Humans dressed up?
When you think of alien life in science fiction, what comes to mind?
For me, the first thing is how aliens are depicted in fiction. The vast majority of aliens we see on the screen just happen to be humanoid. Maybe differently-proportioned, certainly various colors of skin or fur, interesting prosthetics adorning the head, but still fundamentally a person dressed as an alien. Yes, Star Wars and Star Trek, Avatar, and even Alien, I’m looking at you.
With the entire universe at our disposal, to be as inventive as we can manage, is this really the best we can come up with? Of course, one obvious explanation is that the aliens on screen are (almost) all played by actors, who are shamelessly humanoid.
The situation tends to be more varied in writing, freed from the constraints of having to fit a person into the costume, but even they tend to be fairly limited, basing body forms heavily on Earthly mammalian, reptilian, or insectoid species. When authors (particularly old sci-fi classics) stray from these parameters the go-to fallback tends to be amoeboid blobs that the author explicitly makes a point of stating defy description. Read: insert your own exotic picture here because I can’t do it for you.
But the other thing that comes to mind for me is frustration at this narrow perspective. I’ve already touched on a major reason for on-screen aliens to be largely humanoid, but there’s no reason for writing to be so limited. To be fair, some sci-fi authors have been extremely inventive, and a lot depends on the kind of story you’re trying to tell.
Physical appearance
It’s up to you how far you want to depart from familiar Earthly models. It’s worth thinking about where you want to sit on the familiar/exotic spectrum, because this will have a major influence on some aspects of your writing.
Clearly humanoid, maybe with interesting skin shades and maybe odd protrusions if you’re feeling really adventurous, keeps things simple. One line of thinking from early sci-fi goes that because an alien planet is close to Earth-like conditions, the dominant species will inevitably mimic humans. A brief glance at the immense variety of life on our one (Earth-like, by default) planet should show the fallacy in that thinking. So if you’re going with widespread similarity it’s worth having some kind of explanation in your backstory.
The next step into strangeness usually patterns aliens on familiar non-human forms. Cat people seem to be popular, as do lizards and insect forms. Advantage of this approach: it clearly escapes from the hard-to-explain humanoid body form, while still being easy to describe because readers have a close-enough image in mind. Of course, as a writer you’ll be careful to say they are beetle-like without actually being beetles.
Beyond that, you can go to town on body plans. E.E. Doc Smith’s Lensman series merrily committed the logical fallacy of Earth-like conditions implies near-human people, and often used the “too hard to describe” cop-out, but at the same time he was inventive in other species. The Rigellian barrel-like body with domed head, and four equally-spaced mouths, tentacles, and legs, and the wheelmen come to mind. This requires greater effort and imagination but allows you to escape the Earthly comparisons altogether. On the down side, you have to put more effort into descriptions with no clear parallels to draw on.
At the end of the day, if you envisage a technological species you need to figure out how their body plan supports a technological society. Tool use, for example, must be physically possible.
Then you can find ways to blur the need for a well-defined body. The self-organizing plastic nanites in Tanya Huff’s Peacekeeper series are a good example. Or maybe the life form is somehow inextricably woven into its environment: semiconductor veins running through bedrock, filaments (like fungi) running through the ground, chemical gels and protein scaffolding permeating the ocean … there are lots of ways to envisage sufficiently complex self-sustaining systems that could qualify as life, and that could even support intelligence. Extreme examples in sci-fi include life manifesting as or birthing in stars: Frank Herbert’s Whipping Star, and E.E. Doc Smith’s Masters of the Vortex.
Alien life can run the spectrum from familiarity to almost impossible to comprehend. It all depends on what you want to dominate your story.
Chemistry … and related topics
Earth life is based on carbon, with a small cast of major chemical players and many trace elements performing specialized roles. It’s hard to imagine coming up with a radically different mix with complex enough interactions for life to form. If you’re heavily into chemistry and want to stay true to hard science you could certainly have a go. Or if you’re writing at the soft end of the spectrum you can imagine life based on other elements (such as silicon) and hand-wave over the details. It helps if you give some thought to chemical realities. For example, a silicon rather than carbon backbone would probably be more credible in a high-temperature environment.
Even if you stick with carbon-based life, there is nothing to say it has to be anything like ours. Does genetic material have to use DNA? Are there alternatives to proteins to catalyze reactions? Who’s to say that an alien atmosphere would be breathable for humans, or that any food would be compatible? You can play around with all sorts of details that will have profound implications for the story.
Sources of energy
In day-to-day thinking, we’re used to dividing the living world up into plants and animals. Plants are typically immobile and get energy from sunlight. Animals eat other living things. Of course, even on Earth it’s not so simple, and people will belatedly acknowledge fungi, but science currently recognizes five or six kingdoms. So you might consider bypassing the simple “if it’s not a plant, or if it moves around, it must be an animal” classification. John Wyndham’s triffids come to mind.
So, do your aliens eat? Drink? In anything like a way we’d recognize? Or does energy come from sunlight (like plants) or some more unusual source such as heat?
Summary
How far you depart from cozy familiarity depends on what you want to evoke in your story. One of the biggest advantages of the Star Wars/Star Trek approach (body shapes that conform to easily-describable Earthly parallels, compatible chemistry, etc.) is that it gives a touch of the exotic without strangeness dominating the story. This is great for space opera where you want to develop the plot and the characters without too many interruptions.
If you’re aiming for hard sci-fi, though, it pays to give these aspects some thought. If you stick with human-compatible humanoids then it’s all the more critical to have a decent rationale in your back pocket.
Ian S. Bott, Writer and artist 