Vengeance is sweet and expensive

Until now, not much was known about the evolutionary origin of this behaviour. Scientists from the department of social neuroscience at the Max Planck Institute for Human Cognitive and Brain Sciences (MPI CBS) together with colleagues from the MPI for Evolutionary Anthropology (MPI EVA) explored the question at what age we develop the motivation to watch, from our perspective, a deserved punishment and if this feature also exists in our closest relatives -- chimpanzees.

To investigate children's behaviour the researchers used a puppet theatre in which two characters each behaved differently. There was a friendly character, who gave the children their favourite toy back, and an uncooperative one who kept the toy for themselves. Additionally, there was a puppet that played the punishing role and pretended to hit the other two with a stick. The young audience, aged four to six years, could decide if they wanted to watch the pretend hits by paying with a coin, or if they would prefer to exchange the coin for stickers.

In the case of the friendly puppet, the children largely refused to observe how it suffered. However, in the case of the antisocial puppet the six-year-old children's preference to reject the stickers and spend their coins witnessing the punishment was significant. They even experienced pleasure by watching him suffer, shown in their expressions. In contrast, the four- and five-year-old children did not show this behaviour.

The scientists observed similar occurrences in chimpanzees. Their desire to penalise antisocial behaviour was studied in the research unit of MPI EVA at Leipzig Zoo with the help of two zookeepers, who also slipped into contrasting roles; social and antisocial. While one regularly fed them, the other took their food away. In this situation also, another person pretended to beat them both with a stick. As with the children, a significant number of chimpanzees made an effort to witness the disliked keeper being punished. To do so, they had to open a heavy door to a neighbouring room from where they could witness the scene. As for the friendly zookeeper, they refused this option and even protested strongly when pain was inflicted on them.

"Our results demonstrate that six-year-old children and even chimpanzees want to avenge antisocial behaviour and that they feel an urge to watch it. "This is where the evolutionary roots of such behaviour originates, a crucial characteristic to manage living in a community," states Natacha Mendes, scientist at MPI CBS and one of the first authors of the underlying study, now published in the journal Nature Human Behaviour. "We cannot definitely say that the children and chimpanzees felt spite. However, their behaviour is a clear sign that six-year-old children as well as chimpanzees are eager to observe how uncooperative members of their community are punished," adds Nikolaus Steinbeis, the other first author of the study and scientist at both MPI CBS and University College London.