A transmissible cancer in the Tasmanian devil has evolved over the past two decades, with some lineages spreading and replacing others, according to a new study in the open access journal PLOS Biology by Young Mi Kwon, Kevin Gori, and Elizabeth Murchison of the University of Cambridge (UK) and colleagues. The evolutionary dynamics of the cancer help explain how this Australian marsupial has become so quickly endangered, and may shed light on the evolution of other forms of cancer.