With its massive cultural gravity well, Star Wars could have sucked you in for any number of reasons — perhaps you were caught in the tractor beam of the scrappy fairy tale, or Harrison Ford’s perfect chin, or flashy lightsaber battles, or the endless parade of Boba Fett action figures and Lego bricks and lunchbox tins. Star Wars hooked budding biologists with its critters.

The animals in Star Wars are lovingly designed, as anyone who spent formative hours with Terryl Whitlatch’s 2001 The Wildlife of Star Wars: A Field Guide propped up on her or his knobby knees could tell you. Loving design, however, does not mean kind treatment. Star Wars critters are at best mindless and at worst hungry and antagonistic Jungian boondoggles. Even the tauntaun, the most sympathetic of the beasts in Star Wars, smells like shit and ends up butchered. The roughness was part of the charm — these were the galaxy’s true underdogs, just trying to eat and mate and not get blown up by superweapons.

But there’s more to biology than being awed by brobdingnagian scale and tentacles and fangs. The fauna, like pretty much everything else in the Star Wars universe, is preposterous. Let’s consider the origin of George Lucas’s species.

Could a Vegetarian Eat Sarlacc Flesh?

The Sarlacc has a perplexing mix of animal and vegetable characteristics. Like the antlion, it sits buried in the sand, mouth wide to snag passing prey. This evolutionary strategy works if you are a centimeter long and will spend your short life close to a nest of bugs; the large size and immobility of the sarlacc, however, also suggests a root-like anchor that absorbs nutrients as if it were a plant.

There is a species of sea slug that ingests algal genes, letting the animals produce chlorophyll, but that’s about as grassy a critter you can find. Sure, tapeworms can absorb nutrients through their skin, but they require a nice human GI tract to do the digestion on their behalf. Even Wookieepedia, that paragon of Star Wars knowledge, can’t seem to make up its mind on the sarlacc’s oddball features.

Nothing About the Exogorth and Mynock Make Sense.

If there is a carbon center at the heart of Earth’s evolutionary tree, the asteroid-dwelling creatures of Empire Strikes Back are the animals furthest from it. They’re silicon-based lifeforms, though for that tidbit we’ll have to rely on expanded universe lore (which some of us are fond of, but others ‘round these parts don’t take to kindly). Take, for instance, the digestive tract of the asteroid-dwelling space slug. This contains human-friendly gravity, human-friendly temperatures — sauntering off the Falcon wearing only oxygen masks, Han and Leia don’t mention any chilliness on their exposed faces and hands — comfy pressures, and a very moist atmosphere, upon which our favorite nerf herder remarks. There’s a lot to unpack here, but how and why an animal could produce intestinal gravity is one bit that’s toughest for our brain cells to wrap around. Physics tells us that gravity is proportional to mass, and as large as the space slug’s asteroid is, it’s not a planet. Maybe exogorth stomachs are strong in the ways both of starship digestion and boot-attracting Force. Or at least super-sticky.

The leathery-winged mynocks that inhabit the space slug feed off of electricity and rely on silicon the way we rely on carbon: as the backbone of all organic molecules. Silicon has a few similar properties to carbon — both elements have four valence electrons and bond to pairs of oxygen molecules — but as Scientific American pointed out long ago in 1998, silicon oxidizes to a solid, rather than carbon gas, making exhalation a tricky business. Where does that leave the mynock? We have no idea what a true silicon life form would look like, but bat wings, red-colored veins, and lamprey mouths probably aren’t it. Diatoms, algae cells encased in silicon dioxide walls, are microscopic and don’t even have teeny suckers for mouths.

The Krayt Dragon Violates the Square-Cube Law.

If you’ve seen A New Hope, you’ve seen a krayt dragon skeleton, even if you didn’t know it. It’s this guy:

This specimen, estimated at 100 meters long, is altogether too much dragon. (A blue whale stretches to at maximum 30 meters, for reference, and it’s buoyed by the ocean.) A pesky bit of biomechanics rears its head: the square-cube law. Enlarge a bone proportionally, and you triple the volume but only double the cross-sectional area. As the University of Chicago’s Michael LaBarbera points out, a hundred-foot-tall man’s b-movie rampage would begin and end with bones snapping after his first step.

Tauntauns Run Too Hot.

If you consider that the average temperature of a Hoth night is less than minus 70 degrees Fahrenheit, should a tauntaun have normal mammalian internal temperatures, Luke Skywalker wouldn’t have lasted long in the belly of the beast. Because Luke lived, we have to change a variable, and that’s the temperature of a tauntaun’s guts. To solve for that, we’ll need to use Newton’s Law of Cooling and estimate a few things — the cooling constant k and the time Luke has to rescue, namely. Given 3-hour rescue window (k is tricky to estimate, but we’ll aim for an insulation factor of 0.2) that means the body of the tauntaun starts at 230 degrees. The tauntaun, in other words, lives with world-record sauna temperatures in its belly all the time.

Sigh, Midi-chlorians.

Midi-chlorians are the nerd culture equivalent of a scab that won’t come off, despite vigorous pickings, so we’ll be brief. Here’s Lucas on the little buggers, definitely not making it up as he goes along. Via Star Wars.com:

“Midi-chlorians are like a single entity: meaning each one doesn’t think individually and have a life to itself; they think as a unit because there’s so many of them and they’re everywhere. They’re in every single cell. And sometimes there’s more than one in a cell. Sometimes there’s a whole bunch in a cell. But there has to be at least one in a cell, otherwise the cell can’t reproduce. All cells. Plant cells. Every life form has a midi-chlorian living inside of them.”

So they’re pseudo-panspermic, pseudo-RNA — can’t reproduce without ‘em — that have a microscopic hivemind and also let you manipulate hidden energy fields if they’re overexpressed in cells. Do you know what else gets overexpressed? Cancer, George, cancer.

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