I know that Vulcans and Romulan come from the same parent race. But beyond that, how did they branch off? For how long they have been apart? Are they more different than human and chimps? Can they breed?

  • Romulans tip better – Hack-R Nov 30 '16 at 23:44

The Romulans separated from the Vulcans during the Time of Awakening (4th century AD, Terran Calendar).

They are still the same, biologically, and can interbreed. This means nothing in the Star Trek universe, as pretty much anything can breed with anything.

Romulans have several differences from Vulcans. They are subtle, but enough to prevent Crusher from treating Patahk successfully with a technique that works on Vulcans. In that episode it was discovered that Romulans actually have a high degree of compatability with Klingons, enough that a Klingon treatment worked for the Romulans where the Vulcan treatment failed.

Edit: To answer your other question, they are likely more closely related than humans and chimps, though this can't be guaranteed (radically different environments are one of the biggest causes for rapid evolutionary change, though this may be mitigated by a heavily technological society).

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    To add to the Klingon/Romulan compatibility there was also the episode where Worf's blood could have been transfused into a dying romulan. – Xantec Sep 16 '11 at 18:17
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    "I would rather die than pollute my body with Klingon filth!" – Jack B Nimble Sep 16 '11 at 21:32
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    It seems to me that the Romulans and Vulcans probably separated much earlier than the 4th century CE. Gambit indicates that 2000 year old ruins on Baradas III were built by the Debrune, who were a Romulan offshoot. Thus the Romulans separated from the Vulcans a long time before the 4th century CE. long enough to have offshoot cultures. – M. A. Golding Sep 24 '18 at 19:42
  • @M.A.Golding - Star Trek takes place around 2260 (at the earliest). If the Debrune separated from the Romulans within a generation of the Time of Awakening, that would give time for their initial structures to be 'around 2000 years old', given that the approximations for 2+ millennia tend to be rounded by decades. And when a stable society splits, the group which leaves the stable society is more likely to further splinter in the next few years, not decades later. So that doesn't invalidate the 400 CE date. – Jeff Sep 24 '18 at 20:50

Whilst her history was never fleshed out canonically, Saavik was described to be half vulcan, half romulan, confirming that inter-breeding is possible.

According to the novels and comics, Saavik was born on Hellguard, an abandoned Romulan colony. She is half Vulcan and half Romulan. (A line of dialogue that would have revealed this in The Wrath of Khan was edited out prior to the film's release and never restored; as a result, the canonicity of this piece of information has been debated for more than two decades. It does, however, explain her somewhat emotional behavior in that film, though she adopted a more proper Vulcan demeanor in later appearances.)

(As pointed out in another answer, Spock is the product of a human/vulcan relationship and if that's possible, it's logical [sorry - couldn't resist!] to suggest that inter-breeding between two much more closely related species is possible. In fact, they're more "tribes" than species.)

The separation of Romulans was, if memory served, caused by those who didn't want to follow the teachings of Surak deciding to leave Vulcan, eventually arriving on Romulus (and Remus).

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    Later episodes of Enterprise mention medical advancements being made allowing interspecies breeding. Terra Prime comes to mind: en.wikipedia.org/wiki/Terra_Prime – Chad Levy Nov 14 '11 at 9:45
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    A split at fourth century A.D is not really enough time for any evolution to occur in the modern scientific sense of the word. The only plausible explanation for a significant biological difference, is if there was genetic engineering occurring. – Jacob Aug 12 '16 at 7:51
  • @Jacob I would say 10+ generations in an alien environment completely isolated from the rest of the Vulcan population would provide plenty of opportunity for noticeable genetic drift to occur. – chepner Aug 13 '18 at 17:29

Well, as to the breeding question, it has been established that both Vulcans and Romulans can cross-breed with humans (Spock is the product of Human/Vulcan and Tasha Yar had a daughter by a Romulan). And it would be reasonable to assume Humans are less close to either race than they are to each other, therefore I'd think they should certainly be able to cross-breed Vulcan <> Romulan.

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    This is Star Trek. If the plot called for it, Tholians would breed with Cardassians, and the kid would be raised by the Gorn. – Jeff Sep 16 '11 at 18:09
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    @Jeff I look forward to seeing that race. – Xantec Sep 16 '11 at 18:14
  • A split at fourth century A.D is not really enough time for any evolution to occur in the modern scientific sense of the word. The only plausible explanation for a significant biological difference, is if there was genetic engineering occurring. – Jacob Aug 12 '16 at 7:52

While the two species split off only 2000 years ago "as of the TNG era", they have many genetic differences. For example, the foreheads are often different, and many diseases have different effects.

While under normal conditions, they would be near identical, the Romulans were founded by only a limited offshoot population of the Vulcans. After that time, they were extremely isolationist for 2000 years "Enterprise info", and as a result, contact with Romulans was extremely limited, to the point that most Federation people had no clue what they even looked like. Based on this, I'd say that very few new members were added to the genetic pool. On top of that, the star that Romulus orbits underwent a supernova, so it's a pretty safe bet that prior to that incident, it churned out an above-average amount of radiation for a long time, which means a higher mutation rate. So we have an extremely isolated population with an increased mutation rate, so it's a safe bet that evolution would be slightly accelerated in this case. Based on that, it's possible that the difference between the two species could be approximately that of humans and neanderthals.

  • What are the chances that radiation caused any sort of beneficial mutation? non-beneficial mutations would surely have been seen as a deformity, decreasing chances of breeding... and even if there was, there would surely be a majority that did not exhibit mutations. (Or didn't you know, as a general rule hot people only date hot people). 2000 years is not enough generations for a non-beneficial mutation to propagate across the entire population, (i.e., for the genetic traits of the original "hot people" to die out) – Jacob Aug 12 '16 at 7:57

Its never fully adressed and the addition of the green and brow ridged Romulans and the taper off of all the green skin on vulcans just complicates things. orginally in tos you get the impression that Vulcans are greenish and Romulans are brownish making it even more confusing. My best guess is they are more like homo-sapian Idaltu compaired to homo-sapian sapian a only slightly less evolved subspieces or one that had better adapted to vulcan depending if vulcans are native to vulcan or ancient colonists of a now lost race. this would make romulans a little more then a racial group like almost if not a subspecies which would explain it.


Adding to the above, our present understanding of biology includes "Haldane's Rule", which says roughly that for species with sex chromosomes, the gender with the "odd" (in practice, truncated) chromosome is the one that gets hammered worse in interspecies crossbreeds: Less chance for survival (before and/or after birth), and infertility. For Earthly mammals, the affected sex is males with their Y chromosome. This is particularly visible among felines, with crossbreeds such as ligers.

So one would expect that male hybrids among the STU humanoids would be less common than female (due to fetal and early deaths), and likely infertile. On the other hand, much of this could be handwaved by futuristic medicine.


In "The Chase" we learn that many of the Alpha Quadrant species are related to a proto-humanoid species that seeded various planets with genetic material. These species included the Romulans, Klingons, Humans, Kardassians and we can assume others (Vulcans). It would stand to reason the genetic similarities amongst these species would be greater than species from outside of this population. Therefore, Romulans would share a greater family resemblance with Vulcans, but it would not be overly bizarre to have crossbreeding between any of these species.

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Recall in the STOS episode -Return To Tomorrow- Sargon speaks of Henock as being "from the other side" in the contest that devastated their planet; Spock spoke of certain aspects of Vulcan prehistory being explainable as ancient colonization by explorers from Sargon's planet.

Perhaps there were two different species or subspecies making these colonizations together; the more agressive "Othersiders" and the peaceful "Sargonites." The "Sargonites" interbred with some protovulcans, the "Othersiders" with others, starting a diverging genetic line developing different features and prone to a more marshal philosophy.

This culminated in the more violent tribes breaking away from Vulcan during The Time of the Awakening and ultimately founding Roumuls.

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