for National Geographic News
Stone Age humans were adept chemists who whipped up a sophisticated kind of natural glue, a new study says.
They knowingly tweaked the chemical and physical properties of an iron-containing pigment known as red ochre with the gum of acacia trees to create adhesives for their shafted tools.
Archaeologists had believed the blood-red pigment—used by people in what is now South Africa about 70,000 years ago—served a decorative or symbolic purpose.
But the scientists had also suspected that the pigment may have been purposely added to improve glue that held the peoples' tools together.
So researchers recreated the ancient glue using only Stone Age materials and technologies.
The results showed that glue containing red ochre was less brittle and more shatterproof than glue made from acacia gum alone.
"We discovered that when we used ochre, the glue is much more robust, and the stone tool doesn't come off the shaft," said study team member Lyn Wadley of the University of the Witwatersrand in Johannesburg, South Africa.
Smarter Than We Thought?
But making the glue wasn't easy for the ancient Africans.
It was mentally taxing work that would have required humans to account for differences in the chemistry of gum harvested from different trees and in the iron content of ochre from different sites.
"They couldn't possibly have known about chemical pH or iron content but they knew that certain combinations of things worked very well," Wadley said.
The finding also suggests the intelligence of Stone Age humans was more akin to that of modern humans than previously thought, she added.
"Our study shows that there's a lot of overlap between ourselves and these ancient people. Their technology was a lot more competent than we have given them credit for."
The research is detailed in this week's issue of the journal Proceedings of the National Academy of Sciences.
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