Macaques often use stones to crack hard-shelled nuts. Some of their tools break during use – and show specific fracture patterns that bear close resemblance to prehistoric stone tools. Until now, paleoanthropologists have assumed that our early human ancestors deliberately made these tools more than a million years ago. The observations on macaques now call this assumption into question.
The ability to create and use complex tools is considered an important human characteristic. But when did our ancestors begin to design materials from their environment according to their needs? The earliest indications of the deliberate manufacture of tools are found in stone artifacts from East Africa that are up to 3.3 million years old. Numerous clues have led researchers to believe that our ancestors created the sharp-edged stone chips on purpose: the artifacts show very similar, repetitive fracture patterns and were found collected in specific places.
Stone blades as a random product
However, a team led by Tomos Proffitt from the Max Planck Institute for Evolutionary Anthropology in Leipzig has now found that macaques in Thailand’s Phang-Nga National Park also leave similar accumulations of stone artifacts, but apparently produce them unintentionally. To crack the hard nuts of oil palms, the monkeys have developed a technique in which they place a nut on a stone anvil and hit it with another stone. The stones used often splinter in a specific way. This is how blade-like tools are created, which, however, are no longer used by the macaques.
“The fact that these macaques use stone tools to process nuts is not surprising since they also use tools to access various shellfish,” says Proffitt. “What is interesting is that they unintentionally produce a large body of archaeological evidence of their own, some of which is indistinguishable from the hominin artifacts.” Proffitt and his team collected and compared 1,119 stone artifacts of nut-cracking macaques from 40 different sites on the Thai island of Ya Noi with finds that have been assigned to the Oldowan culture in Tanzania, Kenya and Ethiopia and dated at an age of 1.5 to 3.3 million years.
Amazing resemblance
Like prehistoric artifacts, macaque splintered rocks were commonly found in clusters in specific locations, as the monkeys often use the same nut-cracking spots and keep bringing new rocks there. In terms of their shape, too, the accidentally created stone chips were astonishingly similar to the presumably consciously manufactured tools of our ancestors, as comparative analyzes have shown. Although the macaque artifacts were often slightly smaller and thicker than the Oldowan artifacts in direct comparison, they showed such a high degree of similarity that in some cases macaque and Oldowan artifacts resembled each other more than two different Oldowan artifacts resembled each other.
“The macaque artifacts overlap significantly with the technological characteristics of the Oldowan artifacts,” the research team said. “Our results show that between up to 70 percent of an Oldowan collection can be replaced with macaque artifacts without significantly altering the central trend of the original collection’s morphological and technological parameters.” has implications for the range of behaviors we associate with sharp-edged shards in the archaeological record,” says Proffit’s colleague Jonathan Reeves.
Reconsider interpretation of artifacts
It is possible that our ancestors did not consciously manufacture the stone tools interpreted as blades, at least initially. It is conceivable that the sharp-edged stones were created accidentally in their case too – and that they only later recognized their usefulness.
“The intentional manufacture of stone tools represents an adaptive threshold that fundamentally altered the evolutionary trajectory of our lineage. The results of this study indicate that we need to fundamentally reassess the way we define and identify this clearly hominin behavior in the archaeological record,” the research team writes. “Assemblies of artifacts from primates living today can help us recalibrate our interpretation of the oldest artifacts from our ancestors.”
Source: Tomos Proffitt (Max Planck Institute for Evolutionary Anthropology, Leipzig) et al., Science Advances, doi: 10.1126/sciadv.ade8159