These tool-wielding apes shed light on a vast evolutionary mystery

The first tools of our ancestors from the early Stone Age were simple but monumental. Hammer stones, hand axes, and sharpened flakes were their tools of choice—all carved from stone and used for tasks such as hunting and foraging.

The creation of these humble tools allowed our ancient human relatives to use their environment in new ways, ultimately setting them down an evolutionary path that sets them apart from other species.

While scientists have unearthed swathes of Stone Age tools from sites in Africa, Europe and Asia, questions remain about how these objects were made. One way to gain insight is to observe how our evolutionary relatives – today’s primates – make their own tools out of stone.

Researchers turned to macaques, a genus of Old World monkeys, to elucidate what our ancestors might have been doing millions of years ago. It could also help researchers determine which stone artifacts were made intentionally and which were created accidentally.

The results were published in scientific advances on Friday.

smash stones

The critically endangered long-tailed macaques of Thailand’s Lobi Bay have often been the subject of scientific research. Lydia Luncz, primatologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany The opposite that she has been studying their behavior for about nine years.

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

The macaques forage for nuts and shellfish and break them open by repeatedly smashing them with a hand-held rock. Similar tools in the archaeological record, known as hammer stones, were likely used in the same way by ancient human ancestors.

Macaques break palm nuts on stone anvils with hammer stones in hand.

Lydia V. Luncz

But for the new study, Luncz and his colleagues were more interested in what happened when the hammer stones and stone anvils shattered underneath. When smashed, the macaque’s tools would sometimes splinter and break off, leaving small pieces behind.

These pieces resemble another ancient tool known as a stone flake. Researchers believe that ancient people made these flakes because of their sharp properties for cutting meat. But for macaques, a stone flake is basically useless.

“They go for oysters and sea snails and so on – that’s where they get their meat from,” says Luncz. “But you don’t need sharp cutting flakes for that; You need a percussive tool. You need a striking tool.”

Because the macaques randomly created stone flakes, Luncz and colleagues wondered if some ancient primates might have done the same thing — creating objects that researchers today might interpret as intentional tools.

Stunning similarity

For the new study, the researchers compared more than 1,000 macaque-made stone flakes to ancient flakes that formed 1.3 to 3.3 million years ago. The samples came from several archaeological sites in Tanzania, Kenya and Ethiopia.

By looking at the shape, size and markings on each flake, the researchers found that there were very few physical differences between the samples of today and those made by human ancestors millions of years ago.

That leads researchers to believe that some ancient stone flakes may have been misinterpreted as purposely made tools, since the macaques make similar ones without even trying.

“Given these similarities, it may be that some flakes and flake stones originate from Plio-Pleistocene contexts as a by-product of percussive behavior and can easily be misidentified as intentional products,” they write.

However, Luncz cautioned that the findings don’t mean that scientists studying ancient tools need to jettison everything they know.

“We’re just saying that we might need other criteria to tell them apart… the difference between intentionally made stone artifacts and accidental by-products,” she explains.

If you look at individual ancient flakes, Luncz says, it’s easier to confuse them with those made by modern-day macaques. But if you look at an entire archaeological site, it becomes clearer if the people who once lived there intentionally made tools.

A long-tailed macaque seen on Monkey Island.

Arun Roisri/Moment/Getty Images

pieces of the past

Clues beyond a flake’s physical appearance help researchers determine whether a stone artifact was a tool or just a by-product of another process.

Paleoanthropologist Jason Lewis of Stony Brook University in New York narrates The opposite that there are many clues as to how a flake was broken which, if used intentionally, can help piece it together. Lewis was not involved in the new study but is working extensively at one of the archaeological sites included in the study called Lomekwi 3.

“For example, we use other factors for how far certain rocks have been removed from their natural or original location in the landscape,” explains Lewis. Because certain types of rock have properties that make better tools, an early human ancestor may have collected rocks from one area and taken them to another location for specific tasks.

Finding this evidence can help determine if there was thought or intent behind the creation of an artifact.

As for the new study, Lewis says the results are important because examining the behavior of modern primates gives us a better understanding of some of the biggest questions in our species’ history.

“Understanding and identifying the differences between our ancestors and other primates needed stone tools, versus made Stone tools, is one of the key issues in understanding the origins and development of behaviors that are specific to us or very important to our own evolution,” explains Lewis.

Evidence of macaque tool use from such a broad region also makes the study important. But he says it doesn’t seem likely that the results of this study would change the way archaeologists evaluate ancient tools.

“I would say that the other Early Stone Age archaeologists I know and work with have no doubt at all that we can determine whether flakes are accidental or intentional [shaped] to use as tools,” says Lewis.

It makes sense, he says, that stone flakes accidentally made by macaques would look very similar to those made intentionally by our ancient ancestors.

“If we go back in time, it is perfectly logical and to be expected that our tool making was more primitive in the past; it’s going to look pretty damn similar to what other primates do when they accidentally break rocks,” Lewis explains.

But it’s the full context of where artifacts are found and what they’re made of that helps researchers understand if someone made them intentionally.

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