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Basis for cumulative cultural evolution in chimpanzees: social learning of a more efficient tool-use technique.

Shinya Yamamoto, Tatyana Humle, Masayuki Tanaka
DOI: 10.1371/journal.pone.0055768
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Supplementary Movie S1: The “dipping” technique performed by a chimpanzee Ayumu. Note that he uses his mouth to insert the tube into the bottle. In form, his technique is identical to the “straw-sucking” technique. However, instead of leaving the tube in and retrieving the juice via sucking, he removes the tube and licks the tip.
Supplementary Movie S2: Close observation and subsequent switch in technique used. Pal (out of sight in the first view) closely observes the demonstrator, then fetches a tube from the floor (out of sight), and then proceeds to suck the remainder of the juice in the bottle container. Pal had just performed the “dipping” technique prior to observing the alternate technique being demonstrated during the same trial.

Background: The evidence for culture in non-human animals has been growing incrementally over the past two decades. However, the ability for cumulative cultural evolution, with successive generations building on earlier achievements, in non-human animals remains debated. Faithful social learning of incremental improvements in technique is considered to be a defining feature of human culture, differentiating human from non-human cultures. This study presents the first experimental evidence for chimpanzees’ social transmission of a more efficient tool-use technique invented by a conspecific group member.
Methodology / Principal Findings: The chimpanzees were provided with a straw-tube, and spontaneously demonstrated two different techniques in obtaining juice through a small hole: “dipping” and “straw-sucking”. Both the “dipping” and “straw-sucking” techniques depended on the use of the same tool (straw-tube) for the same target (juice) accessible from exactly the same location (small hole 1cm in diameter). Therefore the difference between “dipping” and “straw-sucking” was only in “technique”. Although the two techniques differed significantly in their efficiency, their cognitive and perceptuo-motor complexity were comparable. All five chimpanzees who initially performed the “dipping” technique switched to using the more efficient “straw-sucking” technique upon observing a conspecific or human demonstrate the more proficient alternate “straw-sucking” technique.
Conclusions / Significance: The social learning mechanism involved here was clearly not local or stimulus enhancement, but imitation or emulation of a tool-use technique. When there is no biologically relevant difference in cognitive or perceptuo-motor complexity between two techniques, and when chimpanzees are dissatisfied with their own technique, chimpanzees may socially learn an improved technique upon close observation of a proficient demonstrator. This study provides important insights into the cognitive basis for cumulative culture in chimpanzees, and also suggests possible conditions in which cumulative cultural evolution could arise even in non-human animals.

Article Information
Yamamoto, S., Humle, T., & Tanaka, M.(2013)Basis for cumulative cultural evolution in chimpanzees: social learning of a more efficient tool-use technique. PLoS ONE , 8(1): e55768 10.1371/journal.pone.0055768