What does it take to become a doctor?

DEAR DOCTOR K: You often mention your colleagues at Harvard Medical School. I'm curious, what does it take to become a doctor at Harvard?
DEAR READER: Believe it or not, this is the first time I've been asked that question. Here's how things are organized. We have several hundred medical students. They spend four to five years learning to become doctors. Then they get an M.D. after their names.