Sentient alien species in fiction are almost always at least vaguely humanoid. Is being humanoid required to have human-like intelligence and sentience? If not, what other body builds would be viable for a (intelligence wise) human-like sentient species?

Assume earth-like conditions. For simplicity’s sake, this species should only need to be capable of doing what humans are capable of, such as tool building, construction, researching, social behaviors and utilizing or building vessels if needed. This species should also be placed similarly to humans in the food chain.

  • 2
    $\begingroup$ This seems like more of a discussion prompt about existing works of fiction than a specific question related to a fictional world you're building. $\endgroup$
    – sphennings
    Commented Jun 4, 2023 at 6:23
  • 7
    $\begingroup$ "Sentient alien species in fiction are almost always at least vaguely humanoid": Stanisław Lem's Solaris (1961) (with two film adaptations, one by Andrei Tarkovsky in 1972 and one by Steven Soderbergh in 2002) is an extreme counter-example. Ted Chiang's Story of Your Life (1998) (adapted for cinema by Denis Villeneuve in 2016 as Arrival) is a less extreme but still very intriguiing conter-example. $\endgroup$
    – AlexP
    Commented Jun 4, 2023 at 10:47
  • 1
    $\begingroup$ "tool building, construction, researching, social behaviors and utilizing or building vessels if needed" - other animals do all those things except researching which requires the one thing that separates us from them : language (the only subject here that's been beaten slightly less to death than thumbs). $\endgroup$
    – Mazura
    Commented Jun 4, 2023 at 20:22
  • 3
    $\begingroup$ This is an open-ended question, seemingly asking us to do your work for you. It is more fruitful if you decide upon a build, and ask here if it makes sense. That way you get focused, detailed answers. Alternatively, asking for minimum requirements would put a limitation on the open-endedness of the question which would improve it. $\endgroup$
    – Joachim
    Commented Jun 4, 2023 at 20:47
  • 4
    $\begingroup$ Aliens being humanoid made it much easier for the actors in the past, I guess. The martians in H. G. Wells "The War of the Worlds" are not much homanoid. $\endgroup$
    – U. Windl
    Commented Jun 4, 2023 at 21:26

5 Answers 5


It can be assumed that two basic conditions must be fulfilled:


The being must be able to change its environment (for example, a whale could be more intelligent than a human being - it would still not be able to build a technological civilisation). For this it needs extremities with which it is possible to produce and use a tool. Here it is conceivable that this does not have to have any resemblance to human hands at all. Claws, trunks, tentacles, etc. are also plausible. Similarly, the number of these manipulators does not matter as long as they are applicable for the purpose of tool use. Anything from one to any number is possible. On earth, almost all living beings are symmetrically shaped. Whether this has to be the case universally is questionable, however.

Ratio energy intake/energy consumption

The effort to acquire energy (food) must be in a certain ratio to the consumption of this energy. A being that has to spend most of the day taking in food will find it difficult to find the time to invent the use of tools. Under Earth-like conditions, this would be difficult above a certain weight. At least in the case of mammals, a certain size should probably not be undercut, since a very fast metabolism also consumes too much energy. Apart from Earth-like conditions, almost any form is possible here - it depends on the ecological conditions and these in turn on the planetary conditions.

Apart from these two basic prerequisites, everything is actually somehow plausible.

For a technological civilisation, communication and information transfer over longer periods of time is necessary. Humans have developed language (acoustic signals) and later writing (optical signals) for this purpose. However, other forms are also conceivable for this. For example, optical signals instead of spoken language, manipulation of the magnetic environment, use of a tactile sense and much more.

Whether individual self-awareness is necessary to build a technological civilisation is an open question. It seems at least plausible that collectives of living beings (on Earth e.g. bees and ants) could be able to manipulate their environment to such an extent that a technical civilisation emerges in the end.

A good reading tip on this subject would be Adrian Tchaikovsky's Children of Time, where he describes in great detail and plausibly how spiders build a technical and eventually spacefaring civilisation.

  • 4
    $\begingroup$ I doubt your second point about energy intake because larger animals are generally more intelligent. Humans are one of the largest species on the planet. Elephants are pretty smart too. The larger an animal is, the more it can afford a big brain (it's not just brain-to-body-size that matters for intelligence, absolute brain size also matters). In the extreme of size you could imagine a whole planetary ecosystem that is intelligent with the individual plants and animals acting like neurons. $\endgroup$
    – causative
    Commented Jun 4, 2023 at 18:07
  • $\begingroup$ Fair point. Probably weight really isn't the decisive factor. It's about the ratio. How much time do I have to spend for energy intake? The absolute amount needed could also be decisive, depending on the respective ecological niche. Elephants need about 250,000 kilocalories per day, humans about 2,500. However, elephants are not 100 times bigger than humans - so the ratio is better for humans. $\endgroup$
    – domai2312
    Commented Jun 4, 2023 at 18:59
  • $\begingroup$ @causative Well, how much intelligence does a species need? Recently I had a hard time trying to catch an ordinary house spider; I had no idea how fast they can run! $\endgroup$
    – U. Windl
    Commented Jun 4, 2023 at 21:29
  • $\begingroup$ Is the spider doing "tool building, construction, researching, social behaviours and utilizing or building vessels if needed." (Well, sounds like it doesn't need the vessels!) $\endgroup$ Commented Jun 4, 2023 at 21:48
  • 1
    $\begingroup$ I would like to add that while the number of manipulators does not strictly prevent tool-making, having 2 or more seems to be the best so far, as you can then use 1 to give a stable base for interaction, and the other to hold the thing needed for interaction. You can get by with 1 if you pin the base to the ground, but holding on to the base yourself allows more precise interactions. Too many, on the other hand, can violate condition 2 (energy intake), though that can be fixed by world-building $\endgroup$ Commented Jun 5, 2023 at 14:53

Pretty much all of them

All that a technological species needs is some sort of manipulator, enough sociality to transmit knowledge, and the basic intellect needed to make tools

Every one of these traits can easily arise within almost any bodyplan at all. So long as the animal is macroscopic and not specialised to a low-energy mode of life, then there is absolutely no reason that prohibits it from having manipulators and sociality


The octopus building plan might be fun.

The cognitive capacities and behavioural repertoire of octopuses have led to speculation that these animals may possess consciousness. However, the nervous system of octopuses is radically different from those typically associated with conscious experience: rather than being centralised and profoundly integrated, the octopus nervous system is distributed into components with considerable functional autonomy from each other. Of particular note is the arm nervous system: when severed, octopus arms still exhibit behaviours that are nearly identical to those exhibited when the animal is intact. Given these factors, there is reason to speculate that if octopuses do possess consciousness, it may be of a form highly dissimilar to familiar models. In particular, it may be that the octopus arm is capable of supporting an idiosyncratic field of consciousness. As such, in addition to the likelihood that there is something it is like to be an octopus, there may also be something it is like to be an octopus arm. This manuscript explores this possibility.


All you need is a closed circulatory system(better for transporting oxygen or similar element), a big cranium(big brain means better thinking), manipulatory appendages, and the ability to walk and eat.

A radial body plan isn't the greatest because it may be more energy intensive. There may be a reason why the dominant creatures are bilateral. On a radial creature they would have far better vision because they would have eyes looking in every direction.

The reason humans walk on two legs is because it is less energy intensive. You can absolutely have a four legged creature as long as it has two arms with manipulating hands.

Icthys King and EdvinW both questioned why a large cranium is needed. Unless you are going for a slug or sea star shape, a big noggin is needed. This is because of the massive size a brain would have to be to promote human-like intelligence. In a slug creature the brain would be at the top of the body, alongside the ears, eyes, mouth, and nose. For a sea star creature the brain would be in the center, like that of a sea star.

Icthys King questioned why I originally said opposable thumbs were needed. I said this because the only creature that has ever taken over a planet has them. But other forms of manipulators aren't out of the question. EdvinW asks about tentacles, which would work fine. Octupi use them all the time. An assortment of arms wouldn't be the best idea. This is because many appendages are energy intensive and most creatures evolve to use all the energy they have to the best of its potential.

  • 1
    $\begingroup$ A lot of intelligent species don't have especially oversized craniums, the closed circulation isn't entirely necessary (see bees), and of all animals with manipulators only one group has opposable thumbs $\endgroup$ Commented Jun 4, 2023 at 16:11
  • $\begingroup$ @IchthysKing And you'd call their intelligence human like? $\endgroup$
    – user458
    Commented Jun 4, 2023 at 16:26
  • $\begingroup$ @fredsbend It's possible $\endgroup$ Commented Jun 4, 2023 at 16:32
  • $\begingroup$ Why would the creature need a cranium at all? Why would radial symmetry make it harder to see? @IchthysKing already asked about opposable thumbs: Why not tentacles or a multitude of arms that can hold things between them if necessary? $\endgroup$
    – EdvinW
    Commented Jun 5, 2023 at 12:45
  • 1
    $\begingroup$ @EdvinW You bring up good questions that I then asked myself a few hours after answering. I planned on updating the answer but never got around to it. I will do so now. $\endgroup$
    – Martamo
    Commented Jun 5, 2023 at 12:48


If you're specifically looking at a sapient alien species, then the only realistic choice would be a slug-like or worm-like form, perhaps with leg-tentacles or even some sort of shell

This isn't just for sapients, but all alien animals: All of the special traits like bones and veins and ears are relatively rare among the different phyla of life on Earth, which seems to imply that they'd also be rare amongst the phyla of distant worlds. If we also consider the possibility of more complex phyla being extincted, most worlds would be limited only to simple worm-like forms for all life, including its sophonts

  • 2
    $\begingroup$ I think your argument is a little reductionist. Yes, the vast majority of life is 'simply worm-like forms', we only know of one species that is intelligent (per the question's definition). Following the same logic we could conclude that all intelligent life must be roughly 1 to 2m tall, have two legs and two arms, be mostly hairless, have two forward facing eyes, etc. $\endgroup$ Commented Jun 4, 2023 at 20:17
  • $\begingroup$ In truth, we do not know what the requirements for an intelligent species are. However, we can make some reasonable assumptions, such as that they must be a certain size. This then imposes requirements such as some kind of structural support (e.g. bones in the case of humans) and an efficient circulatory system (e.g. a heart, veins, etc. in the case of humans). What we should expect is that these problems have been solved differently to how earth-life has solved them. So, in my opinion at least, we can expect intelligent life to have a level of complexity greater than a 'simple worm-like form' $\endgroup$ Commented Jun 4, 2023 at 20:21
  • $\begingroup$ @NeilTarrant Why is it reasonable to say that they need to reach some certain size? What's the reasoning? $\endgroup$ Commented Jun 4, 2023 at 20:37

Not the answer you're looking for? Browse other questions tagged .