Heh. But if hard science fiction, elves are a "sufficiently" magical technological society, that can genetically-engineer and nano-shift any species at will.Okay, I'm getting a better picture of your position, and I think I see where @Micah Sweet is coming from in response.
I'm not a fan of making all D&D racial traits learned, or cultural traits. I don't think it's a wrong position to take, heck, I just spitballed above about elven environmental adaptation as being a learned trait, at least in regards to specific environments . . . but I do think that there are some racial traits that flow better if thought of as inherited, or species traits.
But it's all a matter of perspective and preference. Elves, dwarves, orcs and all the rest are, of course, not real species but fictional creations based on mythic and literary tropes. They are a way to explore humanity through stereotypes, a way to focus your character concept. So, to view the fantasy races as NOT being distinct biological species . . . that's okay, it's just not my preference.
Sure, you can cast a spell to shapechange or gain darkvision temporarily, and it's not a stretch to say that powerful magic can make those changes permanent. In old-school D&D, there was even a high-level spell called permanence that did just that. So for a group of elves to have a cultural practice of adapting their bodies via magic to their environment . . . yeah, that can work.
Part of the challenge is that fantasy isn't based on scientific understanding, but mythic tropes. The word species is a scientific word and sounds off to some of us when describing fantasy races. And why should fantasy races be limited to our current understanding (or even misunderstanding) of the science of biology and evolution, and of culture and ethnicity? But, we view the game through our modern lens, and basic ideas about species, evolution, culture, and ethnicity play into that. That's why many of us come into this discussion from an almost science fictional perspective. Positing, "What if elves were a biological species on a world a lot like our Earth . . . what would they be like?"
Worth mentioning is inventing new species, like owlbear and tiefling.