a paleolithic archeologist at the University of Toronto and a co-author of a paper that documents the find, published Monday in the Proceedings of the National Academy of Sciences.
There is ample evidence of the controlled use of fire as far back as 200,000 years ago, when Neanderthals and other close relations to modern humans were on the scene. But the evidence that fire was used during earlier periods is more scarce. Researchers debate whether fire was rarely employed in those times, or is simply too hard to detect in older samples.
To shed light on the question, Filipe Natalio and his colleagues at the Weizmann Institute of Science in Rehovot, Israel, developed a computer algorithm powered by deep learning, a form of artificial intelligence, to evaluate data gathered from fragments of stone they exposed to ultraviolet light. The method can reveal if heating to temperatures of hundreds of degrees altered the molecular structure of the stone. Such signs are invisible to the eye, but can be spotted by the computer-aided system.
After training the algorithm on test materials that were prepared in a laboratory, the group tried their approach on a set of real samples obtained from an archeological site that Dr. Chazan has studied: Evron Quarry, located near Israel’s Mediterranean coast.
The presence of hand-held flint tools there suggests the site was used by Homo erectus – an early human ancestor – to butcher game between one million and 800,000 years ago. No traces of fire use had been found there before.
To the team’s surprise, the deep-learning algorithm spotted the signature of heating in some of the flint tools. Further examination of the material turned up fragments of burned elephant tusk.
“We were excited ... We were not expecting to find fire at this site,” Dr. Natalio said.
The researchers could not exclude the possibility that a natural wildfire produced the result. But the find raises the prospect of a more comprehensive search for evidence of fire at multiple sites of similar or greater age, including places where such evidence could unambiguously be attributed to Homo erectus.
More discoveries in this vein would add weight to a theory, first proposed by Harvard University professor Richard Wrangham, that the use of fire for cooking was a turning point in human evolution because it offered easier access to the calories available in plant and animal tissue. This, in turn, could explain changes in the human body, including the emergence of larger brains and smaller digestive tracts, both of which showed up in Homo erectus about two million years ago. Skeptics point to a lack of evidence for the use of fire at such an early time.
Susan Mentzer, a researcher on fire use at the University of Tübingen in Germany, who was not part of the team that conducted the research, said the technique developed for the Evron Quarry study should now be applied more routinely, even in places where burning is not suspected.
“It’s possible there are many more sites that will yield similar results,” she said.
Dr. Chazan said plans are in the works to do just that at a pair of sites in Spain and Georgia that contain remnants of habitation by early human ancestors.
Another expert who was not involved with the study, Dennis Sandgathe, at Simon Fraser University in British Columbia, praised the team members for their caution in presenting their results. He added that testing should be done in other places of similar age, where no signs of activity by early Homo species are present, so that researchers can better understand the traces left by natural fires in the geological record.
If evidence of heating in such areas proves to be sparse compared with areas where humanity’s distant ancestors were living, “then that really starts to look like they were the ones doing the burning,” Dr. Sandgathe said.
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