Fun With Speculative Biology: What Do Aliens Look Like?

Lee M. Raulin
6 min readNov 21, 2021

One thing that grinds my gears: goofy, stupid-looking implausible alien designs.

Now, I admit that this is my problem, and it’s a bit unreasonable to expect every work of fiction with aliens to present plausible organisms, but… What can I say, I’m a biology nerd.

(I am also annoyed by inaccurate portrayals of space, which is why I adore The Expanse, a show which proves it’s actually possible to make a compelling work of fiction while striving for scientific verisimilitude.)

As philosopher Daniel Dennett puts it, evolution is engineering. It is not a coincidence that bird wings are similar to airplane wings; they both owe their form to the functional requirements of flight. One could imagine an airplane with 10 wings, with little spiky things jutting out from them, and maybe it would be kinda cool… But it would not be aerodynamic, and hence would not be able to fly… And thus a flying creature with such a shape would never evolve in the first place.

However, as per Orgel’s second rule, “evolution is cleverer than you (or I) are”. Because it involves iterative trial and error over deep time, it can come up with solutions even the most imaginative of us probably never would.

However, when many artists try to conceive of an “alien”, they take a form that is familiar, and modify and rearrange it, to make it look obviously “weird” and “alien”…

In doing so, they come up with something that clearly doesn’t look like anything from this world… But would it look like anything from any other world?

I’m very skeptical that these creature would be effective at surviving and reproducing.

This would be like designing a car by taking its obvious external features, and rearranging them, duplicating some, removing others. Like, what if we put the transparent see-through part on the bottom, but removed it from the front? And what if we have twice as many wheels, but sticking out the sides instead of on the bottom? Or just one wheel in the middle?

Wouldn’t that be neat! Well, it would look weird. Could you still drive it?

It looks weird because it’s actually not a good design.

The creatures on other Earth-like planets… Which, given the numbers, definitely exist somewhere… My guess is that, while there would plenty of surprises and weirdness, much of it would be very familiar. I suspect many of them might look very similar to earth creatures… It might even seem as if they were designed by someone who wasn’t very creative.

The reason for that is convergent evolution. There are finite ways to solve any given problem. This places significant constraints on the forms an organism could possibly take.

Shark and dolphin.

Mammal, fish (with or without bones), reptile. On other worlds with aquatic ecosystems, we’ll probably find creatures that look basically like these things.

And they probably won’t have random numbers of eyes in weird locations.

Almost all organisms that move are basically a modified tube, with a mouth on one end, and an anus on the other. There are some creatures, like jellyfish, that, I’m sorry to inform you, use one orifice for both purposes.

But once you have two ends, it makes sense to put all the sensory organs on the mouth end, which, due to the need to move toward food in order to eat it, will be the front end. Hence why heads are a thing.

Creatures that move in an environment in which there is light use light detectors to avoid bumping into things, etc. It helps to have two of them, because because then you can figure out how far away things are.

Why not more? Well, there’s no such thing as a free lunch in evolution, so there’s no point in having extra eyes unless they offer an advantage, which, generally, they don’t, except in some special cases. Also, as that answer points out, “it’s much easier to accommodate extra eyes in an exoskeleton than it is to make new eye sockets in a skull”.

So I saw this little guy, from the second installment of the incredible game series Subnautica:

Obviously an alien penguin. We can tell it’s an alien because it has extra eyes, and its mouth is in the wrong place and sideways.

Seems like an example of the goofy, different-just-to-look-weird style of alien. But I thought about it and decided to give it the benefit of the doubt.

Well, it’s horizontal when in the water and vertical on land, and it apparently has adaptations to accommodate that. The eye part was discussed previously; it’s unlikely but not impossible that it evolved an extra set of eyes for some special purpose.

The mouth appears to be on top of its head, but when it’s swimming, that’s just the front. So I suppose that makes sense. And it opens in the middle. Why are our mouths oriented the way they are anyway?

Well, vertebrate mouths evolved from a modified gill slit. The mouths of arthropods (bugs etc.), on the other hand, evolved from modified limbs, which is why they open side-to-side.

Since mandibles clearly work, perhaps they could evolve in a more vertebrate-like lineage on another world.

I’m not sure how much thought was put into this creature, but while its designers seem to lean into the “don’t use a normal body plan to make it extra-clear it’s an alien” approach, they manage to do so in a way that is at least not completely ridiculous.

Now, I want to make it clear that what I have been engaging is rampant, vaguely-informed speculation. Unfortunately, many people, even ones who should know better, get the mistaken impression that this is all evolutionary biologists and psychologists do when explaining things.

In fact, “The logic of hypothesis testing in evolutionary psychology [and biology] is the same as hypothesis testing in all sciences.” Explaining how they do that is beyond the scope of this article; follow the link for more discussion and examples. But the Big Bang Theory could with as much justification be called a “just-so story”…however, it is one with the cumulative weight of evidence in its favor.

I’ll quote from Wikipedia:

Academics such as David Barash say that the term just-so story, when applied to a proposed evolutionary adaptation, is simply a derogatory term for a hypothesis. Hypotheses, by definition, require further empirical assessment, and are a part of normal science.[6] Similarly, Robert Kurzban suggested that “The goal should not be to expel stories from science, but rather to identify the stories that are also good explanations.”[7] In his book The Triumph of Sociobiology, John Alcock suggested that the term just-so story as applied to proposed evolved adaptations is “one of the most successful derogatory labels ever invented”.[8] In a response to Gould’s criticism, John Tooby and Leda Cosmides argued that the “just-so” accusation is unsubstantiated as it claims evolutionary psychologists are only interested in facts already known, when in reality evolutionary psychology is interested in what can be predicted from already known information as a means of pursuing unknown avenues of research. Thus evolutionary psychology has predictive utility, meaning it is not composed of just-so stories.[9] Steve Stewart-Williams argues that all scientific hypotheses are just-so stories prior to being tested, yet the accusation is seldom levelled at other fields. Stewart-Williams also agrees with the idea that evolutionary explanations can potentially be made up for almost anything, but argues the same could be said of competing approaches, such as sociocultural explanations, so in the view of Stewart-Williams this is not a useful criticism.[10]

Anyway, if you find this kind of speculative biology (and evolution in general) as fascinating and entertaining as I do, there are some really cool shows that attempt to show what life on other planets could look like, as informed by experts in relative fields, like Alien Worlds and Alien Planet.



Lee M. Raulin

Web Developer and former English teacher with an MA in psych.