Thal history was revised in "Genesis of the Daleks" (1975), in which they were depicted as having been involved in a generations-long war of attrition with the Kaleds. This transformed Skaro into a toxic wasteland, with the survivors of each race forced to live under their own huge, protective dome. The Kaled chief scientist, Davros, genetically engineers mutated members of the Kaled species and places the results into travel machines, which he names Daleks (an anagram of Kaleds). Davros simultaneously provides the Thals with the technology they need to destroy the Kaled dome, so as to wipe out all opposition to his plan to create a species consisting of what he considers to be the ultimate Kaled form. He then sends the Daleks to the Thal dome, where they kill nearly all the inhabitants. A small group of Thals use explosives to seal the Daleks and Davros in a Kaled bunker but the Fourth Doctor speculates that they have only delayed the Dalek development and rise to power by a matter of centuries.