In February 2010, cleaners working at Dutch railway stations went on strike for several weeks. Their stations quickly fell to dirtiness and disarray, but most people didn’t mind; public support for the strike was high. But two scientists – Diederik Stapel and Siegwart Lindenberg from Tilburg University – were particularly delighted. In the growing chaos of the stations, they saw an opportunity to test an intriguing concept – that disorderly environments promote stereotypes and discrimination.

Their big idea is that stereotypes, being a set of simplified categories and judgements, can help people to cope with chaos. They are “a mental cleaning device in the face of disorder”. When our surroundings are full of chaos – be it dirt or