Scientists thought that the repeated creation of sharp stone flakes that our ancestors used for cutting up meat is a unique behavior attributed to humans and their ancestors. A discovery in a Brazilian forest, however, showed that this ability may not be that exclusive to our species after all.

An earlier study revealed that wild capuchin monkeys in Brazil use stone tools to open cashew nuts. In a new study, researchers discovered that the animals also created sharp stone flakes similar to those made by early hominins.

Unlike human ancestors, though, these Brazilian primates appear to produce the tools by accident. The animals do not use the flakes for butchering or see them as a potential tool. Researchers said that the tools are just a natural by-product of the species' stone hammering ritual.

"They never use the flakes, they don't care about them," study researcher and primate archaeologist Tomos Proffitt, from the University of Oxford, said. "Completely unintentionally, while they are doing this, the stones are fracturing in the same way as you'd expect an intentionally fractured, hominin-made flake to be."

The monkeys hammer rounded stones against the face of quartz cliff, which leave them covered in razor-sharp rock dust. Primatologists think that the minerals inside of the stones or the lichen that grows on them have some medicinal purpose for the primates. The monkeys may be swallowing the dust to cleanse their digestive tract of parasites.

The monkeys nonetheless ignore the flakes that they produce during the process when they whack one rock on top of another albeit they produce large numbers of these primitive tools.

Researchers said that the findings should remind field scientists to be mindful so they would not be confused by flakes produced by monkeys that look like human-made.

Proffitt said that the stone tools made by the early humans are more complex compared with those made by the Capuchins, although both have the same basic characteristics. The researcher added that there are also often clues that differentiate ancient human tools from monkey tools. One is that human-made tools were used.

"We show that wild bearded capuchin monkeys (Sapajus libidinosus) in Brazil deliberately break stones, unintentionally producing recurrent, conchoidally fractured, sharp-edged flakes and cores that have the characteristics and morphology of intentionally produced hominin tools," the researchers reported in their study, which was published in the journal Nature on Oct. 19.

"The production of archaeologically visible cores and flakes is therefore no longer unique to the human lineage, providing a comparative perspective on the emergence of lithic technology. "