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 races 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.
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". One should note that there can be certain difficulties involved in reproducing between even humanoid species for certain, anatomical reasons. For instance, not all species keep their genitals in the same place.
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 are often rejected by both Bajorans and Cardassians.
Examples of interspecific reproduction
- Betazoid / Human (Deanna Troi, Kestra Troi, Deanna Troi (mirror), Deanna Troi (AMU), Deanna Troi (DMU), Deanna Troi (alternate reality), Deanna Troi (alternate), Devinoni Ral, Anita Pierce, Thaddeus Troi-Riker, Kestra Troi-Riker)
- Betazoid / Tavnian (Lwaxana Troi's and Jeyal's son)
- Cardassian / Bajoran (Mika and Dukat's child, and Tora Ziyal)
- Cardassian / Kazon (Seska and Culluh's child)
- 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 / Angel I native (the crewmembers of the Federation freighter Odin were mentioned to have fathered children with the Angel I inhabitants)
- Human / Boraalan (Nikolai Rozhenko and Dobara's child)
- Human / Betazoid (Deanna Troi, Kestra Troi, Devinoni Ral, Walter Pierce)
- Human / Cardassian (implied above)
- Human / Daliwakan (The Gigolo) (only a hologram, but presumably possible)
- Human / Denobulan (Denobulan child on future Enterprise)
- Human / Ikaaran (Karyn Archer)
- Human / Klingon (K'Ehleyr (medical help was needed, B'Elanna Torres, Miral Paris, Alexander Rozhenko, K'Ehleyr Chazmok, Vixis Chazmok)
- Human / Ktarian (Naomi Wildman)
- Human / Napean (Daniel Kwan)
- Human / Ocampa (Linnis Paris, Andrew Kim)
- Human / Romulan (Sela, Simon Tarses)
- Human / Skagaran (Bethany)
- Human / Terrellian (Human corpse)
- Human / Trill (Yedrin Dax, Lisa, Kelly Martin, several others)
- 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)
- Q has implied that a Human / Q hybrid is possible
- He also stated that the Q could breed with, or as, any species because of their godlike abilities. According to the original script of 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. The 31st century time-traveler Daniels stated he was "more or less" Human, meaning he could be a possible hybrid.
- Klingon / (Betazoid / Human) (Shannara and Eric-Christopher, alternate timeline children of Worf and Deanna Troi)
- Klingon / Human (K'Ehleyr (medical help was needed), B'Elanna Torres, Miral Paris, Alexander Rozhenko, K'Ehleyr Chazmok, Vixis Chazmok)
- Klingon / Trill (not possible without medical help; individuals never appeared, as Jadzia Dax was murdered soon after confirmation that such a pregnancy was possible)
- Klingon / Romulan (Ba'el and several other prisoners in the Carraya IV colony)
- Ocampa / Human (Linnis Paris, Andrew Kim)
- Ocampa / Talaxian (although they decided not to, Kes and Neelix seemed to imply it was possible for them to have a baby)
- Romulan / Human (Sela, Simon Tarses)
- Romulan /Klingon (Ba'el and several other prisoners in the Carraya IV colony)
- 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 / Mylean (Neelix's great-grandfather was Mylean)
- Talaxian / Ocampa (implied above)
- Talaxian / Vulcan (Tuvix, was caused by a transporter malfunction with hybridizing flowers)
- Trill / Human (mentioned above)
- Trill / Klaestron (Benjamin Sisko briefly assumed that Ilon Tandro was the son of Curzon Dax and Enina Tandro)
- Trill / Klingon (referenced above)
- Vulcan / Human (Spock, Elizabeth, Lorian, Spock (alternate reality), Spock (mirror), Spock (AMU))
- Vulcan / Talaxian (seen above)
- It may be assumed that a Vulcan and Romulan would be able to breed due to their common ancestry. The production notes from 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.