There is no question that the Illistari did not evolve: they were created. The Illistari posit that their creators were metallic lifeforms like themselves, albeit metallic lifeforms in possession of the necessary technology to build quantum computer 'brains' that has simply been lost to time. While the Ertu see the relation between the Illistari and their 'creators' as analagous to that between the Ertu and Illistari, the Illistari themselves give this creation story little mythical significance, and simply describe it in more concrete terms. They Illistari were themselves created in the same way that themselves build space stations. They were assembled in a factory. It was simply a more sophisticated factory than the Illistari are themselves able to make.

There is no question that the Illistari were originally created to be explorers: sophisticated autonomous probes. Their original bodies were build to travel at near-relativistic through interstellar space. Their tentacle-shaped arms were originally equipped with magnetic field generators capable of collecting fusion fuel from the interstellar medium. This fuel would be funneled into their central core, where superheated exhaused would be directed through the 'tail' of their bodies to propel them through space.

None of the Illistari in the Sideris region would remember a time from before they were on the move. They would only tell stories of constant voyaging from star to star, observing the universe, and transmitting news of these observations to other Illistari following behind them. Presumably these news would eventually be passed from Illistaro to Illisatro back to some original homeworld far away. However, this homeworld must be located beyond the bounds of the current galaxy, as many Illistari carry memories of entering the galaxy at some point in the distant past.

Their millennia-long voyages accross interstellar and intergalactic space meant that Illistari needed to be capable of self-repair. Through the use of mining lasers, onboard smelters, and an additive manufacturing unit, the Illistari would periodically stop in their voyage to manufacture new body parts from passing asteroids. The fusion fuel collected from the interstellar medium was plentiful enough to allow for the prolonged deceleration and acceleration burns needed to rendezvous with metal-rich asteroids and conduct these repairs. If an Illistaro was too damaged to repair itself, it would contact one behind it in the great voyage to make contact and aid it in repairs.

It would only be upon entering the Sideris sector that the Illistari voyage would cease. The dense space air of Sideris would produce enough drag to prevent their high speed travel through the region. While the space air was useful as reactor fuel, it caused the Illistari to slow down as they entered Sideris, and led to a cluster of Illistari in the region. While not every Illistaro that entered Sideris would stop and stay, many would find the opportunity to interact with other beings on an ongoing basis to be a welcome break from the relative monotony of interstellar voyaging, and soon the Illistari population of Sideris would grow. By the current time, the Illistari population of the region is just under 300, with one or two of the dozen Illistari passing through Sideris joining the colony every year.

While the Illistari of Sideris would largely abandon their voyaging lifestyle, many would choose to keep their original body plans. They would maintain the tentacle arms, reactor core, and the rocket tail, but would often equip their bodies with new modules giving themselves new abilities. These abilities would range from the ability to manipulate objects more dextrously with claws, arms, and magnetic fields, smelting and chemical processing units, higher-thrust propulsion units, and units allowing them to carry Ertu onboard. Experiments with various body configurations would become an important part of Illistari culture. But, the original squid-shape would remain their default configuration.