While humanoids across the galaxy theoretically share a common remote ancestor, from what I remember each species has evolved convergently towards humanoidness by different routes. So we end up with Humans that have iron based blood vs. Vulcans with copper based blood; Klingons with three lungs and eight chambered hearts, etc for other species. These species all look similar outside, but are very different inside.

Has any episode of any ST series ever attempted to explain how these fairly different genomes can intermix usefully? vs. being a nonstarter like a shark and a dolphin hybrid (similar body design, radically different evolutionary background and genome)?

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    As far as I can tell "they all were seeded from Progenitor race" is as much of an explanation as you get from ST canon. Jun 18, 2012 at 20:23
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    It is an interesting Q, especially with the iron vs. copper blood. I would think that would make Vulcan/Human hybrids far less viable - if even possible - than say, Human/Cardassian or Human/Klingon. Makes me think of how the Mass Effect series touched on a similar topic, with the Turians and Quarians having a different base chemistry than the other species of the galaxy.
    – eidylon
    Jun 18, 2012 at 20:53
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    I seem to remember there was a brief discussion about the difficulty/impossibility of interspecies breeding in ENT: Future Tense (2x16), when a corpse from the future was discovered. And in the episode "Demons" (4x20), when T'Pol and Tucker's hybrid child was introduced.
    – Oliver_C
    Jun 18, 2012 at 21:22
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    In the first series novel, The Final Reflection by John Ford, there are several mentions that interspecies hybrids are purposely done; for example, at one point the main character is listening to Surak talk about Spock's conception. Jun 19, 2012 at 20:28
  • I think as DVK pointed out, the Progenitor race used their DNA seeding technology to ensure DNA based, compatible humanoid life would evolve from different stock ancestors that may have looked completely dissimilar (like Worf's devolved form in Genesis (TNG 7x19)). Not only that, but the Progenitor's DNA must have contained some kind of molecular "clock" that would guarantee the various humanoid races featured in Star Trek would eventually evolve and develop civilizations in lockstep after 4 billion years (well, +/- several hundred or thousand years).
    – RobertF
    Jul 18, 2014 at 13:39

4 Answers 4


Oliver_C's comment is correct.

Starting in "Demons" and Ending in "Terra Prime" we see the failed attempts of human xenophobes to clone a Vulcan Human hybrid. This however is not successful:

Meanwhile, Dr. Phlox scrambles to find a cure for the baby, named Elizabeth (for Tucker's late sister) by T'Pol, who is dying due to defects in the Terra Prime doctors' attempts to reconcile Human and Vulcan DNA. Unfortunately, Phlox is unable to save the girl; the leaders of the soon-to-be-incorporated Coalition of Planets later request to attend her funeral.

In the Enterprise episode "E^2" we meet the alternative timeline captain of the NX-01 Enterprise named Lorian. He is the son of T'Pol and Tucker. He is explained as:

a conception made possible after Doctor Phlox found a way of combining the Vulcan and Human genomes.

This presumably means that the initial incompatibility with the species was overcome. And that Vulcans and Humans wishing to procreate would simply need to see their doctor in order to have success.

This is in contrast to the memory-alpha article on Hybrids, which claims many species are able to interbreed with or without the help of genetic technology. In fact, Humans and Vulcans are quite similar.

Obviously some species are going to be more compatible than others. Bajorians and Cardassians apparently were highly compatible, due to the high number of illegitimate children produced during the occupation of Bajor (I view it unlikely those people sought the assistance of a doctor for procreation).

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    Excellent answer: people like to forget Enterprise, but Star Trek definitely went into the problems concerning cross-species breeding in it.
    – user366
    Jun 18, 2012 at 22:37
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    Don't forget Seska and her half-Kazon child. I vaguely remember an exchange between Seska and the doctor along the lines of "Are Cardassians and Kazon even compatible?", "Apparently so."
    – Izkata
    Jun 18, 2012 at 23:02
  • I didn't forget Enterprise, but I find it contradicts so many of the other canon ideas, Star Trek becomes almost, but not completely untenable. I was trying to keep my answers simple out of trying to avoid the complaints I have been getting on complexity. Jun 18, 2012 at 23:03
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    @Thaddeus Feel free to ask questions about those contradictions. I watched Enterprise before any of the other series (ended up doing all series and movies in in-universe chronological order) and can't recall any contradictions off the top of my head. I'd be willing to take a stab at resolving some of those ;)
    – Izkata
    Jun 25, 2012 at 22:53

No single episode deals with the difficulties or rationality of cross-breeding among the collective humanoid species of the Alpha Quadrant.

The capability of advanced genetic engineering does exist (Dr. Julian Bashir being an example of genetic physical and mental enhancement) but is considered illegal in the Federation. (DS9 episode: "Doctor Bashir, I Presume?").

The ability to customize genetic development between species is obviously possible and has been so since the early 22nd century (hence Mr. Spock, a Human/Vulcan hybrid survives to adulthood) but perhaps is difficult or limited to those with the proper clearances or access to the level of required technology.

While there does not seem to be a proscription to the practice of hybridization between species, we are unclear why there has not been more energy (or air-time) discussing the process and rationale behind why cross-species hybridization is considered acceptable while single species genetic enhancement is less than desirable.

Yes, I do remember the Eugenics Wars, and do not necessarily believe that is the only reason for holding back the technology. Perhaps the simplest reason is also the best. Cross-species breeding could challenge the very nature of natural species development and might be considered undesirable by more extreme members of any species.

Known genetic manipulations include Cardassian/Bajoran, Human/Vulcan, Human/Betazoid, Human/Klingon and despite the preponderance of these hybrids, none of them would be possible without medical/technical intervention since all of these species have significant differences biologically to warrant such intervention. In some cases, significant genetic modifications would be required.


Numerous episodes throughout the different series have attempted to STATE that such compatibilities exist, but they've never actually explained any details of how such things as different-element-based blood could be mixed in a potential hybrid, due to such basically being impossible in real science (the shark/dolphin hybrid concept is an effective one, for demonstrating the core issue).

Basically, no matter how awesome Spock has always been, Human/Vulcan hybrids exist in Star Trek solely because the writers say they do.

  • It would be a good idea to site which episodes that state the compatibility's you are referring to.
    – Monty129
    Jul 18, 2014 at 9:27

There is an episode of Star Trek: The Next Generation in which it is discovered that an ancient human race settled all the planets where humanoids are found. And prior to their extinction, they did genetic experiments that allowed there DNA to drive the evolution of secondary humanoid races from animals species on the planets. So all humanoids in StarTrek are descended from one ancient humanoid race.

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    That was TNG 6x20, The Chase, which was mentioned in the question (although you got some details a bit off - they didn't settle on the planets, they seeded their DNA).
    – Izkata
    Feb 3, 2013 at 6:17

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