No Biochemical Barriers: Difference between revisions

{{trope}}

 

{{quote|'''R2''': "Obviously the air is highly caustic and poisonous."

 

In [[Speculative Fiction]], it is far too often the case that writers do not take into account the fact that the differences between terrestrial species and their alien counterparts would run deeper than appearance alone. Given that alien species would have evolved in environments vastly different to terrestrial ones, contending with different atmospheric conditions, different levels of background and cosmic radiation, different soil conditions, different pathogens and parasites, and so on, it is patently unlikely that any aspect of their biology would be directly compatible with their terrestrial counterparts. Aliens in speculative fiction are usually depicted less as properly alien creatures and more like humans from another country, and alien animals are merely exotic species from a different climate.

* '''Cross-Species Disease''' - Humans or aliens affected by alien pathogens or parasites that should not have had time to adapt to their physiology. This in spite of the fact that on Earth there are huge numbers of viruses, bacteria, and parasites that only affect a single species or a few related ones, and that so-called "zoonoses" have generally only been a big deal amongst livestock, which we've intentionally cultivated in close proximity for ages.

* '''All Atmospheres Are Equal''' - While species that breathe something other than oxygen are sometimes seen wearing protective gear when moving in oxygen-based atmospheres, species that are capable of breathing an oxygen-rich atmosphere are never shown to be hampered or even affected at all by the other gases (nitrogen, for example) that constitute the air familiar to humans. Nor do they suffer any problems related to the ''air pressure''—presumably, [[All Planets Are Earthlike]].

 

Some of these are more plausible than others, although not by much. While there is reason to believe that Earth's atmosphere carries life because it is particularly suited to life, this is basically a confirmation bias—we consider it suited to life because it is suited to ''our'' life. This position is called the anthropic principle.

{{examples}}

== Alien Food is Edible ==

* Dita Liebely, the female protagonist of ''[[Vandread]]'', samples the food from Hibiki Tokai's home planet, but she finds it revolting and inedible. Believing the opposite must be true for Hibiki, she feeds him food from her home world, which he found to be delicious. Following this, Dita has little problem spending time with Hibiki on the condition that she feed him. Of course, although Dita considers Hibiki to be an alien lifeform, most outsiders would point out that they are the same species, just different genders.

 

=== [[Comic Books]] ===

* In ''[[Tom Strong]]'' #16, it's established that while unaltered humans can eat Devil's Footstool food, the opposite is ''not'' true. (With a few exceptions, such as coffee.)

* In the backmatter for the second volume of ''[[League of Extraordinary Gentlemen]]'', this is a problem for Alice of all people after she returns from [[Alice in Wonderland|Wonderland]] through the looking glass. Her whole body is reversed left-to-right, so her hair part is on the wrong side - as is her heart. Then, she mysteriously dies of malnutrition, despite eating normally for a while. It's not explained in the text, as Victorian science wouldn't be able to figure it out, but the science-minded reader might conclude that the reversal extended all the way down to the molecular level, and that Alice's amino acids were backwards compared to those in her food.

* In ''[[Transmetropolitan]]'' [[The Greys|the Vilnius]] and late-stage transients (humans turning into Vilnius) can't eat human food, which helps influence the transient secession movement in the first volume.

 

* Many films where aliens, particularly sentient ones, eat humans (humans being eaten by alien beasts can be explained by the alien eating things that act like prey without knowing that it's bad for the alien's health).

* The ''[[Men in Black (film)|Men in Black]]'' films and cartoons imply that all alien immigrants and visitors to earth can eat (or appear to eat, in the case of the [[Mobile Suit Human]]-wearing Arquelliens) human food, although most of them ''need'' to in order to live as [[Muggles|ordinary humans]].

* In ''[[Alien Nation (TV series)|Alien Nation]]'', the Newcomers are perfectly capable of eating earth food, with some variants. They prefer more exotic meats (such as beaver), which they eat raw as they can't absorb nutrients otherwise; they get drunk off spoiled milk; and the drug that drives the plot of the film {{spoiler|looks and tastes like dish soap to humans}}. They also dissolve in seawater and use arsenic flakes as a food seasoning. Justified in that they are a genetically modified life form.

* Averted in ''[[Avatar (film)|Avatar]]'', in which the planet's atmosphere is deadly to humans.

** An aversion comes up as a [[Noodle Incident]] in ''[[Death Star]]''.

{{quote|"How was I to know your kind can't eat sweetweed?"

"Not a chance, Green-Eyes." }}

* Averted in ''[[Fallen Dragon]]'' by Peter F. Hamilton, where alien ecosystems are completely incompatible with human biochemistry—meaning the first step in colonizing a new world is to kill all the native flora.

* Apparently, anything in the universe they can get a hoof into is edible to the [[Animorphs|Andalites]]. They absorb nutrients, not consume them, so presumably they avoid anything they don't need/want. This deprives them of a sense of taste though, so [[Hilarity Ensues]] whenever they [[Sense Freak|morph into humans.]] Ax also complains at one point about accidentally eating snails when he grazes since as a herbivores it's probably quite disturbing to him that he just killed and ate an alien creature.

** Similarly, Taxxons can apparently eat just about anything (or anyone). Also, Hork-Bajir are capable of eating the bark of Earth's trees.

* In the 1992 novel ''Murasaki'', written by several well-known science fiction authors, this trope is averted in an almost sad way. Humans discover the planet Murasaki and mount an expedition. The local life is almost completely poisonous to humans because they use a wider variety of amino acids. The natives, in an effort to make friends with the humans, find one life form that has some parts that are edible to us and present them in a feast. They are delicious. But they are also now extinct. Every last of the animals was harvested in order to provide the feast.

* Subverted in [[Terry Pratchett]]'s ''Strata'' where an important plot point is that the carnivorous Silver has a different biological makeup that makes it impossible for her to eat meat from a different planet. Being a predator, she will however turn into a ravenous badass killing beast which will still kill everyone in sight if her hunger gets the better of her.

{{quote|'''Troll''': I knows what they say about us trolls, but it not true! We made of rock. We don't eat humans!

'''Other Troll''': Swallow. We don't swallow. }}

* Averted in a sourcebook for ''[[Werewolf: The Forsaken]]'' dealing with werewolf physiology and behavior. The book makes it very clear that becoming all fuzzy when you've got chocolate, caffeine or drugs in your system can mess you up something fierce (as chocolate and caffeine are trouble for canines, and... well, the drugs should be fairly obvious, shouldn't they?).

* "Alien Wars", a Military SF setting for [[Hero System|Star Hero]], features the Xenovore race, which can metabolize ''any'' meat regardless of which planet it comes from. [[I'm a Humanitarian|Sentients]] are the tastiest, but they'll eat nonsentients if that's what's available.

 

=== [[Video Games]] ===

 

=== [[Tabletop Games]] ===

** The fluff implies that it's a sort of [[Grey Goo|nano weapon]].

** The Tyranids are a special case. Given what they are - a horrendously adaptive [[Horde of Alien Locusts]] implied to have devoured entire ''galaxies'' - they will go through several evolutionary cycles ''in a matter of weeks'' to adapt to a local ecology.

 

=== [[Web Comics]] ===

 

=== [[Western Animation]] ===

* Most of the aliens in the ''[[Men in Black (film)|Men in Black]]'' films and [[Men in Black (animation)|the cartoon]] get along fine without special respirators, although there are exceptions: one species risked premature aging in earth's atmosphere, while "Atlantis" (actually a [[Ancient Astronauts|sunken space ship]]) is a posh resort for (salt)water-breathing aliens. When Agent Jay is surprised at the fish-like aliens, Agent Kay [[Lampshade Hanging|lampshades]] this with "You think ''all'' aliens breathe oxygen?"

* [[Lampshade Hanging|Lampshaded]] and played hilariously straight in ''[[Galaxy Quest]]'', when [[Cloudcuckoolander|Tech Sargent Chen]] opens the door of the ship while it's on an alien planet:

Chen: (sniffing a few times) Seems okay. }}

* Present ''and'' subverted (and generally just plain [[You Fail Biology Forever|screwed up]]) in M. Night Shyamalan's ''Signs''. Aliens are seen walking around on Earth apparently sans any kind of protection whatsoever, but then turn out to be fatally allergic to water. ([[Fridge Logic|But let's not go into why hydrophobic aliens would decide to invade a planet 75% covered with water, nor how they managed to run through a misty cornfield at night]].)

=== [[Tabletop Games]] ===

* Averted in ''[[GURPS]]: Space'' most of the possible atmospheres are both suffocating and toxic.

 

=== [[Video Games]] ===

* In ''[[Final Fantasy IV]]'', the party goes from the surface of the planet to the [[Beneath the Earth|deep underground]]—with oceans of lava bright enough to provide ambient light. Then they visit the surface of the Moon, a barren wasteland populated by human-sized versions of (single-cell) eukaryotes and prokaryotes. A case ''could'' be made for the latter, but the former should have a noxious atmosphere and should make it impossible for humans to survive in it (to say nothing of the heat and pressure...)

* ''[[X-COM]]: UFO Defense'' (''UFO: Enemy Unknown'' for you Brits) both averted and played this straight. The eponymous aliens comprised many races - some were surgically altered to deal with the atmosphere, others were genetically engineered badasses, some used their [[Psychic Powers|Psionic powers]] to support their atrophied body mass... and some just seem to do fine without any help. [[Gameplay and Story Segregation|Including, apparently, humans on Mars without full environmental armor.]] Possibly an oversight, since by that point in the game, you should probably have all of your troops outfitted with [[Powered Armor]] and plasma weapons.

** Amusingly, General Warfield had specifically stated earlier that the atmosphere could "burn a man alive".

* Averted in the ''[[Myst]]'' Verse, in which one of the major guilds of the D'ni civilization had the responsibility of checking newly-written Ages to determine if they were safe. The first explorers to link to an undocumented or rediscovered Age would do so in protective armor with its own air supply.

 

=== [[Western Animation]] ===

{{quote|The air isn't toxic...? How DARE you open a space ranger's helmet on an uncharted planet! My eyeballs could have been SUCKED from their sockets!}}

** Even funnier when one considers that he doesn't even ''have'' lungs, being a molded hunk of plastic.

 

{{reflist}}

[[Category:There Are No Indexes]]

[[Category:Biology Tropes]]

[[Category:Speculative Fiction Tropes]]

[[Category:Artistic License Biology]]