Tora Ziyal, a female Bajoran / Cardassian hybrid
A hybrid is the end result of mixing two different species in the biological process of reproduction.
Because of the common genetic ancestry of most of the species of the Milky Way Galaxy by way of the ancient humanoids, many species are able to interbreed with or without the help of genetic technology. In fact, Humans and Vulcans are quite similar. (TNG: "The Chase"; ENT: "Demons")
There can be unexpected consequences to interspecific relations and as such, it was a researched topic. Starfleet Academy taught Interspecies Protocol and the Ktarian Doctor Mizan was an expert in interspecies mating rituals, known for his "empirical research." (TNG: "Timescape"; VOY: "The Disease") One should note that there can be certain difficulties involved in reproducing between species, even humanoid, for anatomical reasons; for instance, not all species keep their genitals in the same place. (Star Trek VI: The Undiscovered Country)
In some cultures, children who are born as a result of interspecific relations are rejected by the society of both races. For example, Bajoran / Cardassian hybrids were often rejected by both Bajorans and Cardassians. (DS9: "Indiscretion", "Return to Grace") Klingons referred to hybrids derogatorily as "mongrels". (VOY: "Barge of the Dead", "Prophecy")
Examples of interspecific reproduction 
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Betazoid Edit
- Betazoid / Human (Deanna Troi, Kestra Troi, Devinoni Ral, Anita Pierce, Walter Pierce)
- Betazoid / Tavnian (Lwaxana Troi's and Jeyal's son) (DS9: "The Muse")
Cardassian Edit
- Cardassian / Bajoran (Mika and Dukat's child, and Tora Ziyal) (DS9: "Covenant")
- Cardassian / Kazon (Seska and Culluh's child) (VOY: "Basics, Part I", "Basics, Part II")
Seska also seemed to think Cardassian / Human cross breeding was possible, as she attempted to have Chakotay's child.
Gilora Rejal apparently made the same assumption when she expressed interest in Miles O'Brien.
Human Edit
- Human / Angel I native (the crewmembers of the Federation freighter Odin were mentioned to have fathered children with the Angel I inhabitants) (TNG: "Angel One")
- Human / Boraalan (Nikolai Rozhenko and Dobara's child) (TNG: "Homeward")
- Human / Betazoid (Deanna Troi, Kestra Troi, Devinoni Ral, Anita Pierce, Walter Pierce)
- Human / Cardassian (implied above)
- Human / Daliwakan (The Gigolo) (VOY: "The Cloud") (only a hologram, but presumably possible)
- Human / Denobulan (Denobulan child on future Enterprise) (ENT: "E²")
- Human / Ikaaran / 2 unknown species (Karyn Archer) (ENT: "E²")
- Human / Klingon (K'Ehleyr (medical help was needed (TNG: "The Emissary"), B'Elanna Torres, Miral Paris, Alexander Rozhenko)
- Human / Ktarian (Naomi Wildman, Sabrina) (VOY: "Deadlock", VOY: "Endgame")
- Human / Napean (Daniel Kwan) (TNG: "Eye of the Beholder")
- Human / Ocampa (Linnis Paris, Andrew Kim) (VOY: "Before and After")
- Human / Romulan (Sela, Simon Tarses)
- Human / Skagaran (Bethany) (ENT: "North Star")
- Human / Terrellian (Human corpse) (ENT: "Future Tense")
- Human / Trill (Yedrin Dax, Lisa, several others) (DS9: "Children of Time")
- Human / Vulcan (Spock, Elizabeth, Lorian, Spock (alternate reality), Spock (mirror))
- Human / Xyrillian (Trip Tucker's pregnancy; it should be noted, however, that he was more of a carrier than an actual, biological parent) (ENT: "Unexpected")
- Q has implied that a Human / Q hybrid is possible (TNG: "True Q"; VOY: "The Q and the Grey") He also stated that the Q could breed with, or as, any species because of their godlike abilities.(citation needed • edit)
In an initial story outline of TOS: "Charlie X", Charles Evans was referred to as a Human/Ferndok hybrid, since his mother was a Ferndok (a species which, during the episode's development, was later renamed Thasian).
According to the original script of TOS: "Who Mourns for Adonais?", interbreeding between Humans and the Greek god species is also possible, as Carolyn Palamas got impregnated by Apollo. However, this was cut from the actual episode, but was later used in the Star Trek: New Visions comic Of Woman Born. The 31st century time-traveler Daniels stated he was "more or less" Human, meaning he could be a possible hybrid.
Klingon Edit
- Klingon / (Betazoid / Human) (Shannara and Eric-Christopher, alternate timeline children of Worf and Deanna Troi) (TNG: "Parallels")
- Klingon / Human (K'Ehleyr (medical help was needed), B'Elanna Torres, Miral Paris, Alexander Rozhenko)
- Klingon / Trill (not possible without medical help; individuals never appeared, as Jadzia Dax was murdered soon after confirmation that such a pregnancy was possible) (DS9: "Tears of the Prophets")
- Klingon / Romulan (Ba'el and several other prisoners in the Carraya IV colony) (TNG: "Birthright, Part I")
Ocampa Edit
- Ocampa / Human (Linnis Paris, Andrew Kim) (VOY: "Before and After")
- Ocampa / Talaxian (although they decided not to, Kes and Neelix seemed to imply it was possible for them to have a baby) (VOY: "Elogium")
Romulan Edit
- Romulan / Human (Sela, Simon Tarses)
- Romulan / Klingon (Ba'el and several other prisoners in the Carraya IV colony) (TNG: "Birthright, Part I")
- Romulan / Vulcan (Saavik)
In the novel The Ashes of Eden, Kirk discovered the colony world of Chal, a planet briefly colonized by the Romulans and Klingons during an alliance, populated by genetically-engineered Klingon-Romulan hybrids.
Talaxian Edit
- Talaxian / Mylean (Neelix's great-grandfather was Mylean) (VOY: "Scientific Method")
- Talaxian / Mylean / Vulcan (Tuvix, was caused by a transporter malfunction with hybridizing flowers) (VOY: "Tuvix")
- Talaxian / Ocampa (implied above)
Trill Edit
- Trill / Human (mentioned above)
- Trill / Klaestron (Benjamin Sisko briefly assumed that Ilon Tandro was the son of Curzon Dax and Enina Tandro) (DS9: "Dax")
- Trill / Klingon (referenced above)
Vulcan Edit
- Vulcan / Human (Spock, Elizabeth, Lorian, Spock (alternate reality), Spock (mirror))
- Vulcan / Talaxian (seen above)
In the first draft script of Star Trek III: The Search for Spock, another Vulcan/Human hybrid, called Galt, was to have been introduced.
It may be assumed that a Vulcan and Romulan would be able to breed due to their common ancestry. The production notes from Star Trek: Enterprise state that the creators were planning to reveal T'Pol as a Romulan/Vulcan hybrid if the series had continued. In this case, her baby with Trip would be 1/4 Romulan, 1/4 Vulcan and 1/2 Human. Saavik was intended to be half-Romulan in Star Trek II: The Wrath of Khan, but a scene establishing this was cut.
