Fantasy and science fiction have a very thorny relationship with the concept of essentialism.
I’m not going to claim this problem is unique to the speculative genres; you also see an even more problematic form in mimetic (i.e. real-world) fiction. But before I attempt to unpack that, let’s make sure we’re all on the same page with regards to this word.
Essentialism begins with the idea that something has an essence, a distinctive core. In and of itself, there’s nothing wrong with that; when we say “sharks are predators,” it’s a pretty accurate statement. The issues crop up when you try to apply this idea to other kinds of targets. Racism, for example, rests in part on the assumption that different ethnic groups have some inherent essence which distinguishes them from each other. When you hear someone say that “black people are lazy” or “Asians are good at math,” that’s essentialism at work. It strips away all the context and variation and tries to posit one or more baseline qualities shared by all members of that group, simply by dint of their membership in that group. When I say this shows up in mimetic fiction, that’s what I mean: sometimes stories replicate the essentialist assumptions we’re struggling with in the real world.
If you’ve watched shows like various Star Trek series, you’ve probably seen this in speculative action. Alien species often get presented in very essentialized ways: the Klingons are warlike, while Vulcans are uber-logical. In part this is because a TV series that showcases a new alien species every week doesn’t have a lot of time for nuance . . . but it still leads to a style of worldbuilding where humans are uniquely varied and diverse (a claim often made even when the “diversity” on display is predominantly white, male, able-bodied, and so forth). Our distinguishing cultural characteristic, under this approach, is our lack of a distinguishing cultural characteristic.
This idea isn’t just me reading into the text; in various editions of the Dungeons and Dragons roleplaying game, it’s even been codified as an actual part of the mechanics. If you want to play an elf or a dwarf or a half-orc, the rules mandate certain changes to your base stats and “racial abilities” you gain as a result of that heritage. Some of those are understandably biological, like the ability to see well in dim light, but others are purely cultural: being an elf means your character is proficient at using a longbow, and never mind if she’s never touched one in her life. Meanwhile, humans get a stat boost to put wherever they want, and their racial abilities take the form of other free bonuses to be assigned at will. One sourcebook says outright that “Humans are the most adaptable, flexible, and ambitious people among the common races […] humans are quick to master specialized tasks and varied in their talents […] humans are versatile and capable.”
Part of the reason we wind up with this kind of worldbuilding, in fantasy especially, is because of the genre’s relationship with folklore and mythology. It feels entirely natural to say that dwarves are hardy and good at crafting and able to hold their beer because, well, that’s what a dwarf is. The concept may mutate as it travels through layers of fictional adaptation, but the seed that tree grew from had a very distinctive — dare I say, essentialized — nature.
Folklore and mythology are not generally in the business of nuance. When you encounter a dwarf in Germanic tales, the story is not concerned with the full psychological actualization of that particular dwarf, his childhood ambitions and unspoken anxieties, much less with the complexity of dwarven society. There are dwarven smiths and dwarven warriors, but precious few dwarven schoolteachers or janitors or exotic dancers. Once you start supplying them with all those details and variations . . . pretty soon you’ve got very short humans with a preference for beards. And that doesn’t feel very fantastical.
Which is why I say fantasy has a thorny relationship with essentialism. (Science fiction, too, but there it’s more often a matter of narrative convenience than source material.) Labeling a sentient species with a handful of characteristics apparently possessed by all members of that species leads us in some uncomfortable directions — and a great deal of fantasy over the last few decades has gotten fodder out of problematizing those depictions, giving us asshole elves and sympathy for orcs. But when we do that, we lose some of the mythic feeling the genre is capable of.
I don’t think it has to be all one or the other; you just have to use your essentialized elements in the right places. In the Pathfinder games I’m playing in (that being an incestuously near cousin of D&D), we have an agreement that any sentient mortal race native to the Material Plane has human-style complexity and variation. Forget this business of assigning moral alignments to them as a species: being chaotic good or neutral evil is a matter of culture and individuality, not anything inherent to the species. But when the scope broadens to outsiders like angels and demons, or other immortal creatures like fey . . . they’re a different matter. Certain things do come with the territory of being a demon, and any demon who manages to jettison those becomes something else entirely.
So one key to making this work is paying attention to the context of the group in question and asking: does it make sense for them all to be inherently X? Any group living the normal kind of life where there’s farming and weaving and trade and crying babies (or hatchlings or whatever) is going to feel really flat and one-dimensional if you tell me they’re all honorable warriors with anger management issues . . . but if they’re a deity’s enforcement squad sent down from heaven to smite wrongdoers, I can roll with it just fine.
Similarly, you have to ensure that the essentialized groups are not metaphorically standing in somehow for human diversity. This works in two directions: first, if you’ve got a wide range of human types, then it won’t feel like “human” = “white European” (or any other group, but it’s usually white Europeans) and all other parts of our world are escorted outside the bounds of that category, relegated to inhuman status. And second, if you’re inventing a fantastical creature, make very sure that you don’t set them up to seem like an analogue of a real culture, e.g. “in my setting, Chinese people are elves!” It’s one thing to write about Chinese-derived creatures — that becomes a matter of “do your research” — and another thing entirely to Other and essentialize human Chinese culture as something alien.
It still may be tricky. Our taste right now runs very much toward verisimilitude, meaning that we want to see the kinds of complexity that exist in our own lives, unless we’re reading a story whose overall tone is very mythic or folkloric (or surreal). But I think there’s room for both that and the pure, singular power of an idea given manifestation in the world. Creatures of benevolence or malice, mischief or rigid order; blacksmiths and tree-huggers and wise old teachers; walking personifications of war or fear — these can be wonderful breaks from the recognizable messiness of human nature.