When ancient humans first invented stone tools, they may have been trying to emulate naturally formed sharp stones, meaning they would not have needed a huge leap of inspiration.
“What our hypothesis does is, it really turns the origin of technology entirely on its head,” says at Kent State University in Ohio. Instead of imagining a sharp tool and then figuring out how to make it, early hominins may have used for millennia before anyone tried crafting them. “Rather than hominins creating the knife and then looking for something to cut, we propose that they were already exploiting carcasses,” he says.
One of the defining features of hominins is their ability to both make and use stone tools, which are useful for butchering animals and opening hard fruits. Creating a stone tool requires hitting two rocks together in precise ways, knocking flakes off one of them in order to shape it into a cutting edge.
Advertisement
This is called “knapping”, and hominins have been doing it for at least 2.6 million years. There are even older stone tools from Lomekwi in Kenya, , but these were made using a simpler method: bashing a single stone on the ground.
“It’s been traditionally thought that the very first stone flakes were produced intentionally or by accident, and then early hominins started to look for things to cut with these new sharp implements,” says Eren. He says this story doesn’t make sense. “For a creature to start to use an item, or to invent an item, there has to be a selective pressure first.”
Eren and his colleagues argue that hominins found naturally sharp stones, which they used as cutting tools. By doing so, they developed a habit of cutting and began seeking out such stones.
“Mother Nature is producing knives all over the place,” says Eren. He calls these raw blades “naturaliths”.
The team has compiled multiple examples of naturaliths. Eren has studied stones from Antarctica, which resemble hominin tools but must have been made by natural processes, since no hominin ever lived in Antarctica. Experiments have also shown that tool-like artefacts can be produced when large animals like and horses trample on stones. Monkeys sometimes accidentally knock flakes off stones. There are also processes that don’t involve living animals, such as waves crashing on rocky shores, frost fracture and glaciers grinding over bedrock.
If naturaliths were available in hominins’ habitat, says Eren, it would be easy to start using them. “All they need to do is pick them up.”
For Eren, the appeal of this hypothesis is that it doesn’t require a “eureka moment” of inspiration. “It shortens the cognitive distance between every step in the origin of technology,” he says. He calls it “the most parsimonious proposal” for how hominins invented stone cutting tools.
However, Eren emphasises that this hypothesis is a suggestion, not a fact. He calls it “a big swing”. While the team has listed examples of naturaliths and processes that could make them, many other tests are needed. Eren wants to look for naturaliths from times and places where hominins lived, and find evidence that they were used as cutting tools. That could include distinctive wear patterns or traces of plant and animal material on the sharp edges. It might also be possible to find naturaliths that hominins have transported over long distances.
Such evidence might not be forthcoming. “Simply because the hypothesis is parsimonious doesn’t mean it’s correct,” says Eren.
“I think it’s a really intriguing proposal,” says at the Smithsonian Institution in Washington DC. “Maybe the invention of stone tools wasn’t this major cognitive leap,” she says, but instead a “natural extension of what hominins were already doing”. She also says that the biggest challenge will be testing the idea, in particular figuring out whether an apparent tool was made by a hominin, an animal or a non-biological process.
Identifying the sources of naturaliths is useful, says at the University of Tübingen in Germany. However, the researchers’ “specific story just doesn’t check out”.
Tennie says the proposal relies on an assumption: that inventing stone tools from scratch is too cognitively difficult for hominins to have pulled off. “That’s not true,” he says. Instead, several lines of evidence suggest that hominins were smart and creative enough to come up with knapping unaided.
For instance, in a 1994 study Gregory Westergaard and Stephen Suomi reported that and modified the stones by striking them against hard surfaces. If capuchins could make and use stone tools, presumably hominins could too. In a series of studies published in 2022, Tennie’s team showed that  without training; that , a prerequisite for knapping; and that without help.
“These beings had available certain strategies, certain intelligences,” says Tennie. He thinks hominins didn’t need a helping hand from naturaliths.
Eren thinks they did. He argues that those experiments may not tell us much about early hominins because several of them used captive primates, and modern humans are not the same as hominins that lived millions of years ago. “Even if hominins were clever enough to spontaneously invent stone tools at will, that does not negate our hypothesis that Mother Nature helped them along,” he says.
Archaeometry
Embark on a captivating journey through time as you explore key Neanderthal and Upper Palaeolithic sites of southern France, from Bordeaux to Montpellier, with żěè¶ĚĘÓƵ’s Kate Douglas. 
Neanderthals, ancient humans and cave art: France
