C.E. Evans wrote:
I think in the Star Trek Universe, most humanoid species are compatible. Some more than others, some less. I think real difficulties occur between humanoid and non-humanoid species (like the Horta, Species 8472, and other life-forms that aren't even remotely humanoid in shape or genetic structure (say, non carbon-based).
Dude, you're speaking about a subject you obviously know absolutely nothing about. That is never a good idea. If you have no problem with impossible creatures on Star Trek, that's fine but don't try to argue that they are actually believable. Hybrids are flat-out impossible outside of being genetically engineered and grown in a lab. That is not an opinion.
Unless we make the presumption that some of the humanoid species are either subspecies, or belong to the same genus.
For political reasons this would NEVER be acknowledged (as we saw in "The Chase"), but IRL we have the example of the Felidae for successful, viable interspecies breeding within the same family (and in a couple of cases across genus lines). A serval-house cat hybrid has actually been established as a viable breed of pet, and without any genetic manipulation whatsoever. The offspring, known as Savannahs, are healthy and fertile.
I would not think all Trek species would be compatible, by any means.
But, in terms of believability, I would actually believe a Cardassian-Bajoran child more readily than a human-Vulcan one. If we consider Cardassians to be therapsids and NOT reptilians, and interpret onscreen evidence to suggest that they have iron-based blood, then compatibility there makes more sense than expecting two entirely different blood types to actually mate successfully unless heavy genetic manipulation is involved (which may explain why Spock had almost nothing human about his outward appearance).