The earliest practical intelligence tests, published in 1905, were developed to help spot young Parisians with what we’d now call special educational needs. Created with admirable aims, they were later used to sort and rank masses of people and to give credence to theories of racial difference.

Such tests are direct descendants of tools designed to evaluate children’s mental abilities over a hundred years ago. Today, proud parents on ‘Child Genius’ cite the results of IQ tests as evidence of their children’s innate talents. In the 18th and 19th centuries, physiognomists and phrenologists identified facial features and head shapes consistent with intellectual and creative genius – from sharp-cornered eyes to lumps around the temples. Genius may be indefinable, but people have still spent centuries measuring whatever they think it is.