The idea that intelligent aliens are somehow similar to us in basic physical make-up has occupied both scientists and fiction writers immensely. And it’s understandable why, after all, when we look at the sky, we’re looking for kindred spirits, potential allies, a new mirror to gaze into and understand our place in the Universe. But will what we see really resemble us?
TV series and movies are full of them, and most written science-fiction as well: humanoid aliens.
But how plausible are they?
From an evolutionary perspective, we have become the dominant species on Earth because we were the most adaptable, versatile and social species. We used tools to achieve things other species—probably smarter, faster and more resillient than us—could not. We used speech to coordinate and plan activities that not even the most strategic pack hunting predators could match. We used speech to teach future generations, thus eliminating the tedious trial by error and significantly reducing adaptation times.
And we used our abilities to dominate our environment. We used our brain to coordinate all our other abilities to the sole purpose of reaping the benefits off of everyone and everything around us. We bastards.
But what about sentients evolving on other planets?
What about our most basic physical characteristics, the ones that set us part form our potential alternatives here on Earth: homeothermic metabolisms (we’re warm blooded); bipedal, upright locomotion; bilateral symmetry; a morphology consisting of head, trunk, two arms and two legs; opposable thumbs; and stereoscopic vision.
Would aliens have these same basic characteristics? Do they have to, in order to have functional societies and technology?
Scientists have argued both in favor and against such similarity. When it comes to extraterrestrial life, all we have is speculation and the admission that even our imagination has limits (based on what we conceive as plausible).
Some say the ability to use tools is essential, and being able to move swiftly on any type of ground is essential as well. Thus two arms with opposable fingers, and at least two legs, are a must. Others say that depending on the planet of origin’s environment, more limbs might be absolutely vital (for example on a high-gravity world, where two bulky, stocky legs are far less efficient than four or even six slender ones).
As to the opposable thumbs, these imply the existence of an endoskeleton similar to ours. But what if an alien species has a cartilaginous skeletal structure? Their fingers would be highly flexible. They’d do with only three fingers, being able to oppose them at will, or not. Or wrap them around objects multiple times. Or if they had an exoskeleton to protect their vital organs, and their appendages were entirely made of skin-covered muscle? Can’t get any more dextgerous than that.
There are other characteristics of humans which seem to find their way into fiction, no matter how many limbs the aliens have. The most prominent ones are forward facing eyes (mostly two), and mouths (including some sort of breathing apparatus). But how necessary are they really? And how much do they have to resemble ours?
Take the eyes, for example.
Our eyes are fairly primitive, compared to those of other creatures. Just look at the compound eyes of dragonflies, which give them 360° vision that is extremely sensitive and color-receptive, and has highly accurate movement perception. Or take the incredible depth perception and precision of birds of prey. Or the almost alien ability of sharks to “see” the electromagnetic energy generated by twitching muscles.
We have even more creatures with incredible eyes right here on Earth — like the fascinating Four-Eyed Fish with its split eyes that can see both below and above water at the same time; or the Mantis Shrimp with its unparalleled double trinocular vision; or the unfortunately extinct Trilobite with its compound eye lenses made of freaking crystal (the only earthly creature with inorganic eyes, apart from pirates).
When it comes to eyesight, it looks as though we drew the shorter straw. Even grazing mammals have better eyesight than us. Our pets have better eyesight that us. Imagine what we could have achieved as a species if we had a much superior eyesight. Or… would that really make any difference? Eyesight isn’t everything. There are plenty of creatures with eyes that can’t see squat, and very successfully rely on other senses for orientation.
And what about mouths? Are they vital?
Even invertebrates have mouths. Any creature that could be considered a potential basis for a speculative intelligent alien life-form has some sort of mouth — an internal gut cavity lined with gastrodermal cells, capable of extracting nutrients from ingested matter.
Okay, there’s one creature here on Earth that has absolutely no digestive tract: Olavius algarvensis — a marine worm that nourishes itself with the help of endosymbiotic bacteria. But other than that, all creatures we know of have mouths of one shape or another.
Yet a mouth won’t always look like a mouth. Mouths can consist of a buccal cavity with a tongue, teeth and lips, but they can also be a cavity lined with a fringe of tentacles; it can have a proboscis (or several); or an external tongue (like flies have). It can be filled with baleen to filter out tiny organisms, or have several rows of teeth and no functional tongue, like the shark. Or have rows upon rows of teeth without having a tongue or lips or even jaws for that matter, like the sea lamprey. *shudders*
So while we can definitely conclude that both eyes and mouths are vital for a species to become dominant, or at least to be considered evolved, these really don’t have to be anything close to human eyes and mouths. In fact, our eyes and mouth are decidedly at a disadvantage compared to other species here on Earth.
So what do we have that’s so special? Our brains, right? But aliens could have even more formidable brains than ours, PLUS far superior eyesight and more complex mouths—and thus develop a far better way to communicate and pass down information than our measly written & spoken languages. The probability is quite high, in fact, that an alien species sufficiently evolved to be spacefaring will be far superior to us physically as well. (Death to the flimsy, little gray men!)
As to the similarities…
I think intelligent, evolved aliens will undoubtedly have some broad similarities to humans—the ability to use and create tools, the ability to pass on knowledge (thus communicate through time), and the ability to dominate their environment and manipulate it to serve their own needs on a grand scale. These will mostly be based on their dexterity, the accuracy of their vision, and their ability to communicate. But when you look closer, they will likely be starkly different from us.
In fiction, we are at full liberty to create aliens that are as alien OR as similar to us as possible. All we have to worry about is logical consistency and a smidgeon of scientific plausibility.
And let’s not forget that our fantastically alien (or humanoid) aliens have developed their own technology, potentially far superior to ours. They could have intervened in their own evolution, tailored their genes, embedded technology into their bodies, or even posess entirely mechanical bodies (uploaded minds) thus gaining immortality. Their appearance may be drastically different from what evolution can account for. The possibilities are endless, only limited by our own imagination.
That’s why I love science-fiction so much. I love creating aliens that share some features with humans, maybe even offer the illusion of being humanoid, but who function very differently from us.
In my novel The Deep Link, the alien co-protagonist Amharr is fairly humanoid at a first glance, having two forward-facing eyes, a torso, and two arms with opposable fingers (albeit six, with cartilaginous bones), but that’s about all the similarity there is.
He has no mouth and no gastro-intestinal tract. He has two pair of very different legs which he can use alternatively. He speaks via sonar, tastes the air around him with several mobile feelers, and has embedded nano-technology that has been used in his species for millennia and has greatly modified their metabolism, their nervous system, and even their skeletal structure.
There are quite a handful of apparently humanoid species—but with fairly inhuman functions—in The Deep Link, along with some species that are completely alien. I think the mixture is the most interesting, and also the most plausible. I find it hard to believe our universe birthed ONLY humanoid sentients, just as hard as I find it to believe that we are so unique, no other sentients look anything like us.
What do you think?
Is it plausible for evolved, intelligent aliens to have some basic similarities to us?
How much are you willing to accept in terms of humanoid traits in aliens?