Gene-Seed

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"They shall be my finest warriors, these men who give of themselves to me. Like clay I shall mould them and in the furnace of war I shall forge them. They shall be of iron will and steely sinew. In great armour I shall clad them and with the mightiest weapons shall they be armed. They will be untouched by plague or disease; no sickness shall blight them. They shall have such tactics, strategies and machines that no foe will best them in battle. They are my bulwark against the Terror. They are the Defenders of Humanity. They are my Space Marines...and they shall know no fear."

- The Emperor of Mankind

Gene-seed is the colloquial term used amongst the Adeptus Astartes for the genetic material that allows for the creation of the superhuman Space Marines. The gene-seed is actually those germ cells and viral machines that have been genetically-engineered to develop into the various organs that are implanted into a normal human adolescent male to transform him into a Space Marine. All of the gene-seed was originally crafted in the 30th Millennium by the Emperor of Mankind in his secret gene-laboratories located deep beneath the Himalazian (Himalayan) Mountains for this purpose using the genomes of each of the 20 Primarchs as a template.

The term is most commonly used to refer to the contents of the Astartes Progenoid Glands which must be harvested by a Space Marine Apothecary so that its genetic material can be used to create a new generation of Astartes. There are 19 types of gene-seed, each corresponding to one of the 19 specialised organs implanted into the body of a human male to create a Space Marine. As many of these implants are neural in nature, it is important to note that for many of these implantations the subject must be awake for the surgery and the mind cannot be dulled by the use of painkillers. Many of these organs are cultured in vitro from the gene-seed, whilst others require that the gene-seed be injected into the Aspirant's body and then grow into a new organ using the implantee's own physiological processes. All Space Marine Chapters use the gene-seed organs to unleash and control the metabolic processes that transform an ordinary mortal into a Space Marine. The gene-seed itself is encoded with all the genetic information needed to reshape ordinary human cell clusters into the special organs Space Marines possess in those instances where they are not directly implanted after being cultured outside the body. The gene-seed contains genetically-engineered viral machines which rebuild the male human body according to the biological template contained within it and originally crafted by the scientific acumen of the Emperor. However, even from the beginning of the Astartes' existence, there was never a set way to activate these transformative functions of the gene-seed.

During the First Founding of the 30th Millennium when the Legiones Astartes (or Space Marine Legions) were first created, the process was still highly experimental and many different ways of controlling and managing the transformation from mortal into Astartes were tried.

Great Crusade & Expansion
As the Great Crusade continued the expansion of the nascent Imperium into the galaxy, the discovery of the Primarchs and their newly adopted homeworlds helped to stem an impending crisis that was not widely known of at the time outside of the exalted ranks of the Imperium's ruling War Council: namely, the diminishing stability of the gene-seed itself through over-use and the increasing need for ever greater numbers of Space Marines in the field. This was a matter that only worsened as the Great Crusade pushed ever wider afield into the galaxy. Imperial forces could no longer be concentrated as easily as before, and attrition was taking its toll as years of near-constant battle became decades. To relent the pace of the Great Crusade's progress was for the Emperor simply not an option and so the simple truth was that more Space Marines were needed and they needed to be created faster than before.

A secret conclave of gene-wrights under the Emperor's direct supervision posited the solution that became known as Grabiya's Theorem, which demonstrated that a Primarch's genetic code could be used to stabilise and expand Astartes gene-seed stocks with what was hoped to be "minimal deviation." Alongside this accelerated gene-culturing technique, other previously unavailable genetic technologies were put into effect, reducing the processing time required to create a battle-worthy Space Marine to a single Terran year in some cases. Such accelerated gene-seed techniques, along with absent, inadequate or over-forceful psycho-doctrination techniques, were later found to have unseen fundamental flaws. Many Imperial savants since have come to believe that the drive to create larger Space Marine Legions at accelerated speed played a prime role in the degradation of the sanity and psychological make-up of certain Legions and paved the way for the horror that was to come.

Known Gene Seed Mutations
Just like normal human germ cells, exposure to high concentrations of ionising radiation can effectively render a Space Marine "sterile" by destroying the germ cells within his Progenoids. Over a couple centuries since the Space Marine Legions were first created, a Space Marine Legion's gene-seed can mutate, producing new and hitherto-unknown physiological effects in that Legion's Space Marines or simply becoming non-functional. Repeated exposures to the corrupting energies of Chaos can also cause mutation within the gene-seed.