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The autonomic nervous system (ANS), formerly the vegetative nervous system, is a division of the peripheral nervous system that supplies smooth muscle and glands, and thus influences the function of internal organs.[1] The autonomic nervous system is a control system that acts largely unconsciously and regulates bodily functions, such as the heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal.[2] This system is the primary mechanism in control of the fight-or-flight response.

I am imagining if human can control the heart rate, respiratory rate, etc. so that human can suicide without any equipment (you don't need a gun to shoot yourself) or physical movement (you don't to jump off from a building). People can stop their heart beat or respiratory system by their will. No one can prevent suicide of others. Is it theoretically possible?

EDIT:

To be more precise: Is it possible for an species which can suspend the function of autonomic nervous system to exist?

Is there any evolutionary biology theory says it is not possible?

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    $\begingroup$ By definition, it’s not possible. Anything that’s under your voluntary control is not autonomic, which means involuntary. If what you really want to know is whether some functions that are controlled by the autonomic nervous system in humans could be controlled voluntarily by an alien species then that’s a different question, though I’d say it’s pretty obvious that the answer is yes. $\endgroup$
    – Mike Scott
    Apr 14, 2021 at 19:48
  • $\begingroup$ Those functions are named 'autonomic function' because in the real world science they are not under your voluntary control. I will not use the name 'autonomic function' to call those functions in my fictional universe. $\endgroup$
    – fairytale
    Apr 14, 2021 at 19:54
  • $\begingroup$ Humans have certain degree of control over those systems, easiest to see that is breathing, not sure about heart rate, but it is common plot in certain fiction but not sure how much grip to reality it has, so as how far things can be trained, and other claims I heard are also not exactly trusted sources, I would expect they have certain bearing in reality, but how far it can go, hm. I guess u need to dig in direction of yoga and others which focus in body training, shamans, trance, and clinical psychiatry in aspects how brain disfunctions and states manifest on body functions $\endgroup$
    – MolbOrg
    Apr 14, 2021 at 20:26
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    $\begingroup$ Brain–heart interactions: physiology and clinical implications "The brain controls the heart directly through the sympathetic and parasympathetic branches of the autonomic nervous system, which consists of multi-synaptic pathways from myocardial cells back to peripheral ganglionic neurons and further to central preganglionic and premotor neurons." - I guess it needs it for fast adrenaline rush response in fight flight situatiins, as ANS can't do such jugments, so I guess it safe enough to think certain things are possible. $\endgroup$
    – MolbOrg
    Apr 14, 2021 at 20:33
  • $\begingroup$ The problem with controlling the heart rate is the heart will beat on its own without outside signals. $\endgroup$
    – John
    Apr 15, 2021 at 14:46

4 Answers 4

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TL;DR: Such species already exist.

As @Jonathan already mentioned, most mammals can control their breathing and, to a lesser extent, their heart rate. This doesn't quite qualify for what you're wanting, as there's still an automatic backup to keep the animal from dying.

However, there are some species that do have full control. For example, dolphins and whales have full manual control of their breathing. As such, dolphins have been known to commit suicide by simply ceasing to breathe.

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    $\begingroup$ A fascinating answer. Is there any scientific backup for this? I find it hard to believe that anyone has ever witnessed a dolphin committing suicide. Maybe the dolphin just died of natural causes and stopped breathing for that reason. $\endgroup$
    – chasly - supports Monica
    Apr 15, 2021 at 11:43
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    $\begingroup$ @chasly-supportsMonica here's an article all about dolphins in captivity becoming depressed enough to commit suicide by intentionally refusing to breathe: huffpost.com/entry/dolphin-commits-suicide_n_5491513 $\endgroup$
    – zackit
    Apr 15, 2021 at 12:41
  • $\begingroup$ @zackit Huffpost isn't exactly peer reviewed science. Given that cetaceans drown rather than asphyxiate when they can't reach air, I find it very difficult to believe they can hold their breath to the point of suicide. The very fact that they are found on necropsy to have inhaled water when they drown indicates the ANS taking over and forcing a breath. $\endgroup$
    – stix
    Apr 15, 2021 at 21:15
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    $\begingroup$ @stix in this case it's actually true that their breathing is completely conscious, and it's probably another reason why they never truly go unconscious while sleeping, always keeping one half of their brains awake while the other rests. $\endgroup$
    – ProjectApex
    Apr 15, 2021 at 22:52
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I would answer the question in two manners:

  • Is it possible for an species which can control autonomic function to exist?

Yes

  • Is it possible for an naturally evolved species which can control autonomic function to exist?

No, unless you can come up with strong evolutionary or cultural advantage why that would be beneficial and that can't be compensated for in any other way. Edit: I don't believe Dolphins are an counter example as i would say that the more reasonable interpretation is that they drown themselves, by diving so they are not able to get back to the surface and breathe before running out of air.

From an evolutionary standpoint there is little reason for an stably running subsystem to become totally controlled by an higher order thought process, especially if it enables the brain to perform actions opposed to the survival of the species. Another problem is that centralized process suppressing a decentralized process tend to use a lot of power and an attempt to have breathing/heart beat/digestion perform in a way that hurts the body will likely disable the hostile to life process at which point the decentralized autonomous process can recover the body to stable state.

Note that this only holds for purely evolved beings. It would be simple to build a robot which can deregulate the crystal oscillators, battery control chips and motor controllers, although you would need to have good reasons why, as this introduces an accidental breaking point at the same time.

A technologically enhanced body using today's technology could be build to either trigger permanent damage to the autonomous system, so it can't recover or actively interfere with/control the necessary communication for those processes. This way you can circumvent the problem of controlling circuits being hindered by dis-regulated autonomous functions as technological systems could come with their own power supply.

With sufficient bio engineering capability it would also be possible to enable a species which performs certain modifications being performed over the life time to control their autonomous processes. These modifications would need to include the actual ability to disrupt/suppress/control the processes in question and a energy supply that can't be tapped into by autonomous system and include sufficient reserves to outlast the autonomous system trying to recover.

An more advanced approach could be to change the underlying anti-fragile biology such that it is unstable and will fail by default and only conscious action will stabilize the body and let it live on. This approach has a few problems such as reduced survivability, the problem what performs that balancing when the individual is underdeveloped to perform that action, that such a being would never arise naturally and that often repeated actions tend to become subconscious in the brain we see on earth. These problems could be overcome if a species is sufficiently motivated.

For a species with an autonomous kill switch in literature i am aware of the "bear-cows" from the second trilogy in the "Lost Fleet" series.

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  • $\begingroup$ Your body has strong incentive to stop you from killing yourself due to being inept, especially when you are young and learning to use it. $\endgroup$
    – DKNguyen
    Apr 14, 2021 at 21:43
  • $\begingroup$ I agree, so i don't understand what you are trying to add with that comment @DKNguyen $\endgroup$
    – worldsmithhelper
    Apr 14, 2021 at 22:12
  • $\begingroup$ Just commentary. $\endgroup$
    – DKNguyen
    Apr 14, 2021 at 22:14
  • $\begingroup$ Play dead is another well know example, and would not be suprised if octopuses can do some funny things, but in general see comment to ProjectApex answer $\endgroup$
    – MolbOrg
    Apr 15, 2021 at 13:53
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You can already control your breathing, just not to a full extent, the reason you can control your breathing but not to the point of being able to stop breathing forever is that it's an autonomous function that works subconsciously, and your subconscious decisions, putting it in a simple way, have priority over your conscious ones,especially since breathing is kind of important to keeping you from dying.

The reason for this, and the reason I think it's not possible (or at the very least that it is highly unlikely) for this trait to evolve successfully in a species is because one of your autonomous nervous system's main functions is ensuring you stay alive and healthy by maintaining vital bodily functions and letting you know when your body needs things like food, water and sleep (it also tries to encourage you to reproduce but that's not important here). Simply put: it is there to keep you alive, and disabling it seemingly doesn't provide any evolutionary advantage, rather it seems like a disadvantage, especially if it was possible to accidentally disable it.

Edit: regarding the dolphin's ability to fully control their breathing due to their environment (which is an interesting bit of information), I still don't believe it's a counter example, simply because while it can control its breathing specifically it cannot suspend the rest of its autonomous nervous system's functions as per requested by the question. Their relationship with how their breathing works is also one of the reasons dolphins can never reach unconsciousness, even while sleeping, being forced to only allow one half of their brains to sleep at a time while the other must stay awake so they don't suffocate, which again gives you a good idea of why our Autonomous nervous system exists to begin with.

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  • $\begingroup$ Hibernation is another eample, not only mammals, and not only due external factor, and if we tak about those thingsaspossibility to evolve then it quiteeasy to bring up semidel where it brings advantage, like prey hunter systems - foxes owls are quite good at detecting noises, and another real world example is play-dead, sooo... $\endgroup$
    – MolbOrg
    Apr 15, 2021 at 13:49
  • $\begingroup$ @MolbOrg there's a difference between entering a state of torpor (something you see in hibernating animals and sleeping hummingbirds), where your bodily functions fall to the minimum possible to keep you alive, and completely shutting off all vital functions, the key trait being that one of those is for energy economy and the other can actually kill you if the predator doesn't get away soon enough (aka in around 20 seconds max). Simply playing dead and having glands that release the smell of a decomposing corpse is a much healthier and safer strategy to trick a predator that won't eat carrion. $\endgroup$
    – ProjectApex
    Apr 15, 2021 at 14:40
  • $\begingroup$ do not forget, that u say it not possible in the context of evolution as a process, so not necessarily a specific manifestation, the results we observe today, which we both(i for sure), not that knowledgeable to speak about in the first place, but with evolution, in general, what do we need just imagine a plausible situation where it is beneficial. There is a joke - hedgehog learned to breathe through the ass, sat on a stump, and died - so yes, there is a strong incentive to make it semi-automatic, that is clearly correct statement, but saying in not possible is a bit too much. $\endgroup$
    – MolbOrg
    Apr 15, 2021 at 16:25
  • $\begingroup$ @MolbOrg then allow me to correct myself: it is potentially possible, but not only have we never seen any example of such a thing in any known animal species, it also doesn't seem to provide any actual advantage for the survival or reproduction of the animal and only seems to offer disadvantages for the individual itself as well as its species. Just look at the exploding ants which can and do kill themselves, but not simply out of a lack of desire to live. $\endgroup$
    – ProjectApex
    Apr 15, 2021 at 17:32
  • $\begingroup$ good, that's a progress. "have we never ... example of such" - okay, I guess u know more than me, but last bit on the subject. rudiments. there is a distance between a multicellular organism - multicellular with neuron tissue - multicellular with neuron tissue which function separation - same with developed distinct functions and some degree of segregation. in humans and I guess mammals in general - all sorts of connection exists between CNS and ANS, it works. And how far it can go, quite far ncbi.nlm.nih.gov/pmc/articles/PMC2600114 it not necessarily beneficial but it is there. $\endgroup$
    – MolbOrg
    Apr 15, 2021 at 19:19
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Breathing is an automatic function in humans, however, you can choose to control it manually. I think it would be theoretically possible (with enough willpower) to hold your own breath until unconsciousness, but at that point, automatic control would take over before a person could kill themselves by refusing to breathe.

ed:

There are hidden dangers in breath-holding in a sense of how it all works, it is not exactly automatic per se, but is regulated based on co2 concentrations, and the system isn't smart or perfect.

Here is an article about some problems involved, a bit on a for simple folks side, but still describes some problems:

The key to preventing hypoxic blackouts is getting to the root cause of how athletes faint when exposed to breath-limiting, high stress practices. The body’s autonomic nervous system controls our breathing at an unconscious level and bases your need to breathe on the balance of oxygen and carbon dioxide (CO2).

A build-up of CO2 in the body signals the response to exhale the toxic build-up of CO2 and bring in fresh oxygen to nourish our vital organs and muscles; however, when CO2 levels are relatively low due to hyperventilation, whether intentional or from a difficult practice, our brain loses the ability to signal to take a breath. It thinks we don’t have enough waste product built up to require a breath, when in reality, our body needs that breath of air to survive.

there is free diving aspect as well, a wiki page Freediving blackout

Freediving blackout, breath-hold blackout[1] or apnea blackout is a class of hypoxic blackout, a loss of consciousness caused by cerebral hypoxia towards the end of a breath-hold (freedive or dynamic apnea) dive, when the swimmer does not necessarily experience an urgent need to breathe and has no other obvious medical condition that might have caused it. It can be provoked by hyperventilating just before a dive, or as a consequence of the pressure reduction on ascent, or a combination of these. Victims are often established practitioners of breath-hold diving, are fit, strong swimmers and have not experienced problems before.

yeah, and thinking about free divers, there are quite a number of high-profile cases, at least which got to be made into documentaries about them(okay, at least one), which got in the scope of a random guy like me.

All those above do not state specifically it is ANS fault, but Do Not count on it it isn't a fail-safe bug fixed microcontroller program that just works, it is a biological system.

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    $\begingroup$ Just a piece of Warning, just in case, do not test if ANS will kick in, with 80 certanty I can say it is a guess of the guy, and matter is a bit more complex, and if I recall correctly, some diving breath holding training related stuff, it may not kick in, as it works until certain treshold and then fails, may happen remembered it wrong, but... $\endgroup$
    – MolbOrg
    Apr 15, 2021 at 13:43
  • $\begingroup$ @MolbOrg you might want to add that in as an edit, as it's pretty relevant to the answer I gave. $\endgroup$
    – Jonathan
    Apr 15, 2021 at 20:06
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    $\begingroup$ it was a long long time ago I read it, but okay it seems easy to find those things those days - holy internet, let's pray. $\endgroup$
    – MolbOrg
    Apr 15, 2021 at 20:32

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