May 23, 2024

Monkeys inadvertently make stone tools

Macaques often use stones to crack hard-shelled nuts. Some of their tools break during use – and show specific fracture patterns much like prehistoric stone tools. Until now, paleoanthropologists have assumed that our early human ancestors deliberately made these tools over a million years ago. Observations on macaques now call this assumption into question.

The ability to create and use complex tools is an important human trait. But when did our ancestors begin to tailor materials from their environment to their needs? Early evidence of deliberate tool making is found in stone artefacts from East Africa up to 3.3 million years old. Several clues have led researchers to believe that our ancestors made stone flakes with sharp edges on purpose: the artifacts show very similar, repeated fracture patterns and have been found clustered in specific places.

Stone blades as a random product

However, a team led by Tomos Profet of the Max Planck Institute for Evolutionary Anthropology in Leipzig found that macaques in Phang Nga National Park in Thailand also leave similar accumulations of stone artifacts, but appear to unintentionally produce them. To crack the hard nuts of the oil palm, the monkeys developed a technique in which they placed the nut on a stone anvil and struck it with another stone. The stones used often crack in a specific way. This is how blade-like tools are created, which, however, are no longer used by macaques.

“The fact that these macaques use stone tools to manipulate nuts is not surprising because they also use tools to access various shellfish,” Proffitt says. “What is interesting is that they have inadvertently produced their own large body of archaeological evidence, some of which is indistinguishable from hominin artifacts.” The Thai island of Ya Noi with finds that have been assigned to the Oldowan culture of Tanzania, Kenya and Ethiopia and dated to an age of 1.5 to 3.3 million years ago.

Chips unintentionally produced by macaques. © Profet et al. 2023 / Max Planck Institute for Evolutionary Anthropology

A striking similarity

Like prehistoric artifacts, fragmented macaque rocks are commonly found in groups at specific locations, with monkeys often using the same nut-cracking areas and continuing to bring in new rocks there. Also in terms of their shape, the accidentally created stone flakes were strikingly similar to tools supposedly consciously made by our ancestors, as comparative analyzes have shown. Although macaque artifacts were often smaller and thicker than ancient artifacts in direct comparison, they showed such a high degree of similarity that in some cases the macaque and Oldowan artifacts resembled each other more than two of the artifacts ancient archaeological.

“The artifacts of macaques overlap significantly with the technological properties of the ancient artifacts,” the research team said. “Our results show that up to 70 percent of the Oldowan collection can be replaced by macaque artifacts without changing the central tendency of the morphological and technological parameters of the original collection.” in the archaeological record,” says Profet’s colleague, Jonathan Reeves.

Reconsider the interpretation of artefacts

It is likely that our ancestors did not consciously craft stone tools interpreted as blades, at least at first. It is conceivable that the sharp-edged stones were accidentally created in their box as well – and that they only later realized their usefulness.
“The deliberate manufacture of stone tools represents an adaptive threshold that fundamentally altered the evolutionary trajectory of our lineage. The results of this study suggest that we need a radical reassessment of the way we identify and clearly define hominin behavior in the archaeological record,” the research team wrote. “Collections of artifacts from primates living today can help us recalibrate our interpretation of the most ancient artifacts from our ancestors.”

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Source: Tomos Proffitt (Max Planck Institute for Evolutionary Anthropology, Leipzig) et al., Science Advances, dOi: 10.1126/sciadv.ade8159