Over 500,000 years ago, a single gene mutated. It spread over time, becoming critical in the journey that transformed our earliest ancestors into fully modern humans, capable of navigating the entire planet and beyond. A few thousand years ago, humans started outsourcing knowledge to writing, displacing art and music from the heart of learning. This is the extraordinary story of a gene that makes us uniquely human. Dr Lynne Kelly recounts how a widespread congenital disorder was the critical clue she and her collaborators needed to identify this gene as the supergene that has long eluded researchers into human cognition.