These tool-wielding monkeys shed light on a huge evolutionary puzzle

The first tools that our early Stone Age ancestors made were simple but massive. Hammerheads, handgrips, and sharpened flakes were their favorite tools—all carved out of rock and used for tasks like hunting and foraging.

The creation of those humble tools allowed our ancient human relatives to exploit their environments in new ways, ultimately leading them down an evolutionary path that set them apart from other species.

While scientists dug Swabs of Stone Age tools From sites in Africa, Europe and Asia, questions remain about how these things were made. One way to gain insight is to watch how our evolutionary cousins ​​- today’s primates – make their own tools out of stone.

The researchers turned to macaques, a genus of Old World monkeys Highlighted What our ancestors were doing millions of years ago. It can also help researchers determine which stone artifacts were made on purpose, and which happened to be by chance.

The results are published in Science advances Friday.

smash stones

the endangered Long-tailed macaques in Lopi Bay, Thailand, have been frequent subjects of scientific research. Lydia Longsa primatologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany inverse that she had been studying their behavior for about nine years.

“Out of the hundreds of species of primates, only a handful use stone tools,” says Luncz, a co-author of the new study. These macaques are one of a select few, making them ideal candidates for understanding how to use simple stone tools.

Macaques feed on nuts and shellfish, which they break by repeatedly smashing with a hand stone. Similar tools in the archaeological record, known as hammer stones, may have been used by ancient human ancestors in the same way.

But for the new study, Luncz and his colleagues were more interested in what happened when the stone hammer and anvil underneath shattered. In the process of smashing, the macaque’s tools would sometimes chip and break, leaving behind small pieces.

These pieces look similar to another ancient tool, known as a flake stone. Researchers believe that ancient humans made these chips for cutting meat, due to their sharpening properties. But for macaques, stone chips are basically useless.

“They go for oysters and sea snails and things like that — and that’s where they get their meat,” says Luncz. “But they don’t need sharp chopping chips to do that; they need a percussion instrument. They need a pounding instrument.”

Because macaques created stone flakes by accident, Loncz and his colleagues wondered if some ancient primates might have done the same thing—making things that today’s researchers might interpret as intentional tools.

clear resemblance

For the new study, the researchers compared more than 1,000 stone fragments made of macaques and ancient flakes dating from 1.3 to 3.3 million years ago. The samples came from several excavated sites in Tanzania, Kenya and Ethiopia.

By looking at the shape, size, and markings on each shell, the researchers determined there were very few physical differences between specimens from today and specimens made by human ancestors millions of years ago.

This leads the researchers to believe that it is possible that some of the ancient stone flakes may have been misinterpreted as tools made on purpose, because macaques make such similar flakes without even trying.

“Given these similarities, some falling flakes and stones from Plio-Pleistocene contexts may have been derived as by-products of rhythmic behavior and could easily be misidentified as intentional products,” they wrote.

However, Luncz cautioned that the findings do not mean that scientists studying ancient tools need to throw everything they know out the window.

“We’re just saying we might need different criteria to distinguish … the difference between intentionally made stone artefacts and accidental by-products,” she explains.

When looking at individual old chips, Luncz says it’s easier to confuse them with the ones macaques make today. But when looking at an entire archaeological site, it becomes clear whether the individuals who once lived there were deliberately working with crafting tools.

Pieces of the past

Clues beyond the chips’ physical appearance are helping researchers determine whether the stone artifact is a tool, or just a by-product of some other process.

paleontologist Jason Lewis of Stony Brook University in New York says inverse That there are many more cues beyond how to break the shell that can help piece together if used intentionally. Lewis wasn’t involved in the new study, but he’s been working extensively on one of the archaeological sites – it’s called Lomekoy 3 included in the study.

For example, “we use other factors about how far certain rocks were moved from their natural location or that they originally occurred on the landscape,” Lewis explains. Because certain types of rock have properties that make better tools, early human ancestors may have collected rocks from one area and transported them to another for certain tasks.

Looking for this evidence can help determine if there was any thought or intent behind creating the artifact.

For the new study, Lewis says the findings are important because studying the behavior of modern primates gives us a better understanding of some of the biggest questions in the history of our species.

Understanding and identifying differences between our ancestors or other primates user Stone Tools, vs to make Stone tools, one of the key issues in understanding the origins and evolution of our behavior, or very important in our evolution,” Lewis explains.

The presence of evidence of macaque tool use from such a wide area also makes the study important. But he says it does not seem likely that the findings of this study will change how archaeologists evaluate ancient tools.

“I would say that other Paleolithic archaeologists that I know and work with are not at all dubious about our ability to detect whether the chips came from an accidental hammering operation or if they were intentional. [shaped] To use them as tools,” Lewis says.

It makes sense, he says, that the stone flakes the macaques accidentally made look a lot like the ones our ancient ancestors made on purpose.

“As we go back in time, it’s perfectly reasonable and expected that our tool-making was more primitive in the past; it will look a lot like what other primates end up doing when they accidentally break stones,” Lewis explains.

But it is the full context of where the artifacts were found and what they are made of that helps researchers understand whether someone made them on purpose.