Form Equals Form Equals Function
Why is it that the most enduring, recognized form for aliens to take in our stories is “humanoid”? Walking upright, two legs, two arms, two eyes, etc. The most stereotypical term to refer to visiting aliens is “little green men“. Why do we so often assume that aliens will be so similar to us?
Part of it is undoubtedly because there is a comfort in familiarity; if they look kind of like us, they must be like us, right? (Conversely, we feel more confident when the bad, violent aliens look nothing like us.) A certain lack of imagination on the part of those who craft the stories also plays a role. And let’s not discount the practicality of putting a human actor in a roughly human-shaped costume.
But there’s actually a reasonable scientific justification for an alien life form to have a similar form to ours. It’s called convergent evolution.
Convergent evolution occurs when two different species evolve a similar physical characteristic independently of each other. For example, the honey possum of Australia has a pointed snout and a long, thin tongue that it uses to gather nectar, very like a hummingbird.
Typically convergent evolution occurs when the differing species each fill a similar ecological niche. The aye-aye of Madagascar and the striped possum of Australia each have a single long, skeletally thin finger which they use for prying grubs and other invertebrates from under the bark of trees. The particular food source was available because both Madagascar and Australia are free of woodpeckers. (The late Douglas Adams described convergent evolution as it relates to the aye-aye and striped possum in his magnificent nonfiction book Last Chance to See, with Mark Carwardine. Go out and buy a copy now, it’s an amazing read!)
Humans have evolved into our current form for various reasons, but each change we’ve undergone has helped us survive and thrive. And it’s not unreasonable to assume that another species on some distant Class M planet went through a similar evolutionary progression. Hence, aliens that look very similar to us.
One side note. I’m hardly the first person to talk about convergent evolution as it relates to humans and humanoid aliens. My fellow SiMF blogger Athena Andreadis covered the topic in some detail in her book To Seek Out New Life: The Biology of Star Trek. Author Joan Slonczewski has written about it too. And there are others.
Both Andreadis and Slonczewski mention the virtual impossibility of two alien species, no matter how physically similar, being able to interbreed. As superficially similar as the two species may appear, the genetic differences would almost certainly be too great to enable procreation.
This demonstrates a very common problem in science fiction writing, the ignoring of reality in favor something cool, or to make the story work. While to a certain extent this isn’t a problem, pretending facts don’t exist makes it difficult to suspend disbelief. Giant bugs couldn’t really exist, they’d be crushed under their own weight. There are plenty of ways to create fascinating stories and aliens while remaining grounded in fact.
Surprisingly enough, human/alien convergent evolution on its own doesn’t add a new depth to extrapolation in science fiction. Any physical trait we speculate on for ourselves, we can also consider occurring in an alien species; so long as we invent an environmental or ecological reason for the change to occur, we can assume the same reason could occur for the aliens. In other words, anything we can imagine for ourselves, we can imagine for aliens.
But where extrapolation can get very interesting is when we consider what evolutionary traits we might share with an alien species because of our interactions with them. Meeting aliens would absolutely be a dramatic shift in our understanding of the universe, and could lead to any number of interesting changes down the line:
- If we visited the aliens’ homeworld, we would be forced to evolve and acclimatize: survival against viruses we’d never encountered, ability to sustain ourselves on native foods, etc.
- We and the aliens could encounter a language/speech barrier, and overcome it by evolving psychic abilities which allow us to convey complex emotions to each other. (this is admittedly somewhat fantastical.)
- In a slightly more science-based vein, we and the aliens could develop a new shared sense that we’d previously had no use for, that enables us to communicate.
- If aliens visited us and shared their knowledge of space travel, we could send a large population of humans into space. Those humans could then evolve bodies more suited to space travel – something the aliens should already have done.
That last speculation touches on another interesting concept. If a large population of humans went out into space, and evolved to accommodate for space travel, they would end up drastically different from the humans who stayed on earth. That would be divergent evolution – and that will be the topic of my next post.
Oh, this is a good game.
Which bits are functional, which bits are coincidence?
It’s useful to have your eyes up off the substrate, and it’s useful to have more than one so you get depth perception. But is there any reason to have two or would seven work just as well?
It’s useful to have your brain really close to your major sensory organs (which may not be eyes or ears) because your nerve pathways only work so quickly. Unless you have more efficient nerves.
It’s useful to have opposable manipulators that can grasp at a distance, but there’s definitely no reason that four fingers and a thumb is the correct combination. Arms seem plausible, but again why two?
The bilateral symmetry vs radial symmetry split in terrestrial organisms goes way back. Is there any reason that one should be favored over another? And are there other arrangements that would work equally well?
Convergent evolution is all about function – some shapes work better for particular tasks. But the underlying body plan constrains everything: not all options are even available.
There’s constraint, function and coincidence, and they all go together to make an organism.
I think the main reason why so many fictional aliens look humanoid is because until recently human actors or puppets were the only options in live action films or tv shows. Also it’s easier for audiences to relate to humanoids than to something that looks like a cross between a giant bat and a starfish (the To’ul’h, from Orion’s Arm).
Thank you for highlighting my book, Bart! I also wrote about this issue more briefly in my Making Aliens 6-part series (starting point: http://www.starshipreckless.com/blog/?p=24) and in Dreamers of a Better Future, Unite! (http://www.starshipreckless.com/blog/?p=60).
There is no question that people would have to evolve if they lived on other earth-like planets, unless they were content to live forever under domes, a scenario that would resemble a prison or an ICU unit, rather than a new world. Evolution of this type would lead to speciation, which I suspect will be the topic of your “divergent evolution” post.
To enlarge on the excellent point of the strictly-by-function scoring system of evolution: we won’t know which attributes of living organisms are universal and which are parochial until we have an independent life sample. The gamut of terrestrial lifeforms alone and their divergent solutions to the same problem already show that only the outcome matters. The ability to fly, rather than exactly how to do so (insect, bird and bat flight is based on very different principles). To ability to see well enough to survive, thrive and propagate; and so forth.
Also, there are other senses that we don’t possess that are useful to other terrestrial organisms — sensing EM, for example, or being able to smell pheromones (something that humans cannot do no matter what the tabloids say, because our vomeronasal organ is not functional). So one interesting question of diverging humans beyond earth is what other senses may become important in the new context, and what accommodations our body and brain can/will make to develop them. We’ve done it before: we became able to read, for example. Making chlorophyll, on the other hand, may require a bit more effort!
It just occurred to me that one example of a very divergent body plan that would fulfill all requirements that Sarah listed is the octopus: they are very intelligent, they have excellent vision and they can manipulate tools. So races of intelligent cephalopods might just be in our future encounter list!
The bilateral versus radial symmetry body plan was indeed coincidence and then inertia, as the instructions got embedded into the developmental program (the famous Hox genes and their relatives).
The “future is wild” series (www.thefutureiswild.com) imagines, among other things, cephalopods moving into several ecological niches previously occupied by mammals, including monkey-like “squibbons” (squid + gibbon, get it?), as well as other examples of niche swapping, such as fish becoming airbreathing and airborne and replacing birds. While I have my doubts about the plausibility of many of these scenarios (particularly the flying fish, which while nicely bold, would require a pretty big shift in metabolism), demonstrates convergent evolution as dictated by ecological niches.
There is a race of intelligent cephalopods in Sheila Finch’s story collection, The Guild of Xenolinguists. Your comment brought them immediately to mind.
Aw, dangit Athena. You beat me to the comment I first thought of when Bart posted this!
As a matter of fact, I’m working on a piece of art in which an amphibious cephalopod species comes to Earth. Titled “Take Me to Your Mother”
I love radial symmetry.
I really like this post! I wonder if you’ve ever had a chance to read This Alien Shore by C.S. Friedman, which is related to this discussion by virtue of the fact that the human interstellar diaspora in her novel was mutated by the use of a star drive. As a result, her entire universe is full of “aliens” who are in fact humans. I always thought this was rather a clever way of approaching the problem.
Writing the “almost human” is the biggest challenge of all. C. S. Friedman’s In Conquest Born also featured diaspora-drifted human cultures. Equally exciting and challenging are Melissa Scott’s Shadow Man and Donald Kingsbury’s Courtship Rites.
On the side of alien creation, Poul Anderson was the best, in my opinion. He created a constellation of vivid, believable aliens in a cycle of short stories linked to his rogue hero, Nicholas van Rijn, The Earth Book of Stormgate (the most memorable is The Man Who Counts, in which he tackles the issue of speciation) — plus, of course, his flying Ythrians and Adzel and Chee Lan, the two marvelously drawn alien partners of David Falkayn.
In line with Bart’s point, the dilemmas and conflicts that arise from these interactions are similar to those between different terrestrial cultures, particularly first-contact situations, with occasional added biological complications.
I have a suspicion I will really like Sheila Finch…