SFA episode 5 spoilers!!!

We were just introduced to Illa Dax, the latest host of the Dax symbiont, in the most recent episode of SFA, 'System Acclimation Mil'. This has sparked some consternation in certain online Trek circles, because in the Disco episode, 'Jinaal', Adira claimed that is rare for a Trill symbiont to live past 800 years, but not unheard of. The Dax symbiont was born in 2018, so as of 3195 when SFA takes place, the symbiont is 1177 years old, give or take a bit to account for time travel or what have you.

Some thoughts!

in 'Jinaal', the discussion revolves around the Bix symbiont, that was active in the 24th century. The Trill xenobiologist, Jinaal, joined with Bix so that his knowledge of the Progenitors would live on past him and could be passed on to someone worthy of using the information. However, we don't know anything about Bix's hosts.

Jinaal could very well have been its first host, but I don't think that's likely given that it seems unlikely the symbiosis commission would agree to grant a new symbiont to a host simply because he "has some really important information," and "trust me, bro!" More likely Jinaal discussed it with Bix's previous host, and the symbiont agreed that Jinaal's mission was an important one.

Also, not for nothing, but Dax was over 150 years old when it was joined with its first host, so assuming that is standard, even if Jinaal was Bix's first host, it would be closer to 950 years old.

Regardless, it is unusual for symbionts to live to be more than 800. Fair enough. That information comes from Adira, who is joined to the Tal symbiont, so presumably they would know. In the liminal space where Adira meets and is accepted by the previous Tal hosts, one them is wearing a Starfleet uniform from the late 24th century, and it's established that he was not Tal's first host, so Tal is presumably also closing around 800 years of age.

In 'Jinaal' it's stated that Bix and its current host, Kalzara, are both essentially waiting to die, only holding on so they can pass on the knowledge of the Progenitor's power. Kalzara does die, and then Bix is returned to the pools of Mak'ala while be eulogized by Grey and Xi, the implication being Bix did not live much longer.

So, we know:

    • Most symbionts don't live past 800

    • The Dax and Bix symbionts did live past 800, and signs would indicate that so the Tal symbiont did as well.

    • Bix was ready to die when its purpose was finished.

I would venture that symbionts have some measure of control over their natural lifespan. They don't necessarily age the same way other beings, but so long as they're in an environment they can survive in, such as the pools, or a living host, they can survive for many centuries undeterred.

But, after a certain amount of living, symbionts choose to die. And I think that's because of who who their hosts are. In season one of DS9, we saw the recently joined Jadzia explain to Bashir that Trill attempt to "live on a higher plane" and avoid temptation. Obviously that inclination did not last very long for Jadzia, but I think it speaks to the sort of individuals the Symbiosis Commission selects to be joined. Only the best of the best get to join, and most often we see joined Trill as, reserved, high minded, trying to live up to the ideal of their species.

Several of the Dax hosts are a bit different, though. Jadzia had a lust for life that we saw on screen. Even early on, we're told that Curzon was lustful and adventurous. Torias was a test pilot. Emony, an Olympic gymnast who caroused with Starfleet officers. Dax hosts have frequently broke the mold. They go out and they live life, which is not the impression we get of most joined Trill.

So, I think the reason most symbionts choose to not live to 800 years is that they get bored. Their experiences are limited by the sorts of people who make it through the Symbiosis Commission selection process.

The ones who live longer are those like Bix, who have a specific purpose they feel the need to fulfil, or Dax who is constantly going out and experiencing new things. I suspect the Tal symbiont is in that later group, considering three of it's five hosts prior to Grey were all Starfleet officers.

Further, I believe that this could also explain why in the 32nd century, there are not enough Trill capable of joining anymore, as we learned in 'Forget Me Not', despite it being established in 'Equilibrium' that more Trill than it was commonly believed were capable of joining. The symbionts aren't finding the staid, tranquil life of the Trill to be fulfilling any more. They seek out new experiences, and, especially post-Burn when space travel was severely curtailed for 100 years, new experiences were more difficult to come by.