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

The first tools made by our Early Stone Age ancestors were simple, but monumental. Hammers, bifaces, and sharpened shards were their tools of choice, all carved out of rock and used for such tasks as hunting and foraging.

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

While scientists have unearthed swaths of Stone Age tools from sites in Africa, Europe and Asia, questions remain about how these items were made. One way to glean insight is to look at how our evolutionary cousins ​​– modern-day primates – make their own tools from stone.

Researchers have turned to macaques, a genus of Old World monkeys, to shed light on what our ancestors may have been up to millions of years ago. It could also help researchers determine which stone artifacts were made on purpose and which arrived by accident.

The results were published in Scientists progress Friday.

breaking stones

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

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

Macaques search for nuts and shellfish, smashing them by repeatedly smashing them with a hand stone. Similar tools in the archaeological record, known as hammers, were probably used in the same way by ancient human ancestors.

Macaques cracking palm nuts on stone anvils with hammers in their hands.

Lydia V. Luncz

But for the new study, Luncz and his colleagues were more interested in what happened when the stone hammers and anvils beneath them shattered. During the crushing process, the macaque’s tools chipped and sometimes broke, leaving small pieces behind.

These pieces resemble another ancient tool, known as a stone shard. Researchers believe that ancient humans made these flakes to cut meat, due to their sharp properties. But for macaques, a stone shard is basically useless.

“They go for oysters and sea snails and stuff like that – that’s where they get their meat,” Luncz says. “But they don’t need sharp shards to do that; they need a percussion tool. They need a hammering tool.

Because macaques created stone shards by accident, Luncz and his colleagues wondered if some ancient primates could have done the same, creating objects that researchers today might interpret as intentional tools.

striking resemblance

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

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

This leads researchers to believe that it is possible that some ancient stone shards have been misinterpreted as intentionally made tools, since macaques make similar ones without even trying.

“Given these similarities, it may be that some shards and shards from Plio-Pleistocene contexts are derived from percussive behaviors and can be easily misidentified as intentional products,” they write.

However, Luncz cautioned that the findings don’t mean scientists studying ancient tools should throw everything they know out the window.

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

When looking at individual ancient flakes, Luncz says it’s easier to confuse them with those made by macaques today. But when you look at an entire archaeological site, it becomes clearer whether the individuals 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 shard’s physical appearance help researchers determine whether a stone artifact was a tool or simply a byproduct of another process.

Paleoanthropologist Jason Lewis of Stony Brook University in New York says Reverse that there are many clues beyond how a flake was broken that can help piece together whether it was used intentionally. Lewis was not involved in the new study, but is working intensively on one of the archaeological sites – called Lomekwi 3 – included in the study.

For example, “we use other factors to determine how far certain rocks have moved from where they would have naturally or originally occurred in the landscape,” Lewis says. Since certain types of rock have properties that make them better tools, an early human ancestor may have collected rocks from one area and moved them to another location for certain tasks.

Researching 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 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 the distinctions between when our ancestors or other primates used stone tools, against do stone tools, is one of the key issues for understanding the origins and evolution of behaviors that are specific to us, or very important in our own evolution,” explains Lewis.

Having evidence of tool use by macaques in such a large area also makes the study important. But he says it doesn’t seem likely that the results of this study will change the way archaeologists value ancient tools.

“I would say that other Early Stone Age archaeologists I know and work with have no doubts about our ability to detect whether the shards are from an accidental or intentional percussion process. [shaped] to use as tools,” says Lewis.

It makes sense, he says, that stone shards made accidentally by macaques look a lot like those made intentionally by our ancient ancestors.

“As we go back in time, it is absolutely logical and expected that our tool making was more primitive in the past; it’s going to be a lot like what other primates do when they accidentally break rocks,” Lewis says.

But it’s the full context of the discovery of the artifacts and their composition that helps researchers understand whether someone made them on purpose.

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