Nut-cracking chimps provide clues to the origin of tools

Ethoarchaeology attempts to use observation or experimental approaches to animal behaviour to shed light on  features of fossil occurrences that relate to human origin.  One example is examining the gnaw marks on bones in the dens of predators to check if they match similar signs on the bones of early hominids.  Another is knapping flints to see if the flakes or debris produced match finds of broken fragments at sites with no clear sign of early-human involvement.  Chimps use lumps of stone to break nuts on wooden anvils, and so provide natural subjects to probe what early hominids may have been up to.  Anthropologists from George Washington University in the USA and the Max Planck Institute for Evolutionary Anthropology in Germany have painstakingly excavated the debris from a nut-cracking site beneath a large tree “traditionally” used as a source of nut protein by Ivory Coast chimps (Mercader, J. et al. 2002.  Excavation of a chimpanzee stone tool site in the African rainforest.  Science, v. 296, p. 1542-1455).

Broken fragments inadvertently created by the chimpanzee troupe do resemble the earliest Oldowan tools, which appear in the fossil record at around 2.5 Ma.  The chimps can be shown to have brought hammer stones from several rock outcrops.  However, any old rock serves their purpose and there is no sign of deliberate selection, unlike the makers of Oldowan tools, who clearly selected rocks that break to give sharp edges from outcrops up to several kilometres from the fossil sites.  The first Oldowan tools demonstrate that they are the end product of what was probably a progression from accidental stone breakage.  The way in which broken fragments from patterns around chimps favourite anvils for nut cracking should help identify earlier assemblages in the steps towards proper tool making.  With luck, they may relate to fossils of the actual beings who were involved.  The 2.5 Ma Oldowan tools from Ethiopia have yet to be linked to a hominid species.  The earliest direct link between tools and their makers is the association of Oldowan artefacts with remains of Homo habilis about 2 Ma ago.

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