R. Star wrote:
They're all subspecies of whatever that lady in "The Chase" was
Pretty much, yeah (use of the same actress notwithstanding) - or Preserver. For the most part, it would appear that, with some minor biological divergences like organ placement and skeletal-muscular configuration, most "major" humanoid races can interbreed in the Trek universe. We've seen Vulcan/Human (Spock), Vulcan/Romulan (Saavik), Romulan/Human (Sela), Klingon/Human (K'Ehleyr, Torres), Klingon/Romulan (the myriad kids from "Birthright"), Cardassian/Bajoran (Ziyal and tons of Occupation Children), Betazoid/Human (Troi), etc., etc. and so on.
While I'm not a biologist, it would definitely seem that all these different-yet-similar races are subspecies of the female humanoid from "The Chase" and are, for the most part, genetically compatible.
What I find most fascinating (and amusing), is that we see the torture and general ridicule that Spock endured at the hands of his classmates and other members of both Vulcan and Human society throughout his life, yet Sela seems to have been so completely accepted into the Romulan social structure, that she attained a high rank and command of her own, and at a far younger age than Spock did. One could almost think that the Romulans were far more socially and psychologically developed than the Vulcans OR Humans were. I also find it intriguing that they both shunned their Human half quite thoroughly in addition to being treated oppositely by the cultures they embraced. For that matter, while I despise Nemesis as a film, that same acceptance applied in the Reman culture to Shinzon. He didn't even have Reman or Romulan DNA like Sela, yet he was fully accepted by the Remans and feared and respected by the Romulans alike. Based on early Vulcan attitudes towards Humans in Enterprise, I cannot ever imagine seeing any Human child having been fully accepted like that on Vulcan, much less hold any kind of position of authority in their society.