Cancer arises when mutations drive cells of the body to abandon their usual functions and to instead embark upon a “selfish” evolutionary programme underpinned by abnormal growth. Most cancers exist only within the bodies of the hosts that spawn them; rarely, however, cancers can acquire adaptations allowing them to spread between individuals. In such transmissible cancers the cancer cells themselves become agents of infection. Elizabeth Murchison discusses recent research on the origins and evolution of the naturally occurring mammalian transmissible cancers affecting dogs and Tasmanian devils.
