CRICKETTE M. SANZ1,2*, DAVID B. MORGAN2,3, AND WILLIAM D. HOPKINS 4,5
1 Department of Anthropology, Washington University in Saint Louis, Saint Louis, Missouri
2 Congo Program, Wildlife Conservation Society, Brazzaville, Republic of Congo
3 Lester E. Fisher Center for the Study and Conservation of Apes, Lincoln Park Zoo, Chicago, Illinois
4 Neuroscience Institute and Language Research Center, Georgia State University, Atlanta, Georgia
5 Division of Developmental and Cognitive Neuroscience, Yerkes National Primate Research Center, Atlanta, Georgia
The Video recordings were scored using Mangold INTERACT.
Tool donors experienced significant reductions in tool use and feeding, while tool recipients significantly increased their tool use and feeding after tool transfers. These transfers meet functional criteria for teaching: they occur in a learner’s presence, are costly to the teacher, and improve the learner’s performance. Donors also showed sophisticated cognitive strategies that effectively buffered them against potential costs. Teaching is predicted when less costly learning mechanisms are insufficient. Given that these chimpanzees manufacture sophisticated, brush-tipped fishing probes from specific raw materials, teaching in this population may relate to the complexity of these termite-gathering tasks.
Social learning facilitates the transfer of adaptive information within groups for a wide range of animal taxa and can generate group-specific behavior patterns. When these behaviors persist over generations and are transmitted through social learning, they are deemed cultural. High-fidelity social learning is hypothesized to distinguish human from animal cultures by promoting cumulative culture; identifying what mechanisms underpin the social transmission of complex behaviors among animals is thus essential for comparative studies.
Of foremost interest is teaching. A functionalist approach identifies teaching when certain criteria are fulfilled regardless of whether there is evidence of intent to facilitate another’s learning. The most broadly applied criteria are that the behavior occurs in the presence of a naïve learner, at some cost or at least no benefit to the teacher, and that it facilitates learning in another individual. Using these criteria, strong experimental evidence for teaching has been found for meerkats, ants, and pied babblers. Sensitivity to learner competence, or evaluation, and ostensive cueing have been suggested as further criteria. Linking functional criteria to cognitive correlates of candidate teaching behaviors can improve inferences about the evolutionary origins of teaching.
One such candidate behavior is the transfer of tools between individuals, which has been observed among wild chimpanzees in several tool-using contexts. Chimpanzee tool repertoires vary between populations, and this can be attributed in part to social learning. This variation could also be associated with differences in the types of social facilitation necessary to maintain behaviors that range in complexity from simple tasks, involving only a single tool and target, to more complex tasks involving the use of tool sets.
For example, tool transfers have been documented during termite gathering among chimpanzees in the Goualougo Triangle, Republic of Congo. There, chimpanzees are highly selective for plant species used to manufacture tools and intentionally modify herb stems to fashion brush-tipped fishing probes. In addition, chimpanzees use two tool sets to gather termites from epigeal (above-ground) and subterranean nests. At epigeal nests, chimpanzees may use a perforating twig to open sealed termite exit holes on the nest surface before using an herbaceous probe to fish for termites. At subterranean nests, chimpanzees must breach underground nest chambers with a durable, woody puncturing stick before fishing. Teaching is predicted to evolve when it is required to facilitate learning and when the fitness benefits accrued from a pupil’s competence outweigh the costs of teaching. Given the complexity of these tool tasks, we hypothesized that tool transfers from skilled chimpanzees to less competent conspecifics constitute a form of teaching.
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