Researchers from the Max Planck Institute for Evolutionary Anthropology have discovered artefacts produced by old world monkeys in Thailand that resemble stone tools, which historically have been identified as intentionally made by early hominins. Until now, sharp-edged stone tools were thought to represent the onset of intentional stone tool production, one of the defining and unique characteristics of hominin evolution. This new study challenges long held beliefs about the origins of intentional tool production in our own lineage.

The research is based on new analyses of stone tools used by long-tailed macaques in the Phang Nga National Park in Thailand. These monkeys use stone tools to crack open hard-shelled nuts. In that process, the monkeys often break their hammerstones and anvils. The resulting assemblage of broken stones is substantial and widespread across the landscape. Moreover, many of these artefacts bear all of the same characteristics that are commonly used to identify intentionally made stone tools in some of the earliest archaeological sites in East Africa.1

• 1. “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. Our study shows that stone tool production is not unique to humans and our ancestors,” says lead author Tomos Proffitt, a researcher at the Max Planck Institute for Evolutionary Anthropology. “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 accidently produce a substantial archaeological record of their own that is partly indistinguishable from some hominin artefacts.”