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this is my first time asking something so please bear with me 🥵

I want to know how we could have humans that can stretch their body’s very far. Like what evolutionary pressures or things in cells. The stretching of the human will only activate when any part of their body is pulled or pushed farther than our normal limits. Example: If you pull someone’s arm it will only stretch when it is near its limit. (About to dislocate)

I also want to know what are the evolutionary benefits to this stretching and what are the downsides.

every part of the body has this stretchy ability so their organs and other body parts won’t be damaged.

edit I forgot to mention that the body snaps back when it can. Sorry for adding this but later 😬

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    $\begingroup$ Welcome. Have you heard of Balaenoptera physalu, it is a whale and it has a stretchy nerves to swallow large quantity of water during feeding without experiencing headache every time... imagine you try to fit an apple whole into your mouth! ;D $\endgroup$
    – user6760
    Jan 17, 2021 at 5:24
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    $\begingroup$ Welcome to worldbuilding. You may want to rephrase your question - like having the bolded line be a one line summation of the question (Like "Is there a biologically plausible mechanism for such a stretchy human?") An ideal question is a single question with a best possible answer. Fun topic, BTW. I'll have to give it some thought. Individual body parts can be this flexible, but how to get the whole body functioning like that? Are the bones rigid? $\endgroup$
    – DWKraus
    Jan 17, 2021 at 6:37
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    $\begingroup$ I made a question about this, search "muscles that push" on the stackexchange search bar $\endgroup$
    – user81643
    Jan 17, 2021 at 11:34
  • $\begingroup$ @DWKraus The bones are ridged like ours only when they are within normal limits. Example: Let’s say you have your leg crushed by a heavy object, if you were normal say good bye to your leg. Otherwise it would be fine because it would squish. $\endgroup$
    – user81937
    Jan 17, 2021 at 20:53
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    $\begingroup$ I think your people would still have a lot of tissue trauma. For bones, THIS question isn't exactly what you are asking for, but it seems close enough you might want to check it out. My answer has some very adjustable bone structure proposed. worldbuilding.stackexchange.com/questions/193864/… $\endgroup$
    – DWKraus
    Jan 25, 2021 at 4:13

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The stretching of the human will only activate when any part of their body is pulled or pushed farther than our normal limits.

I can't see how this would be an advantage at all.

Let's start from a newborn, just out of the mother's womb. The first advice when handling a newborn is "hold their head". Why? Because their neck muscles are not strong enough yet to withstand the head's weight, and will take some month for them to be. I guess that in those few months a baby of this species would end up looking like a giraffe. I am not sure it would be able to breathe normally with an overly stretched neck, considering the size of lungs and breath ways. And a newborn has many more joints and muscles which need to develop before being decently functional.

Also in an hypothetical adult things don't go better. First of all, we have pain in place to warn us when we are overloading parts of our body. If our body isn't capable of exerting a certain force, what's the benefit of extending under that load?

Let's say your subject has lassoed a buffalo and their arms are not able to hold the rope under the buffalo's pull. While a normal human would either get dragged by the buffalo or let the rope go, your human would simply end up stretching their arms until an unspecified point, probably until the buffalo decides that the run has been enough. So now your human has still no buffalo but a few hundred meters long arms, which will have to be drawn around. I guess running away from a lion would be a tad cumbersome.

And I am not even venturing into the energetic needs for this. Stretching a body long would require a very surprising ability to quickly make new cells in order to overcome the thinning imposed by volume conservation, and that would require very large internal storage of the needed substances.

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The human body is already very elastic. Your skin is amazingly stretchy. Most of your soft tissues and organs can be moved around to a significant extent. The most significant limitation on our ability to contort is those big, hard things inside of us that don't bend, known to the lay man as bones. Cephalopods such as octopods and squids, have no bones at all. This allows them to squeeze through tiny cracks with no issues. Clearly the issue with stretching and squeezing is caused by our skeletons.

However, having bones that are stretchy or bendy (or no bones at all) would be a major disadvantage. The skull has to be rigid to prevent the brain from being bruised or squashed. A solid ribcage protects most of your other vital organs. And strong leg bones are necessary for our terrestrial locomotion.

Some animals have much more flexible skeletons. Rats, for example, have solid bones like us, but they lack collar bones and their ribs have flexible joints at the spine. This allows them to squeeze through holes that are smaller than they are. Snakes are able to to eat things bigger than they are because they can move their bones apart. Their jaw is made up of three bones, which are only loosely connected, and their ribs will bend away from their spine in order to make room for what they swallow.

With a little more flexibility around the joints, it is possible to twist the body a great deal. Contortionists have the same bones as normal people.

The answer for the second part of your question is a little trickier. Some of the benefits I can think of are related to the environment your human variants are native to. If they live in a place with lots of narrow caves or tunnels, being able to stretch could be a big advantage in gathering food and escaping predators. Alternatively, it could be motivated by reproduction - perhaps elasticity is a marker that females use for sexual selection.

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