It's a new form of life. Carl Zimmer discusses a Cell paper by Murgia and coworkers describing a transmissable cancer of dogs (doi: 10.1016/j.cell.2006.05.051; Cell's own lousy nomenclature, until the DOI works: PIIS0092867406009123) and finds something "freaky". A dog with Sticker's sarcoma doesn't have its own cancer - it has the cancer of a dog that died hundreds of years ago, an immortal tumour cell-line that propagates as a non-fatal venereal growth. This creature has sprung in a saltational leap from a domesticated social carnivorous mammal to an undifferentiated niche-specific parasitic mass that lives for hundreds of years (thousands of dog years!). Mitochondrial Eve and Y-chromosome Adam just got a pet. This won't be unique - Carl mentions the Tasmanian devil facial tumour disease but I bet there's more. He's right about the "freaky" - I think it's the freakiest thing I've heard all year.