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The Linkers is a human-Mother collaboration/conspiracy to combine the species. It was begun when the Radical Unificationalists encountered humans and began to think about integrating them into the web; they contacted a few likely human prospects and slowly the organisation developed.
The main idea is that humans and Mothers should be able to link together cybernetically, becoming of similar mind. Not necessarily joining into a groupmind like Unity, but at least becoming a Grandmother Mind. Views differ on how far the symbiosis can be taken, but the interest is high for exploring the possibilities.
The Linkers have their own moveable homebase placed somewhere in the human sphere, a typical Mother fractal city/ship/complex called Base Human. A large section has been devoted to a biotechnology lab and around 40 humans live there. The group has other people on many planets, promoting its ideas or secretly undertaking various experiments. Here Nova bionics, Arcadian biotech and Mother nanotechnology are combined to develop radical new implants and modes of thinking.
One problem is that the organisation, being dominated by Unificationalist Mothers and radical humans, doesn't act openly with many of its experiments (basically, the group doesn't quite get normal human psychology). Understanding that some humans would dislike them, they instead make secret experiments and keep the existence of the organisation secret. Over time, as the Li affair develops, this approach forces them to more and more subterfuge, making it ever harder to act openly given all the dirty deals the group has been involved in.
Another problem is schisms: the Li is a bit too ruthless for many members, and they either protest or try to back out. Being security-minded and not very individualistic the Linkers will try to neutralise them by giving them a modified Li that makes them loyal to the Linkers.
They have some front organisations, such as PsychoTechnologies United at Dionysos and the Wuntai Trade Organisation at Penglai.Most presence is at Nova (where the two or three unities involved handle things; they have not yet informed Unity as a whole about their involvement), Penglai and New America, but there are agents on Arcadia, Atlantis and Dionysos.
The Linkers are years ahead of everybody when it comes to neuronano, the molecular remodeling of the human brain. The Mediator-Atlantean cooperation is much less driven, given that the Mediators prefers to let the humans do the actual research, they just provide nano know-how and will in the end reap the profits. The Linkers are much more ambitious.
Basic neuronano can go into the brain and break or make new connections at specific places. Getting exact locations right is hard; most fine work is best directed in a lab setting using advanced scanners, but simpler operations (or operations where the neurons have some detectable properties) can be done "in the field" - the nanodevices are injected, they drift into the brain, crawl to their destinations and do whatever they need to do.
The Li was discovered by accident, as a neurosurvey found a cluster of neurons in the limbic system that appeared to be linked to social emotions. The Linkers tested modifying it, and found that it caused people to become loyal to something; the target could be tuned in various ways. This was the basis for the Li, although the original use was mostly intended to test if humans could get the Mother family loyalty.
Switch on-switch off: Neuronano can even create switchable changes, producing options for how the nervous system reacts or ways of testing changes. The switching can be run using a neurocomputer, chemical signals or even linked to certain mental states.
Li immunity: a precaution against the Li. The Li nanite is built to recognise certain triggers, which makes it go dormant. This can prevent it from infecting a person, although it cannot help somebody already infected. This is of course a weak point in the nanite, but it is unlikely humans can figure out the trigger given the obfuscated design of the Li nanite. Linkers in the field also often have nanoimmune systems.
Nanotech neurointerface: a neurointerface far beyond the best Unity interfaces, using nanotechnology to interface the human brain with a computer. This is the main thrust of research at Base Human, and much Unity-derived hardware and psychological software is used in translating human mental representations into Mother-representations and vice versa.
Human-Mother chemical adaptation: a nanodevice system in the bloodstream, skin and gut that neutralises the harmful chemicals in the Mother environment and makes it possible for humans to live long periods in their vicinity.
Killer nano: something the Linkers can do but have so far not found a reason to use. By combining neuronano with replication and a DNA-detection sense it can be turned into a fearsome weapon. The nanodevices are simply spread around, replicating slowly using certain local materials and waiting until the right DNA sequence appears - at that point they spring into action, get into the brain and either kill using a subtle haemorrhage or perform some other nefarious effect. Then they dissolve. This weapon can be directed towards individual people or groups of people, being completely safe for everybody else.