What are the limits of multiculturalism? How far is cultural diversity compatible with a working society, by which I mean people's ability to live side-by-side peacefully and co-operatively? This question arises for the world as a whole. But it arises far more sharply when people live in the same country.

We are cultural animals: someone without a culture is not human. But the cultures we possess vary enormously. Indeed, that variability, over time and space, is the great evolutionary advantage of humanity. Instead of changing biologically over millennia, human beings can change culturally over decades.