Chances are when we meet actual extraterrestrials, they'll be so different, our minds will be blown. But science fiction has to make do, which is why we get so many humans with wacky foreheads. Sometimes, though, we meet an alien race that could never have evolved, no matter what. Here are the 10 most unbelievable alien races.

We asked about the most unbelievable alien races on our Facebook page, and here's what you guys told us. The races below are unbelievable either because of biology or culture, or some combination of both.

10) The Sensorites from Doctor Who

These telepathic aliens on Doctor Who may be distant cousins of the Ood from the new series. But they make zero sense as a species, and as a civilization. A major plot point of this story revolves around the notion that the Sensorites can't tell each other apart. So one Sensorite is able to impersonate another just by stealing his sash. You read that right: just putting on someone else's sash makes you look like that person. It's fine that the Sensorites all look alike to humans — but how would you develop a functioning society among creatures who can't tell each other apart? Plus they're telepathic, for Crom's sake!

9) Pierson's Puppeteers, from Larry Niven's Known Space books

These aliens get points for originality and not simply being humanoid. As Tim Morris explains, "Its biology is singularly bizarre, it has 2 heads (each with one eye, one mouth, and three lip-fingers), neither of which has a skull or brain. The brain and skull are actually on top of the rib-cage, at the base of the 2 "necks", this essentially makes the "heads" simply glorified elephant trunks or eye-stalks. Also, they have three legs, 2 front, and one back." But a number of people singled out these creators of insane high technology as not really holding up. Says Sean Toleson, "They don't have hands to make things, and are consummate cowards."

8) The Vorlons, from Babylon 5

"I love the show," says Jason Dolph, but the Vorlons are probably a bit too over-the-top to believe: "Super-psychic squid/energy beings who had genetically manipulated most of the younger races with daddy issues." Their attitude just isn't believable, adds Gregory Thompson.

7) Vogons, from the Hitchhiker's Guide to the Galaxy

These are the bureaucratic, poetry-writing aliens who demolish the Earth. As Matt Leach notes: "So much paper work just to have intercourse. They would have died out quickly." (Plus, also from Hitchhiker's Guide, the Hoovooloo, a hyper-intelligent shade of blue. Which, yeah, not really that likely.)

6) The Palanians, from the Lensman books by E.E. "Doc" Smith

These are creatures that live at extremely low temperatures: close to absolute zero. (There are also creatures evolved to live at near-zero in Niven's Known Space books, which some people called out. Plus some other creatures in the Lensman series live near absolute zero.) As David Gustafson says, "Love 'em all, good & bad, but the idea of life at three degrees Kelvin, with an innate extra-dimensional link supplying them with energy needed for life, is dubious at best."

5) Humans.

Yep, us. So many people voted for "humans" over on Facebook that I had to include the human race — we are totally unbelievable, as a species, in science fiction. Not only would you not believe in the human race if we were made up ("They're destroying what keeps them alive, and they're supposed to be intelligent?" to paraphrase Jo-Ann Child), but the versions of humanity in science fiction often feel totally contrived. Like, once you put humans among a bunch of other humanoid races, humans become exaggeratedly noble because a lot of our worst characteristics are off-loaded onto non-humans. Ronny speaks for a number of people: "Humans. Always brave, moral, self-sacrificing, in fiction. Immoral, spineless, coward scum, in reality." Adds Gary Layng: "Imagine, a species as self-destructive and superstitious as them, surviving to create colonies in space." So yes, we're one of the least believable races in science fiction. Be proud!

4) The Changelings from Star Trek: Deep Space Nine

And really, most shape-shifting alien races who can add or subtract mass at will seem highly unlikely. A few people also pointed to the Transformers, although I'm not sure the Transformers actually add or lose mass. Adds Molly Michelle Kuester, "I can believe a super intelligent sea of goo... and I can believe that a goo could develop a shape shifting ability, but I don't think it would be as "stable" as Odo was shown being... grappeling with enemies and doing quick movements and such." Plus their super-telepathic shared consciousness in the Great Link also seems highly implausible.


And honestly, there are so many implausible Star Trek races. Including the Ocampa, who only live for eight or nine years and can only reproduce once. And all the humanoid races who can interbreed with humans. And the godlike aliens like Q. And the Tamarians from "Darmok," who only speak in references to other stories — what do those texts they're referencing consist of? Etc. etc.

3) The Asari, from Mass Effect

As Jay Steinbrecher puts it, "Sorry, but it's genetically improbable to have a species which can genetically adapt — to and reproduce — with ANY species solely based on touch. It's just an excuse to have hot and slutty alien blue people." Adds Carter Moore, "I'm sorry, guys, I know they're hot and all, but a race that can incorporate DNA from every race in the galaxy? C'mon."

2) Kryptonians

Sure, it's comic-book science. But still. As Kirk Parsons puts it, "Hey, this planet's sun is hotter that that of my birthworld. That means I'm impervious to harm and can see through walls!" Adds Tim Welsh, "Our yellow sunlight makes them virtually indestructible — and yet none of them decided to come here on purpose."

1) The Aliens in Signs

We pick on this movie a lot, but still. Guh. Their main weakness is water — so they decide to invade a planet which is mostly water, and eat humans, who are mostly water. As James Philips notes, "How can a lifeform, especially a humanoid-looking one, even exist if its cells react with water in such a way, considering that most scientists believe that water is a key ingredient for life? Even if it isn't necessary for all life in the universe, I still have trouble believing something could evolve that's actively harmed by it." Adds Robin Lmaogaard Bäcklund, "Don't forget that there's water in our atmosphere so the aliens in Signs should have started burning way sooner."