House He Bite'em ad Infinitum
One of my favorite series is Fox's House. John Hawks does a diagnosis of the show's success:
But unlike most fictional detectives, House and his team average around seven wrong diagnoses per episode before they finally arrive at the right one. That adds to the drama, but it also adds a bit of transparency to what is really going on. House is reading signs.
All medical diagnosis is essentially semiotic: the physician examines the patient, looking for signs. Sometimes these are physical or physiological signs -- a swelling on the knee, vomiting, blood. Sometimes the signs can't be directly observed, but are communicated by the patient: nausea, chills, pain in the chest. The doctor has a script intended to discover these patient-reported signs: "Are you feeling light-headed? Any pain? How often do you have these spells?"
When a physician makes a diagnosis, she has found a set of these signs that point to an underlying disease or condition with some fidelity. Sometimes it helps to know how a disease progresses, but this is not strictly necessary. It almost never requires knowing why the disease exists. The evolutionary origins of many human diseases are mostly or entirely unknown, and physicians do quite well recognizing and treating them without any such knowledge. Together, these facts imply that the mechanism by which a disease causes a symptom is not necessarily of importance to the physician; the symptoms are quite sufficient in themselves as signs.