A type of tumor that can pass between dogs is showing researchers how cancer cells evolve. (Credit: Jess Wealleans/Shutterstock)

Thousands of years ago in Asia, a dog got cancer. A single cell underwent a mutation that turned it into the beginnings of a tumor. The dog eventually died, but not before passing on a unique legacy: its cancer cells.

Today, those cells are still growing in dogs across the globe. That’s because this particular kind of cancer cell turned out to possess an incredi