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Are there any realistic tissues that could be used in place of muscles in alien carbon-based life? There are some real structures that move without muscles, but they don't seem like potential replacements for muscles. For example, rapid plant movement generally depends on changes in pressure that are far slower than muscles, or on pressure build-up or elastic structures which while fast, are slow to reset. The latter problem also applies to myonemes, which also seem a bit too much like muscles to me. Erectile tissue (and similar approaches like in spider feet) seems a little better in its speed to fill and reset, but it only ever supports smaller structures, and also seems to require muscles to work

Considering all this, is there any tissue that could allow animal-like motion without the need for muscular tissue?

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  • $\begingroup$ tendons as springs? kangaroos use this technique to provide extra bounce in their legs for each jump (storing some of the impact force each time they land to help with the next jump), problem with that of course is you still need muscles or some external factor to 'wind them up' so not an answer for your question. $\endgroup$
    – Pelinore
    Sep 18 at 12:57
  • $\begingroup$ Humans do the same @Pelinore (less than kangaroos of course), which is why the Achilles is the biggest tendon even though connected to a fairly small joint $\endgroup$ Sep 18 at 13:17
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    $\begingroup$ @I-Stand-With-Palestine true, practically all animals do to some degree, kangaroos are just one of the more extreme examples of it. $\endgroup$
    – Pelinore
    Sep 18 at 13:20
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    $\begingroup$ I expect an answer will be for most outward locomotion? The heart is practically impossible to replace, as well as things like blood vessel constraints. $\endgroup$
    – Trioxidane
    Sep 18 at 13:35
  • $\begingroup$ @Trioxidane I'd prefer an answer that would completely replace muscular tissue $\endgroup$ Sep 18 at 13:40
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Yes absolutely.

Bear with me, this'll take some explanation.

Biochemist Michael Behe has made a splendid video showing some of the amazing things bacteria can do with nano-motors.

Amazing molecular flagellum.

Discovery channel, Michael Behe 2021 fair usage

Amazing facts:

They sit in the cell wall, with the tail in the surrounding medium. These motors can rotate at speeds of up to 100,000 RPM, they can be stopped - within a quarter of a rotation - and can then be reversed to the same speed. The impulsion of a single one of these wiggly things can only propel a tiny bacterium along at a modest pace. So far so remarkable.

If these can be aligned inside a tiny capillary to all pump in the same direction, and a system of these capillaries is connected to a crumpled tube inside a sheath of semi-rigid and very strong material such as connective tissue - made of tendon-like fibers, then a pushing or pulling force can be generated as the tube is inflated and deflated. This would constitute the basic building-block of an hydraulic muscle-system, it would just need to be scaled-up to power the whole organism.

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    $\begingroup$ this is the same thing the spiders do with erectile tissue, and suffers the same problem, its slow and can't generate much force. $\endgroup$
    – John
    Sep 18 at 17:46
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    $\begingroup$ @John I'll have to take your word for that, google scholar's not giving me a thing on the subject except lots of "we don't know how it works" type comments in papers. Goodness knows what advertising they'll show me now ;) $\endgroup$ Sep 18 at 17:58
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    $\begingroup$ I'm chiming in, and as a biologist, this could certainly work - if you're willing to be flexible about how the force is finally applied. After all, the actual mechanism of muscle function is quite crude, but it works multiplied millions of time over. This mechanism could become a series of hoists, or even a pully system, if applied as rotational mechanics like an engineer would. The bacteria could form a basis of organelles in the same way mitochondria do - acquired by eukaryotic organisms, then reduced to a minimal functional unit, attached to some type of bio-cable. $\endgroup$
    – DWKraus
    Sep 18 at 18:25
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    $\begingroup$ Here is a good reference article ncbi.nlm.nih.gov/pmc/articles/PMC6680979 $\endgroup$
    – DWKraus
    Sep 18 at 18:33
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    $\begingroup$ It's basically an organic electric motor, but using the flow of ions instead of electrons for power. The upper reasonable limit is 1700 revolutions per second, still faster than a formula one race car. This is the basis of several nanite concepts I've seen, but can be applied to macro-engineering. $\endgroup$
    – DWKraus
    Sep 18 at 18:41
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Nothing on earth.

On earth there is nothing with performance even close to muscle. Keep in mind muscle is basically just a specialized form of the cytoskeleton, so most cells come equipped with it already, and the path of least resistance is usually just to use it and not invent something else.

Hypothetically, something else could exist in aliens but if their biochemistry is similar it would function just like muscles, with induced protein shape change, so you are back to the myonemes problem.

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    $\begingroup$ I think that the very hypothetical is the answer he's looking for. $\endgroup$
    – Demigan
    Sep 18 at 18:31
  • $\begingroup$ @Demigan there is no existing hypothetical, it is just biochemically possible for something else to exist. $\endgroup$
    – John
    Sep 18 at 19:31
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Depends on what you define as as a muscle, but to me the answer could be very definitely if you simply define not muscle as something that works in a different way.

I would consider a contractile cell that works by a different bio-mechanical principle to be different than a muscle — A C-Cell.

  1. Include an internal fibrous tissue that connects both end of the C-Cell. Then twist the fiber, contracting the cell, (similar to the manner you can tighten a tourniquet by twisting it). The twisting torque could even be supplied by a bio-electric motor — I even referred to the flagellum motor as a non-muscle in a prior answer on Worldbuilding, so I'm consistent :-)

  2. Reduce the overall volume of your C-Cell by triggering a phase change in some portion of the cell. Suppose you have an internal chamber that normally contains a gas kept at a temperature just above the boiling point of whatever substance is needed for the exo-biology. To contract the C-Cell, quench the internal chamber, converting the contents to liquid. This would be ideal for C-Cells that rarely need to contract/expand but ideally maintain either either state with little energy expenditure, such as sphincters.

  3. Replace part of C-Cell using a biological equivalent to shape memory alloy, SMA. Although SMA metals are activated by temperature changes, protein-based versions could also activate via enzymes or perhaps electrically.

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Cilia

(I would include a Wikipedia image here, but Imgur can't seem to handle a simple link, so you'll have to click it)

The answer above showcases the bacterial flagellum, which is indeed a molecular motor capable of whirling a protein around outside the cell. Paramecia, humans, and other eukaryotes have a more sophisticated device, consisting of nine sets of microtubules around a central core, surrounded by an extension of the cell membrane. Motor proteins (dynein arms) on each microtubule push against the others. The concept is similar to muscle motion, but this structure is capable of bending in many different directions.

In humans, cilia can form the basis of rather remarkable structures, such as in the photoreceptor where a single enlarged cilium forms the "outer segment" of the cell - a large piece of the total cell, anchored by one small connection.

In your aliens, hundreds of cilia might link an "outer segment" and an "inner segment" of a cell, and be capable of moving the outer segment in a two-dimensional plane relative to the inner segment. Assuming many such cells are stacked in a large array, each moved a little further by the preceding (one more step proximal) level of the array. the small displacement at each step would be amplified, allowing them to move a large tentacle as far as it can bend, in many possible directions. The tentacle could be bent in different ways at any point along its length, much as can (at least conceptually) with an individual cilium.

Such a tentacle would have no visible "muscles", and there would be no specific way to control it muscle by muscle. Rather, a set of nerve-like signals, carried by more traditional nerves to each position along the tentacle, would have to pass through all the cells at that proximodistal level. The pair of signals would control the motion in each of two directions. This implies that each cell would need to be able to pass two different kinds of action potential at the same time, each having its own effect, without confusing them. Perhaps the cells could have an innate rhythm, being open to depolarization action potentials at one stage in the cycle and hyperpolarization action potentials at the other. The frequency and pattern of each type, relative only to itself, would determine how far the cilia bend in one of two perpendicular directions.

The circulation nourishing the cells could pass through the narrow spaces within each cell that are bridged by the hundreds of cilia. This might supply the energy source needed for contraction extracellularly, directly to the membrane of the cilium, from which the energy could be routed directly to the dynein just inside the membrane.

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No muscle replacements at all

If aliens don't use muscle, it is plausible nothing on the alien planet does. That means that everything is slower, making respective speeds important. You can have every creature move much slower with plant methods and such. The key is low energy usage during the active hours/days. Although much would change in how they live, it can certainly have an ecosystem adapted to this.

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Well, in theory you could use expanding tissue instead of contracting tissue to move a body. Let's call this an "antimuscle," as this pushes on the skeleton instead of pulling.

I say "in theory" because using tension is simple and compression is not. The tension in a muscle keeps it in a proper shape. Most muscles are connected to two different bones using two tendons and that's all they need to work properly.

Meanwhile, an antimuscle would require much more external support to keep it in shape. Muscles are flexible and not rigid, while hydraulic pistons have to be rigid in order to properly push. Even though antimuscles probably aren't hydraulic, they will still need their force to be directed. If there's a weak spot in the containment for an antimuscle, it's going to spill out and waste energy and strength doing that.

The closest to this containment we see in vertebrates is ligaments that route tendons through joints, like at the wrist and ankle in humans. But these are not full containment along the length of a muscle like we would see with antimuscles, which would require a lot of connective tissue.

This may be a viable type of tissue when combined with an exoskeleton as the internals of the exosketelon can provide a lot of containment for the antimuscles as they push. Internal air sacs would provide more support, and also allow for easily changing muscle volume as individuals bulked up and lost muscles.

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YOUR QUESTION:

Considering all this, is there any tissue that could allow animal-like motion without the need for muscular tissue?

MY ANSWER:

enter image description here

Motors made of Bone, Dentin, Iron enamel, regrow all the broken parts the same way nails are regrown.

Iron is so common in nature and in food that people easily get iron itoxication from foods. Beavers need to break their iron teeth on purpose cause they grow too much. The resources are there.

Use chemical energy, gas pressure or heat to keep the motor going.

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    $\begingroup$ The big problem here is that an organic locomotive suffers the same problems of an organic chainsaw, as in it needs loose parts, and it may look fine to just remove the blood vessels so they are not In the way, but without blood vessels and tissues surrounding the dead engine parts (because if there's nothing giving it food, it's going to be dead), if they ever break (which they likely will since there's nothing to maintain them, unlike our own bones) the creature will likely be doomed. There's also the problem of growth, because dead cells cannot multiply and therefore cannot grow. $\endgroup$ Sep 18 at 14:40
  • $\begingroup$ @ProjectApex sharks grow thousands of teeth per month $\endgroup$
    – sleeves
    Sep 18 at 15:12
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    $\begingroup$ Indeed, and those teeth grow from places filled with tissues and blood vessels. Furthermore, the only movement they have to perform is to slowly move to the front of the jaw, all while still attached to the gums that produced them in the first place. Their function is to stab prey effectively and be easily replaceable, not to move like a gear in an actual perpetual 360 degree fashion. This is also true for T-Rexes and some crocodilians (minus the moving part) $\endgroup$ Sep 18 at 15:23
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    $\begingroup$ Ultimately the problem with making a machine like a car, or a train or even a plane with the components available to carbon based life is that 1- the things it can do, like bones, muscles and the like, are usually too weak so sustain the stresses metal engines need to be able to handle. And 2-the materials that would make it possible aren't as easily (or straight up cannot be) processed by carbon-based lifeforms. Yes it can assimilate iron into teeth, fangs and other structures to make them stronger and more durable, but it cannot make a steel alloy even if it was given the right components. $\endgroup$ Sep 18 at 15:31
  • $\begingroup$ Feel that this answer could have been elaborated on a bit more, eg. giving an example of a structure that works logically, but unsure if it needed so many downvotes. $\endgroup$
    – Enthu5ed
    Sep 19 at 14:33
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  • Terrestrian animals can have horns with no blood vessels inside, the horns can regrow the same way hair grows.

  • Shoulder shoulder joins are capable of 360 degrees movements in most terrestrial and even in acquatic animals.

  • Terrestrial life is capable of exerting enough energy to crush rocks and break metal bars.

  • Terrestrial life is capable of exering internal pressures strong enough to counter the pressure of the deepest ocean.

You have all the ingredients in the above list, now arrange them into a biological locomotive powered by heat/internal pressure.

Millipedes already look like bio-locomotives, you just gotta change of the internal clockwork.

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    $\begingroup$ That is not a replacement for muscle you are proposing just because we can equalize our body pressure when diving does not mean we can build a muscle able to wield that power for instance. In fact its a very very slow process, hence divers that get up to the surface too quickly have to go into a pressure tank and slowly raise their pressure instead. I dont even know why the shoulder joint and horn growth have anything to do with muscle replacement. $\endgroup$
    – Demigan
    Sep 18 at 13:19
  • $\begingroup$ @Demigan Gears, Wheels, Levers.... they can't work if there are blood vessels in the way $\endgroup$
    – sleeves
    Sep 18 at 13:23
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    $\begingroup$ Sleeves we do appreciate your time in making an answer. Still, all the examples do not propose how a carbon based lifeform makes movements without muscles. Giving some examples of movement does not make a compelling answer of how carbon based life can move without muscles. If you can make it apparent how this can work, I'll reconsider the answer happily. $\endgroup$
    – Trioxidane
    Sep 18 at 13:32
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    $\begingroup$ @Sleeves the problem is that you have to fit it in a biological body. The question specifically tells us that plant hydrostatic pressure is too slow for a proper replacement. Spiders actually do use hydro pressure to move their legs, but this mechanic does not scale well at larger animals hence nothing larger than insects use it. Similarly an exoskeleton (or your bone engine) does not scale up well. The power to weight ratio does not let you use it in a biological body, not to mention that the erosion of the body would be too fast with bone for engines to work. $\endgroup$
    – Demigan
    Sep 18 at 14:07
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    $\begingroup$ You seem to have posted two answers on the same basic subject... it'd be great if you can edit one of them to combine the best bits and delete the other one. $\endgroup$ Sep 18 at 17:05

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