Conceptual origins of the Daleks
On the planet Skaro, during the final days of the Thousand Year War between the Thals and Kaleds, both sides suffered mutations caused by nuclear, biological and chemical agents. Some of the mutant survivors, the mutoes, survived in the wastelands. (TV: Genesis of the Daleks) Shan, a young Kaled scientist, authored a paper. With both Kaleds and Thals competing for resources, she called the only way out of this dilemma "the Dalek Solution". Davros presented the paper to the Kaled Council as his own. (AUDIO: Davros).
Another account stated that Davros found a prophecy in the forbidden Book of Predictions, written in the extinct language of the Dals, which stated "...and on that day, men will become as gods." In the original language, the final word was pronounced "Dal-ek." (AUDIO: Guilt)
The first Daleks
Later, Davros, now crippled, became one of the Kaled Scientific Elite. He had begun experiments on living subjects and hoped to deify the Kaled race. Davros pushed through legislation enabling authority (and ownership) of all Kaled infants under the age of five years old and to be delivered to Pediatric Facility K99, which he used as a laboratory for surgical experiments. Davros transplanted the brain from Baran, a captured Thal spy, into a Mark I Travel Machine. (AUDIO: Guilt)
Davros reveals the Daleks
Davros did not immediately show the results of his Dalek experiments to the Kaled Scientific Elite. He improved and developed the shell for the organic components of the Daleks, housing them in tank-like and armed Mark III Travel Machines similar to his own life support chair. He maintained a nursery of embryonic Dalek young. As well as nurturing the physical form of his creations, Davros shaped their minds. The Daleks did not understand concepts such as pity. It did not exist in their "vocabulary banks".
The Fourth Doctor was sent on a mission by the Time Lords to prevent the creation of the Daleks in the first place, or at the very least lessen the damage they would do in future. Many other members of Kaled Scientific Elite attempted to shut down the Dalek project. To prevent this, Davros arranged for the Thals to aim a missile at the Kaled Dome where his people resided. (TV: Genesis of the Daleks)
The Daleks revolt against their creator
The Daleks were sent to exterminate the Thals, supposedly in retaliation for the attack on the Kaled Dome. They turned on Davros, as they were not programmed to recognise any creature as superior to them, which included him. They apparently killed him. Accidentally, whilst attempting to stop the Doctor, a Dalek triggered an explosion which destroyed the embryo room before the Thals sealed the bunker entrance and trapped the Daleks there. In the aftermath, the Doctor believed he had only held back their progress by about a thousand years or so, and they would return (TV: Genesis of the Daleks). Davros survived his "death" in a state of suspended animation. (TV: Destiny of the Daleks) The same Dalek that fired on Davros later became itself the Dalek Prime and eventually proclaimed itself to be the Dalek Emperor. (PROSE: The Evil of the Daleks, War of the Daleks)
Subsequent to their creation, the Daleks, confined to their city believed the war was a quick neutronic war and that both sides of the war were horribly mutated from their original humanoid forms. (TV: The Daleks)
Yarvelling and the Dalek Emperor
Another account states tells of short, blue, humanoid Daleks, whose warlord, Zolfian plotted to use neutron bombs against the Thals. Zolfian employed a scientist, Yarvelling, to develop war machines against the survivors and ordered the factories to mass-produce more of them. Two weeks later, a meteorite strike destroyed the factories and the neutron bomb stores. After two years, Zolfian and Yarvelling climbed out of a fallout shelter to find a mutated Dalek which Yarvelling described to Wolfian as having "a brain a thousand times superior to ours", had crawled inside one of the war machines and used it a shell. Before they died of radiation sickness, the "machine Dalek" forced the two survivors to make more war machines. (COMIC: Genesis of Evil)
However, prior to the writing of that story, Terry Nation, the real-life creator and copyright holder of the Daleks, elected to allow at least three separate origin stories for his creations. The reason for the multiplicity of origins is unclear, but it likely had something to do with the time in which they were written. In the 1960s and early 1970s, Nation and the rest of the Doctor Who team didn't really believe they were creating "permanent" works. Written long before the advent of home video, the internet, or even the existence of a robust market for reprinted comic strips, the various origins told during the first decade of Doctor Who were likely considered as disposable as the episodes themselves turned out to be. Hence, Nation contradicted not just other writers, but himself, when positing various origins for the Daleks.
The first Dalek story, TV: The Daleks, gave viewers a tiny sliver of an idea of where the creatures came from. Far from a full-fledged origin, The Daleks tells us the Daleks came from a race called "the Dals" who had survived an atomic war. This narrative "plank" was certainly incorporated into Genesis of the Daleks, although the name of the parent race wasn't.
TV Century 21 comic strips
Nation allowed writers David Whitaker and Alan Fennell to tell a Dalek origin in their 1965 TV Century 21 comic strip, Genesis of Evil. This was the first published attempt to tell a more-or-less complete origin, and it posited that the Daleks were mutated from a race also known as the Daleks. There is no reference at all to any part of Genesis of Evil within televised Doctor Who, and very little more than an occasional, sly reference in other forms of Doctor Who fiction.
The TV Century 21 version went unchallenged by any other story for eight years until Nation himself was commissioned to write a short prose story for the Radio Times Doctor Who 10th anniversary publication in 1973. Entitled We are the Daleks!, the piece substantively contradicted Genesis of Evil and The Daleks, and the later Genesis of the Daleks. The most contradictory and surprising feature of this piece was the notion that Daleks were actually evolved from future humans.