Editing Genestealer Cult

The biology of genestealers has undergone heavy revision over the years as Games Workshop developed the concept from their original appearance as wild animals to their current status as a Tyranid hive fleet component.

The original "genestealer" is closest in appearance and ability to what is now called a "purestrain genestealer." It is a roughly human-sized, six limbed creature possessing incredible strength, speed and durability. At melee range, purestrain genestealers can best nearly any opponents in the W40K universe. Unless they have the advantage of vast numbers, genestealers favor stealth and ambush tactics. Purestrain genestealers are depicted as being extremely intelligent for animals, but lack the ability to use tools or engage in speech. Genestealers, like all tyranids, are capable of telepathic communication with one another within a limited range.

Due to the human-centric nature of most W40K fiction, most genestealer infestations that have been depicted thus far have occurred on purely human worlds. Despite this, there is evidence that non-human species can be infected in an identical fashion. In the Ciaphas Cain novel "For the Emperor," it is strongly suggested that Tau can be infected in an identical fashion to humans.

In current canon, small numbers of genestealers are infiltrated on to worlds populated by sentient humanoid species to prepare the worlds for invasion by a Tyranid hive fleet. These genestealers are "pure strain" and thus capable of using their sharp tongues as an ovipositor to insert a "seed" into the host's body. The "seed" immediately alters the host to suppress any memory of the infection. It also alters the host so that they will have a strong urge to reproduce and to protect whatever children are subsequently born. Unfortunately, the "seed" also alters the host so that any children born are monsters strongly resembling the original genestealer. These infected humans also become psychically linked to one another and to the genestealers.

All genestealer-infected humans produce what are known as "genestealer hybrids." Hybrids reproduce like the host species and produce more hybrids. With each subsequent generation, the hybrids become less and less like purestrain genestealers in appearance. The first generation is depicted as slightly more intelligent than purestrain genestealers and only slightly less physically powerful. A 4th generation hybrid is nearly human in appearance and intelligence. Unfortunately, when 4th generation hybrids reproduce, they produce only purestrain genestealers. These genestealers can continue the process by infecting non-infected humans.

All hybrids, regardless of generation, share the tyranid psychic link of the original genestealers and this psychic link provides the communication network for the genestealer cult as it grows. As the fourth generation begins reproducing, the number of purestrains (and the number of newly infected humans) rapidly increases. The psychic traffic between the many members of the cult and their purestrain genestealer descendents increases drastically at this point. Beyond a certain threshhold, this intense psychic activity draws the attention of any nearby Tyranid hive fleets, who will set course for the world to consume it. Just prior to the arrival of the hive fleet, the genestealer cult (by now in direct psychic contact with the hive fleet) will engage in widespread rebellion and sabotage to weaken any defense the world might undertake against the fleet. If this is successful, the genestealer cult ends up being consumed by the hive fleet along with all life on the planet.