https://www.sciencedirect.com/science/article/pii/S0047248424001337
Abstract
The use of broad tool repertoires to increase
dietary flexibility through extractive foraging
behaviors is shared by humans and their closest
living relatives (chimpanzees, Pan troglodytes).
However, comparisons between tool use in ancient
human ancestors (hominins) and chimpanzees are
limited by differences in their toolkits. One
feature shared by primate and hominin toolkits
is rock selection based on physical properties
of the stones and the targets of foraging
behaviors. Here, we document the selectivity
patterns of stone tools used by wild chimpanzees
to crack nuts at Bossou, Guinea, through
controlled experiments that introduce rocks
unknown to this population. Experiments
incorporate specific rock types because previous
studies document hominin selection of these
lithologies at Kanjera South 2 Ma. We investigate
decisions made by chimpanzees when selecting
stones that vary in their mechanical properties—
features not directly visible to the individual.
Results indicate that the selection of anvils and
hammers is linked to task-specific mechanical
properties. Chimpanzees select harder stones for
hammers and softer stones for anvils, indicating
an understanding of specific properties for
distinct functions. Selectivity of rock types
suggests that chimpanzees assess the appropriate
materials for functions by discriminating these
‘invisible’ properties. Adults identify mechanical
properties through individual learning, and
juveniles often reused the tools selected by
adults. Selection of specific rock types may be
transmitted through the reuse of combinations of
rocks. These patterns of stone selection parallel
what is documented for Oldowan hominins. The
processes identified in this experiment provide
insights into the discrete nature of hominin rock
selection patterns in Plio-Pleistocene stone
artifact production.
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