Genestealer

Genestealers (Corporaptor Hominii) are an alien species in the Warhammer 40,000 universe, and the opponents of the marines in the Space Hulk board game. In more recent versions of that universe, Genestealers are a biological subgroup of the Tyranids, a nomadic alien race comprising many genetically engineered forms.

In 4th Edition of the wargame, there are two subgroups of the Genestealers: the Broodlord and the Genestealer. In the 2nd Edition of the game, there are five subgroups, representing the Genestealer Cult variant army: Genestealer Patriarchs, Genestealer Magus, Genestealers, Genestealer Hybrids, and Brood Brothers. For information concerning biomorphs and other mutable genetic characters of the Genestealers in the game, see Tyranid Genetics (Warhammer 40,000).

Background
Genestealers appeared in the first edition of Warhammer 40,000 (Rogue Trader), but at the time were not related to Tyranids. They were simply noted as an "enigmatic monster ... from one of the moons of Ymgarl", now "spread throughout space" and "threatening to become a real menace". Since then it has been revealed that they are the advance forces of a Tyranid invasion and are now often seen as part of a Tyranid army.

The Genestealer Cult is a sub army that has been introduced several times for Warhammer 40,000. The initial introduction by Paul Murphy, Bryan Ansell, and Nigel Stillman was printed in White Dwarf issues 114-116 (1989). Original inspiration for the idea came from a novel by Harris Moir. This book was followed by an article from Andy Chambers and Jervis Johnson in White Dwarf issue 145 (1992) that detailed the Genestealer Cult as part of a Tyranid Army. Later, Tim Huckelbery detailed the Genestealer Cult Army in issues 40 & 41 of the Citadel Journal, under the title Codex: Genestealer Cults. This official supplemental Codex provided official rules for using Patriarchs, Magi, Hybrids and Broodbrother units. It even included rules for a "Transport Coven Limousine." Later, in the first Codex Tyranids, these rules were incorporated as the "Genestealer Cult Army List" and included all of the characters in their previous form sans Limousine.

In the Codex for 3rd Edition, there were no rules provided for the Genestealer Cults. With the introduction of the Broodlord in 4th Edition, Genestealers could once again be fielded as their own army. Before the 4th edition introduced new sculpts for them, the 3rd edition Genestealers were the oldest models in use to date, being the same designs used in Rogue Trader and the Space Hulk game.

Biology
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. Furthermore, in another Ciaphas Cain novel "The Emperor's Finest" infected Orcs are described protecting a genestealer hybernaculum.

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 threshold, 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.

Imperial response to Genestealers
The Imperial response to genestealer infestation is often used as storytelling device to illustrate the ruthless and brutal nature of 41st millennia humanity. It also frequently serves to justify that ruthlessness and brutality as a rational response to the threat that the Tyranids represent.

The typical Imperial response to discovering signs of a genestealer infestation is to hunt down and kill all genestealers, hybrids and infected humans. The authorities then institute strict screening measures for detecting newly infected humans and quickly kill any that are found. If the infestation was widespread before discovery, the entire sector is then typically put on alert for impending Tyranid attack.

The Ciaphas Cain novel "Duty Calls" depicts the disruptive consequences of a late-stage genestealer infestation. It also depicts efforts undertaken to eradicate the infestation from local PDF regiments as the Imperial Guard prepares to fend off a Tyranid hive fleet that has been attracted to the infestation.

If the infestation is too widespread to eradicate, the typical response is to write off the uninfected human population and use orbital bombardment to wipe out the infestation wholesale. If the entire planet falls (whether to a genestealer cult insurrection or the inevitable arrival of a hive fleet) the entire planet is laid waste in an Exterminatus.

Army list
The most recent Genestealer Cult was published in Citadel Journal and was released for the 3rd edition Warhammer 40k. As such it is outdated and not tournament legal; however, due to the similarity of the 3rd and 4th edition rules for Warhammer 40k it was still usable with the latter edition. Some players preferred to use the Lost and the Damned army list to represent a Genestealer Cult, with Traitor Guardsmen representing Brood Brothers and Mutants representing Genestealer Hybrids. Others have tried to modify the Imperial Guard list using the Doctrines rule to mimic the Genestealer cult. In the more recent 5th edition of Warhammer 40k, the Doctrines rules and Lost and the Damned rules are no longer present, leaving the Imperial Guard codex as the last viable rules set to use.