Tough as they might be, though, Tasmanian devils were in trouble. A singular epidemic was sweeping across the island, not quite like anything veterinarians had seen before. A devil would develop a fleshy growth in or around its mouth. In a matter of weeks, the growth would balloon, and within a few months, the animal would starve or suffocate. These growths were first observed in 1996 in the northeast corner of Tasmania, and over the next few years they spread over most of the island, killing off tens of thousands of devils. By the early 2000s, the species looked like it might become extinct in a matter of decades, killed by a disease scientists didn’t understand. It would take them years to realize that these devils were chimeras, and that their cancers descended from the cells of a long-dead animal.
The DNA fingerprint from tumor cells didn’t match the healthy cells from the same devil’s body. Instead, they matched cancer cells from devils who died dozens of miles away. It was as if all the sick devils had gotten a cancer transplant from a single tumor.
At some point in the early 1990s, [Elizabeth] Murchison’s research showed, a single Tasmanian devil in the northeast corner of the island got cancer. The mutations may have initially arisen in a Schwann cell. The descendants of that original cancer cell grew into a tumor. During a fight, another devil bit off the tumor. The cancer cells did not end up digested in the attacker’s stomach. Instead, they likely lingered in the devil’s mouth, where they were able to burrow into the cheek lining and work their way metastatically into the other tissues in the devil’s head. The cancer cells continued dividing and mutating, until they broke through the skin of the second devil’s face. At some point, that new victim also got bit, and its own attacker took in the cells from the original cancer. A single carrier could pass the cancer on to several other devils if it was especially aggressive, and thus help accelerate its spread. Passing through host after host, the tumor cells gained about twenty thousand new mutations.
Consider this fair warning!