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Morty: I didn't know that there were bugs out in space.
Rick: Well, what did you think, Morty? Life just developed on Earth by itself?

Lots of people wonder about the origins of life on Earth. Were we placed here by a benevolent god? Did we arise out of a primeval soup of microbes? If the former is the case—well, why? And who? And how? And if it's the latter, how exactly did the vast chemical stew of hydrocarbons and proteins somehow get together and become self-replicating? And then how did those cute little squirmy germs grow and change and evolve enough to become, well, us?

Some stories attempt to answer these questions. But others decide to skirt this touchy ontological issue entirely, by bringing into it a different element: Outer space.

In other words, they propose that life on Earth is not of this earth.

Panspermia (get your mind out of the gutter) is a scientific idea which proposes that life on Earth came to it from outer space, as aliens. This is a real scientific hypothesis, mind you. It's considered very unlikely, but not so much so that supporting it necessarily makes you a crackpot. (That Other Wiki, of course, has plenty of information.) This isn't the "Little Green Men"-style of alien, either. We're talking more along the lines of "cosmic pond scum hitching a ride in some water vapor in a comet." In fiction, panspermia (or exogenesis, which is similar but not identical) tends to gravitate toward the former, though—that aliens of some kind were actually the origin for life on Earth, or some other planet.

In fiction, this idea tends to pop up in one of two forms:

  • Literal panspermia and/or exogenesis. Microbes from space landed on Earth (or another planet, in more sci-fi oriented settings), and evolved into the lifeforms that now populate that planet. This can be used both to get around the idea of having to answer how life arises in the first place, or as a justification for the similarities between life forms on very different planets.
  • "Alientelligent Design." Sufficiently Advanced Aliens, Precursors or Ancient Astronauts planted either the seeds for life or primitive multicellular lifeforms on a planet to begin with, and, depending on the type of alien, either left them to their own devices or "guided" their evolution in a large-scale Gambit Roulette.

Frequently, this as used as part of a Reveal, and can lead to navel-gazing. Occasionally leads to Mars Needs Women, in cases of literal panspermia. See also Transplanted Humans, which is this trope in reverse (alien life coming from Earth); and Humanity Came from Space, which is only about the human species being extraterrestrial in origin. If a species exists on multiple planets without achieving spaceflight themselves and hasn't sufficiently differentiated it's Transplanted Aliens.

It may be worth noting that while this theory may offer an explanation for how life got its start on Earth (and/or other relevant planets), it ultimately does not in and of itself answer the question how life arose wherever and whenever it did so for the first time.

Due to its nature as part of The Reveal, examples for this trope are frequently full of spoilers. Be warned.


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    Anime & Manga 
  • In Andromeda Stories, Earth is seeded with life when the twins Jimsa and Affle crash land and perish after escaping the destruction of their homeworld, located in the Andromeda galaxy.
  • A 1990s OVA titled The E.Y.E.S. of Mars provides an interesting subversion by showing that life on Earth didn't originate from outer space, but human consciousness and sentience did. The last of Humanity (who migrated from the planet of Titan— itself destroyed and now the asteroid belt) lived in a domed city built in a crater on the inhospitable Martian surface. Years of rising tension over the increasingly worse air and water quality and confined spaces finally resulted in everyone going to war and ultimately destroying the dome, collapsing the structure into itself and exposing everyone to the unbreathable atmosphere. As a last ditch effort, the superpowered main characters transferred everyone's souls into the developing Homo primates that were just learning to walk upright.
  • Life on Earth was manipulated by the Creators/Advent/Uranus in Guyver as part of their goals to create a powerful bio-weapons platform. Humanity was the end result, a base form that could be adapted into specialised combatants like Zoanoids and Zoalords. The experiment was aborted near completion when they gave a base level human one of the bio-armour units that worn by the Creators themselves and it turned out not only far more powerful than expected but completely immune to their telepathic control.
  • In Neon Genesis Evangelion, Humanity (indeed, all life on Earth), and Angels were both created by Sufficiently Advanced Aliens who had a thing for spreading life all over the galaxy. It's All There in the Manual.
    • The progenitor of Earth-like life is a type of alien called a "Lilith", while the progenitor of Angel-like life is a type of alien called an "Adam". Many copies were spread throughout the known universe in order to seed life toward an unknown purpose.
    • Also, Earth was meant to be inhabited by Angels, but before they hatched from Adam, the Sufficiently Advanced Aliens screwed up and accidentally crash-landed Lilith on the planet, resulting in Adam's Lance of Longinus activating and putting him in stasis. Then came the Katsuragi expedition...
  • Planet With: Earthlings, Siriusians, and Realians are all humans, but transplanted to different planets. There are also a few humans within the Nebula organization.
  • Pokémon: The Series: In the original series, Pokémon are alleged to have come from somewhere in outer space...early on. This hypothesis from the first generation was quickly dropped in all subsequent generations, to the point that we eventually meet Pokémon that created the earth, the physical universe, and all of time and space. In other words, the series progressed from panspermia to intelligent design. Try to make sense of that.
  • In Super Dimension Fortress Macross, both humans and giant humanoid Zentradi are stated to be descended from an extraterrestrial race of precursors called the "Protoculture". Subsequent Macross series go on to imply that all intelligent humanoid species in the Milky Way are "Children of the Protoculture".
  • A "Great Prehistoric Civilization" that seeded all the Human Alien planets in the galaxy is occasionally mentioned in Tenchi Muyo!. The Tenchi Muyo! GXP novels reveal that the civilization originated millions of years ago on the Earth where Dual! Parallel Trouble Adventure is set and that Tenchi's Earth isn't the original.

    Comic Books 
  • The Authority: One story has the team face off against an alien life-form the size of the moon — "the closest thing to God" that had "planted" life millions of years ago. Subverted in that life on the planet didn't develop as it should have, leading to, among others, the rise of humanity.
  • DC Comics Presents #1-2 has an alien race whose Living Ships' exhaust was microscopic organisms that started life on both Krypton and Earth, among other planets. (This story has been reprinted because it's also a Superman/Flash race.)
  • The 1980s Polish comic series Expedition tells the story of how Sufficiently Advanced Aliens come to Earth and help apes evolve in their image, creating the basis for several religions and mythologies in the process.

    Films — Animated 

    Films — Live-Action 
  • 2001: A Space Odyssey: The aliens didn't necessarily seed Earth, but most definitely influenced the evolution of mankind.
  • In the Intelligent Design "documentary" Expelled, Ben Stein gets Richard Dawkins to concede that it is theoretically possible that life on Earth could have originated by being seeded from life on other planets. The film treats this as some sort of coup for Intelligent Design, but a moment's reflection would clarify that this doesn't have any bearing on the question of how life itself first developed.
  • In the Mark Hamill film Laserhawk, aliens seeded life on Earth so they could come back millions of years later and harvest us for food. There is another race whose goal is to sabotage these seeding efforts. They attempt to do so on Earth but fail.
  • This is The Reveal of Mission to Mars.
  • The opening scene of Prometheus shows an alien sacrificing himself in order to seed the earth with his DNA. At least, that's what we think was going on there.

  • Animorphs:
    • The Ellimist (an extremely powerful Last of His Kind god-like being) seeded many planets with life during his war with his Evil Counterpart Crayak. This included custom-making the Pemalites and giving them a mission to spread life across the galaxy themselves. Crayak also created his own species — the Howlers.
    • Also, several Earth vegetables were apparently imported by crab people during the Cretaceous period.
  • This is part of The Reveal in At the Mountains of Madness; it turns out that all Earthly life evolved from microbes that the Old Ones planted here for food.
  • In The Cobra Trilogy, it's mentioned that almost all of the ecosystems in local space (including Earth) share similar biochemistry. The alien Troft theorize that this is due to these worlds being colonized by advanced spacefarers over a billion years ago, who were then wiped out by a chain of supernovas leaving behind only their bacteria to grow into the various species and worlds that arose later. It's mentioned as being very convenient for colonization when even in a new ecosystem you can probably find something edible; not so convenient is when the native predators realize that YOU are also edible.
  • The more scientific sort is a suggested origin of all life in the CoDominium universe (at least until The Mote in God's Eye introduces truly alien aliens).
  • In Nancy Kress's Crossfire, this is (or at least is suggested to be) the reason why planets around nearby stars have DNA-based life, which tends to make things easier for settlers. However, it's shown not to be universal when a plant-like, spacefaring alien species is encountered which is not DNA-based.
  • Eric: Rincewind drops a sandwich in a tide-pool and the narrator wonders what life would have been like with mustard rather than mayonnaise.
  • Extraterrestrial Civilizations:
    • Discussed; after the theory of Spontaneous Generation of life is discarded, the next theory advanced is that life on Earth was begun by spores traveling through the universe. It, in turn, is also discarded, because of the complications required for such microscopic life to both survive the trip to a second planet in a new solar system and the fact that it merely displaces "how does life originate?" to a different planet.
    • A footnote describes how Fred Hoyle has advanced the theory that comets, approaching close enough to Earth's orbit, are the source of viral pandemics.
  • The Darkness from Gone is an alien virus that was riding a meteorite when it crashed into Earth — specifically a nuclear plant, which caused it to rapidly mutate and somehow become a mind-devouring god-like being.
  • Hainish: The stories use this trope for human and semi-human life, spread by the Precursors in the title.
  • The History of the Galaxy: One of the novels reveals that biological life in the galaxy (possibly, the Universe) is an unintentional side-effect of an Energy Being's attempts to survive. The being was "born" in the magnetic fields of a gas giant but foresaw that its homeworld would eventually die. In order to escape, it created artificial proto-plasmic semi-sentient creatures called Forerunners. They would travel through space and spread the Energy Being to other compatible gas giants. The Forerunners were themselves mostly energy, but parts of them were organic and composed of rudimentary DNA (how else do you program an organism to do something?). Over billions of years, the Forerunners spread through the galaxy and, possibly, beyond. Some of them died, and their remains ended up on planets, unintentionally starting the process of life. This, of course, raises more questions than it answers, such as how the Energy Being came to be, and how it was able to create a semi-biological organism.
  • The Hitchhiker's Guide to the Galaxy Trilogy reveals what Earth really is. It is implied though that no organism on Earth is older than a few million years, and all were likely brought in from other places. Furthermore, humanity is the descendants of middle-men who crashed here 2 million years ago, completely unplanned by Earth's architects.
  • Incandescence: DNA-based lifeforms have evolved on many planets thanks to collision ejecta spreading the replicators between star systems. There are also ten other panspermias of different kinds of replicators. All are believed to have originated between twenty and thirty thousand light years from the center of the galaxy. The discovery of a meteor containing DNA in the central bulge of stars is surprising news partly because conditions there are believed to be too hostile to support the development of a biosphere.
  • Known Space:
    • Nearly all alien species evolved from food yeast grown to feed the Thrintun and their subjects, which was left to run willd when the Thrintun empire collapsed a billion and a half years ago. This is the reason why there are No Biochemical Barriers between most known ecologies and sapient species, which share the same common biochemistry, DNA, and preference for oxygen-rich planets around Earth's temperature range. There are some exceptions, as other biospheres developed on their own on other worlds, and tend to be very different from the Thrintun-derived norm; examples include Gummidgy, whose native life is deadly poisonous to offworlders and vice versa; the Trinocs, who evolved on a very cold outer-system world, breathe methane, and don't have distinct cells in their tissues; and the Outsiders, who have a biology base on liquid nitrogen and prefer to live in freefall and hard vacuum.
    • About million years ago, a species called the Pak, native to a world near the galactic core, sent out colonization fleets to seed new worlds farther out in the galaxy. In all instances, the hyper-intelligent, post-adult "Protectors" died out for one reason or another, leaving only the animalistic "breeders" to run wild and evolve. One such colony was Earth — modern science knows Pak breeders as Homo habilis. Another was the Ringworld, which is now inhabited by a wide variety of hominid species.
  • Last and First Men: At the end, the solar system is about to be destroyed by increasing radiation from the sun. The Last Men devote their remaining time to sending out "the germs of life" on the solar wind.
  • Lensman: The backstory states that all life in Earth's galaxy came from Arisian spores. Mentor tells at least one Lensman that this is why he's offering the Lens to the Galactic Patrol — they're "family".
  • A Lord from Planet Earth,: It's common knowledge among Human Aliens (no Starfish Aliens) that life on all of their planers began with intentional panspermia by the mysterious Seeders, who also left behind numerous Lost Technology and temples on each planet (except for Earth). What they don't know is that the Seeders are, in fact, humans from the future, who need an army but do not have the time for a massive breeding program. They send autonomous seeder ships into distant past to spread life and leave behind carefully-selected pieces of technology to accelerate the development of these cultures. They also choose planets in unexplored systems in order to avoid any temporal paradox and ensure that their "children" are unable to get to Earth via conventional means before the time is right.
  • Quintaglio Ascension: This is alluded to. Turns out that there was a ridiculously powerful species that lived in the universe that existed before this one, all but one died when the universe we know was formed, and that one last being seeded different planets with life forms — from Earth, which is the only planet where life formed naturally.
  • Spin: This is raised as a possibility by Jason Lawton, who theorizes that the Hypotheticals' slow migration throughout the galaxy for billions upon billions of years has resulted in unintentional seeding of habitable planets with life. Given that the Hypotheticals are fully capable of creating brand-new worlds capable of supporting life and full of "natural" resources, this is not unlikely.
  • To Be Taught, If Fortunate follows a group of astronauts ecologically surveying four planets in the twenty second century. Life is known to be common in this universe, but its origins are murky. On Earth, all cells have a chiral preference (left-handed amino acids and right-handed sugars.) However, because both types of amino acids and sugars occur evenly when whipped up in the lab, there are two possibilities: 1. Chiral preferences are a necessity for life or 2. Life originated from a meteorite slamming into Earth, which happened to have mostly left-handed amino acids. On their last planet, they discover single cellular life that has no chiral preference. Which means life uses whatever is on hand, and so life on Earth very probably originated from off-world ingredients.
  • Transpecial: Ten planets have been found that support life, and all known lifeforms use similar amino acids. The ky'iin have long believed that they're descended from a panspermia.

    Live-Action TV 
  • Referenced in Babylon 5. An early episode states that the Centauri claimed at First Contact that they and humans had a common origin, but DNA testing by the humans proved they weren't related. Centauri Ambassador Londo Mollari blames this on a clerical error.
  • Doctor Who:
    • The Time Lords were one of the earliest races to evolve, and they either seeded the universe with their genetic material or affected the fundamental properties of the universe itself, so it's not that Time Lords are humanoid, but humans are "Time Lord-oid".
    • "City of Death" says that life on Earth was accidentally started by an exploding Jagaroth ship.
  • In perhaps its biggest predictive stretch, an episode of Life After People proposes that this could happen to Europa, one of Jupiter's moons, which is believed to have water oceans. With no humans left to direct it, a deep-space probe crashes there and introduces Earth bacteria to these oceans, which gradually give rise to an entire complex aquatic biosphere.
  • Red Dwarf inverts this trope. Every single lifeform encountered, no matter how alien, is ultimately of Earthly origin. The first novelization even claims that it has been proven that no other life exists in the Universe, although exactly how you can prove this isn't clear. In the series XI episode "Krysis", the crew talk with the Universe itself, who backs this by expressing regret over only bothering to make one planet with life on it during its mid-life crisis.
  • In the final episode of Space: Above and Beyond, it's revealed that the aliens evolved from Earth bacteria that was deposited on their moon through panspermia.
  • Stargate-verse:
    • The Ancients are a race of Advanced Ancient Humans that originated as a splinter faction of the Ori and emigrated to the Milky Way millions of years ago, using their technology to create life in human form in the Milky Way and Pegasus galaxies (on multiple planets in Pegasus, on Earth alone in the Milky Way; the Goa'uld started raiding Earth and creating slave colonies elsewhere way later). They also inadvertently created the Wraith in Pegasus and were driven out of the galaxy by them. The Ori appear to have done the same in their home galaxy, probably where the Ancients got the idea.
    • The Asgard appear to have evolved independently, though, despite the fact that their original form (seen only once) is very similar to that of the humans. It was the millennia of cloning that resulted in Clone Degeneration (apparently, keeping the original DNA on file is beyond a race of Sufficiently Advanced Aliens).
  • Star Trek:
    • Subverted in the Star Trek: The Original Series episode "Return to Tomorrow" when an alien, Sargon, says that the human race may have developed from a colony of his people. The ship's astrobiologist rejects that, citing that there is a vast amount of evidence showing that humans evolved independently on Earth. Spock, however, realizes that may actually fit with the origin of Vulcans. To be fair, it was something that Sargon's species tended to do, and he had no information whether Earth or Vulcan specifically were colonized in this way.
    • In the 6th season Star Trek: The Next Generation episode "The Chase", it's revealed that the first starfaring species, which emerged 4 billion years ago, was so lonely that they seeded the entire Milky Way galaxy with a "genetic program" which would cause emerging life to, eventually, evolve into a form that physically resembled them. Since such a genetic program would likely herd all the different planets' developing genomes along the same narrow path, it actually makes sense that all humanoid species would be genetically similar enough to interbreed.
    • The Star Trek: Voyager episode "Year of Hell" establishes that life on several planets in the Krenim sector is the result of the same comet passing through their orbits in distant past.
  • The Twilight Zone (1985): In "A Small Talent for War", the alien ambassador explains to the United Nations Security Council that Earth is one of several thousand planets that his people seeded with life and where they sped up evolution two million years ago. They have deemed the experiment on Earth to be a failure due to the small talent for war that humanity displays. The Security Council doesn't realize until the next day that the aliens breed warriors to fight for them across the galaxy and that humanity's talent for war is too small to be of any use to them.

    Multiple Media 
  • In Halo, the Forerunners believed that the Precursors, a hyper-advanced race originating outside of the Milky Way, were responsible for seeding lifeless planets and speeding up the evolutionary process on planets that already had life. This is confirmed in Silentium, Mythos and Warfleet. The Precursors explored the universe for billions of years and seeded countless galaxies with the building blocks of life and sped up the evolutionary processes of certain species. It may actually go further than that as Silentium heavily implies that the Precursors didn't just create life throughout the universe but that they created the universe itself.
  • Star Wars:
    • Not Earth per se, but with all the life in that galaxy far, far away, the Star Wars Expanded Universe and Star Wars Legends must use this trope. The precursors have definitely created the Corellian system, and a cluster of black holes known as the Maw.
    • It's actually that most sentient life colonised most of the habitable planets in the Galaxy for so long, people aren't completely sure of its origins, but Coruscant is suspected to be the homeworld of most Humans, along with most other Humanoid deviations. Most Planets do seem to have their own native species on them, so it's not completely Panspermia.
    • The Celestials definitely made the Corellia System artificially, though the exact details of their influence, origins, and status as resident Sci-Fi Creator Gods are in question.
    • The Celestials are actually the first force users, or at least, members of the celestials were the first force users, the Father, the Daughter, and the Son. With the help of the Kilik Race, they created the Maw black hole cluster and Corellia in order to contain "The Mother", a.k.a. Aboleth.

  • In the Ayreon album 01011001, it is revealed that a technologically advanced race of fish aliens seeded a passing asteroid with their DNA, which then collided with earth—exterminating the dinosaurs already present there and allowing humans to flourish. They then directly tamper with human evolution and technological progress.
  • Implied in the Epic Rocking Nightwish song "The Greatest Show on Earth":
    From the stellar nursery
    Into a carbon feast
    Enter LUCA

    Tabletop Games 

  • At the end of Firebringer, Chosen reveals herself to be a member of an alien race who seeded Earth Billions of years ago.

    Video Games 
  • The H'riak in Alien Legacy are a violent race whose goal is to seed the galaxy with violet life that attacks anything not related to the H'riak. The Centaurians and the Empiants are the two known examples of their work, and this is the reason why the Centaurians attacked Earth the moment they found it. The Empiants were, actually, a failed experiment at creating life that can survive in a gas giant.
  • Not life per se, but human evolution is this way in Chrono Trigger: "Grown like farm animals, waiting for the slaughter. All our history, all our art and science, all to serve the needs of that... beast."
  • Corpse of Discovery sees humanity accidentally seeding an alien world (that may or may not be Earth) after the death of several explorers cultivates new life.
  • In Fossil Fighters, it is eventually revealed that multicellular organisms were created on Earth in order to be "guided in evolution" to recreate a lost race. Of course, things went wrong, creating humans instead of proper Lizard Folk. A in the end, it turns out subverted: all the creatures the dinaurians planted died out. Humans and everything else evolved out of Earth's natural life forms after all.
  • Kolibri's backstory, explained in the manual, includes a shard of an advanced planet landing on Earth after the advanced planet exploded. This crystal begat all life on Earth, and in Kolibri's time sustains it.
  • In Pokémon, all animal life on Earth, as well as the handful of known extraterrestrial ones, is descended from the Pokémon Mew who could potentially inhabit other areas of the universe as they have been shown to be capable of flying through the vacuum of space.
  • In Polycon, the Takari created the Polyconians to terraform worlds for Takari use, intending to later employ a "killswitch" virus to exterminate them. Unfortunately for them, some of the Polyconians survived, while the virus jumped species and wiped out the Takari instead.
  • Seedship: One of the game over dialogues mentions the titular ship crashing into a planet and the bacteria and organic matter from the remains of the colonists leading to the creation of new life.
  • Spore uses the proper definition of the theory. That is, alien bacteria hitching a ride on a rock to a different planet. This is the opening animation for the cell stage (the first stage). This was added to avoid answering the always difficult (and for now unanswerable) question of how life actually arose, and also to try to explain why all life in the universe is made of the same handful of parts.
  • In both the Pact and subsequent OG-verses of the Super Robot Wars metaseries, all life in the universe was actually created by an ancient lost civilization originating on Earth, handily justifying the numerous invading Human Aliens that appear as antagonists. Strangely, other continuities, such as Super Robot Wars Judgment feature Earth life being created by aliens, which they're going to have a hell of a time working into the OG-verse.
  • UFO: After Blank: Mentioned after studying the body of a Reticulan as a proposed reason for their amazing similarity to human biology in Aftermath.
  • The Big Bad reveals this during his Hannibal Lecture at the end of X-COM: UFO Defense, in an attempt to convince humanity that they should work together. Since the aliens have spent the entire game trying to brutally subjugate and murder the human race, and the aliens have been observed studying humanity as if they had no idea about our species, the point is pretty easily disproven. And then your soldier blows him up.
  • Xenogears: Life on the planet was created by an intergalactic war machine, to be harvested later for spare parts. However, it does have some native life forms, as evidenced by Balthasar's paleontological studies. While their planet's fossil record goes back millions of years, no evidence of humans or related beings can be found any further back than ten thousand.

    Web Original 
  • Hamster's Paradise: The planet HP-02017 was a lifeless but tectonically active world terraformed by an advanced spacefaring humanity in an attempt to make a colony. The lifeforms chosen were mostly plants and invertebrates that would be beneficial to people such as food plants, pollinating insects and decomposing microorganisms. Only one vertebrate was placed on the world as a way to test its habitability before being officially settled, the chinese dwarf hamster. However, for reasons unknown they abandoned the world before they could go any further and never returned, leaving the hamsters to spread and evolve into the planet's dominant lifeforms.
  • All life on Sagan 4 originated from a single cell planted there by the Nauceans, placing it somewhere between literal panspermia and alientelligent design. In the Alpha timeline, panspermia occurred again later as microbes hitched a ride on the seeds of the orbit voltflora and were shot directly to Mason, Sagan 4's moon.
  • Serina was seeded with select species by "mysterious creators", who then left them to evolve without intervention.

    Western Animation 
  • In Ben 10: Omniverse, it's revealed that the universe itself was created by a race of Sufficiently Advanced Aliens from the fifth dimension called the Contumelia, and all life in it arose from a race of unicellular aliens working with them called Slimebiotes.
  • Maury from Big Mouth claims that life in Earth started when a giant alien had sex with a hole in the ground.
  • According to the South Park episode "Cancelled", all life on Earth is one big intergalactic Reality Show, in which different species from other planets had been brought together for the amusement of the viewing public.

    Real Life 
  • It's possible life on Earth started that way, but as of right now there is no solid evidence of life anywhere else in the universe for that life to have come from.
  • It has been pointed out that if life on Earth did arrive this way, it still doesn't provide us any answers as to the origin of life — it just displaces where it originated from in the first place. A fairly convincing model of how the first cells might have formed on earth doesn't help.
  • While this may or may not happen with other life forms, it can happen with viruses. Well, for SARS, at least.
  • Invoking this trope via exploration, colonization, and eventual terraforming of other worlds is one of the explicit long-term goals of human space research. If there isn't already life out there, it'll be up to us to bring it.

Alternative Title(s): Alientelligent Design, Exogenesis