The Trill were a species first introduced in an episode of Star Trek: The Next Generation; this species later re-appeared, and was given fuller treatment, in the Deep Space Nine characters of Jadzia Dax and Ezri Dax. I’m trying to put together the “facts” about the Trill and their culture as revealed in the Star Trek series. The following sums up what I know/remember on my own. Assistance from any Doper Trekkies, either with corrections or additional info, is greatly appreciated!
(1) The Trill are a “joint” species, consisting of sentient humanoids (“hosts”) and a sentient “symbiont” beings which are carried inside the hosts.
(2) A symbiont must be “joined” to (implanted in) a host in order to survive; however, a Trill humanoid does not require a symbiont to survive.
(3) Therefore, “joined” Trill would seem to constitute a minority (though perhaps a sizeable one) relative to the un-joined humanoids.
(4) While the host has the lifespan typical of other humanoid species (roughly that of humans, presumably), the symbiont can and usually does live much longer than any single host. Thus a given symbiont will have lived through several/many humanoid lifetimes in several different humanoid hosts.
(5) The symbiont has an inherent personality of its own, but also carries with it the cumulative experiences, memories and personality elements of its humanoid hosts.
(6) Upon joining, the humanoid host has access to the experiences and memories of the previous “incarnations” of the symbiont, and over time will imprint his/her own distinct personality on the symbiont. The resultant personality of the joined trill is thus a merging of the individual host personality with the cumulative personality of the symbiont.
(7) For this reason, a potential host undergoes rigorous training and psychological evaluation, to ensure that the host’s inherent personality is strong, well-established and capable of successfully integrating the symbiont without being overwhelmed in the process. It seems important for the current humanoid host to be the dominant, though not domineering, personality after joining. (Note: this host-symbiont balance was presented differently in the original TNG episode, where it was stated several times that the host was “just a shell”, and demonstrated that the symbiont’s personality was dominant.)
(8) Because of (3) and (7), it is considered a high honor among the Trill to become “joined”. Joined Trill have names reflecting their humanoid and symbiont identities. For instance, Kurzon Dax, Jadzia Dax and Ezri Dax were three successive joinings of the symbiont known as “Dax”.
(9) Symbionts are joined to new hosts only when the current host has died. (Or are they sometimes forcibly removed when something “goes horribly wrong”? That is, does a joined Trill have an inviolate identity which can no longer be forcibly separated into symbiont and host without irreparable harm?)
(10) Humanoid hosts are male/female gendered, and can mate and have offspring as any typical humanoid, whether joined or not.
(11) Symbionts do not appear to have gender, nor is it clear how – or if – the symbiont itself can reproduce in any fashion. (Or is it?)
(12) Newly-joined trill are discouraged from continuing, or seeking out, ties to family, friends and associates of the previous host, but rather are expected to move forward with the new life in the way established by the host (hence, in part, point (7)). This is not exactly a taboo – Jadzia Dax re-establishes the friendship Kurzon Dax had with Captain Cisco, and Ezri Dax is posted back to DS9 after Jadzia’s death – but it certainly a strong injunction, for reasons which Ezri’s situations with both Worf and Julian demonstrate. (Note: this too was presented differently in the original episode; all three incarnations of Odan had strong romantic feelings for Beverly Crusher, and we see no signs that it is considered “bad form” for Odan to express these feelings to Beverly in all three joinings. Again, this episode suggests that it is the host who is just “along for the ride”.)
That covers the basics of what I know and/or remember. Contributions great and small are welcome.
Thanks!