Let's say you have some advanced aliens seeding life on multiple earth like worlds. They want sapient roughly humanoid creatures to evolve from this starting seed. However, they are not dropping humanoids on the world, they are leaving smaller non sapient creatures.

The seed can be non sapient animals if it must be, but ideally there would be no obvious gaps in fossil records or otherwise clear evidence to an alien species that their world was seeded rather then evolved naturally. If the aliens can get away with only seeding microbes that would be great but that might be asking too much.

I will not accept convergent evolution as the sole answer. I don't believe the whole human shape is likely to be the only type of sapience to evolve due to convergent evolution alone on alien worlds, which will have some differences in temperature, pressure, gravity, and atmosphere. I want an answer for how the aliens can further encourage their desired body plan evolving.

Whatever the aliens do must be subtle enough it won't be detected, or what is detected can be written off easily enough without asking too many questions, by aliens with technology equal to or slightly more advanced then our own. So for instance they might have something in the DNA of their microbes designed to encourage evolution to a given form, except once the aliens can study DNA they likely would notice any DNA encoding complex enough to persist itself and continue to tweak other DNA over hundreds of thousands of years as something too unnatural to be likely to have evolved and so know something unnatural happened.

I'd prefer aliens to be completely hands off after the seeding. if that's simply not possible then I'd prefer options that that require the least amount of ongoing alien effort; like say some automated system left somewhere aliens wouldn't detect that does something every thousand years.

I won't accept an all knowing strong AI. Advanced very sophisticated AI is fine, thinking sapient AI is not.

So given the rather difficult limitations I have placed is it possible for seeded planets to be encouraged to create hominoids?

  • 2
    $\begingroup$ By smaller non-sapient creatures being seeded, do you mean something like ancestors in the anthropoid sequence? Something like the common ancestor of humans and chimps. Or did you mean something earlier? Say the common ancestor of all mammals. Or something else? Also, what timescale are you looking for evolution of sapience? $\endgroup$
    – Boba Fit
    Commented Feb 15, 2023 at 16:32
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    $\begingroup$ Natural evolution is not a directed process, and, additionally, powerful unpredictable external events do happen. E.g., consider life on Earth 100 million years ago, middle of the Cretaceous; mammals were small nocturnal mouse-like creatures with no reasonable expectations of development; multiple lineages of flying and non-flying, feathered and not feather dinosaurs coexisted. You may remember that a certain unpredictable event happened 66 million years ago, which dramatically altered the course of natural evolution... $\endgroup$
    – AlexP
    Commented Feb 15, 2023 at 16:40
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    $\begingroup$ "that will likely grow to the same humanoid form" .. likely? they can't, the only way you get likely is if they hang around to guide it through selective breeding (and that's not exactly the hands off approach typically implied by 'seeding life') and if you were going to hang around to do that then why would you start so far back on the chain of life rather than with an animal that's already almost there, it would just be a waste of time not to and if you had to be there to guide its evolution why be there longer than you have to be. $\endgroup$
    – Pelinore
    Commented Feb 15, 2023 at 19:09
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    $\begingroup$ @AlexP "You may remember that a certain unpredictable event happened 66 million years ago" like it was yesterday, it quite spoiled my breakfast you know ;) $\endgroup$
    – Pelinore
    Commented Feb 15, 2023 at 19:16
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    $\begingroup$ Play the numbers. Seed 10 Billion planets, good likelihood to get a few thousand humanoid lifeforms. From an evolutionary perspective, similar conditions and environment can be enough to produce similar forms, even if they are from completely different trees. $\endgroup$
    – user458
    Commented Feb 16, 2023 at 21:22

11 Answers 11


Artificial selection

This is a completely heartless way to go about it, but that might be what you are looking for. This is eugenics taken to an extreme, and would be considered an abomination to most people.

Start by picking the species that is closest to what you're looking for. Have a machine intelligence with murder-bots that purposely seeks out the evolutionary steps that don't head towards the humanoid shape. Have it assist that animal to make important steps, like bipedal stature or air-breathing.

What you're looking for is a cycle of glut and famine. Repeatedly allow the species to spread far and wide, then introduce a challenge that kills most of them off. During the glut sequences, perform surgical assassinations. Nanobot infections would probably be the best route for that, preferably introduced before the creature hits breeding age. This would be indistinguishable from a curse from God, and it shouldn't introduce a change in behavior.

Note that you won't wind up with creatures that are cross-breedable with humans. That is essentially impossible without gene grafting.

  • $\begingroup$ Doesn't this method lead to DNA diversity going down rapidly, and then to inbreeding, and then to extinction? $\endgroup$
    – virolino
    Commented Feb 16, 2023 at 11:10
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    $\begingroup$ That's why the cycles of glut and famine. The famine specifically weeds out the weak. When the famine ends, it will have opened many environmental niches for the the survivors to spread out into and create new biodiversity. $\endgroup$ Commented Feb 16, 2023 at 16:16
  • 1
    $\begingroup$ If the goal here is to make sure humanoids don't find out that aliens screwed around with their planet's ecosystem, this approach doesn't seem very stealthy. Future biologists would come across strange patterns of extinctions of species. "This should be indistinguishable from a curse from God" - this will only work for humanoids that are religious. $\endgroup$ Commented Feb 16, 2023 at 17:29
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    $\begingroup$ @GiantSpaceHamster, How can you be sure that it didn't happen to us? The 41k cycle of ice ages is suspiciously regular.... climate.nasa.gov/news/2948/… We had no idea how diseases spread prior the last couple of centuries. You don't have to have religion to posit an unprovable theory of how things die. $\endgroup$ Commented Feb 16, 2023 at 17:36

They seed the world with micro-organisms that contain vast amounts of specifically chosen "junk" DNA. Although this junk DNA has no direct impact on the micro-organisms this DNA does specifically encode many of desired traits, such as left-right symmetry, sensor cluster near a brain at the top, four limbs plus a tail, etc.. As the micro-organism evolves this junk DNA will often be accidentally incorporated in various new species. Encouraging the development of those traits. It isn't a fool proof plan, and could easily result in strong divergences but it could still work to increase the statistical likelihood of certain desired traits appearing in the final sapient species.

  • $\begingroup$ Not a bad idea. Of course if you just tossed DNA like that into an organism it would not look random enough to be believed to be natural. But with an advanced AI and simulations you probably could make something that doesn't quite encode things that looks random while still being close to the desired effect. Well, realistically maybe not given the utter randomness of evolution and gene interaction, but close enough most laymans will accept it as an explination. $\endgroup$
    – dsollen
    Commented Feb 16, 2023 at 14:59
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    $\begingroup$ @dsollen It's not clear that this would be particularly obvious, except possibly to an observer with at least the same level of expertise as the instigator. If you encode more complex traits in introns, surrounded by traits that could quickly produce a variety of fairly simple extremophiles, you'd have something likely to survive but only gradually and carefully shedding enough to expose the more complex traits. While chromosome counts vary widely among Earth life (en.wikipedia.org/wiki/List_of_organisms_by_chromosome_count), the upper end is dominated by microorganisms and plants. $\endgroup$ Commented Feb 17, 2023 at 21:43

So given the rather difficult limitations I have placed is it possible for seeded planets to be encouraged to create hominoids?

Only one that I can think of.

Start with animals that are already almost there anyway, so that would be monkeys and apes, or your alien equivalent.

If you want older fossil records than that provides then you'll just have to fake it .. read Strata for some ideas on that one.

And combine that with a scatter-shot approach.

You seed multiple worls, hundreds, thousands, millions or more, as many as you can.

Most of your seeded worlds will fail to produce intelligence and some of the seed monkeys and apes will evolve away from the desired hominid body plan .. but we're playing a numbers game here and the odds are that at least one of your seeded planets will bear the desired fruit.

Seed enough planets this way and the odds rise to a certainty.


Frame Challenge: a geological rather than biological solution

From the way the question is worded, you seem to be looking for a way to have a species with our current level of technology to not be able to figure out that they got placed on the planet in an unnatural way.

The answer for this may not lie in biology, but geology.

Pick a planet with a lot of geological activity. Tectonic plates that "recycle" themselves on the scale of a few tens of thousands of years rather than millions like on Earth. This would erase any fossil record, it would make it impossible to gather geological records for atmospheric makeup from a significantly distant period.

Once you find that planet, terraform it and place uneducated modern humans on it. They'll know how they got there, but without writing or recording systems the story will spread by word of mouth and will quickly turn into a myth and a swath of religions that will die off over the next few thousand years.

The fact that there is a lack of fossil record, or any record that we use today on earth to explain our past is a non-issue, due to the geology of the planet you would not expect to find such evidence. It would look the same whether they got dropped off by ancient aliens or if they evolved on their own.

  • 2
    $\begingroup$ You would need to at least seed a whole bunch of other animals so evolution can make sense, plus so we have something to eat. This would work for fossil record. i suspect there is some other historical records that would look wrong, but I can't say what exactly. You might have the problem that the creatures really shouldn't evolve the way they are on a world so active potentially, but that's probably something that can be written off as something scientists wonder about but no one is leaping to aliens as a solution. $\endgroup$
    – dsollen
    Commented Feb 17, 2023 at 15:37

There are 2 answers that spring to mind:

1: Same environmental challenges.

Evolution is driven by adaption to the Environment - so if the environment is mostly the same, it should stand to reason that the evolutionary output would be mostly the same.

So the Aliens artificially influence the Environment to nudge the evolution in the direction that they want - however this does violate the hands-off aspect of the seeding project.

2: Hard-wired Sexual Selection.

So this is a bit of a cheat, but in humans, Females are selective mates. This is differs from other animals, where whoever gets to be in the prescence of the females, gets to mate (Either by fighting off the dominant Male or by deception).

If we make the females choosy mates to begin with and we hardwire them to find certain characteristics attractive, then we can let the system do it's thing.

  • 1
    $\begingroup$ In the vast majority of cases, females are the drivers of sexual selection. That is, most usually females are the choosy sex. What cases of sexual selection do you know where males drive sexual selection? (In fact, humans may be one of the few such cases.) $\endgroup$
    – AlexP
    Commented Feb 15, 2023 at 20:39
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    $\begingroup$ "if the environment is mostly the same, it should stand to reason that the evolutionary output would be mostly the same" - random mutations are ... random, so there seems like to be a whole bunch of variation across repetitions of the same species being put in the same environment. Although there are also certain traits that may provide a big enough advantage that it would essentially always be selected for. How similar the end result would be is a non-trivial question. $\endgroup$
    – NotThatGuy
    Commented Feb 16, 2023 at 13:46
  • 1
    $\begingroup$ If you hardwire attraction to certain traits, the first few generations would strongly select for that, but that hardwiring could disappear quite quickly if there isn't a selection pressure for it (or some mechanism for it to remain hardwired). I expect attraction is driven by environmental suitability, so that would overwrite any hardwiring. $\endgroup$
    – NotThatGuy
    Commented Feb 16, 2023 at 13:51
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    $\begingroup$ @NotThatGuy You cannot really hardwire attraction to certain traits to a simple organisms. Hell, you probably cannot do it at all, unless you are at clark-tech level in bio-sciences $\endgroup$
    – Negdo
    Commented Feb 16, 2023 at 15:35
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    $\begingroup$ @TheDemonLord to claim that dominance based hierarchies, such as in most packs or places where males compete in competition to win mating access, is not an example of female choice is to miss the whole point of how these systems came about. They exist because the female was being picky and basically forced males to prove their right as a mate by winning dominance. There are females that have promiscuity and even Polyandry mating strategies, but they are the exception. Ironically early hominids likely were far more promiscuous then many mammals, there is a reason they obscure ovulation! $\endgroup$
    – dsollen
    Commented Feb 16, 2023 at 19:42

Step 1: Find a good planet

For this, you're going to want a planet that meets all of the following:

  • In the goldilocks zone of it's star
  • Is around a fairly stable star (no crazy solar storms please)
  • Has an intact magnetic field (gotta keep the UV levels down)
  • Has a surface gravity less that 1.2 G (or else large life forms won't be practical)
  • Has surface water
  • Has developed life already

The last assumption is tough from a worldbuilding perspective. We have no idea yet what the chance is that a planet will develop life, nor do we know all the chemical compositions that can possibly sustain life. However, most of the normal journey to intelligent life is at hundreds of millions of years of unintelligent life that do a lot of atmospheric changes. If you're starting with barren planets, you'll have to fake the whole geologic record, and that's hard. We're also going to assume that the life on these planets is chemically compatible with the progenitor species (ex. all of them use DNA or equivalent).

Step 2: Terraform the planet

I do actually mean "terraforming" to mean "make it like Earth". We're starting with a planet that's pretty close, but there will be some nudges that need to happen. You may need to add/remove some CO2, melt/freeze some ice caps, add/remove some active volcanoes, etc. We want this planet to have an ideal habitat for 1-3 meter in size land animals. While we're at it, we ought to top off the planet's supply of those key metals (iron, copper, tin, zinc) to enable technology use.

Step 3: Tweak the biosphere

One big thing you're going to want to do here is kill off any mega-fauna that would be excessively dangerous to humanoids. This might happen as a natural side-effect of your terraforming, but if not, a well placed asteroid ought to do it.

Next up, you want trees. Trees are key for so many reasons. They give a big evolutionary advantage to hands/claws, because with hands, you can climb. They also tend to produce really energy dense food in the form of fruits and nuts that help with that big brain development. Finally, wood is really great for all sorts of technology, like fire, spears, and dwellings. Make sure to edit your tree seeds to match the local DNA.

Step 4: Prime a candidate species

Next, you want to find a good candidate species and give them a boost. This species should be land-based, have bilateral symmetry, have some hand-like appendages (claws are fine), and any complex neural infrastructure. Make a few targeted viruses to bestow this species with some genetic advantages. These advantages should give this species survival advantages that also push it in the direction you want, such as prehensile appendages, upright stature, bigger brains, etc.

Step 5: Let it cook

Evolution takes time. You're going to need to chill out for some 10s of millions of years for this plan to come to fruition. Maybe go hang out in your stasis pods or go hyperspace racing to pass the time.

Alternative plan

If that plan is too slow, we're going to need to be really technologically advanced. (Hmm; if only you had 10s of millions of years to develop better techniques for this...)

If technology level is no object, you could search for barren planets, drop onto them a fully formed ecosystem with humanoid precursors included, and then fake the geological record and fossil record to make it look like life evolved their naturally. The fossil record is the easy part; you just need to bury dinosaur skeletons and trilobite fossils with the right balance of radioactive isotopes. The geologic record is a lot harder to fake, because you need to oxidize huge parts of the crust (assuming oxygen doesn't show up in sufficient quantities without life).

Then, you can leave it for only a few million years and let evolution make some final tweaks to your proto-humanoids. In fact, with this level of technology and effort, you could have fully formed humanoids in a few thousand years if you wanted to; it's just a question of how much time you want evolution to have to create variation.

  • $\begingroup$ I was all ready to point out that DNA of your existing aliens wouldn't match the DNA of your microbes but you already caught that so god job there ;) $\endgroup$
    – dsollen
    Commented Feb 16, 2023 at 19:14


Your planet needs to have an occasional ice age to attempt to kill off all the life on it.

Back in the early years of our world, reptiles ruled the planet. It was simple. Reptiles are cold blooded, require less energy and hence had a much better chance of survival since they didn't need to feed as much. Mammals were mostly restricted to small terrified balls that had to scuttle around these massive dinosaurs and hope they weren't noticed.

However that changed once the Ice Age hit. The reptiles, no longer able to regulate their body temperature became lethargic and weak and slowly died out. Mammals were now left to thrive, and eventually evolve.

Dry Spells

Surviving the Ice Age is one thing. You can do it if your Fat and Hairy. Or if you had Fire. The manipulation of Fire is a key step for intelligent creatures and the ability to manipulate fire means your creatures will have dexterous limbs. A regular dry season helps promotes fires, and with the exposure to fire, your creatures should eventually develop the ability to use that fire to their benefit.

Just take a look at the FireHawks down in Australia that use fire to force prey into clear openings to make them easier to hunt. Maybe given enough time, they could have become sentient as well.

(*Added in After: Fire also lowers Oxygen levels which will help stop our Insect overlords from becoming the dominant species).

Arms and Legs

With a combination of these two elements, its just a matter of time until you get a creature with limbs that can weld fire and a huge investment into the use of their Brain instead of raw strength and power. These creatures will naturally develop the 2 arms and 2 leg system almost all mammals adopt today. Why two arms and two legs? Because only having 1 arm is a huge risk. Investing the energy to develop 2 arms greatly increases your chances of survive. And investing even more energy for 3 arms doesn't see the same payoffs as having 2 arms did, so its just less likely to happen. This also applies to legs, ears, eyes and nostrils. although I can't really explain the Nose/Mouth situation.

Standing Up

After all this invested energy, our creature will have its final change into a humanoid form. Standing up on two legs. The investment of evolutionary energy into the brain, and dextrous limbs is accompanied by the weakening of our muscles. We no longer need to be strong, powerful or fast. Instead we need to be efficient, because our huge brains are consuming an ungodly amount of energy compared to everything else. So we develop strong leg muscles and weaker arm muscles. We stand upright to balance on our leg muscles and our hands become more delicate and refined, capable of even greater tool manipulation.

  • $\begingroup$ Sorry to nitpick, but reptiles survived numerous ice ages, and while there was an ice age after the meteor that killed most dinosaurs and mammals raised in dominance, it's generally agreed that it wasn't the ice age but the dying out of most of the (likely warm blooded and not reptilian...) dinosaurs opening up a number of new niches for mammals to spread into that lead to mammals rise in dominance. In other words I'm not convinced ice ages lead to mammals. $\endgroup$
    – dsollen
    Commented Feb 16, 2023 at 16:08

You want your beings to achieve two important traits: intelligence and humanoid form. I can see three paths to achieving that.

  1. They become humanoids AND intelligent in parallel. Probably the most difficult.
  2. They become humanoids, and only LATER they become intelligent.
  3. They become intelligent, and only LATER they become humanoids.

Of course, if you choose path 1., you might have to restart the seeding many times, before the good things start to happen, and time might run too short for practical purposes.

So we go ahead trusting paths 2. and 3. (more likely to succeed), but not necessarily discarding path 1.

If the planet is big enough, seed several independent groups, ideally in areas which makes it impossible for them to interbreed (e.g., different continents). Ultimately, seed different planets.

Pure evolution might not do the job, but some form of higher intelligence (natural or artificial) will guide the evolution through changes in the environment.

In parallel, the advanced aliens might even "plant" some species which are very skillful and intelligent, but "ignorable" (dogs, rats, sparrows...). They have the ability and the "tools" to influence the evolution of the target species, and nobody will really care to analyze their DNA. The tools can be some bacteria which they can produce as-needed, when-needed, in order to influence the numbers of populations (increase or decrease). They should not influence the numbers too much, too often - obviously. They might destroy exactly the good individuals by mistake.

Bonus: the "guardian" species has a kill-switch - when the target species (intelligent humanoid beings) are at the right sage of evolution, with the right traits, in the right numbers, in the right place - they just lose their extra-intelligence and their memories of everything that happened. Practically, they devolve slightly to completely hide their purpose.


A lot of humanoid factors locked in over 400 million years ago.

First of all "it's just convergent evolution" actually is not a bad answer. There are tons of reasons I will discuss below about why humanoids are the most likely body plan for sapient life, but by introducing something along the lines of a lobe fish, you can already have enough evolutionary factors locked in to pretty much guarantee humanoid life.

Let's delve into this a bit. Intelligence has evolved a lot of times here on Earth. Many species of birds, dolphins, whales, and cephalopods demonstrate level of intelligence comparable to early hominins and all beat our ancestors to this level of intelligence by million years... but despite evolving intelligence, means of communication, and basic tool use similar to what we had just a few million years ago, none of these animals took the final steps that we humanoids did. These organisms never developed tool using beyond that of found or slightly modified objects.

I know sapience means a lot of things depending on who you ask but for the remainder of this answer, I will used sapient to mean capable of forming technologically advanced societies, simply for lack of a better word.

Sapience can't evolve in aquatic life

It has been argued that several marine animals are at least as smart as humans, but none of them seem to be able to wield any technology more advanced than a sharp rock. In order for any animal to get past the early stone age, it needs to master fire. This basic skill is required for ceramics, metallurgy, cooking, glue making, etc... practically every human technology that makes us more advanced than chimpanzees requires at some point in its production, the application of fire. So, all the smart stuff that evolves in the water never becomes an industrialized society because they can't make the tools of the trade.

Seeding Caveat: DNA is rarely preserved for more than 1-2 million years; so, when comparing the fossil records of animals 400 million years ago, there are no genetics to compare, just shapes and forms embedded into stone. This means that if your aliens are seeding a young world that already has complex aquatic life, but no dominant terrestrial fauna, they could decide to drop in something like a lobe fish. This way, they could make sure that thier seed organism wins the land race, but the seed life happened so long ago that by the time sapient land life emerges that any sketchiness in the fossil records would fall into the "to be expected" category.

Sapience can't evolve in small life

This is more than just a limitation on brain size. It goes right back to the fire issue. Small fires made by small creatures behave very differently than large fires made by large creatures. Fire is not practical for a stone age creature much smaller than humans because it takes so much fuel to keep them burning. Containing the heat of a fire to concentrate it for things like ceramics, smelting, and baking also requires a certain minimum size to be effective. This means that even if you had a super smart squirrel like creature, the effort it would take to gather the amount of wood it would take to smelt ore or fire clay would be proportionally immense. A wood kiln for example consumes a minimum of about 1 cubic meter of wood. This is true if you are firing a single small cup or a whole tea set because it takes a continuous burn and trapping of heat to get up to and maintain temperatures without shattering your clay and make it bind.

Seeding Caveat: Animal size evolves up and down very quickly. There is no real controlling for the ability to introduce a seed organism and ensuring it becomes big, but you can introduce a seed organism and expect that some of its descendants could be big, and those will be the most likely to develop sapience.

Sapience will be extremely rare in species with more or less than 4 primary appendages.

Bilateral symmetry is the preferred body plan of nearly all complex life forms. While evolution likes to start off with asymmetry, the prevalence of bilateral symmetry in complex life on Earth seems to indicate a strong preference for this across all evolutionary paths. This means that body plans with 1 or 3 primary appendage is unlikely in more complex life forms. 2 primary appendages generally won't work with terrestrial life because if terrestrial life evolved with only 2, there is guaranteed to be a lot more evolutionary pressures to makes those into specialized feet than hands. This means that in the vast majority of cases, sapient organisms need at least 4 appendages to have both specialized walking and tool using appendages.

But... as I said previously, small life and aquatic life does not make good sapient life, which leaves the question about if more than 4 limbs is likely. Appendages are heavy and take up a lot of resources. The bigger an animal gets, the more expensive extra limbs becomes in terms of the square cube law and pure energy requirements to maintain them. This is why pretty much all large terrestrial life on Earth are tetrapods. It's a perfect compromise between have enough libs to get the job of surviving done without having so many limbs that you are wasting resources. Just like every branch of large terrestrial life is tetrapods on Earth, it seems feasible that this body plan will be the norm on other worlds (at least those with similar gravity).

Seeding Caveat: Here on Earth, we pretty much locked into the tetrapod body plan very early on. Tetrapods emerged even before we moved to land, and we never once had a mutation lead to any significant populations of children with more or less primary appendages. So, if you seed with a tetrapod, they will likely stay tetrapods.

Sapience requires a World with Earth like mass

A heavy world requires smaller life which I've already explained comes with a lot of limiting factors, but what about smaller worlds? Well as it turns out smaller worlds become dead worlds much faster than big ones. The core cools, the magnetic fields disappear and the atmosphere blows off into space. This means smaller worlds won't give evolution enough time to get to intelligent life.

Seeding Caveat: Very Earth like worlds may be a prerequisite of your progenitor species. While it might be possible for life to evolve in lots of strange places, if we humans wanted to seed another world, we'd have to pick something VERY Earth like. Earth like atmosphere, hydrosphere, gravity, mineral composition, temperature, year length, axis tilt, EM field, etc... if your alien progenitors are seeding the universe with THIER primitive life forms, then they will have to be a lot more picky than natural evolution meaning that all worlds where thier seed organism establish a foothold must provide very similar evolutionary pressures to thier homeward.

Sapience requires something like hands

While there are some pretty smart birds and bears with relatively dexterous feet, none of these animals can manipulate things with nearly the ease and precision that a humanoid can. This will make getting past primitive technology very hard for those without the hands to perform intricate tool use. While I don't think exactly 5 fingers with 3 joints each will be a given, I do think that something with multiple flexible finger like protrusions will be necessary.

Seeding Caveat: Like Tetrapoda, fingers locked in pretty early too. While an animal could perhaps evolve with tentacle like hands, pretty much all tetrapods here on earth have 5 fingers and toes. So, even if tentacles or 6 fingers is more common among native organisms, the seed organism will likely go on to have 5 fingers. Scientists will note the mutation in the fossil records, but this will not cause any red flags, but be part of thier early evolution narrative.

Non-humanoid life gets out-competed by humanoids when it does happen

With all the selective pressure pushing towards humanoids, this means that in the rare case where another very different body plan is selected for, that body plan will typically go extinct once its world also evolves a humanoid.

Seeding Caveat: In natural evolution, there is no guarantee that humanoids will ever evolve to compete with native sapient life, but if you introduce just about any tetrapod ancestor, the humanoid form becomes a lot more likely


What all of this means is that there is a LOT of pressure for convergent evolution in sapient life. Just like the general form of a cat/dog/hyena etc. is selected for over and over again for terrestrial predators, we will see something generally humanoid selected for over and over again in sapient life. There will be a lot of variance, sure, but by-in-large they will nearly always be upright terrestrial tetrapods of roughly human size with 2 specialized hands and 2 specialized feet... aka humanoids. Especially if you seed the planet with a tetrapod to get things started.


  • $\begingroup$ Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Worldbuilding Meta, or in Worldbuilding Chat. Comments continuing discussion may be removed. $\endgroup$
    – L.Dutch
    Commented Feb 16, 2023 at 20:19
  • $\begingroup$ As The Law Of Cosmic Humanoidity states "All sentient lifeforms must be more or less humanoid in shape, because reasons". This works well, except when a humanoid race encounters e.g. a blobbonian race which only knows about the Law Of Cosmic Blobbonianness ("All sentient lifeforms must be more or less blobby in shape, because the blobby gods insist that it be so") and a xenophobic holy war of annihilation ensues. $\endgroup$ Commented Feb 17, 2023 at 17:55

Sorry. Evolution doesn't work the way you'd need. In Wonderful Life: The Burgess Shale and the Nature of History Stephen Jay Gould emphasizes the role of contingency in evolution.

Gould's thesis in Wonderful Life was that contingency plays a major role in the evolutionary history of life. He based his argument on the extraordinarily well preserved fossils of the Burgess Shale, a rich fossil-bearing deposit in Canada's Rocky Mountains, dating 505 million years ago. Gould argues that during this period just after the Cambrian explosion there was a greater disparity of anatomical body plans (phyla) than exist today. However most of these phyla left no modern descendants. All of the Burgess animals, Gould argues, were exquisitely adapted to their environment, and there exists little evidence that the survivors were any better adapted than their extinct contemporaries.

Gould proposed that given a chance to "rewind the tape of life" and let it play again, we might find ourselves living in a world populated by descendants of Hallucigenia rather than Pikaia (the ancestor of all vertebrates). Gould stressed that his argument was not based on randomness but rather contingency; a process by which historical outcomes arise from an unpredictable sequence of antecedent states, where any change in the sequence alters the final result. Because fitness for existing conditions does not guarantee long-term survival — particularly when conditions change catastrophically — the survival of many species depends more on luck than conventional features of anatomical superiority. Gould maintains that, "traits that enhance survival during an extinction do so in ways that are incidental and unrelated to the causes of their evolution in the first place." Gould earlier coined the term exaptation to describe fortuitously beneficial traits, which are adaptive but arise for reasons other than incremental natural selection.


One thing I can think of is to drop in a self-maintaining computer system running an AI or even a simple recursive computer program to "domesticate" and facilitate selective breeding of the non sapient animas until sapience is achieved. (aka start with species, and look for and promote traits that lead to sapience by either inhibiting others or actively helping the target) To that end, if the machine is durable and self repairable enough, you can just drop that one in and then it can work out a sapient humanoid from existing beings on the place it was dropped in.

That or within the seeding animals, there already lies the genes, unexpressed, and little by little it is unlocked through evolving the genes for the proteins needed to express it. DNA can't really be taken from fossils so its technically not cheating. The only worry is that the DNA information may warp over time or the animals will evolve away from the target genome but yea.


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