If you have seen as many movies and TV series as I have you may have asked the question. Why are so many aliens humanoid? Is it because of a lack of imagination on the part of movie and TV producers? Budgetary constraints? Other? I know in the original Star Trek they had constraints of budget, and developed a mythology to explain the preponderance of humanoid species in the Galaxy other than “the studio was too cheap to let us come up with cool nonhumans.” They developed a race of ancients who seeded the Galaxy with humanoids (not sure why), which explained why Vulcans could mate with Humans and produce Spock (thought they used blood with different carrier molecules for Oxygen, so no sure how that worked). Otherwise, no matter the compatibility of sexual equipment, you would have more luck reproducing with a tree slug than an alien, even if they did use DNA (which is also not a given). Now Cheesy old movies used humanoids even if they had scaly skins or claws, because the humanoid actors had to fit into those monster suits. Or if the aliens were very nonhuman they didn’t move much, because that was beyond the effects wizardry of the time. I think one of the hookiest aliens was G-Man from Robot Monster, which was a guy in a Gorilla suit with a single eye stalk coming out of his shoulder area. Of course it wasn’t bad enough to not be retread for Lost in Space later on. Or maybe it was bad enough, which is why it was used. In later series the humanoid form was again used often. The Newcomers from Alien Nation, the invaders from V, even though makeup can be hard, its not as difficult as making a mechanical construct to play a truly alien creature.
Now this isn’t saying that the humanoid form is not a good one, and that convergent evolution won’t happen. I don’t buy the theory that in a million planets developing life every single phylum, class and order will be completely different than anything we have on Earth. I expect to see Reptilians, though with more limbs in some cases. And the humanoid form is a robust form. If I had to go to war I would love for it to be against Posleen like in John Ringo’s novels. They could run, but they couldn’t climb, duck or hide in holes or trenches, all useful tasks in a shooting war. And there were a lot of aliens from Star Wars that looked weird and unusual, but didn’t look like a good choice for a Galaxy winner, which is probably why the Galaxy was dominated by, you guessed it, Humanoids. I don’t expect humanoids to look exactly like us, though that could possibly happen. I really don’t expect for them to have the same genetic structures, internal organs or even number of fingers and toes. Our internal organs and their arrangement are a genetic accident. For example, look at the arrangement of our air pipes and food pipes, which cause so many problems. There was a fish with an opposite arrangement that would have been so much better, but it didn’t win the lottery to become land vertebrates. So we have a bad arrangement of pipes that cause problems.
Books have always had better aliens than movies until recently. A writer could create the truly alien with the stroke of a few keys. They didn’t have to worry about how it would look or move, or how much it would cost to make it do so. Dracocentaurs and other aliens from Poul Anderson, all the forms from Alan Dean Foster, the list is endless. Now, with the improvement in CGI technology the movies can bring forms like these to life on the silver screen, and we are no longer stuck with merely redressed faces on obvious humans. Look at the Tharks in John Carter, or the natives in Avatar. Sure, both were more or less humanoid, but with some big differences that brought them to life. Or the alien in Super Eight, which was powerful, fast, and definitely not humanoid. I look forward to some other creations appearing at a theater near me. Today the only limitation is the imagination of the artist, and the time of the CGI artists, to make anything we dream come to life.