There Are No Extraterrestrial Peacocks

Why humanoid aliens are pure fantasy

In this article, I will explain why real aliens, if they exist, will not look at all like humans.

Before I get into the details, we have to be clear on what we are talking about. What exactly does “humanoid” or “similar to humans” actually mean? Since similarity is such a vague and subjective concept, I should at least attempt to clarify what I mean by it.

To me, humanoid means ‘like a human’ but possibly with a slight modification, such as blue and/or scaly skin, pointy ears, bulbous black eyes, lumpy forehead, bat wings, or antennae.

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Mantis from Guardians of the Galaxy — a human with minimal modifications to make her look ‘alien’

A bird is bilaterally symmetric, has four limbs, is bipedal, has an endoskeleton, a head with eyes, ears, and mouth, breathes air, has its reproductive system mixed with its excretory system, and uses the same orifice for eating, breathing, and vocalizing. I wouldn’t call a bird humanoid, even though it shares a lot of characteristics with humans, but I would still argue that birds are more similar to humans than any alien will be.

To make it simpler, let me use images from science fiction:

Aliens cannot possibly look like this:

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Jadzia Dax from “Star Trek: Deep Space 9”

This is more plausible, but still too human in terms of body configuration:

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Christopher Johnson from “District 9”

This is the kind of thing that we should expect aliens to be like:

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Abbott and Costello from “Arrival”

Not exactly like that of course, since we can’t predict what they will look like, but that level of similarity to humans, that is, not similar at all.

Science-Fiction loves Humanoid Aliens

Humanoid aliens are extremely prevalent in science fiction. TV shows and movies, particularly those made before CGI became so easy to use, are replete with human actors playing the parts of aliens. Books allow for much more creative representations of aliens because budget and scope are non-issues, but even so, novelists are informed by other media, so a lot of books fall back on the humanoid alien trope because plausibility isn’t the focus.

Here are three main reasons why there are so many humanoid aliens in TV and movies:

  1. Culture: Most science fiction is produced in countries with an ostensibly religious background, particularly Christianity. Even if the people creating the stories are not religious, they were still raised in a culture that teaches that God created us in his own image. There is still a ubiquitous concept of the divinity and specialness of the human form as the apex of creation/evolution, which is further reinforced by all the shows featuring humanoid aliens. It is a concept in the zeitgeist that is difficult to shake off.
  2. Pragmatism: It is far quicker, easier, and cheaper to slap some latex ears or nose-ridge on an actor than it is to construct and control an imaginative animatronic puppet. You get much better performances too. These days CGI is getting cheaper and cheaper, but it’s not easy and not perfect. So for TV and movies, it is a pragmatic choice, saving both time and money.
  3. Emotional focus: Science fiction can let us look at aspects of human society from an objective viewpoint. For example, the original Star Trek series had an episode with people who are black on one side of their body and white on the other. However, which way round the black/white sides were determined their place in society. It was of great importance to them and divided their species. It allowed the creators of the show to tell a story about the ridiculousness of racism from a completely objective viewpoint, something that can’t be done without a fantastical, sci-fi twist. Captain Kirk couldn’t understand their prejudice regarding something so trivial, just as an outside observer wouldn’t understand how we could be prejudice based on something as superficial as skin tone. For this kind of story, the audience is not interested in scientific plausibility, they just want to see human stories in a science-fiction setting. So humanoid aliens are the best fit for this kind of story.

Convergent Evolution, Hybridisation, and Panspermia

In any discussion about aliens, and specifically, whether they will look human, there are three concepts that are always brought up. These are,
convergent evolution”, “hybridization”, and “panspermia”. Let’s address them one-by-one.

Convergent evolution: This is often cited as a reason for why aliens will look exactly like us, but that is a huge misunderstanding of what it is, and what it can do.

Convergent evolution is an evolutionary pressure that encourages disparate species to develop vaguely similar shapes based on things like shared physical environment, predators, prey, and climate.

The best-known example of this is the similarity in body shape between sharks, ichthyosaurs (an extinct aquatic reptile), and dolphins. A fish, a reptile, and a mammal all evolved similar shapes due to living in the same oceans. And it seems pretty compelling. At first glance, they are indeed quite similar. But are they though? Are they really?

Dolphins have a horizontal tail. That’s a pretty fundamental difference. They also have their nostrils on the top of their head, and sharks have gills because they breathe water. Again, a huge difference. The people championing convergent evolution are biased and dismiss those differences as superficial, but they’re not. We should apply the same sloppy standard of similarity to the possibility of humanoid aliens, so as long as they have four limbs and a couple of eyes somewhere, then we’re good. Right?

Sharks do not look like dolphins. They may have a roughly similar outline but there are vast differences. What it does show is that while the overall shape might be somewhat similar, there is still a wide variety of configurations that still makes sense in the environment, and the details are not part of the overall shape. Perhaps there are aliens out there with four limbs, but they will never be able to wear a hat and walk among us unnoticed.

Most importantly of all, using the example above as to why aliens will look humanoid is cheating. Sharks, ichthyosaurs, and dolphins all share a common, sophisticated, fishy ancestor. A bilaterally symmetric animal, with an endoskeleton, a spine, and a brain (in a head) with eyes, jaw, nostrils, etc. They had a huge head start with their similarity.

It’s curious that nobody ever mentions squid in this discussion. Squid evolved in exactly the same oceans, feeding on the same kind of prey, and they too developed a torpedo shape to cut through the water. The reason why they are so different is that it didn’t start from a fish. But even so, squid share a (more distant) common ancestry with all those others, it is still made from the same materials, the same genetic mechanisms, the same developmental systems. Aliens will not share anything at all with terrestrial life. Not material composition, biochemistry, genetic systems, developmental mechanisms, gravity, atmospheric/oceanic pressure, or temperate range. Nothing.

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Convergent evolution and vaguely similar shapes (

Hybridization: This is the idea that aliens came to earth and manipulated life here through genetic engineering into becoming like them, in particular, mixing their DNA with that of apes to produce humans. A lot of alien conspiracy theorists subscribe to this idea, and it is explored a lot in science fiction, but some big questions need to be answered. Why is life on earth already biochemically compatible with aliens, why are naturally evolved apes already 99% similar to the aliens, and why do we find intermediate hominid forms in the fossil records in regions and at a pace conforming to natural progress?

This idea is a modern take on the imaginative hybrid creatures of ancient mythology, such as centaurs and gorgons, using a vague idea (but no solid understanding) of modern scientific principles to support it.

It’s a nice idea for fiction, but it is not a reality.

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Aliens will have very different biochemistries and developmental systems. Hybrids are not possible (X-Files)

Panspermia: This is the idea that life may not have originated on Earth, but instead, came here either by accident (such as an extraterrestrial bacteria hitching a ride on a comet) or intentionally being planted by intelligent, space-faring aliens.

In science fiction, this idea has been explored many times, perhaps best known from an episode of Star Trek called “The Chase” and Ridley Scott’s Alien prequel, Prometheus. In both those stories, humanoid aliens seeded life with their own DNA. The idea is that we evolved our shape because life on Earth is based on their genes.

In the first scene of Prometheus, a muscular humanoid alien stands on a barren planet and sacrifices his life by drinking some advanced alien goo. It breaks down his body into DNA fragments which is supposed to suggest that their species seeded planets with their own genetic material. Earth is one such planet and therefore we are as we are, because of their genes.

While watching it I kept asking myself when that scene was supposed to take place. If it was at the origin of life on Earth, nearly four billion years ago, then why did only our particular branch of the tree of life become humanoid? Why didn’t all life develop towards a humanoid pattern? Why do we see horses and eels and bees and fungi if all life here shares the propensity for the humanoid form? But if it was just a few million years ago, as in the hybridization theory, then why are apes already humanoid? Because of convergent evolution? That’s just mixing fallacious concepts. The panspermia scenario in Prometheus makes no sense at all.

This whole idea comes from a fundamental misunderstanding of evolution. It is pure fantasy. I blame whoever it was who first called DNA a ‘blueprint’. That’s the reason Joe Public thinks DNA contains all the information for the final form of an organism. It doesn’t. DNA is not a blueprint, it is a recipe. The sugar molecules in chocolate don’t encode for a black forest gateau. A single soap lipid in a bubble doesn’t know what ‘spherical’ means. And DNA doesn’t encode for the final form of an organism, at least not directly.

The form of an organism comes about through the expression of the genes in response to the environment. We can’t grow humans from a zygote in a vat of nutrients because the specific physical/chemical environment of the womb is important for development. Plants grow weird in zero-gee because gravity is needed to determine directions in their growth phase.

You simply cannot inject humanoid DNA into a bacteria, throw it onto a barren planet, and expect to see humanoids a few billion years later, no matter how advanced your technology is. That’s just not how biology works. That’s like throwing tennis balls off the peaks of two separate mountains on two different planets with different gravity and atmosphere and vegetation and crust composition, and expecting the downward paths of the balls to be completely identical because “the balls were exactly the same!!!”

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Directed panspermia cannot ‘make’ humans (Prometheus)

Universals and Parochials

Something useful to know regarding this topic is the difference between “universals” and “parochials”.

Universals are structures (and behaviors) that evolution will settle on more than once because they are relatively simple to evolve and solve a universal problem. They’ve evolved multiple times on earth, so it’s fair to say that evolution on other worlds may discover similar solutions to similar problems. Things like wings, eyes, fur, fins, legs, etc. Again, these are very vague concepts, and there is an extremely wide variety of forms these things can take. A dragonfly wing performs the same function as a bird wing or bat wing, but they are very different forms and they developed in very different ways. So to say that some aliens might have some kind of wing is not much of a stretch at all, but to say they will have a wing exactly like that of a bat, with skin stretched between five elongated digits is a bit of a reach, but then to say the rest of the creature will also look exactly like a bat, complete with convoluted nose structure, beady eyes, Sydney-Opera-House ears, fangs, and echolocation is pure fantasy. And so it is when applying that logic to humans too.

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Photo by vishu vishuma on Unsplash

Parochials on the other hand are things that we shouldn’t expect to see often, or even ever again. They are idiosyncrasies of particular lineages, not favored in any way by evolution, but they are the way they are simply because they were random ‘choices’ that became baked into a species. Why do we have a single orifice for eating, breathing, and communicating? Why are our reproductive and waste excretory systems mixed? Why do we have five digits instead of four or six or eleven? At the time our fishy ancestor crawled out of the oceans onto the land, there were other competing species that had different numbers of proto-digits in their bony fins. The one that happened to win had five, and so that is why we have five fingers. That semi-random ‘choice’ is why we have five fingers, but just as easily a six-proto-digit-finned fish could have dominated. It’s certainly possible that there might be an alien lineage that does have limbs culminating in five digits, but it will be a coincidence. And that’s just one tiny tiny detail out of many. To get slightly close to ‘human-like’ aliens would require billions of coincidences like that.

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Photo by Luis Quintero on Unsplash

Sexual Selection

Sexual selection is where the evolution of a species is highly influenced by their sexual desires, particularly those of the females, who are the selectors of the species. We see its profound effects in many birds, most notably the peacock, but sexual selection is working across many many species more subtly. And it is highly likely that sexual selection was a major factor in human evolution, especially our intelligence. Sexual selection is in some ways the opposite of natural selection, they are opposing forces. Natural selection is trying to keep species camouflaged, lightweight, agile, and strong, whereas sexual selection is trying to make them as flamboyant and outrageous as possible. It is a wild, undirected, unique, flailing process, which CANNOT be replicated. It is specifically unique. It is a parochial feedback system. There is no possible way peacock tails exist on another planet, and for the same reason, there is no possible way that humans do either. There certainly may be creatures with structures just as flamboyant as a peacock’s tail, but they won’t be similar.

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Photo by Steve Harvey on Unsplash

Argument from statistics

The most common line of argument for people claiming humanoid aliens might exist go like this:

“The universe is so big, statistically, humanoid aliens are almost inevitable.”

The universe may be big, but complex, intelligent, technology-using life is not abundant. It is extremely rare. How do I know this? Because we have never found any evidence of intelligent life out there. It’s irrelevant how tiny a portion of the universe we have looked at is.

Our galaxy is about 100,000 light-years across. So if any species got to the point of developing radio communication in our galaxy at any time in its history before humans evolved, then it would expect to see signs of it.

We have been spewing radio waves out into the sky for decades now, and there is no reason we won’t continue doing so forever. We have landed on the moon and sent robots to other planets and bodies in our solar system. In a few centuries will live on other planets and will at least have sent out self-replicating Von-Neumann probes to star systems in our local neighborhood, which will land, build, replicate and spew out more probes and more radiowaves. To suggest that intelligent aliens are likely to evolve on another planet means that an advanced race should have already evolved in the past. A million years ago, a hundred million, a billion? They would have spread and we would have detected some evidence by now. The fact that we see nothing speaks volumes about how rare technologically developed, intelligent life is.

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Photo by Shot by Cerqueira on Unsplash

That doesn’t mean there aren’t intelligent aliens out there, but it does mean they are rare and that you can’t argue humanoids based purely on statistics.

It’s certainly possible that a species of space-faring aliens just happened to become sapient at the same time as us, and that a wave of colonization is happening on the other side of our galaxy, and their signals haven’t reached us yet just as ours haven’t reached them. And it is also possible, perhaps even probable, that out there, whole galaxies have been colonized by intelligent species.

But they won’t look like Spocks or Yodas, because evolution doesn’t want to make Spocks and Yodas. They will be a product of their environment, crafted by a unique evolutionary history, subject to the individual constraints of their world, the biochemistry that their life is built on, and the genetic systems that happened to evolve there.

In conclusion, the universe doesn’t want to create humans. There is nothing particularly special about our form, and in fact, it is specifically unique thanks to sexual selection. If you ran evolution again here on Earth from the same starting position but with a single amino acid out of place, humans would absolutely not form. Humans evolved by filtering random mutations through a very long series of particular environments, which included coevolution with other species and within the same species, and sustained sexual selection which took our species in a unique direction. Aliens will have their own unique evolutionary history, presumably with their own subtle, or perhaps unsubtle, features that evolved due to sexual selection.

Aliens certainly won’t look like us. That’s for sure.

Scifi writer, roboticist, and game developer, 2x Quora Top Writer. I write about writing speculative fiction, computer graphics, AI, evolution, and programming.

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