What makes humans unique? Recent findings from a population of wild bearded capuchin monkeys in Brazil tell us that it certainly isn’t tool use. At Serra da Capivara National Park, capuchins regularly select quartzite cobbles to deliberately break against firmly rooted stones that serve as anvils in order to ingest powdered quartz, or to consume the lichens that grow on rocks. Motivations aside, the result fascinates: the fractured rocky elements that the capuchins leave behind look exactly like the stone tools that were deliberately produced by the earliest hominins .
For many years, some of the best evidence for the exceptional nature of human kind was our command of material culture, the ability to manufacture and use tools. This notion persisted until 1960 when a young Primatologist named Jane Goodall tapped the study of human origins on its unsuspecting shoulder and forced the world to head back to the drawing board. Jane had discovered that a population of wild chimpanzees in Tanzania were utilizing tools to fish for termites, selecting twigs in a goal-directed way and stripping them of leaves to create effective probes. Tool use in general could no longer be considered a uniquely human trait, but what about other, more complicated technologies?
Enter the importance of stone tools. At roughly 2.6 million years ago (mya), approximating the origin of the genus Homo, a beautiful stone tool industry emerged in the archaeological record. Known as the Oldowan, the toolkit was comprised of large stone pieces called “cores” that were pounded and chopped to create smaller fragmentary “flakes”. The tools were so profound that in 1964 researchers began calling the hominin found in association habilis, which literally translates to “handy man”. Though today there is considerable debate as to who actually made the earliest stone tools (Australopithecus garhi is found nearby Oldowan tools at around at ~2.5 mya, 3.3 mya stone tools were recently found in Kenya, and cut marks on animal tissues exist in Ethiopia at ~3.4 mya), an important conclusion was drawn: non-human primates were not capable of creating stone tool industries. Chimps, you can keep your twigs.
Unbeknownst to mankind, however, those wily chimpanzees had a secret technology that would remain undiscovered until the 1970’s. At field sites in Côte d’Ivoire and the Republic of Guinea, chimpanzees were found not only to crack nuts using a hammer stone in one hand and an anvil in another, but to preferentially select stones based on their raw material properties. Researchers would further discover that when chimpanzees used stone tools, they unintentionally created flakes that fell within the size and morphology of the earliest tools from the Oldowan. Because chimpanzees share a common ancestor with humans at approximately 5 – 8 mya, this led to the logical assumption that tool use would be a behavioral trait not just of humans, but of the Pan-Homo lineage. But sure enough…
…the Serra da Capivara bearded capuchins came out of left field to tell us otherwise. And this finding is truly out of left field: capuchins are a type of New World Monkey that would have diverged from Old World Monkeys and Apes at roughly 35 mya. This means that humans and capuchins are so distantly related that any commonalities in our tool use behaviors are unlikely to be the result of shared ancestry. What this also suggests is an alternate route towards the emergence of stone tools. Capuchins lack humanlike hand proportions, dexterity and cognitive abilities; therefore, creating a “human” tool doesn’t necessarily require human properties .
So, were the earliest human stone tools made unintentionally? Did their creation require advanced cognition? And, most importantly, were they actually made by the earliest humans? Additional data from non-human primates and the archaeological record will help to unravel these questions. Until then, an image of tiny, bearded capuchins working tirelessly to amass an archaeological assemblage as a Homo habilis sits back an thinks, “yeah, this will throw them off,” will have to suffice as a working hypothesis.
 Proffitt et al. 2016. Wild monkeys flake stone tools. Nature. 539, 85-88.