飼育下におけるチンパンジーが道具を作成し利用する能力については、既に古くから明らかにされてきた。
The ability of chimpanzees to make and use tools in captive environments has been demonstrated previously.
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A typical example is the experiment conducted by Köhler in 1914.
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In this experiment, a banana was placed on the other side of a fence, out of the chimpanzees reach, while a stick was placed within their reach.
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Most of the individuals quickly succeeded in using the stick to pull the banana toward themselves, and even when there was no stick, some broke off a branch to use as a substitute.
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In particular, a chimpanzee named Sultan was able to efficiently pull a banana toward himself by joining together hollow stems of different thicknesses to make a long stick.
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Combining tools like this to solve problems demonstrates the high cognitive abilities of chimpanzees.
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Furthermore, in another experiment, a wooden box about 50 cm long was placed in the corner of a room with smooth walls that could not be climbed, and a banana was hung in a high place out of reach.
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Sultan realized that he couldnt reach it even if he jumped, so he pulled the box over, stood on it, and was able to get the banana.
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When the bananas were hung even higher and he had to stack multiple boxes, Sultan struggled at first, but gradually learned how to pile up the boxes to reach them.
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Other chimpanzees also imitated this behavior, and eventually an individual named Grande succeeded in stacking four boxes.
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These stacked boxes can be regarded as a kind of structure built for a specific purpose.
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In the experiment using this box, two interesting phenomena were observed.
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もう一つは、協同作業と見なされる行動が現れた点である。
箱を積み上げる方法を理解している個体同士が集まると、各自が競って箱を積もうとし、結果的に箱が崩れてしまうことが多かった。
しかし一度だけ、グランデが離れた場所にあった大きな檻を利用しようとした際、一頭では動かせなかった檻を、ランとズルタンが駆け寄り、三頭で協力して目的のバナナの近くまで運ぶことに成功した。
ただし、完全な協同作業とは言い難く、ズルタンが檻の上に飛び乗ってバナナを獲得し、他の二頭は何も得られなかった。
このことから、彼らの行動は互いの意図を即座に理解しながらも、最終的には各自の利益を追求した結果であったと考えられる。
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