All dogs may go to heaven, but there's at least one who's apparently stuck in limbo, long gone as an individual animal but living on in an extremely unlikely form. According to one of the most bizarre science articles I've ever read, a particular kind of cancer found in dogs is (a) contagious and (b) descended from an "Eve," probably a wolf or an ancient Asian breed like the noble Tibetan mastiff above. Every cancer cell found in dogs with Sticker's sarcoma can be traced back to that one individual animal, who died several centuries ago -- but not before passing his cancer cells on to another dog, probably in the act of mating. Note that we're not talking about the transmission of a virus that causes cancer, like HPV -- the tumor cells themselves got out of their original host and into a new one.
What is this thing? Is it a medieval Chinese dog that has found immortality? If so, then it resembles HeLa cells, a line of cancer cells isolated from a woman named Henrietta Lacks who died in 1951. After her death, scientists have propagated her cells.... One biologist suggested that the cells should be considered a new species.
Do hamsters and Tasmanian devils also get this kind of contagious cancer? And why, for that matter, aren't tumors contagious in humans? Did our ancestors spend millions of years warding off "cancer parasites," and is that why our immune systems are so robust today? There's lots more equally fascinating stuff in the article; I can't recommend it enough.