Depending on how you look at it, in humans the sixth year of life is either when children develop a sense of justice or when they decide its worth paying to see someone punished.
That’s the faintly disturbing conclusion arising from research conducted by a team led by Natacha Mendes from the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig, Germany.
In a study published in the journal Nature Human Behaviour, the team found that at age six children were prepared to pay – in this case, by handing over treasured stickers – to see a wrongdoing peer punished. It was a desire shared by chimpanzees.
Mendes and colleagues to took as their start-point the well supported observation that for humans the sight of someone experiencing misfortune induces distress in the observer.
The scientists wondered, however, if that distress would be lessened or removed if the misfortune experienced was in some way deserved or justified.
To test this, they set up a series of experiments using four, five and six-year-old human children, and chimpanzees.
For each experiment the cohort group was introduced to peers who behaved in either pro- or anti-social ways. Pro-social peers, for example, shared toys and food, while anti-social players refused to do so.
The interlopers were then subjected to punishment out of sight of the groups. The researchers then asked the children and the chimpanzees if they would like to witness the punishment. Wishing to do so carried a cost – handing over stickers in the case of the children, and undertaking physical exertion for the chimps.
The team found that younger children were not interested in such a transaction, but six-year-olds and the chimps were prepared to pay the price to watch anti-social transgressors be punished.
Mendes and her colleagues suggest that by the age of six, children have sufficient emotional and cognitive development to have an interest in sacrificing their own resources to ensure the stability of social systems. It is, the researchers suggest, a strategy with deep evolutionary roots.
The paper concludes: “These findings provide evidence for the evolutionary origins of an increased motivation to watch punishment of antisocial behaviour with — at least in children — possible links to feelings of pleasure underlying such a motivation.
“Such a motivation seems to develop at a protracted rate, similar to higher-level cognitive skills, and might emerge at an age at which children begin to care so much for justice that they are willing to pay for it.”
Andrew Masterson is a former editor of Cosmos.
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