...Unless we make the presumption that some of the humanoid species are either subspecies, or belong to the same genus.
That works for Vulcans/Romulans and MAYBE Humans/Betazeds. We already know the Vulcans and Romulans have a common origin and one might be able to make a case that the same is true with Humans and Betazeds but when you look at species like Human-Vulcan or Human-Klingon or Andorian-Vulcan or Cardassian-Bajoran, forget it. Notwithstanding the scientific illiteracy of some of the posters here, we know how genetics works and we know that natural hybrids between such disparate species is impossible. Even genetically engineered unions are hard to see.
TNG-The Chase was a nice effort to try to fix the mess they created. Unfortunately, the writers either didn't understand how evolution works or they underestimated the scientific knowledge of the typical Trek nerd.
