But paleoanthropologist John Shea isn't convinced by the idea that "heat treating" stone was a sign of the transition to modern human behavior.
"People rush immediately to look for evidence of a transforming event in the course of Homo sapiens evolution to distinguish modern humans from so-called early ones," said Shea, of Stony Brook University.
"My position is that you shouldn't assume this transformative event—you have to prove it," Shea said.
To begin with, scientists would need to verify that the various human species preceding H. sapiens in South Africa did not also heat-treat stones.
Even so, Shea praised the study, saying it will inspire people to seek out other heat-treated stone tools undetected in the African record.
The tools were apparently created during a burst of cultural growth, when the human population was slowly recovering from a severe glacial period.
At the South African sites, humans were designing jewelry, such as shell beads, and grinding up ochre to paint themselves and decorate their caves, study leader Brown said. (See "Oldest Jewelry? 'Beads' Discovered in South African Cave.")
Heat-treating stone could have been "one of the technologies in their toolkits that allowed [them] to adapt to different areas as they expanded out of Africa," Brown said.
But heat treatment probably didn't improve the tools, and may have even made them more likely to shatter, Stony Brook's Shea said.
Instead the flashy artifacts might have been ways that "some humans showed off that they had time on their hands," Shea said.
"Going into woods with a bunch of arrows that would shatter on impact is another way of saying, I'm a really good hunter; I don't need backup."
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