Research press release


Nature Communications

Animal behaviour: Chimpanzees are not as helpful as we thought



今回、Keith Jensenの研究チームは、チンパンジーを対象として、いわゆる向社会性行動の程度を調べるため、13匹のチンパンジーに木製の止め釘を抜き取る行動を学習させた。そして、6匹のチンパンジーの場合には、止め釘を抜き取ると、目の前にいる知り合いのチンパンジーが食料を手に入れられるようにし、残りの7匹のチンパンジーの場合には、止め釘を抜き取ると、他のチンパンジーが食料を入手できなくなるように実験を組み立てた。13匹のチンパンジーには、止め釘を抜き取る行動が別のチンパンジーの役に立つのか、邪魔をするのかを見えるようにしたが、13匹のチンパンジーの行動に差はなかった。その後行われた追試では、チンパンジーを隣接するチンパンジーのケージに入れるようにした。止め釘を抜き取ると自分自身の採餌量に明白な影響が出るようにしたところ、チンパンジーの行動が変わり、止め釘を抜き取ると食料が得られる場合には止め釘を抜き取るようになり、止め釘を抜き取ると食料を受け取れなくなる場合には止め釘を抜き取らなくなった。


Unlike humans, chimpanzees are not naturally helpful but rather engage in certain behaviours regardless of whether they are helping another chimpanzee, shows a study published in Nature Communications. This finding suggests that, among primates, humans are unique in how they have evolved their social behaviour and kindness towards others.

Scientists observing our evolutionary ancestors, various species of non-human primates, in the wild have reported acts of kindness, cooperation and helpfulness. These include primates grooming one another, coming to the aid of another during a fight, and taking border patrol duty to keep the rest of the group safe. Similar observations have been made with trained monkeys, yet it is not known whether these behaviours are done to help others or for the delayed benefits these behaviours engender.

To investigate the extent of so-called pro-social behaviour in chimpanzees, Keith Jensen and colleagues trained 13 chimpanzees to release a peg. For six chimpanzees, this action resulted in another, visible and familiar chimpanzee receiving food. For the other seven, the same action blocked the other chimpanzees access to food. Though all 13 chimpanzees could see that their actions either helped or hindered another chimp, they did not show any differences in behaviour. In a follow-up test, chimpanzees were given access to their neighbors’ cage. When releasing the peg had a clear effect on their own food consumption, they showed different behaviour, releasing the peg when it yielded food and not releasing it if it would block their own food.

Taken together, these results suggest that prior evidence for pro-social behaviour may have been the by-product of experimental designs, merely producing an illusion of helping.

doi: 10.1038/ncomms13915

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