Scientists have observed wild capuchin monkeys in Brazil forest deliberately break stones, that look very similar similar to the flakes produced by early Stone Age hominins for cutting up meat. The discovery however, showed that this ability may not be that exclusive to our species after all.
The difference, researchers explain, is that the capuchins’ flakes are not intentional tools for cutting and scraping, but seem to be the by-product of hammering or ‘percussive behaviour’ that the monkeys engage in to extract minerals or lichen from the stones.
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The paper, published in Nature, says this finding is significant because archaeologists had always understood that the production of multiple stone flakes with sharp cutting edges was a behaviour unique to hominins. Such shaped stones are seen in the archaeological record in Africa well over 3 million years ago.
These stone flakes were later refined into Stone Age tools known as hand-axes — typically teardrop-shaped, with a rounded end for gripping and a sharp end for cutting.
While hominins made stone flake tools for cutting and butchery tasks, the researchers admit that it is unclear why monkeys perform this behaviour. They suggest that the capuchins may be trying to extract powdered silicon (known to be an essential trace nutrient) or to remove lichen for some as yet unknown medicinal purpose. At no point did the monkeys try to cut or scrape using the flakes, says the study.
‘Within the last decade, studies have shown that the use and intentional production of sharp-edged flakes are not necessarily linked to early humans (the genus Homo) who are our direct relatives, but instead were used and produced by a wider range of hominins, ” lead author Dr Tomos Proffitt, from the School of Archaeology at the University of Oxford, comments. “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.
‘This does not mean that the earliest archaeological material in East Africa was not made by hominins. It does, however, raise interesting questions about the possible ways this stone tool technology developed before the earliest examples in the archaeological record appeared. It also tells us what this stone tool technology might look like. There are important questions too about the uniqueness of early hominin behaviour. These findings challenge previous ideas about the minimum level of cognitive and morphological complexity required to produce numerous conchoidal flakes.’
The monkeys were observed engaging in ‘stone on stone percussion’, whereby they individually 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.
The research team examined 111 fragmented stones collected from the ground immediately after the capuchins had dropped them, as well as from the surface and excavated areas in the site. They gathered complete and broken hammer-stones, complete and fragmented flakes and passive hammers. Around half of the fractured flakes exhibited conchoidal fracture, which is typically associated with the hominin production of flakes.
Bearded capuchins and some Japanese macaques are known to pound stones directly against each other, but the paper remarks that the capuchins in Serra da Capivara National Park are the only wild primates to be observed doing this for the purpose of damaging the stones.
‘Our understanding of the new technologies adopted by our early ancestors helps shape our view of human evolution, ” Co-author Michael Haslam, from the University of Oxford, says. “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. 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.’
