Stone fragments made by some monkeys found to resemble ancient human ancestor tools, study finds

Stone fragments produced by macaques in Thailand have been found to bear similarities to early human ancestor tools unearthed in some of the earliest archaeological sites in East Africa, a new study has found.

Researchers, including those from the Max Planck Institute for Evolutionary Anthropology in Germany, analysed tools used by long-tailed macaques in the Phang Nga National Park in Thailand that use stones to crack open hard-shelled nuts.

The study, published recently in the journal Science, found that the fragments resulting from the monkeys’ use of stones bear the same characteristics commonly used to identify intentionally made stone tools by early human hominin ancestors.

“The ability to intentionally make sharp stone flakes is seen as a crucial point in the evolution of hominins, and understanding how and when this occurred is a huge question that is typically investigated through the study of past artefacts and fossils,” study lead author Tomos Proffitt said.

“Our study shows that stone tool production is not unique to humans and our ancestors,” Dr Proffitt said.

The use of stone tools by the monkeys is “not surprising”, scientists say, adding, however, that the accidental production of a “substantial archaeological record” by the macaques is “indistinguishable” from some early hominin artefacts.

Researchers compared the stone fragments made by the macaques with those from some of the earliest archaeological sites.

They found that many of the artefacts produced by monkeys fall within the range of those commonly associated with early hominins.

“The fact that these artifacts can be produced through nut cracking has implications for the range of behaviours we associate with sharp edged flakes in the archaeological record,” Jonathan Reeves, another author of the study, said.

The macaque stone tools, researchers say, offer new insights into how the first technology might have started in our earliest ancestors.

They say the origin of tool use in early human ancestors may have been linked to similar nut cracking behaviour that could be significantly older than the current earliest archaeological record.

“Cracking nuts using stone hammers and anvils, similar to what some primates do today, has been suggested by some as a possible precursor to intentional stone tool production,” Lydia Luncz, another author of the study, said.

The findings, researchers say, open the door to identifying similar archaeological signatures in the future.

“This discovery shows how living primates can help researchers investigate the origin and evolution of tool use in our own lineage,” Dr Luncz added.