Devil Facial Tumor Disease

Devil Facial Tumor Disease is a transmissible cancer that spreads between Tasmanian devils when they bite each other during mating and feeding. Unlike normal cancers that die with their host, DFTD jumps bodies - it's essentially a parasitic organism that happens to be made of cancer cells. Since its discovery in 1996, it has killed approximately 80% of the Tasmanian devil population.

DFTD succeeds because Tasmanian devils have extremely low genetic diversity - so low that their immune systems don't recognize the foreign cancer cells as different from their own tissue. The business parallel is monoculture vulnerability: populations (or organizations, or markets) with too little diversity are vulnerable to threats that diversity would naturally resist. A disease that would stop at genetic boundaries spreads freely through homogeneous populations.