How To: Creating Aliens in Science Fiction Writing

Contributed by Dave Robertson

 Photo credit: Andrew Collins

Photo credit: Andrew Collins

The Background

For years, science fiction gave us aliens that were upright, bipedal beings that looked like variations of humans. Some were small and green, some had pointed ears, but they looked very much like humans. Those “aliens” were made to look like that for a variety of reasons. For television or movies, putting makeup on a human was much easier and more cost effective than trying to create, make, and animate a creature. The second reason was that moviegoers could still identify facial expressions if an alien was just a human actor with make up. That made it a lot easier for everyone from writers and actors to producers. But if you’re creating a race of aliens for your next sci-fi epic, you can do better than modified bipedal people if you think of biology and evolution.

The Science Behind Us and Potential Aliens

Have you ever wondered why so much health research is done using mice? It is because humans and mice share 95% of the same genes. Yep, change 5% of what makes us human and you’ve got a small rodent. So what are the chances that half way across the galaxy, in another solar system, with entirely different DNA, the creatures look basically human? Not likely.

Applying the Science to Your Alien Characters

So, how do you create an alien race? First consider their biology. All life forms have to take in, digest, and expel nutrients. They all have to interact with their environment in some way; they need to see, feel, or smell what’s around them. They need to have some sort of nervous system to process what they sense.

If you are creating an advanced race that can fly a spaceship, and fire weapons, they need some way of holding and manipulating objects. Consider that there are a number of ways these functions could be carried out and human anatomy isn’t the only model.

For example, a human has a fairly simple stomach that typically holds about a liter of food, while a cow has a complex, four part stomach that can hold up to 25 gallons. Both provide the same basic function, but the two creatures could never look similar, based on their biology. A bee has two antennae, three simple eyes, and two compound eyes. They see many more frames per second than humans and can see polarized light. Bats use a form of radar to echo-locate obstacles and prey. Humans have two eyes, each with hundreds of small photoreceptors.

There are a number of ways that an alien creature might sense its environment and that would affect its physiology, its appearance, and its behavior.

For example, If an alien race received most of its sensory information from its sense of smell, it would deal with humans very differently. It is known that humans release different chemicals based on their emotions. We would be unable to deceive or lie to those aliens about what we were thinking or feeling!

Humans have what is called “external bilateral symmetry”. We have a left leg, and a corresponding one on the other side, a certain number of ribs on one side, matched by the same number on the other side. If you drew a line from your forehead down to the ground, right down the center of your body, all the main structures and appendages on each side match the ones on the other side. There is no telling whether an alien would have such symmetry. There might be biological reasons for a lack of symmetry or their world may not even have symmetry. No central nervous system? radial symmetry? Prehensile body parts? Creatures on Earth have all these diverse qualities, why wouldn’t a distant race be at least that different?

Another consideration is the type of environment where your aliens live or evolved. Creatures adapt over time to survive in their environment. Monkeys have adapted light, strong bodies and long arms to live and move in trees. If they were to live in a more open environment, like the savannah, they would be too weak and slow to avoid predators.

But, here’s a more extreme example: there are organisms on Earth that live hundreds of feet below the ocean’s surface.The pressure down there is massive and light doesn’t reach those depths. These creatures live near hydrothermic vents in the ocean floor where superheated sulfides and metals are released into the ocean. The temperatures there are 200-300 degrees, beyond boiling. The water only remains liquid because of the incredibly high pressure. It’s dark down there, extremely hot, and full of what we might consider toxic chemicals. Yet these organisms thrive and survive there, living off the hydrogen sulfide. They have adapted to a very extreme environment.

There is another category of creatures on Earth called scotophiles, creatures that live in complete darkness. In the darkness, they cannot see, but neither can the predators. Consequently, they do not develop any of the bright colors or natural camouflage that other creatures have. Instead these species, over time, undergo a process called troglomorphy. Their eyes diminish or disappear, they lose their pigmentation and become colorless, pale, or even translucent, their appendages get larger and they develop long antennae to sense their environment. In short, they look the way they do because of the conditions they live in. Your aliens should too.

When you’re creating an alien race think of the conditions where they would live and thrive. What unique biological traits would they need? Think of their biological processes. Do they get most of their sensory input from their eyes? antennae? Do they echo-locate like bats? What kind of nervous system or digestive system do they have and how would that change the way they look? Look at the diversity of life right here on Earth and make your aliens at least that different.

About Dave Robertson

Dave Robertson is a writer living in the big sky country of Montana. He writes advertising copy, articles, and web content to pay the bills and fantasy, horror, and science fiction to exercise his brain. His latest novel, Strange Hunting II is available on