Why do humans (mostly) cooperate? Following social norms to punish others for selfish behaviour plays a part, according to a new study – and this develops across diverse societies as early as middle childhood.

Humans have evolved unique ways to compel people to conform to their culture’s social norms, and a team led by Bailey House, from the University of York, UK, suspected consequences for selfish acts like not tipping or paying taxes could play a role.

“This sanctioning of others is called third party punishment – a key pillar of cooperation in human societies,” House explains, “and it can come in forms such as gossip, social shunning, fines or something much more severe.”

Children presented an ideal means to explore whether social norms motivate third party punishment of selfish behaviour – in turn eliciting cooperative behaviour – as evidence suggests they become sensitive to prosocial cues during childhood.  

The team recruited more than 600 children aged four to 13 from four different urban regions – the US, Argentina, Germany and India – plus the Shuar people from Amazonia and Wichí people from Misión Chaqueña, Argentina.

They used a child-friendly version of the experimental Third-Party Punishment Game, often used to study punishment in social interactions.

Child participants were told about the choices of third parties who could decide how to split a quantity of rewards. This third party could either share with someone else or keep everything for themselves.

Participants could then pay one of their own rewards to punish the third party – but they were given different social norms about how to punish.

Some were told that punishing selfish third parties was good, some that punishing prosocial third parties – those that shared – was good, and others that it was okay to punish both selfish and prosocial third parties.

“This allowed us to describe how children’s tendency to conform to social norms develops, whether this develops similarly across societies, and whether certain kinds of social norms are more influential than others,” House explains.

The international team found that children started to dole out third-party punishment during middle childhood. This developmental trajectory was similar across societies but was less consistent in children from the two indigenous South American cultures.

Overall, norms stipulating the punishment of selfishness had more influence than those requiring the punishment of prosocial behaviour.

While confirming that punishing selfishness is important in all societies, and is a universal response to social norms, the study highlights that children’s prior knowledge of local norms could explain societal variation in the development of punishment and prosociality, House says.

“In particular, the results suggest that children already know a lot about their society’s norms by middle childhood, and that what is changing… is their tendency to conform to those norms.”

The study is published in the journal Proceedings of the Royal Society B.