http://www.newsweek.com/american-dogs-cancer-dynasty-1011310

Cancer can be frighteningly complex and unpredictable. Cancer can evolve, change, evade and resist, but one thing we can usually rely on is that cancer can’t infect. For a handful of unlucky species, however, this isn’t the case. Thousands of dogs around the world—from Aboriginal camp dogs in Australia to street dogs in Buenos Aires—are affected by an extraordinary type of infectious cancer that causes genital tumors and can jump between individuals, known as Canine Transmissible Venereal Tumour or CTVT.

All of these tumors are clones—genetically similar to one another but genetically distinct from their hound hosts. DNA from the tumors can trace them to a single individual, the “founder dog”. This cancer arose only once, thousands of years ago, from the cells of this “founder dog”—an unsuspecting pooch. Since then the tumors have persisted through the millennia by transmission of cancer cells between dogs during mating. The founder dog has spawned a modern-day doggy cancer dynasty. This story begins and ends with the question of when and where this mysterious founder dog lived when its cancer lineage first emerged.