‘Read monkeys for pre-existence’ wrote the twenty-nine-year-old Darwin in one of his notebooks, pondering Plato’s assertion that our ‘imaginary ideas’ derive from the pre-existence of the soul. Two years earlier, when HMS Beagle had returned from its circumnavigation of the world, Darwin was still a creationist, albeit one who had entertained doubts. Keen to capitalise on his wide-ranging collection, and to make a name for himself, he arranged for various experts to examine the specimens. Fairly quickly during the ensuing discussions, Darwin realised that his doubts concerning the stability of species were ready to burgeon into a new and disturbingly materialist worldview.