During the show, various political and social themes were addressed as well. Throughout the series aspects of the relation of Terrians to the planet and to the colonists reflect the history of colonies with native populations and slavery. In "The Enemy Within", Julia is left behind by the group because of her treachery, addressing briefly what punishments are moral or even inhumane. Another aspect of this issue is addressed in "The Man Who Fell to Earth (Two)", when the group meets a man named Gaal who claims to be an astronaut but is revealed as a marooned criminal; when it is revealed that G889 had been used for many years as a penal colony, questions arise as to the motivations of the Council and their right to do so. In "Redemption", the group encounters a genetically enhanced killer called Z.E.D., who was left on the planet to dispose of all the humans he finds, who at the time had been criminals.