Norms about violence and hygiene have become increasingly strict, a development that has been going on for hundreds of years. Until now explanations have been sought in societal changes, but new research published in the journal Nature Human Behaviour shows that we might actually find the answer in human psychology, namely, in our tendency to punish behaviors that we perceive as threatening.

The way we behave in different situations is often governed by social norms, informal rules about what is considered normal or acceptable. Understanding how these norms spread and develop is therefore interesting in all contexts where one wants to achieve behavioural change.

Previous research has shown that norms around hygiene and violence have become increasingly stricter for a long time and in many societies, regardless of culture. Explanations have been sought in societal changes such as technological advances, increased welfare and tougher laws, but they have proven to be inadequate. In a new study, researchers look closer at human psychology to find the solution.

In a study published in Nature Human Behaviour, Pontus Strimling from the Institute for Futures Studies in Stockholm, together with Mícheál de Barra and Kimmo Eriksson from Stockholm University, show that changes in norms can occur in the meeting between individuals where one of them punishes the other for a behavior that feels threatening.

The researchers show that people who have a strict view of hygiene and violence tend to feel more threatened by behaviors that signal a looser attitude toward such norms, than the other way around. People who fell threatened are more likely to penalize those who exhibit the looser kind of behavior. People being punished tend to change their behavior to avoid punishment, no matter how common the stricter norm is in the general population. Thus, a norm that prevails in a small part of the population, can change the behavior of a majority of the population over time.

"Our results indicate that norms of violence and hygiene are influenced by general human psychology. It's exciting because it can make it possible to say something about how our behavior can change in the future in several areas," says Pontus Strimling, Institute for Futures Studies.

A better understanding of how social norms spread and develop can also be helpful in situations where you need an uncommon behavior to spread to a larger majority of people.

"Several hundreds of thousands of children could be rescued from death every year if people just washed their hands after toilet visits. We hope our results will help in improving hygiene in different parts of the world," says Pontus Strimling.