Purity

The Thirteenth Doctor observed that the Daleks were "pretty obsessed" with purity, ironically for a species born out of mutation. (TV: Revolution of the Daleks)

As the Last Great Time War persisted, the Dalek ideals of racial purity were weakened. A Brief History of Time Lords claimed the Cult of Skaro were a result of this, (PROSE: A Brief History of Time Lords) though the members of the cult were known to be "pure" Daleks. (TV: Daleks in Manhattan) A group of the Dalek Scientific Division sought to restore the Daleks to a humanoid form, ignoring orders to stop over concerns of purity. (AUDIO: A Thing of Guile)

The Dalek Emperor in the Last Great Time War insisted that his Dalek of human origin were not "half-human", an observation from Rose Tyler which he found blasphemous. He claimed that everything human had been purged from them, that he had "cultivated pure and blessed Dalek." (TV: The Parting of the Ways)