At the turn of the twentieth century, four revolutionary scientific discoveries were made almost simultaneously: the gene, the electron, the quantum and the unconscious. One of the more important, if under-appreciated, developments of modern intellectual history is the way in which, as the decades passed, three of these discoveries brought the sciences together in a process that the American zoologist Edward O Wilson called ‘consilience’.

Niels Bohr was first, showing how atomic structure explained chemical behaviour, followed by Linus Pauling, who showed how atomic structure determined the physical properties of substances – why some are yellow liquids and others black powder. In the 1940s Erwin Schrödinger showed how physics determined the structure of