Nut Cracking Tools Used by Captive Chimpanzees (Pan troglodytes) and Their Comparison with Early Stone Age Percussive Artefacts from Olduvai Gorge
Adrian Arroyo, Satoshi Hirata, Tetsuro Matsuzawa, Ignacio de-la Torre
Between 6 and 8 million years ago, the extinct relatives of chimpanzees (Pan) and hominins shared a common ancestor who probably used unmodified stones as tools. This has important evolutionary implications, especially following the recent discovery of the earliest stone tools (Lomekwian) at Lomekwi 3 (West Turkana, Kenya), which has pushed back the dawn of stone flaking to 3.3 Mya. The Lomekwi assemblage shows that hominins were intentionally flaking stone tools, and suggests the emergence of stone tool knapping during a period close to the divergence of panin and hominin lineages. Therefore, stone flaking might not be associated exclusively with the genus Homo, but may have occurred in other taxa. At 3.3 Mya, the only hominins known (and therefore the likely makers of the Lomekwian tools) had brains no bigger than living African apes. Thus, comparison of hominin and chimpanzee products of behaviour are apt, and the use of living non-human primates as an analogy on which to model and understand earlier stages of human evolution, has become more relevant than ever [4–9]. It has been suggested that prior to the appearance of stone tool knapping, hominins probably used various organic tools that are archaeologically invisible. The use of pounding tools is a common behaviour recognized in both living non-human primates and the archaeological record. Pounding activities could have played an important role in hominin behaviour and probably contributed to the emergence of stone tool knapping; the latter is a major research topic in the archaeology of human evolution and the subject of much debate. Research in recent decades has focused on the use of chimpanzees as a reference to model hominin behaviour and the emergence of stone knapping. However, the models generated have limitations, as they directly compare flaked archaeological tools with pounding tools used in chimpanzee nut cracking activities. As the archaeological record also contains pounding tools that can be compared with battered artefacts produced by modern primates, it is possible to develop cross-disciplinary comparative frameworks. This study provided a unique opportunity to develop a comparative approach, as it combined primatological behavioural observations and analysis of stone tools used by captive chimpanzees. We collected raw materials at Olduvai Gorge (Tanzania) and conducted a series of experiments with captive chimpanzees at the Kumamoto Sanctuary (Japan). We used techno-typological descriptions and low magnification microscopic and use-wear spatial distribution analyses of captive chimpanzee experimental artefacts (see below). The results can be directly compared with findings from other studies on modern humans and wild chimpanzees, and contribute to the creation of a larger dataset with which to better understand the role of percussive activities in human evolution.