Disadvantages [of the biological species concept, which defines a species as a reproductively isolated community]:
• Exceptions exist, different species sometimes do interbreed … Captain Kirk?
Like on one hand it’s charming that the professor is trying to connect the concepts of the material covered in class to popular culture but on the other this reference doesn’t actually illustrate the concept because Kirk just slept with aliens, he wasn’t a human-alien hybrid, and genital compatibility does not necessarily indicate general reproductive compatibility, especially not when offspring have to be considered reproductively viable for the definition to hold.
Captain Kirk is a good example of prezygotic isolation not existing between humans and assorted alien species, but to demonstrate that postzygotic isolation doesn’t hold true some alien lady would have had to present him with her half-human offspring. Did that ever happen in TOS? I don’t think it did, but my knowledge isn’t encyclopedic.
(Spock would have been a much better example of a rare hybrid event making the biological species concept a little suspect, although as I recall he had to be engineered in vitro? So there’s postzygotic isolation again.)
Really, no matter which species concept you espouse, the evidence suggests that speciation is a process and not a hard boundary, which makes rare hybrid events not really that much of an issue for the BSC, IMO. But then, I’m a partisan of it, so… yeah.