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Hominins living near Tanzania's Olduvai Gorge were preferentially selecting material for different types of stone tools as early as 1.8 million years ago.

New research suggests the decisions made by tool makers among Early Stone Age hominins accounted for both the requirements of specific tasks and the unique mechanical advantages offered by different types of stone.

Previous archaeological studies have documented the selection of different materials -- lavas, quartzite or chert -- for different tools among among Early Stone Age hominins.

Authors of the latest study, published Wednesday in the Journal of the Royal Society Interface, looked at why hominins choose the materials they did.

"There has been decades of research at Olduvai Gorge studying which raw materials were used for certain types of stone tool, how these types of tool were used -- i.e. their function -- and how close artifact sites were to raw material sources," lead researcher Alastair Key, a lecturer in biological anthropology at the University of Kent in Britain, told UPI. "We wanted to help understand these trends already identified in the archaeological record."

Key and his colleagues did so by conducting mechanical tests of the raw materials available to and used by Early Stone Age hominins -- identifying which were sharper and more durable.

Their analysis showed that the mechanical qualities of the different materials help explain the logic behind the material selections made by early hominins.

"So, for example, we know that during the Early Stone Age Olduvai populations preferentially used quartzite for small flake tools," Key said. "We also know through previous research that this trend is consistent across multiple sites in the gorge, and that flake tools were likely to have been expediently used -- i.e. not used for long periods of time -- to butcher animal carcasses and process plant materials such as fruits, tubers, wood, etc."

"Given that our data revealed quartzite to be the sharpest raw material at the gorge, it makes sense that individuals chose to produce flake stone tools from this material as it would have reduced the energy, time and forces required during tool use," Key said.

Because quartzite isn't very durable, it's use would only make sense for quick jobs like butchering animals and preparing foods. Tools that early hominins used for longer periods of time, like a handaxe, required more durable materials.

Researchers determined that lavas deposited at the Olduvai Gorge offered more durability.

"This difference is reflected in the artifact record, as handaxes, cleavers and other larger tool types are frequently made from basalt and other lavas," Key said. "Flakes, however, are more rarely made form this raw material type."

Tests also showed chert offers the best of both worlds. It is both sharp and durable, but it wasn't always readily available.

"The use of chert at the gorge is particularly interesting as it was only available for a relatively short period, or at least, short in geological terms," Key said. "We identify chert to be almost as sharp as quartzite, but much more durable. Again, this is reflected in the archaeological record, as whenever chert is available hominins preferentially chose this raw material for multiple tool types due to its ability to reduce cutting forces and energy use, while also remaining sharp for a long period of time."

Key and his colleagues hope that moving forward, more archaeologists will use mechanical and engineering tests to provide context for the artifact. There are still unanswered questions about the use of raw materials by hominins, questions that mechanical tests could help answer.

"For example, it remains to be seen whether individuals at even earlier archaeological sites similarly selecting raw materials based on their relative sharpness," Key said.
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