Monkey hammering on rock resembles tools made by early human ancestors | Science

Throwing a rock the size of a potato, wild long-tailed macaques (Macaca fascicularis) in Thailand crush palm oil on stone anvils. As they move away, sharp flakes sometimes fly from their hammerstones – flakes that are “almost indistinguishable” from stone tools made by early human relatives more than 3 million years agoaccording to a controversial new study. Indeed, the researchers argue, ape flakes are so similar to the tools of our ancestors that many archaeologists would classify them as early stone tools without a second thought.

The study, published today in Advances in Scienceadds to another recent finding that Brazilian white-faced capuchin monkeys also produce stone flakes. Together, they “show that human manual and cognitive skills are not necessary for the production of stone tools,” says Ignacio de la Torre, an archaeologist at Spain’s National Research Council who was not involved in the work.

Other archaeologists, however, are not convinced. “Sure, some flakes on [ancient] Archaeological sites may come from apes banging rocks together and accidentally making flakes,” says Jason Lewis, a paleoanthropologist at Stony Brook University. “But this is a hypothesis that needs to be tested.”

The earliest described stone tools—consisting of stone flakes and anvils—date back to 3.3 million years ago. They were discovered in Lomekwi, Kenya in 2011. Scientists don’t know which of the earliest human relatives made the flakes or how they used these sharp blades, but they predate the appearance of our genus. Homosexual, which arose between 3 million and 2.5 million years ago. Much more is known about Oldowan stone tools, first discovered in Olduvai Gorge in Tanzania in the 1930s. They range in age from nearly 3 million to 1.5 million years and are found at sites across the African continent, as and in Europe and Asia.

Other primates also make and use stone tools. Brazilian capuchin monkeys have been using stones to crack seeds and nuts for at least 3000 years, and chimpanzees in Ivory Coast have been doing so for more than 4000 years. In 2016, scientists showed that Burmese long-tailed macaques on Thailand’s Piak Nam Yai Island have been using stones to open oysters for at least 65 years, over two generations or more.

If an archaeologist found the flakes analyzed in the current study in 3-million-year-old African sediments, “I would say [they] they were definitely made by humans,” says Tomos Proffitt, an archaeologist at the Max Planck Institute for Evolutionary Anthropology and lead author of the study.

Lydia Luncz, a primatologist also at the Max Planck Institute and co-author of the new study, first recognized the rock-peeling behavior of the macaques in 2016. In a palm grove perched atop a limestone cliff, she stumbled upon “what looked like nut-cracking site,” he said, similar to those he had seen left behind by Ivory Coast chimpanzees.

Luncz set up camera traps and recorded the macaques cracking open palm nuts (see video, above) with hammer stones. It was only after nearly cutting her hand off on a flake that she realized the site would be “a big deal for archaeologists”. She showed the flakes to Proffitt, who studies stone tools, and he pressed her: “Are you sure a monkey did that?”

In 2017 and 2021, researchers collected 1119 rock fragments from 40 nut cracking sites on Yao Noi Island in Lobi Bay. They then compared the macaquemade flakes to stone material dating from 3.3 million to 2 million years ago from archaeological sites in Africa.

The scientists analyzed the size, shape and other characteristics of each macaque flake and compared them to the Oldowan flakes. They found that the macaque flakes were smaller and thicker than their Oldowan counterparts, yet “within the range of diversity” of early anthropogenic flakes, they write. And that points to a problem for archaeologists, Luncz says. “How do we know when we found the first purposeful stone tools?”

Other researchers strongly disagree with the group’s analysis. Sonia Harmand, an archaeologist also at Stony Brook, says the new study simply shows “random, haphazard detachment of fragments without any particular organization or control.” Furthermore, he argues, “to prove exfoliation, you don’t look at the flakes primarily. you look at the cores,” meaning the hammerstones. Only by analyzing the cores, which bear the marks of deliberate strikes, “can you read the intention, the deliberate organization of the removals [of flakes].”

The authors of the new study agree that there is one important difference between the macaque flakes and those left behind by early humans: The apes do not peel the rocks on purpose. Instead, they are accidental byproducts of nut cracking. Indeed, the animals drop every hammer stone that peels. “For them, it’s broken,” Luncz says. “They’re looking for a new one,” which is easy to find among nearby cobblestones. (In contrast, early hominins 2.5 million years ago in Olduvai Canyon hiked for miles to pick up rocks that would be good for picking.) And apes don’t need the sharp flakes, because they have sharp canines.

Still, the study serves as a warning to archaeologists, says Rick Potts, a paleoanthropologist and stone tool expert at the Smithsonian Institution. “As tiny and inadvertent as these flakes are, they are similar to those from early archaeological sites. That means we have to find a way to factor in [them] out in the Oldowan sites’. More importantly, the study shows that these macaques “have the ability to knock stones together in this fracture,” he adds. “That’s the missing link that led to our ability to make tools.”

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