Purity is an ancient alien race that is spreading in the universe, creating life or life forms in many worlds and colonizing them subsequently, probably in order to replenish its dwindling forces in its billions of years-old voyage across the void. It masters the art of genetics to an extreme degree and considers itself the most superior of beings, clearly superior to its creations. A member of Purity will look down on anything that soils Purity's genetic superiority and it will consider equal only a being with the same genetic purity -- hence its denomination as "Purity". More of its life cycle can be learnt here.

Its normal appearance is that of a humanoid grey alien. But it can also spread as a sentient liquid, the Black Oil, which contains a virus-like entity bathing in hydrocarbons. The Black Oil can behave like a virus, infect a host organism and trigger the creation of what will become a grey alien. The strain of the Purity DNA in the Black Oil is a simplified strain compared to the full Purity DNA, so that the Black Oil can be versatile and spread more effectively; the Black Oil DNA was stripped down of all the complex and voluminous genetic information necessary for the creation of the grey alien. That information is to be found in the host's DNA; the Black Oil uses the host's DNA to re-create the original Purity DNA and make a grey. The host contains Purity DNA because it was placed there when Purity created the host race. In essence, the host's DNA is used as an 'external information tank' called upon when necessary by the Black Oil, and the host's only use is to allow Purity to regenerate itself. This extra DNA is normally not in use by the host; it is 'junk DNA'. In principle, Purity can only colonize, ie create greys out of host bodies, races that it had previously created.


The races of the so-called Shapeshifters and of the Humans are creations of Purity, they are Children of Purity. They were created from Purity DNA and from genetic material present in their home planets. This is why humans in general can be seen as hybrids as well, hybrids between alien and terrestrial DNA -- but to avoid confusion we won't use that term to describe humans.

The humans' affiliation with Purity is why alien and human DNA are compatible and why it is so easy to create hybrids between these two races, compared to two other completely alien races. The humans are targeted for colonization by Purity in the close future. The Shapeshifters were apparently colonized by Purity in the past; only the Black Oil-controlled Alien Bounty Hunters and the Rebels survive out of the Shapeshifter race. The Shapeshifters' affiliation with Purity also explains why alien/human hybrids resemble Shapeshifters so much: the hybridization process in humans expresses genes that are already part of the Shapeshifters' normal makeup, genes that originally come from Purity.





Key episodes: 5X13: Patient X, 5X14: The Red and the Black, 5X20: The End, Fight the Future, 6X01: The Beginning, 6X11: Two Fathers, 6X22: Biogenesis, 7X03: The Sixth Extinction
See also: Primer 1