What stone macaques can tell us about early human tool use

Consider the possibility that all human technology began with a mistake—or at least a lack of hand-eye coordination. In pursuit of this idea, Lydia Luncz and Tomos Proffitt, both at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, traveled to an abandoned palm plantation near Thailand’s Phang Nga Bay and collected stones that crack the nuts that were used by an army. long-tailed macaques. Macaques pulp dry palms by placing them on a flat stone and pounding their shell with another stone. These monkeys often lose the nut and inadvertently break the stones, producing sharp flakes. In a new study, Luncz and Proffitt argue that such misshapen flakes may have been the first step by our ancient ancestors or other now-extinct early human relatives toward creating the sharp tools they used to butcher animals and cut edible plants. . In other words, these are the kinds of tools that set our species on its evolutionary path to become increasingly productive hunter-gatherers and technological artisans.

Macaques are one of three modern nonhuman primate species that use stone tools (the other two being chimpanzees and capuchin monkeys). Luncz and Proffitt have studied the idea that sharp flakes accidentally produced by activities such as cracking nuts may have led hominids—a group that includes humans and their extinct ancestors and close relatives—to intentionally make flakes for tools. “This is completely wild behavior,” says Proffitt. “And it’s a behavior to take food. In that sense, you can start to say that this could have been a mechanism for the emergence of flake technology.”

For their study, which was published Friday in Advances in Science, the international team of researchers collected more than 1,100 pieces of stone that macaques in Thailand had used to crack palm oil nuts and compared them with archaeological collections from some of the earliest known stone tool sites in Tanzania, Kenya and Ethiopia. Their analysis revealed a surprising fact: The flakes produced unintentionally by the macaques closely resembled the oldest stone tools intentionally made by humans: an assemblage of Lomekwian and Oldowan stone tools, discovered at sites dated between 3.3 and 1.5 millions of years. . “If we took the kind of assemblage we find with macaques and dropped them somewhere in East Africa, everyone would think they were definitely made by early humans,” Luncz says.

Long-tailed macaques in Ao Phang Nga National Park in Thailand crushing palm oil using stone hammers and anvils. Credit: Lydia V. Luncz

Luncz and Proffitt found similar results with stone flakes produced by capuchin monkeys in Brazil’s Serra da Capivara National Park. “What’s extremely exciting is that we find another primate species on the other side of the world that shows us exactly the same phenomenon,” says Luncz. “You don’t need a huge brain to make sharp cutting tools. The challenge is to use the stone tools. I think that’s where the difference lies.” This difference appears when the assemblage of Macaque tools and flakes is compared with tools from Lomekwian or Oldowan sites. Macaques don’t use the sharp flakes they create for anything, Luncz says, noting that monkeys have sharp teeth and don’t need cutting tools. Ancient stone tools, however, show that they were used for cutting work.

“I think this study is useful because it really drives home the point that people need to make careful behavioral interpretations of their objects,” says Thomas Plummer, a paleoanthropologist at Queens College of the City University of New York, who was not member of Luncz and Proffitt’s group. Plummer is part of a research team studying fossil sites in Nyayanga, Kenya. Excavations at these sites, which date between three and 2.6 million years ago, have found Oldowan tools, as well as two teeth from an extinct species of hominid. The researchers analyzed use-wear patterns on the tools and found that some were used for pounding and processing plant foods. Some of the flakes also showed damage along their edges, indicating that they had been used for cutting. Cut marks on hippo bones and a fossil of a species of cattle revealed that humans had used stone tools to butcher the animals, making it clear that the sharp stone tools were anything but the unintended byproducts of other hammering activities. However, this does not necessarily mean that these tools were made by a human ancestor.

Hominid teeth found with Oldowan tools at Nyayanga belonged to a member of the genus Inhumanwhich is on a different branch of the human family tree than the one he leads Homo sapiens. Oldowan tools had been found with Inhuman at other sites, including the Frida Leakey Korongo Zinj (FLK Zinj) site in Tanzania’s Olduvai Gorge, where the first Inhuman fossils were discovered. At the time, paleoanthropologist Louis Leakey argued that a more immediate relative of humans found nearby, the slightly larger brain Homo habilis, he must have made the Oldowan tools. And he proposed the manufacture of stone tools as one of the criteria for separating humans from other apes. But evidence from sites like Nyayanga begins to point to both Inhuman and H. habilis being a machinist. And the assemblages made by macaques and capuchin monkeys suggest that the use of stone tools may have begun much earlier in evolutionary history than previously thought. Humans last shared a common ancestor with capuchin monkeys about 35 million years ago and with macaques about 25 million years ago, Luncz says. “I would be surprised if the use of stone tools was a very recent development in the human lineage,” he says.

Luncz and Proffitt hope to eventually learn how primates made the leap from accidentally producing sharp flakes to collecting and using them. But for now, scientists can only speculate. Plummer suggests a scenario in which a group of hominins encountered an animal carcass and used stones to break its bones and get at the nutrient-rich marrow: During this process, a hominin lost the bone and pulled out a sharp flake from the stone he used. Then that humanitarian had the idea to use this flake to cut the meat from the carcass. “It could be that humans were just experimenting,” says Plummer.

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