Monkey and human stone tools show astonishing parallels

The Max Planck Institute for Evolutionary Anthropology uncovered artifacts made by old-world monkeys in Thailand that resemble stone tools, which have historically been regarded as purposely made by early hominins.

Sharp-edged stone tools were previously supposed to indicate the beginning of purposeful stone tool manufacturing, one of hominid evolution's defining and distinct aspects. This new study calls into question long-held assumptions regarding the origins of purposeful tool manufacturing in our ancestors.

Based on examinations of stone tools made by long-tailed macaques in Thailand's Phang Nga National Park, they break open nuts using stone tools.

The resulting collection of broken stones is sizable and dispersed throughout the countryside. In addition, many of these artifacts share the same traits that can be used to distinguish deliberately created stone tools from other types of stone tools in some of the earliest archaeological sites in East Africa.

"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 artifacts and fossils," says lead author Tomos Proffitt, a researcher at the Max Planck Institute for Evolutionary Anthropology. "Our study shows that stone tool production is not unique to humans and our ancestors."

"The fact that these macaques use stone tools to process nuts is not surprising, as they also use tools to gain access to various shellfish as well. What is interesting is that in doing so, they accidentally produce a substantial archaeological record of their own that is partly indistinguishable from some hominin artifacts," he added.

The development of stone tool technologies

The researchers demonstrated that many of the artifacts generated by monkeys fall within the range of those often associated with early hominins by comparing the inadvertently created stone fragments formed by the macaques with those from some of the earliest archaeological sites.

“The fact that these artifacts can be produced through nut cracking has implications for the range of behaviors we associate with sharp-edged flakes in the archaeological record," said co-lead author Jonathan Reeves.

The recently discovered macaque stone tools provide insights into how our earliest ancestors may have developed the first technology. They suggest that this origin may have been connected to behaviors comparable to nut-cracking that may be much older than the earliest archaeological records.

The study was published today in Science Advances.