As humanity expanded out into space during the Interplanetary Age, spacers were among the first people to make extensive use of wireless neural interfacing technology to link themselves together. This was usually at the level of vehicle crews, allowing members to communicate, send one another images and data, share senses, link to computers, control remote systems and so on.
As time went on, some groups developed software that allowed them to integrate communications and data from all those in the link, giving members the ability to see and so on via their links, in and from multiple points of view, to assist with planning, tactical assessment, organisation, and suchlike. Additional software was used to streamline communications by having certain classes of message received in such a way as to seem to be part of the thoughts of the receiving person rather than something from outside, making responding smoother and more instinctive.
With their increased utility these links came to be active between members of the groups in question for a greater and greater percentage of the time. This eventually reached the point of linkage being maintained even when a member was asleep, and allowed the body of the sleeping person to be remote-controlled in case of need. In many cases this led to the erosion of the walls between the personalities of those involved.
Most groups using this technology disliked this idea of the loss of the self to the link, and took precautions to stop it and preserve their individual personalities. One group, the Silver Collective, a communistic mining and trading group, saw advantages in just the opposite, and worked to totally break down the walls between its members.
Over time software was developed to allow members of their link to share and integrate not just sensory data and impressions over their network, but also memories, ideas, and emotions, in a conscious attempt to link them all into a single gestalt entity - a hive-mind who would allow them to truly implement their communist ideals. A selfless thing, giving their all to the whole, with nothing of importance being lost in the process.
Although there were a good many problems with the implementation of this, and a number of instances of people being entirely lost as their personalities dissolved away into the link, eventually in 1002 A.T., during the Early Federation Age, the Silver Collective succeeded in their goal. They became a hive-mind gestalt entity. Not of a higher toposophic level, but a single massively parallel human being distributed and co-ordinated across many bodies. Not lonely - not created to be so - and also not uncreative, either. Harnessing the power of all of the minds making it up.
The new hive mind, now calling itself the Silver Mind Collective - soon shortened to the Simico - proved to be both stable, and successful. It grew, learning and optimising its networks as it did so, and learning how to incorporate new people - humans, vecs, and others as well as, more importantly, new members born into it - into itself as circumstances required. Eventually it also learned how to reproduce, splitting into smaller gestalts when light-speed lags made maintenance of a single gestalt impractical. The Simico technology and techniques have formed the basis of many of the hive-mind and gestalt entities created since then.
Contact with non-collective members kept most Simicos from becoming solipsists, though some, especially those who were, for whatever reason, more isolated from others, did become so nonetheless.
Over time Simicos have spread across Terragens space. They now exist in a vast range of sizes, from ones with a few bodies to, in some cases, world-sized ones with billions or tens of billions of bodies, though these last are, of course, limited to places where such a large population can live sufficiently close together that light-speed lags do not become a problem. These very large gestalts also seem to show the highest risk of solipsism and stagnation.
The original Simico has long since split and evolved away from its original form, but its descendant groups are still to be found everywhere, as well as other groups using the same forms of technology. Many of them form the crews of large space vehicles, or perform other roles where their particular skills are useful.
Externally, members of most Simico gestalts appear entirely human, apart from their lack of hair which is replaced by a fuzz of hair-like network transceiver antennas that link them into the gestalt as a whole. This is mainly a visual affectation; there are Simico who hide their antennas, while others are or include vecs or other forms.
Some Simico gestalts have, over time, ascended to higher toposophic levels.
Network security is, unsurprisingly, a matter of great important to all Simico. Their networks are heavily protected, by all the methods practicality allows.
The need for such security was especially driven home to them during the Version War, when they generally supported the Standardizationist side, but suffered significant casualties from fragmentation when their mind networks were compromised by a number of new and innovative attack forms. Modifications since then have made such a disaster unlikely to happen again (at least as long as they are attacked by entities of an equivalent toposophic level). But still, they try to avoid complacency in such matters.