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I won't go too much into detail because I'm still trying to figure things out but my humanoid species lack organs used for eating and swallowing (because they're not required to eat). Here's the list of organs they lack:

  • Esophagus
  • Liver
  • Stomach
  • Gallbladder
  • Pancreas
  • Colon
  • Small intestines
  • Rectum

Because of this, they can't eat, swallow, burp, or fart (I'm assuming). However, they can breathe (in and out of their nose and mouths), speak, laugh, scream, and make (other) noises. Is this plausible? And since they don't have a colon and small intestines, how would their stomach be positioned?

Note: My species is plant/flower-based.

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – L.Dutch
    Aug 3 at 3:12
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It really depends on why, as you say, they’re not required to eat. There are a few examples of organisms with reduced or non-functional digestive tracts, such as the silkworm moth (lives off larval fat storage and doesn’t feed as an adult; lifespan is one or two weeks), the male of certain anglerfish (becomes a semi-absorbed symbiont of the larger female and metabolises what she eats) and some other parasites. You may still need some form of waste excretion, depending again on what sustains these organisms: see Life without excretion?

Edit based on additional photosynthesis info and @Willk’s observation: these humanoids are the final, reproductive stage of a long-lived plant; they don’t eat because the plant has left them with a store of energy built up over many growing seasons. These beings look humanoid because humans are their pollinators. Like a bee orchid, they look beautiful and desirable to humans, who end up as carriers of their pollen after [sex? Physical contact?] with the plant-humanoid. Humans are the most mobile, social and enterprising of species - what better vessel for spreading your plant species far and wide? As the human “mates” with a second humanoid pollen being, the seed can form and its humanoid carrier (or even the human involved!) gets an irresistible urge to “set down roots” in a secluded, sunny place. Fertilised by the decaying remains of its carrier, the seed starts a new decades-long growth as an unassuming plant, until the cycle starts again.

On the shape of the remaining organs, mostly you’d have to decide what the abdominal cavity would be filled with, if anything. The organs themselves are pretty squishy - check out x-rays of Victorian corsetry to see all sorts of creative rearrangements. However, if you’ve ever seen a butcher at work, you’ll know there’s a pretty large volume of guts sitting in the abdomen; if you take these out, you’re either left with a very freaky-looking hollow abdomen (and possibly a very fatigued diaphragm that has nothing to rest on) or you have to fill the cavity with something else (packing peanuts? Handy little storage pouches?).

Also if you want them to be able to speak, you’ll probably need a lubricant - we use saliva, which we swallow, so they may need to drool it out if swallowing is out of the question.

Ultimately, you need some break from reality to justify your initial “no need to eat” choice. The consequences can’t be entirely realistic because the premise can’t be either. So you might as well go with whatever works best narratively.

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  • $\begingroup$ The reason why they're not required to eat because they aquire their energy through photosythensis (they're a plant/flower-based life form). I think the only way they can excrete waste is the same way that plants do. They'll just need leaves on their body, in the same style elemtilas suggested. They'll be able to produce salive and keep their mouth hydrated through water and I think storage pouches or useless but useful organs can fill in the stomach so it wouldn't freakishly hollow. $\endgroup$
    – Sydni
    Aug 2 at 18:19
  • $\begingroup$ @Sydni The energy from photosynthesis is very small when compared to the energy an humanoid being uses to move out and about. While a creature that walks about could use photo as a complement to their diet, it wouldn't be enough to keep a living humanoid being working, by itself. $\endgroup$
    – T.Sar
    Aug 2 at 19:43
  • $\begingroup$ @Sydni to put it another way your human need more than 100 times the energy they can get from the sun. $\endgroup$
    – John
    Aug 2 at 20:25
  • $\begingroup$ @Sydni to put it in perspective my plants get 24 hours of light and they get exactly enough energy to just sit there and grow slowly. $\endgroup$
    – Aww_Geez
    Aug 2 at 20:27
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    $\begingroup$ @Willk maybe that could also resolve the energetic problem - they live very long lives as plants, slowly collecting a large energy store (fundamentally a potato) that they use in one short “flowering” after which they die, like an agave. They start out as these irresistibly charming sexy party animals, and as their potato runs out they grow faded and tired and start looking for a nice burrow to rest in… Basically the humanoids are really the plant’s pollen, and it turns out this plant has come up with the most fantastically elaborate way to make their pollen mobile. $\endgroup$
    – Guest
    Aug 3 at 7:39
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Any living system, being a highly organized ensemble with low entropy, works against the thermodynamic law stating that entropy has to grow.

To make it possible it has to constantly use energy and increase the entropy somewhere else. That's why every living organism eats and produces wastes.

A thing which, as you state, doesn't need to eat is not alive and cannot work as a living organism.

If it had energy storage in the body it could survive for a while, slurping off that energy. But I doubt a humanoid could do that.

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  • $\begingroup$ That makes sense. I had a feeling that missing certain organs wouldn't work out. Living things require eating and produce waste, like you said. $\endgroup$
    – Sydni
    Aug 2 at 6:02
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    $\begingroup$ Adult ephemeroptera don't eat. Yet they are alive. $\endgroup$
    – Stef
    Aug 2 at 14:12
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    $\begingroup$ @Stef, they live for what, 24 hours? $\endgroup$
    – L.Dutch
    Aug 2 at 16:14
  • $\begingroup$ It would be perfectly possible for them to have some method of energy gathering other than eating. Photosynthesis perhaps? Or they live off of gasses they can breathe and liquids they can absorb through their skin. Bigger problem is that several of the listed organs have purposes other than digestion which are likely to still be necessary in some form or another. $\endgroup$
    – Perkins
    Aug 2 at 17:32
  • $\begingroup$ To live you must get energy somehow. Could be by absorption, photosynthesis or some other means. The Green Men in Gene Wolfe's cycle live by photosynthesis. $\endgroup$
    – Ben
    Aug 2 at 19:02
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You've already posited that humanoids who don't need to eat exist in your world, thus the answer to your question is a resounding

YES.

This is 100% plausible. The only question that is actually important here is how is this state of affairs plausible in the first place?

Essentially, all living organisms -- whose definition of "living" conforms broadly to Life As We Know It -- requires some means of acquiring, processing & utilising energy followed by some means of expelling waste byproducts.

LAWKI animals do this by eating something else: teeth tear and rend; stomach churns and breaks down; intestines absorb; liver and kidneys filter waste; bladder and rectum store & expel waste. If you remove any one of those components and the creature will soon die.

Your people will simply have an alternative means of acquiring energy and expelling waste. Two obvious suggestions pose themselves immediately:

  1. Symbiosis: in stead of intestines and stomachs and so forth, your people play host to a symbiont that does the eating, digesting and waste processing for both itself and the host. In order to eat, the hosts prepare a large dish of food, set it on the floor and then recline upon comfortable couches while the symbionts' extrude their esophaguses towards the food. People can chit-chat while their symbionts gorge themselves.

  2. Photo/chemosynthesis: in stead of being the recipient of someone else's energy production, your people have some "plant"like characteristics. In stead of intestines, they have a bulbous organ that processes and stores the energy acquired through photosynthesis. The organ is attached to four large, leafy wings upon their backs. All they need to recharge is a day out in the abundant light of their world's sun!

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    $\begingroup$ My species is a plant/flower-based species (I should've probraly specified that). So I though instead of them eating, they get their energy from photosythensis. I like the idea of number 2! $\endgroup$
    – Sydni
    Aug 2 at 18:05
  • $\begingroup$ Keep in mind that roots on plants are not just about keeping it anchored in the wind. They take up vital nutrients and water. Not sure if your beings just maybe slather on nutrients like lotion on a certain part of the body or something, esp. if they're not eating/drinking anything. $\endgroup$
    – coblr
    Aug 2 at 19:32
  • $\begingroup$ @coblr Right, right. I was thinking about them putting on nutrients like lotion on their body. Maybe that could be a substitute for photosynthesis. $\endgroup$
    – Sydni
    Aug 4 at 1:31
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Be a mobile fungus, they have no internal organs.

"they acquire their food by absorbing dissolved molecules, typically by secreting digestive enzymes into their environment." from https://en.wikipedia.org/wiki/Fungus

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To function as an organism, you need to consume energy. And this normally means you also produce and excrete waste. Biologically, the cleanest you may be able to do this is to function like a plant, photosynthesise, and absorb the rarer, non-airborn nutrients through some kind of semi-passive system like roots.

This is not enough of an energy source for a humanoid like animal. A trend you'll notice in natures is that anything that gets its energy from photosynthesis, is either very, very small, or it doesn't move.

So you'd need something that provides higher amounts of energy to allow such movement.

These 'people' would also have to be very, very different to humans, as the biological functions that allow our bodies to exist and move are founded on the premise of consumption and waste. So there would be many, complicated biological systems that would need to be replaced with 'renewable' alternatives. i.e. alternatives that transition between two states using/releasing energy alone, conserving all of the involved materials for re-use. The only consumption/waste that would still be allowed, would be those involved in breathing.

Via a battery

The easiest way to achieve this, is something like a cyborg. If your 'people' have a battery, they could afford human-like acts and movements using the battery charge. However even if you had almost perfect solar-panels for skin, you wouldn't be able to capture enough energy for constant movement. I don't know the exact numbers for this. But I'd guess your people would have to spend days in a dormant state collecting solar energy before they could spend a single day of full activity.

So you could have other ways of providing power to this battery. For example if you had some kind of energy network your people regularly connected to. Either with a physical connection, or maybe with wireless charging to a possibly hidden infrastructure for a lost-technology setting (Why does everyone who leaves the city/major roads for too long get more and more tired until they collapse and die!?)

Or, similarly to the Silkworm Moth in Guest's answer, your cyborgs are born with a battery. To last a life span, probably a radiation based one... Which makes conception an interesting topic you may or may not want to answer.

Via breathing

This is probably not actually plausible, but you may be able to make a convincing narrative with it. If your humanoids live on a planet with a large enough amount of airborn 'exotic' materials that they could get all of the required materials to construct a biological organism from just breathing it in. This would require a planet in a probably similar state to Venus.

Any biological organism being able to endure an atmosphere like Venus for longer than a few minutes would be an incredibly feat. Nevermind actually harvest it for the nutrients required to continue living there.

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  • $\begingroup$ I should've (did) specified that they were plant/flower-based. I've been told, including you, that photosynthesis wouldn't be enough for a human. $\endgroup$
    – Sydni
    Aug 2 at 23:18

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