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The path of human evolution may need to be rewritten after archaeologists discovered that monkeys also produce ‘tool-like flakes’ that were thought to be uniquely man-made.
In a discovery that calls into question decades of research, a band of wild bearded capuchin monkeys in Brazil were seen hammering rocks to extract minerals, causing large flakes to fly off.
Previously archaeologists believed the flakes were only made by humans through a process called ‘stone-knapping’ where a larger rock is hammered with another stone to produce sharp blade-like slivers which can be used for arrows, spears or knives.
The flakes were thought to represent a turning point in human evolution because they demonstrated a level of planning, cognition and hand manipulation that could not be achieved by other animals.
But the new research suggests that flakes can be made without any such foresight. In fact they can simply be made by accident.
“The fact that we have discovered monkeys can produce the same result does throw a bit of a spanner in the works in our thinking on evolutionary behaviour and how we attribute such artefacts,” said Dr Michael Haslam, lead of the Primate Archaeology project at the University of Oxford.
“Our understanding of the new technologies adopted by our early ancestors helps shape our view of human evolution. The emergence of sharp-edged stone tools that were fashioned and hammered to create a cutting tool was a big part of that story.”
A team from Oxford, University College London and the University of Sao Paulo studied monkeys in the Serra da Capivara National Park in Brazil.
The capuchins were observed engaging in ‘stone on stone percussion’, whereby they selected rounded quartzite cobbles and then using one or two hands struck the ‘hammer-stone’ forcefully and repeatedly on quartzite cobbles embedded in a cliff face.
Their actions dislodged more cobbled stones and also fractured their hammer-stones, so that flakes flew off. The researchers managed to collect 111 fragments once the capuchins had left the area.
The team identified complete and broken hammer-stones and complete and fragmented flakes, half of which had ‘conchoical’ fractures where the break is round and smooth in appearance. It was previously thought that such fractures could only made by hominids.
The researchers believe that the capuchins hammer the stones to extract powdered silicon, an essential trace nutrient, or to remove lichen for a medicinal purpose. None of the monkeys tried to cut or scrape using the flakes.
Lead author Dr Tomos Proffitt, from the School of Archaeology at the University of Oxford, said: “Within the last decade, studies have shown that the use and intentional production of sharp-edged flakes are not necessarily linked to early humans who are our direct relatives, but instead were used and produced by a wider range of hominins.
“However, this study goes one step further in showing that modern primates can produce archaeologically identifiable flakes and cores with features that we thought were unique to hominins.
“These findings challenge previous ideas about the minimum level of cognitive and morphological complexity required to produce numerous flakes.”
Bearded capuchins and some Japanese macaques are known to pound stones directly against each other, but the Serra da Capivara capchins are the only animals observed doing it to split the stones.
The archaeologists say it shows that how the flakes were "used", rather than how they were "made", is what separates hominid behaviour from monkeys.
“While humans are not unique in making this technology, the manner in which they used them is still very different to what the monkeys seem capable of,” added Dr Haslam.
The research was published in the journal Nature.