The broken rocks of monkeys look eerily like something we used to do: ScienceAlert

We humans may no longer have tails, but we may have more in common with our smaller primate relatives than we thought.

Analysis of accidentally broken rocks used by macaques to crack nuts shows that monkeys inadvertently broke up boulders that are strikingly similar to intentionally made tools found at the world’s earliest known archaeological sites in Africa.

This discovery could help scientists contextualize how ancient humans developed their first forms of technology.

The finding raises the possibility that handcrafted tools were originally the result of accidental use. When rocks were smashed against larger anvils – behavior still seen in crab-eating or long-tailed macaques (Macaca fascicularis) in Thailand – sharp shards of stone that broke loose may have accidentally provided the community with another useful tool.

“The ability to intentionally create sharp flakes of stone is thought to be a crucial point in hominin evolution, and understanding how and when this happened is a big question, typically explored through the study of earlier artifacts and fossils,” says the Paleolithic archaeologist Tomos Proffitt from the Max Planck Institute for Evolutionary Anthropology in Germany.

“Our study shows that stone tool making is not just limited to humans and our ancestors.”

The development of stone tools is considered a pivotal moment in human history as it can be traced back millions of years. Early stone tools, found in significant numbers at sites containing the remains of ancient hominids, which include the ancestors of modern humans, were fairly simple. They were stone cores shaped to form a sharp edge that archaeologists believe were used for cutting, chopping, scraping, and butchering.

But these simple tools have become increasingly complex technologies.

Tool use is not unique to humans, however, and there are a number of primates known to use rocks to perform percussive tasks — cracking open nuts or shellfish, grinding seeds, and digging up roots. Crab-eating macaques have been using rocky materials to crack nuts and oysters for possibly thousands of years, and their range is littered with shattered shards of rock shattered with use.

Proffitt and his colleagues collected a number of these fragments and conducted a thorough analysis by comparing them to stone tools used by ancient people. And they found that in the absence of behavioral evidence, archaeologists may have interpreted the macaque fragments as evidence of intentional tool-making.

Stone flakes accidentally created by long-tailed macaques. (Proffit et al., SciAdv2023)

“The fact that these macaques use stone tools to process nuts is not surprising since they also use tools to access various shellfish,” explains Proffitt. “What’s interesting is that in doing so they inadvertently create a sizeable archaeological record of their own, some of which is indistinguishable from some hominin artifacts.”

When cracking nuts or oysters, macaques regularly and unintentionally produce shell-shaped flakes of stone with a sharp edge, similar to those seen in the hominid archaeological record. The macaques are not known to use these flakes; Once a stone tool is broken, the shards are useless to the macaques and they go in search of other tools.

The team carefully examined these broken flakes and found that they often displayed attributes used to diagnose intentionally made stone tools from archaeological sites. Perhaps this is not surprising; The macaques crack nuts by placing them on a stone anvil and then hitting it with another stone. Early stone tools were made by beating stones with other stones. The action and result are similar; it is the intention that differs.

The dataset, the researchers say, represents the largest dataset to date of percussive flakes and flakestones produced by nonhuman primates, and could help distinguish between human and nonhuman primate flake production in the future.

In addition, it could offer a window into our own past.

“Cracking nuts with stone hammers and anvils, similar to what some primates do today, has been suggested by some as a possible precursor to the deliberate manufacture of stone tools,” says archaeologist Lydia Luncz of the Technological Primates Research Group at Max Planck -Institute for Evolutionary Anthropology.

“This study, along with previous studies published by our group, opens the door to identifying such an archaeological signature in the future.”

The research was published in scientific advances.

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