Sat. Oct 1st, 2022
It turns out that the robot uprising will be equipped with (checks notes) sharp chert flakes.
enlarge It turns out that the robot uprising will be equipped with (checks notes) sharp chert flakes.

A team of archaeologists recently applied high-tech engineering tests to stone tools, and the results suggest that even very early members of our genus, such as gay habilismanaged to select stones with the right combination of sharpness and durability for the work at hand.

Species on the hominin family tree, as far as we know, have been making and using stone tools for about 2.6 million years; you could call it a family tradition. In the Olduvai Gorge in northern Tanzania, layers of sediment dating back to about 1.8 million years ago contain simple stone tools — the handiwork of a tiny hominin called gay habilis† That species was an early member of our genus that walked upright and had a mixture of human and ape-like features. About 1.2 million years ago, a later hominin species called homo erectus made more complex stone tools, such as hand axes.

Think of a stone flake from the oldest layers at Olduvai. That simple tool exists because 1.8 million years ago a gay habilis picked a stone, molded the stone into the right shape, and then used it to do something. Archaeologists can learn a lot about what ancient hominids knew and how they lived by studying the wear and grinding marks on such tools. But the rock itself has a story to tell. Why did a hominin choose 1.5 million years ago? this one kind of rock, and why? this one particular part of it?

Archaeologists working in Olduvai decades ago noted that those now-extinct hominins had preferred certain types of stone to certain types of tools. Quartzite, for example, was a favorite for making the small, sharp-edged cutting tools called flakes, while basalt and other lavas seem to pop up more often in the form of large cutting tools like hand axes. To find out why, University of Kent anthropologist Alastair Key and colleagues subjected Pleistocene-style stone tools to a battery of tests commonly used in modern engineering research.

We have always been engineers

Key and his colleagues wanted to know whether H. habilis and H. erectus knew how to choose the most practical materials for specific tools or jobs. To find out, the archaeologists compared the sharpness and durability of Olduvai basalt, chert and quartzite—three of the most common materials for stone tools in and around the canyon. And for that you had to make a robot play with some replica stone tools.

An engineering test machine lowered each sharp rock flake onto a 2mm wide piece of PVC pipe and recorded how much force had to be applied to cut through the pipe and how much the surface of the pipe gave way before splitting. To test durability, Key and his colleagues set the machine to work cutting oak branches with the replica flakes, then measured how well each blade held its edge between uses.

Quartzite turned out to be the sharpest stone on the list, with chert a close second. The sharpness of Basalt was not very impressive; cutting something with a basalt flake takes about twice as much energy as using a chert or quartzite flake. So it makes sense that hominins in the Olduvai rift would choose quartzite or cherts for small flakes — quickly made cutting tools that would have been thrown aside after use (they’re the plastic traces of the Pleistocene).

A brand new basalt ax is a bit duller than a barrier made of chert or quartzite, but the basalt tool will hold its edge much better over time. And it seems that H. habilis toolmakers knew this 1.8 million years ago, because dull but sturdy basalt was a more common choice for heavier work or for larger cutting tools that would be used over and over again. Key and his colleagues suggest that’s no coincidence.

“While Pleistocene individuals may not have been aware of this, they took advantage of a set of mechanical principles routinely applied during the design of modern metal cutting tools,” Key and his colleagues wrote. Naturally, H. habilis did not accurately measure how much force it took to cut off a limb of a freshly killed antelope and then make plans for a more efficient knife. But it seems they noticed which materials made sharper blades and which offered a compromise between sharpness and durability, and then applied that knowledge to tool making.

That’s no small cognitive feat, especially for such an early member of our family tree. You would probably recognize it H. habilis as a relative, but you are unlikely to mistake one for a modern person. They were about three feet long, with a mostly monkey-like facial structure and long arms that were still adapted for a life partly spent in the trees. But it turned out that they were quite sharp.

Royal Society Interface2020 DOI: 10.1098/rsif.2019.0377 (About DOIs).

By akfire1

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