At least thats a explaination.

@Otokichi786 :✌: I couldn't have said it better myself. Bravo!

@Otokichi786 said:

In the "Star Trek: The Next Generation" episode, "The Chase," a common Alpha quadrant ancestor is discovered when disparate DNA strands found across the area produce a holographic last message. So, the Klingons, Cardassians, Romulans/Vulcans. and Terrans are the result of ancient space farers seeding the quadrant. Thus, Vulcan/human coupling is "all in (distant branches of )the family." While not as disturbing as "Philip J. Fry" being his own "grandfather," it's "love your Neanderthal DNA" time in the Alpha quadrant.

So within Star Trek or at least TNG, there might not be any such thing as bestiality. But that's just within the TV show. And until that episode, there was no reason to believe there was any such genetic connection between the various races/planets. (Sargon suggested that his ancestors might have been responsible for the Vulcans, and hence perhaps the Romulans. But not humans. And The Preservers apparently seeded some worlds including Miramanee's. But nobody knows how many others, or specifically which ones.)