Star Trek Guide

Star Trek Discovery Theory: How A Human Can Be A Trill Host

Star Trek: Discovery season 3 has introduced Adira, a human bonded with a Trill symbiont — but how is that possible? The crew of the USS Discovery are finally living up to the franchise's promise to take its stars "where no one has gone before." They've been blasted into the 32nd century, a quasi-dystopian future where the Federation has declined after a mysterious calamity called the Burn.

Star Trek: Discovery season 3, episode 3 is a first for the franchise. It introduces a new crew member in the person of Inspector Adira, initially one of a number of Earth Inspectors who board the Discovery. The character is actually played by Blu del Barrio, the first non-binary actor cast in Star Trek. What's more, it swiftly becomes clear there's more to Adira than meets the eye; she recognizes Discovery's antique technology, and is so curious about the spore drive she sabotages the ship to ensure she can't be forced to transport out. Eventually she reveals she's something the crew of the Discovery have never encountered before — a human bonded to a Trill symbiont.

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While Discovery's crew were familiar with the Trill, they didn't even know they bonded with symbionts, so the whole thing comes as something of a surprise to them. But how is this possible?

Trill and Symbionts Explained

The Trill are a humanoid species who originate from the planet Trill, and they have developed a symbiotic relationship with a species of vermiform common to their homeworld. It's a mutually beneficial relationship, with the symbionts gaining the experience of many lifetimes, while the host can grow through accessing the skills and memories of previous hosts. There are far fewer symbionts than there are Trill, and not every Trill is compatible; the joining is therefore traditionally overseen by the Symbiosis Commission, who carefully police the process for fear of the symbionts being seen as prizes to be competed for and fought over.

The Trill had joined Starfleet by the 23rd century, but they initially kept their symbionts a closely-guarded secret; as revealed in John Jackson Miller's canon novel Die Standing, they even avoided using transporters for fear bio-scanners would identify something strange about them. Starfleet learned the truth in the 24th century, after an incident aboard the USS Enterprise told in the Star Trek: The Next Generation episode "The Host." The Trill were featured prominently in Star Trek: Deep Space Nine, with the Trill Jadzia Dax serving aboard the station. Benjamin Sisko was apparently one of the few Starfleet officers to be aware of the symbionts before "The Host," as he had built a strong friendship with one of Dax's previous hosts.

Humans Are Not Traditionally Compatible With Trill Symbionts

"The Host" reveals Trill symbionts can indeed bond with humans, but it's hardly a pleasant experience. In "The Host," viewers were introduced to the Trill diplomat Odan, who was critically injured during an attack on a shuttlecraft. This led to Dr. Crusher conducting a medical examination of Odan, and she discovered the Trill symbiont. Dr. Crusher realized the symbiont would die without a host, and Riker volunteered, allowing himself to become the first known human to join with a symbiont. The joining was successful for a time, with Riker able to continue diplomatic talks, but the strain ultimately proved too much for his body and he collapsed. Fortunately a replacement Trill host arrived in time to save the symbiont from death.

Viewers have generally taken this to indicate Trill symbionts cannot join with humans without significant risk, but the truth may be a little more complex. It's important to remember less than half the Trill themselves are actually compatible with the symbionts, and thus there's no reason to assume the same is not true with humans as well. While Riker was not compatible, that does not mean there are no other humans who can join with a symbiont. Even if he is in fact the rule, there can quite easily be exceptions to it.

How Did A Trill Symbiont Remain On Earth?

The Trill are a curious race, hungry for new experiences and reveling in discovery and exploration. They are therefore perfectly suited to service in the Federation, and it wouldn't be a surprise to learn that most of the active hosts wound up pursuing careers in Starfleet (like DS9's Jadzia, and later Ezri, Dax). Unfortunately, that may well have had tragic consequences when the Burn happened, and most of the dilithium in the galaxy was suddenly rendered inert. Many hosts and symbionts would have died in the resulting catastrophes, as warp cores breaches and ships exploded. Those who survived would have been stranded, unable to travel back to their homeworld of Trill. Their hosts would have aged, and ultimately died. The symbionts would have been unable to survive if they did not find a compatible host.

It's reasonable to assume this is exactly what happened with Adira's symbiont, which was apparently previously joined to Starfleet Admiral Senna Tal. It's unclear whether Senna Tal was a high-ranking Trill who was stranded on Earth, or whether he was actually a human; whatever the truth, Adira's symbiont eventually had no choice but to bond with a human. This particular joining appear to have been a lot more successful than Riker's, given it has apparently been sustained for 12 years, since the Admiral's death. But it is not without its own complications, because Adira struggles to access the memories of previous hosts, something that comes easily to Trill.

Trailers for Star Trek: Discovery season 3 showed the symbiont pools of Trill, suggesting the crew of the USS Discovery will come up with a simple way to access the memories of Admiral Senna Tal; they will take the symbiont back to its homeworld. It's too soon to say what that will mean for Adira; will she let her symbiont go, or will they be bonded again, finding a better union as a result of Trill meditative exercises? Whatever the answer may be, it looks as though the story of this symbiont will be a key one this season.

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