Trill

Kell Perim, a Trill Female in 2375

The Trill, or Trills, were a humanoid species native to the planet Trill. A small percentage of the Trill population co-existed with a sentient symbiotic organism known as a symbiont inside their bodies. The resulting joined Trills had personalities which were a synthesis of the two beings including the memories, and to some extent the personalities, of the previous hosts of the symbiont. This way, the joined being gained all the skills and occupations of the previous hosts. As late as 2367, the fact that some Trills exist as a joined symbiotic species was widely unknown, even to Federation scientists. (TNG: "The Host")

## Physiology

Most Trills are distinguished by two rows of spots going down each side of their bodies, from forehead to toe. Their skin color could vary. One of the main neurotransmitters in the Trill brain is isoboramine. (DS9: "Equilibrium") Joined Trills are also extremely allergic to insect bites; the biochemical connections between the host and symbiont cannot tolerate the reaction caused by the insects' venom. (DS9: "The Siege") It may be noted that Trill are known for having cold hands. (DS9: "A Man Alone")

The few Trills that are given a symbiont are typically joined in their early- to mid-twenties. The physical process of being joined is irreversible. Once joined, the host and symbiont are dependent on each other after ninety-three hours. If the symbiont is removed from the host, symbiont and host will die within hours, even if they are otherwise healthy, unless they are reimplanted with another host or symbiont. (DS9: "Dax", "Invasive Procedures")

The brain of a joined Trill has two cerebral nuclei and two different brain wave patterns. Julian Bashir compared them with two linked computers, which both work for the same task, in 2369. (DS9: "Dax")

## Society

The Trill were a space-faring race by the early-23rd century, at which point Trill could be found visiting Vulcan. By the 2240s, they could be found on Earth, and by 2257, it wasn't unusual to see a Trill on Qo'noS. (DS9: "Destiny", "Trials and Tribble-ations", DIS: "Will You Take My Hand?")
Despite the relatively unusual nature of being a joined species, that aspect of their culture was not widely known until 2367, when the Odan symbiont had to be given a new host during the middle of tense negotiations on Peliar Zel. Such a public example of the dual nature of the Trill brought to the forefront what had previously been a very private matter to Trill for several millennia. (TNG: "The Host")

In contrast to the greater revelation of their nature, the Trill are not a secretive species. To them, the joined nature of their culture is normal and not something they would think to comment on without prompting. Indeed, joined Trills can be seen as particularly genial and many have served the Federation as distinguished ambassadors, including Odan and Dax.

Jadzia Dax joked that Trills don't look for romance the way Humans do. Joined Trills consider it quite a nuisance and view it as a weakness of the young. While hosts may have romantic feelings as often as any other sentient species, symbionts try to live on a higher, more spiritual plane and try to rise above those sorts of temptations. (DS9: "A Man Alone")
Trill law forbids re-association between subsequent hosts of joined persons, whose symbionts were romantically involved in their previous hosts, and the people who the previous hosts were romantically involved with. This is because the main purpose of the transfer of symbionts is to experience new things in life. Trills who are found guilty of re-association are expelled from Trill society, meaning that their symbionts die with their current host. (DS9: "Rejoined") Beyond the illegality of it, Trills almost universally view re-association as a cultural taboo, but the degree to which they follow it is up to the individual. Some Trill take it so far as to not associate with any of their previous hosts' friends, family and colleagues, beyond the rare chance encounter. Others have a very narrow interpretation, and freely associate with the friends and acquaintances of their previous hosts & symbionts, avoiding only those with whom their previous hosts were intimately involved.

The Trill are a technologically advanced species and the Trill Science Ministry is a leading center of learning and experimentation. (DS9: "Rejoined", "In Purgatory's Shadow")

## Joining

On average, only three hundred symbionts are available for hosting each year and about a thousand Trills apply for joining. Because there are many more humanoid Trills than symbionts, prospective hosts are weeded out by a demanding selection procedure, overseen by the Symbiosis Commission. (DS9: "Equilibrium") The competition for the few symbionts is fierce and attracts the brightest and most highly motivated of Trill society. Often, the would-be hosts excel in their chosen fields and it is not uncommon for them to hold several degrees or distinctions prior to their joining. Prospective hosts may eventually become initiates under the supervision of a field docent, a joined Trill who evaluates the prospective host's suitability for joining and makes a recommendation to the Commission. A negative recommendation usually means the initiate is cut from the joining program. (DS9: "Playing God")

Common belief in Trill society holds that only one in a thousand Trills make acceptable hosts. In fact, this figure is vastly understated, and nearly half of the Trill population is capable of being joined. The myth is perpetuated very carefully, though, in order to avoid widespread chaos which would probably arise if the information were made public, since the symbionts would become, essentially, objects to be fought over, as people fought to gain the few prized symbionts. (DS9: "Equilibrium")

Unless the joined Trill objects, a prospective host may request a specific symbiont. If a host is weak, the personality of the symbiont will overwhelm it. Joined Trills have several tools at their disposal for dealing with various aspects of their previous hosts. The telepathic ceremony of zhian'tara allows a current host to divest the symbiont of the personality and all the memories of a previous host, which are temporarily hosted in volunteers. The transferring process is performed and supervised by a symbiont Guardian, an unjoined Trill telepath. The ceremony creates a chance for closure by having the new host address the previous hosts directly, as a means of distinguishing their voices and cementing the sense of finality of its latest transition. Similarly, the Rite of Emergence can focus the voice of a single previous host among the memories of the other, allowing for a more direct conversation in times of need for the current host.

The zhian'tara ritual is roughly similar to the Vulcan fal-tor-pan ritual, since both enable the respective species to perform a synaptic pattern displacement, the transfer of what could be considered as a soul (katra, pagh, etc.). (DS9: "Invasive Procedures", "Facets", "Field of Fire")

### Trill Symbiont

"She came to visit me on Trill and I was still a little confused. When she walked into my room, I put on a big smile, looked her straight in the eye and said, 'Hi, Mom, it's me, Curzon.' Things kinda went downhill from there."
– Ezri Dax, 2375 ("Prodigal Daughter")

A Trill symbiont was a sentient vermiform lifeform from the planet Trill. They primarily lived symbiotically inside hosts of the humanoid species Trill, also native to the planet. Through the experience gained from multiple hosts, many symbionts gained distinguished reputations from other species as Trill. Also as a result, they were long-lived compared to most humanoid species, and could easily live beyond 550 years.

## Physiology

The Trill symbionts were teardrop-shaped and could swim in their natural pools, such as the Caves of Mak'ala. The symbionts communicated with each other via electrical impulses transmitted through milky water that they inhabited. They also had a limited form of communication with certain Trill while not joined. (DS9: "Equilibrium")

A Trill symbiont joined with a new host through a surgical procedure in which it is placed in the abdomen, where it developed a connection through the narrow part of its body to the host's body. Once a symbiont was joined for over ninety-three hours, the symbiont became dependent on its Trill host and vice versa; the Trill would die within hours without a symbiont, and the symbiont could not return to the Caves of Mak'ala (if joined for the first time) nor survive a significant period of time outside of a host. (DS9: "Dax", "Invasive Procedures") Assuming that a symbiont survived a host's unexpected death away from Trill, it would be removed and stabilized for medical emergency transport back to Trill to be joined with another appropriate host. However, if the symbiont's condition deteriorated to the point that it would die en route, the only way to save its life would be joining with the closest non-joined Trill. (DS9: "Tears of the Prophets", "Shadows and Symbols")

After and during joining, symbionts took with them all of the memories of their previous Trill hosts so, upon joining, the new Trill host gained those memories. The brains of the symbiont and host were able to communicate, and, indeed, did not function separately. Analyzing the brain wave patterns of the symbiont separately from the host was possible, and, to a degree, the symbiont's patterns do not change significantly from host to host. (DS9: "Dax")
Although Humans could be used as a host to a symbiont, the symbiont could not remain in their bodies for long without physically harming the Human host. (TNG: "The Host") A symbiont could survive normally in a partly Trill host, however. (DS9: "Children of Time")

## Society

The Trill symbionts relied on the Trill to survive through hosts. The Symbiosis Commission oversaw the joining of the vermiform symbionts and humanoid Trills. Through the Commission, the symbionts were cared for by Trill Guardians and implanted only into Trill that had undergone a rigorous testing process, ensuring the new host had a high intelligence, balanced personality, and would not reject the symbiont. (DS9: "Dax", "Invasive Procedures", "Equilibrium")

In the 24th century, about 500 symbionts became available for joining, each year, compared to approximately 5,000 Trill becoming initiates per annum. The relatively low quantity of symbionts resulted in Trill society hiding from their general populace the fact that virtually 50% of the population was suitable for joining, and the general belief in the 24th century was consequently that only one in every 1,000 Trills was suitable for joining. (DS9: "Equilibrium")
ntil the mid-24th century, it was not widely known that Trill were actually a joined species, as it was considered a private matter. New hosts often had to produce false stories as to why he or she had certain memories of previous hosts. This true nature became known to the United Federation of Planets in 2367, when Ambassador Odan's male host at the time died, forcing the Commission to send a new host, Kareel, to the USS Enterprise-D for joining. Beverly Crusher became the first Starfleet doctor to learn and perform the process. (TNG: "The Host")