Capuchin monkeys have been observed smashing stones to produce flakes — but why they do so remains a mystery.
Technology is often a tale of seamless acquisition and refinement of skills — from rocks banged together, and bows and arrows, to steam engines and integrated circuits. But the appearance of artefacts is a different thing from their makers’ intentions — if any.
As researchers show in a study published online in Nature this week (T. Proffitt et al. Nature http://dx.doi.org/10.1038/nature20112; 2016), capuchin monkeys (Sapajus libidinosus) from the Serra da Capivara National Park in Brazil smash rocks in a way that produces sharp-edged stone flakes; were these flakes associated with an early Stone Age site, they might be regarded as intentionally produced. Indeed, progress in Stone Age technology is sometimes measured in terms of an increase in the number of sharp edges that can be coaxed from a given amount of raw material. This, of course, presupposes that producing flakes is, in fact, the intention. But capuchins, having created stone flakes, let them lie.
Why the monkeys go to all that effort remains a mystery. However, the researchers observed that about half of the monkeys sniffed or licked the broken surfaces afterwards, suggesting that they break rocks to extract mineral supplements in a conveniently powdered form. Other monkeys bash rocks together, but the capuchins are the only wild, non-human primates known to do so with the seeming intention of breaking them. Chimps sometimes break rocks by mistake, but even when taught to bang rocks together with intent, bonobos don’t create anything that resembles what is found in the hominin record.
Recognizing the earliest stone tools for what they are is not always easy, but certain features mark artefacts as the product of intent. These include the ‘conchoidal’ flaking that leaves a distinctive percussion mark; the production of several flakes from a single core, and the use of specific patterns of flake removal. Such features distinguish artefacts from geofacts — that is, rocks broken by natural processes, rather than objects made by non-human animals — but they say little or nothing about how the artefacts might have been used. As the capuchin example shows, the intent of the makers of the earliest artefacts can be hard to discern. The producers of the earliest stone tools to be generally recognized as such (S. Harmand et al. Nature 521, 310–315; 2015) lived 3.3 million years ago, and were very different from modern humans.
The capuchin study should also dampen ideas that the human hand, with its precision grip, together with advanced hand-eye coordination, must necessarily have been evolutionary products or prerequisites of technology. Capuchins break rocks without the benefit of either.
In the end, the activity of banging rocks together should be seen as precisely that, and not as the first, proleptic step towards the stars. The ape-man at the start of 2001: A Space Odyssey that throws a bone in the air that becomes a space station was, after all, a modern human in a gorilla suit.