So there's a language problem. The other day, I described this problem as "one of the oldest conundra of the fantasy genre". Which is, of course, hyperbole; the fantasy genre is older than any of the words involved, let alone the science involved.
The problem is this: in fantasy, we need a word for various groupings of individuals, e.g., elves, humans, orcs, dwarves, halflings, etc. "Race" is the usual one, though "species" sometimes gets used. But both have meanings in English, and neither meaning lines up very well with their usage in works of fantasy.
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Once upon a time, not really very long ago at all, "race" meant the same thing in fantasy as it does in modern English, but the meanings have diverged.
Nowadays in English, "race" means something like "ethnicity" or "skin color". We've got the "black race" and the "white race" and so on, and the various races are almost entirely indistinguishable, genetically. Even phenotypically, most human races are hard to tell apart, and individuals from one race are usually within the expected range of variation for every other race.
An orc and an elf are much more dissimilar than a dark-skinned human and a light-skinned human, so "race" has become an inappropriate term for this distinction.
Moreover, we might want to keep "race" in case we want to distinguish between fantasy ethnicities -- e.g., Men of Gondor, Men of Rohan, the various Men of the East and South under Sauron's dominion. Or, for that matter: Orcs of Mordor, Orcs of Isengard, and Orcs of Moria. Or Mirkwood Elves and Lothlorien Elves. And so on. Tolkien's actually pretty good about ethnicities/subraces/whatever.
Or take my setting's distinction between Shell humans, Omorashi humans, and Romus humans. (Side note: I was horrified the other day when I realized that I had neglected to include dark-skinned humans in my campaign setting. Then I realized that no, many or most Omorashi humans have dark skin -- the one way in which the Omorashi Empire deviates from a bog-standard
wutai.)
Though, really, "ethnicity" does just fine for this usage, and I'd be completely okay with discarding the word "race" from the language -- both mundane and fantastical English -- altogether.
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"Species" is sometimes used as a backup, but it has an even more specific meaning than "race" does. Two individuals are members of the same species if they can breed and produce fertile offspring. The "half-dragon" template alone means that all living, corporeal creatures are the same species as True Dragons. Dragons and gelatinous cubes are the same species! This is of course a.) preposterous and b.) not useful.
Actually, there's another, slightly more technical meaning of "species". Basically, reckon how much DNA two individuals need to have in common in order to produce viable offspring. A species is any group that has that much DNA in common. This almost could work, if you use the percentage from our world (it's a very high percentage), but you then stipulate that D&D genetics works very differently and can produce viable offspring with a much lower percentage of DNA in common. So dragons and gelatinous cubes are different species but can interbreed.
But this hurts my head by how badly it misunderstands basic biology. Not least because D&D biology pretty clearly, if not quite explicitly, doesn't run on DNA at all. (See: Living Spells, elementals, and most or all Outsiders (created, not biologically, but from the very stuff of their native planes).) There's no way for DNA to do half the things that happen with genetics in D&D. Better to leave it out and say a wizard did it. And if we're leaving out Earth biology, we should leave out the jargon of Earth biology.
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So what's left? There are lots of options, many of which have been used. But I'm partial to one that dates back roughly to the time period D&D attempts to emulate but which hasn't since acquired a technical meaning -- or, really, any meaning at all (which comes up when creationists try to use the word without realizing how meaningless it really is). The word is "kind".
Elves and humans are different kinds. Omorashi humans and Romus humans are the same kind. Mordor orcs and Isengard orcs are the same kind.
If you want to get really technical, you could also throw in superkinds and subkinds. Orcs, goblins, and hobgoblins are different kinds, but the same superkind. Arctic orcs and aquatic orcs are the same kind but different subkinds. Humans, elves, halflings, dwarves, and gnomes are the same superkind but different kinds. And so on.
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We can even set up a fairly complete D&D taxonomy!
Kingdom: distinction between creatures and objects. A creature is anything with a wisdom and charisma score (other ability scores optional). An object is
anything without a wisdom and charisma score.
Subkingdom: You can further differentiate between living and non-living objects, allowing you to be old-fashioned and make the distinction Animal, Vegetable, or Mineral. Normal, mundane plants and trees, as well as
slimes, molds, and fungi, are living objects. Rocks and things are non-living objects. (Fun fact:
disintegrate has no effect on living objects, only creatures and non-living objects.) You can also distinguish nonliving creatures (constructs, undead, deathless) and living creatures (all other creatures).
Supertype: One wants to put things like "canines" and "felines" in, but there are e.g. feliform Animals (cats, lions), Humanoids (catfolk, gnolls), Magical Beasts (displacer beasts, sea cats), Outsiders (rakshasas, hellcats), etc. So this is an example of a supertype. Since "Humanoid" is taken for a type, perhaps we shall use "anthropoid" as a Supertype to describe anything with two arms, two legs, a head, and a torso.
Type: Aberration, Animal, Construct, Dragon, Elemental, Fey, Giant, Humanoid, Magical Beast, Monstrous Humanoid, Ooze, Outsider, Plant, Undead, or Vermin. (Only creatures have Types.)
Superkind: Among Humanoids: reptilians, goblinoids, near-humans, gith-s, etc. Among Outsiders: demons, devils, archons, guardinals, etc. Among Elementals: fire, water, air, earth, etc. Among Constructs: golems, living constructs, etc. Among aberrations: Illithidae, beholderkin, etc.
Subtype: Some subtypes actually indicate kind (e.g. [human], [elf]). Some indicate superkind (e.g. [reptilian], [goblinoid].) Some are merely descriptive and can be possessed by any or many Types (e.g. [aquatic], [extraplanar], often the alignment and elemental subtypes). Some indicate relationship to some other Type (e.g. [dragonblood], [augmented]). Subtype, while useful, pertains to too many levels of the taxonomy to really be included. BUT, I want to include Tanar'ri, Obyrith, Baatezu, etc, and there's not really anywhere else to put them. So let's put them, probably bafflingly, below superkind.
Kind: Among near-humans: humans, elves, dwarves, etc. Among animals: horses, dogs, etc. Among tanar'ri: succubus, balor, etc.
Subkind: Arctic elves, fire elves, aquatic elves, etc. Ponies, war ponies, horses, war horses, etc. Dogs, riding dogs, etc.
This is incredibly messy, not even very useful, and unlike biological taxonomies (where there is a single correct taxonomy that can be derived from sufficient information), it's mostly a matter of opinion. It was just an exercise.
