“‘People who menstruate.’ I’m sure there used to be a word for those people.” With those words, JK Rowling threw herself into perhaps the most febrile debate in contemporary society. Even Covid-19 has not dampened the furore over transgender rights. As two world views collide, fundamental truths that previous generations thought were self-evident have been cast into doubt. What is a woman? what is a man? and how can we tell them apart?