Humans don’t take kindly to outsiders: history is heaped with the corpses of those who were lynched, bayoneted or gassed because of their race, religion or nationality. Even within the relatively civilised sphere of economic relations, there is plenty of room for discrimination. People earn less because of their race or their sex, even in the richest countries in the world.

For example, according to a recent summary by the economists Michael Clemens, Claudio Montenegro and Lant Pritchett, white men earn 27 per cent more in the US than white women. That figure compares the hourly wage of full-time workers with similar qualifications and experience. Again making best efforts to compare like with like, the economists found that white men earn 7 per cent more than black men in the US. Look back to 1939, and the like-with-like wage premium for whites in the US was 60 per cent. In modern Pakistan, meanwhile, men earn three times as much as equally qualified women. None of these numbers is trivial: most are appalling.