The Graft is a colloquial term referring to the forced genetic engineering of the Cardassian hierarchical instinct into the human race in an alternate universe where the Dominion won its war against the Federation, Klingons, and Romulans. Another less frequently-used term is "Cataclysm," after the climatic Cataclysm of Cardassia Prime. (Star Trek: Sigils and Unions--"The Nature of the Beast")

The Dominion had apparently been engineering the virus that would deliver its genetic payload before the end of the war; by the time the Federation surrendered, they were already in place to infect staggering numbers of Starfleet's surviving troops with the virus. The Graft was intended as a control device short of installing the same sort of automatic worship genes embedded in the Jem'Hadar and Vorta genome. In their estimate, it would serve as a means of suppressing rebellion while still leaving the altered humans with independent minds that they hoped to harness for tactical and scientific innovations to use against the Borg.

Whether or not humans were the only species capable of carrying the virus is unknown; however, its effects were only on the human race and possibly some human hybrids.

The Graft virus had a long latency and incubation period (a year or more), with no outward symptoms to tip off the returning troops to the fact that they were carrying it. How exactly the Graft virus spread is unknown in part due to Dominion suppression of information and investigation into its makeup and behavior, but it was contagious enough that with carefully supervised "free" travel throughout Federation and human-inhabited territories, it spread to every known area inhabited by humans.

Once the virus had lived in its host long enough, it began to insert its genetic payload into the human host's genetic code. This code went to work building new neurological structures in the brain, though in a staged fashion that did not "activate" them until they were completed.

The "activation" was the most dangerous part of the actual disease process. The actual moment of the new structures coming online in an infected human's brain could have a variety of results: some "simply" had to confront a sudden influx of information and guidance they were unused to processing, some experienced seizures of varying degrees, and a minority of humans were disabled or killed as a result of activation.

Just as traumatic, however, were the effects of the virus upon society. The hierarchical instinct had dramatic effects upon the organization and conduct of all social relationships, to include familial relationships. Some of the infected committed suicide, especially those who had carried the virus before it was known what was happening, and those who realized they were carrying it but were forced by the Dominion to knowingly infect their peers.

The people of Earth and its settlements eventually fell into a new social order that bore a resemblance, in some fashion, to that of Cardassian society. In fact, when Cardassians were brought in to assume "possession" (insofar as the Dominion granted such authority) of one of the Alpha Quadrant's most populous and troublesome species, they began to discover the subconscious commonality the Graft had brought between them and the altered humans: they found their inborn gestures, tones, and ways of relating to those around them echoed in a way they had never experienced with any other race they had come into contact with. In spite of themselves, certain members of both races began to discover the common ground for friendship--which eventually became common ground for rebellion and the overthrow of the Dominion. Ironically, the very reaction the Dominion had hoped to suppress by introducing the hierarchical instinct came about in some ways because of their actions.

After the overthrow of the Dominion, the altered humans were faced with a serious moral dilemma. Nearly 45 years had passed since the Graft took hold on their species, and two generations had been born knowing nothing else. Given the Graft's effects upon social relationships and individual and collective identity, simply removing it was not as easy an option as it had seemed at the start. Was it right to excise something that had always been a part of them? Should the people of human descent make a corporate decision or an individual one and if separate decisions, would the resulting two species be able to live together or not? Would this outcome be too undesirable to chance?

And what was this species?

The final arguments at the end bear a strong resemblance to the debate surrounding neurodiversity in real life.
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