This series is intended to help writers brainstorm the elements that go into creating convincing aliens*. It can also be applied to creating convincing nonhuman fantasy creatures, artificial intelligences, and so on.
My science fiction novel, Absence of Blade, is set in a universe where humans are only one of many intelligent species, who maintain an uneasy coexistence in a complex web of interstellar relations. I pushed the creative envelope by making the lead characters members of a nonhuman species, the Osk, and narrating large sections of the novel through their eyes. To do so effectively, I had to create characters with relatable emotions and inner lives who were nonetheless distinctly alien.
Part 1: Biology and Ecology
Creating convincing aliens starts with establishing a well thought-out biology and ecological niche for your alien species. The more thought you put into an alien’s basic biology and environment up front, the less chance you’ll end up contradicting yourself and dispelling the aura of verisimilitude around your invented species once you begin to write. Taking the time to make notes on your critter’s biology and environment will also help you start thinking about the ways your aliens differ from humans in their worldview, culture, and society, which saves time when you’re developing these details later.
Where to begin defining an alien’s environment? Try starting with the big picture: did they evolve on a planet? While that’s definitely the place of origin most ready to hand, it’s far from the only possibility. Take Robert L. Forward’s Cheela, the arguable protagonists of his novel, Dragon’s Egg: the Cheela are flat, wormlike entities who evolved on the surface (and in the crushing gravity) of a neutron star.
Taking an environment that is extreme or seemingly inhospitable to life and imagining what kind of creature could live there is a great way to create really alien aliens like the Cheela, or the sentient hydrogen clouds of Fred Hoyle’s novel The Black Cloud, which evolved in the cold wastes of interstellar space.
If you do decide your aliens evolved on a planet, start thinking about their potential ecological niche. Do they dwell on land, in the oceans, or in floating cities? Do they prefer a narrow range of environments, or are they generalists like humans? Are they herbivores, carnivores, or omnivores? Or perhaps that doesn’t apply at all–maybe they draw sustenance from inorganic sources, by photosynthesis or metabolizing hydrogen sulfide from deep ocean vents. Try looking at terrestrial examples for inspiration: Earth possesses stunning biodiversity, and there’s no reason to believe alien species wouldn’t be just as diverse.
Of course, if you’re like me, you may have thought up your alien’s basic biology before considering the environment that spawned it. That’s okay! In this case, you can work backward from what you know about your species to imagine the environment that gave rise to it. When applied to a work in progress or in the late outlining stage, this method can also help you spot inconsistencies in your species’ design that don’t make sense given their environmental niche.
What Not to Do: Human with a Coat of Paint
Unless there’s a conscious reason for it, avoid creating aliens that are very similar in appearance to humans or other Earth animals. This can come off as lazy worldbuilding because your readers are likely aware that a “space” version of an existing animal is very unlikely to be discovered.
An exception to this rule is if the author is consciously writing humanoid aliens for reasons relevant to the story. Ursula K. LeGuin’s Ekumen universe concerns several different societies of humanoids who are implied to be offshoots of our own species, but who possess varying biologies and cultures that she uses as a vehicle for commentary about our own society.
Similarly, aliens who look nonhuman but think or behave exactly like modern humans probably won’t pass muster with your readers either. I’ll explore how to create convincing nonhuman worldviews and cultures in Part Two.
*I use the term “convincing aliens” rather than “realistic aliens” because at present humans have never made contact with an alien species. It’s disingenuous to comment on what a realistic alien would be like, biologically or socially. However, for the purpose of writing fiction, we can make certain assumptions about the beings that might evolve from a given ecological niche that provide a foundation for creating a convincing nonhuman ontology.