ネズミにも同調圧力？　「傍観者」次第で手助けしたり、しなかったり

【ワシントンＡＦＰ＝時事】ネズミには困っている仲間を助ける習性があるが、近くにいる他のネズミが協力的でない場合、手助けする確率が下がるとの実験結果が8日、米学術誌「サイエンス・アドバンシズ」に発表された。いわゆる「傍観者効果」に新たな光を投げ掛ける研究だ。（写真は自由なネズミが拘束器具を開け、捕らわれていたネズミを解放する様子。シカゴ大学提供）
　論文の上席著者であるシカゴ大学の神経生物学者、ペギー・メイソン氏は今回の発見について、警官の過剰な暴力を居合わせた同僚が傍観してしまうのはなぜか、など特定の人間の行動を説明する一助になるとＡＦＰに語った。
　実験ではまず、ネズミは器具の中で身動きできずにいる仲間に出くわすと通常、扉を開けて救出しようとすることを確認した。
　次に、鎮静薬ミダゾラムを少量投与した１～２匹のネズミを、救出を手伝わない「傍観者」として実験に投入した。すると、困っているネズミと一対一のときには仲間を助けようとしたネズミは、今度は何もせずそばにいるだけで、救出しようとしなかった。
　さらに、鎮静剤を与えないネズミを「協力的な傍観者」として実験に投入したところ、ネズミは一対一のときより張り切って仲間を助けようとした。
　メイソン氏は、米警察の人種差別に抗議する最近のデモで、負傷した参加者を助けるため他の参加者が集まる一方、警官らが傍観している点に言及し、「これは非常にタイムリーな研究だと思う」と主張。「ジョージ・フロイドさんの事件では、他に３人の警官が現場におり、うち１人は黒人に対して警察が過剰な暴力を振るう現状を変えたいと思って警官になった人物だった。それでもなお、彼は止めに入らなかった」と述べた。
　メイソン氏の研究チームは、人間でもネズミと同様に、相手を助けるか否かの決定は誰が責任を負うべきかという概念よりも、脳内の報酬回路に関係するとみている。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2020/07/10-11:50）

Rats are less likely to assist a fellow rodent in need if other members of their group are being unhelpful, according to a study that sheds new light on the so-called bystander effect.
Peggy Mason, a neurobiologist at the University of Chicago and the senior author, told AFP the findings helped explain certain human behaviors such as why police officers fail to intervene when one of their own is engaging in brutality.
In an experiment published in Science Advances on Wednesday, scientists found that when a rat encountered a distressed peer in a restrainer, they were generally interested in opening a door and rescuing them.
One or two bystanders, who were rendered unhelpful by giving them a low dose of the anti-anxiety drug midazolam, were then added to the scenario.
In the presence of these unhelpful bystanders, a rat that had previously been helpful in a one-on-one interaction now stood by idly and did not rescue the subject.
On the other hand, when undrugged, helpful bystanders were placed at the scene, a rat that had been helpful one-on-one became even more keen on being a good Samaritan.
I think this is a very apt study for the times, said Mason, pointing to how during recent US protests against police racism, protesters rushed to aid injured peers while police stood by.
In the George Floyd case, there were three other police officers, including one who went into the police force to change the narrative about police brutality against black people -- and nonetheless, he stood by and did not intervene, she added.
Mason likened these officers to the drugged rats, except they didn't take the chill pill, they took years of training.
If a person does not help, that individual is less likely to be a bad apple and more likely to just be an apple in the orchard, the orchard of mammalian behavior. This is what we do.
- Paradigm shift -
The term bystander effect was first coined by psychologists after the 1964 murder of Catherine Kitty Genovese in New York, whose death was reportedly witnessed by more than 35 of her neighbors, none of whom intervened.
The story was later found to be highly misleading -- but the basic finding held up in controlled experiments where human subjects were placed in distressing situations, such as smoke entering the room or a person having a seizure.
When bystanders were added to these scenarios, members of the public who weren't a part of the experiment often failed to respond.
This led psychologists to hypothesize that perhaps people weren't willing to take responsibility when others were present.
Mason said the hypothesis suffered from a fatal flaw -- the fact that the bystanders were in on the experiment and were acting indifferently on purpose.
A study led by Richard Philpot and published in American Psychologist last year in fact found that in the real world, bystanders rarely stood by.
This paper reviewed more than 200 violent incidents recorded on surveillance cameras and showed that people intervened nine times out of 10.
Mason said her paper built on Philpot's by showing that having helpful bystanders enhanced the desire to help, compared to when there was no audience watching.
On the other hand, having passive spectators decreased the impulse to assist, which reinforces what psychologists found in their early experiments decades ago.
Mason's team belives that in humans, as for rats, the decision to help or not is more likely linked to the brain's internal reward circuitry than it is to notions of who should be responsible.