As a young medical student, I remember sitting in an embryology lecture, staring at a diagram of the early embryo. The notochord sat there like a quiet rod in the middle, a slender axial structure that somehow knew how to orchestrate the rest of the body. From its signalling, the neural plate would arise, fold, and become the neural tube—the future brain and spinal cord. The heart fields were also taking shape, destiny encoded in tissue that only days earlier had been a seemi