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On Earth, most animals have tongues, albeit in many forms. This is due to the evolution from a common ancestor. Tongues are not necessary for communication, be it auditory or otherwise. However, they are essential for eating in a humanoid fashion, they keep food between the teeth during the process of chewing.

Let's assume that they kept chewing in a humanoid manner, with a similar mouth composition, despite its disadvantages. Would increased acidity of saliva suffice? If not, what adaptations (not including a tongue) could have evolved?

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    $\begingroup$ I mean it depends on what you want for your world? We have another question that covers alternative means of communication besides sound, and honestly nothing says you HAVE to use a tongue to have a language. Being able to taste doesn't have to be limited to a tongue either. Whether you want your creatures to have one or not is kind of up to you. $\endgroup$ – Pleiades Mar 18 '18 at 5:27
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    $\begingroup$ Jawed vertebrates have muscular tongues. It's a shared character inherited from our distant ancestor: what cladists call a plesiomorphy. On the other hand, arthropodes don't have muscular tongues; the structure called a tongue in some arthropods is fundamentally different. And with respect to "without a tongue it's not possible to speak to the same extent", consider parrots; parrots do not use their tongues to shape sound, yet they can make all the sounds we can, and more. To quote a famous fictional character, life finds a way. $\endgroup$ – AlexP Mar 18 '18 at 5:28
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    $\begingroup$ Many animals do just fine without tongues. There are other organs that allow for a sense of taste, and most species communicate without sounds. There are even many species that do make sounds without tongues. $\endgroup$ – Renan Mar 18 '18 at 5:29
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    $\begingroup$ @Lutro: Read for comprehension. Parrots are jawed vertebrates. Of course they have tongues. The point is that they do not use their tongues to shape sound -- birds make sounds in way very different from mammals. This deflates your naive assumption that a tongue is necessary for speaking. $\endgroup$ – AlexP Mar 18 '18 at 6:00
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    $\begingroup$ @Lutro I'm not sure it does. I read your original question, the comments & the answer which was concerned with communication. The current edit doesn't a function of the tongue to having a civilization. I looked at the present version and asked myself: this is about what?? My answer: I don't know. What is connection between the tongue & civilization you hope to find -- if any? You are too close to your question. Step back, think a bit about what you want & edit accordingly. Well, fellow Aussie, you're wise to steer clear of instant noodles. $\endgroup$ – a4android Mar 18 '18 at 8:02
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They simply can't keep chewing in a humanoid manner, if you want them to chew you need to completely redesign the face and mouth around a different mechanism, like Indigo's insect open mouth. Chewing requires a way to manipulate the food physically to get it onto the chewing surface after each motion otherwise the mechanism of chewing serves no function. HUmans who lost their tongue had to live on soft foods because of this.

More importantly without a tongue swallowing anything not a liquid is all but impossible.

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EDIT

This answer was provided before a considerable edit was made to the question and was one of the reasons the question was edited. It no longer answers the OP's question, but I've left it for reference purposes.


I believe everyone here would agree that a civilization of sentient beings would require communication.

However, is a tongue required for communication?

  • If their communication is telepathic, they wouldn't need vocal cords, much less a tongue.

  • The value of the tongue for communication is the formation of hard sounds (in English, the "th," "d," "t," "z," etc. sounds). But, do you need them? Probably not. Your language would sound more like horns, but it would be just as complex (and it would likely have a greater dependency on using mouth shapes to modify sounds... I'm just thinking out loud here).

Frankly, from the perspective of communication (which I'm assuming due to your desire for a sentient species), the tongue is absolutely unnecessary.

HOWEVER

Communcation is not the original purpose for the tongue. At least in humans, "the tongue is vital for chewing and swallowing food...." I wouldn't be surprised if that basic statement was true for every species that has a tongue. It's a useful critter that makes moving food around in your mouth very easy. And spitting. It's great for spitting.

So, knowing that you don't need a tongue for communication, but it's a pain in the wazoo to move food around in your mouth without it. The real question is, how does your species eat?

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  • $\begingroup$ That's a really significant factor I overlooked, the tongue keeping food between the teeth while chewing is quite an oversight. Assuming the species has a mouth almost identical to humans, would a tongue like structure be necessary to eat? If so, what would you propose to be feasible? $\endgroup$ – Lutro Mar 18 '18 at 7:53
  • $\begingroup$ There is also sign language, which doesn't even require vocal chords. $\endgroup$ – Erik Mar 18 '18 at 8:02
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    $\begingroup$ Birds communicate vocally too, they don't have vocal chords and the tongue is not really needed. You could have a whole society of bird like twittering. $\endgroup$ – Borgh Mar 18 '18 at 11:39
  • $\begingroup$ @Borgh, excellent example of high-pitched horns! $\endgroup$ – JBH Mar 18 '18 at 17:25
  • $\begingroup$ @Lutro, sharks don't have tongues and don't chew. They swallow whole - and that's the issue. If the digestive system of your species requires chewing you pretty much need a tongue to keep the food from being swallowed too early. If they can take their food whole, then the teeth are only for ripping and no tongue is needed. That's why I asked how your aliens eat. Also note that snakes have tongues, but don't chew (swallowing their food whole). The tongues are used to radiate heat and cool the body. There are many uses for a tongue. $\endgroup$ – JBH Mar 18 '18 at 17:28
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Perhaps multiple rows of teeth across where our soft palate and tongue lies, or stiff but flexible ridges that guide food towards each row of teeth with each movement of the jaw.

It wouldn't be precisely human-like, but it would permit chewing.

many teeth! https://imgur.com/gallery/XFR1T6u

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The main purpose of a tongue is to assist in chewing food. Most vertebrates generally have one or several rows of teeth, a cavity behind those teeth, and a tongue for moving food around - pushing it into the teeth for further processing or back into the throat when it's ready for swallowing.

But this is not the only way. There are plenty of invertebrates out there that use an entirely different mechanism for chewing. Many arthropods, for instance, have small, leg-like structures around their mouths for moving food into the right place for mashing or tearing with their powerful mandibles. Since an insect's mouthparts are "open", unlike a vertebrate's, their "hands" can manipulate food as much as they like until it is ready to pass to the throat.

If a species has hands or hand-like structures, it doesn't really need a tongue - it can use its hands to manipulate food around the "chewing" organs instead. But the vertebrate jaw is built around the tongue - it's hard to use your hands to manipulate food inside your mouth. So your species would require a pretty compelling reason to lose their tongue over the course of evolution.

The only reasonable reason I can think of is that their world was inhabited by a parasite that infects the tongue specifically. (Sounds silly, but there actually is a creature that does this to fish. And replaces their tongue with its own body.) This could potentially lead to tongues growing smaller and eventually disappearing altogether.

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