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librathefangirl · 2 months ago

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nnt hc: Demon Thermoregulation

Seeing as it has been featured in multiple of my fics now, I figured it was about time to actually develop and explain this headcanon :)

The short explanation of this headcanon is that the demons' thermoregulation works counteractive against the temperature of the environment. This means, you could say that it works reverse to human thermoregulation; demons go hot in cold environments and cold in hot environments. Of course, that is just the short, simplified answer. The long answer is a bit more complicated (because biology~), especially when you consider the differences between the Demon Realm (the demons' "natural habitat") and Britannia. So, that's what I'm going to explore more in this post.

Continue reading for explanations of:

How does the demons' thermoregulation work?

Why does it work like that?

What are the downsides? (aka the source of the whump >:])

Quick note: I will from here on talk like these are actual facts about the nnt demons, but it is, of course, just my headcanon :)

How does it work? (biology)

First of all, for those not familiar with the term, thermoregulation is defined as "the maintenance or regulation of temperature", and does in this case, specifically refer to the maintenance of a particular body temperature. Maintaining a stable temperature (within a certain range!) is crucial in order to keep the body functioning as it should. If the body temperature goes too low or too high, bad things happen (e.g. water freezing inside cells or vital enzymes and proteins breaking down). But what exactly that ideal temperature is, and how narrow of a range it allows, differs between different animals (e.g. in humans a normal body temperature is around 36-37°C (97-99°F).

Demons, having a different biology, also have a different ideal body temperature than humans. But before we get into that, I want to quickly talk about normal (or "real" if you will) thermoregulation, to help us better understand this headcanon. (If you absolutely do not care about this, just skip this next paragraph).

When it comes to thermoregulation in our world, animals can broadly be divided into two groups: endotherms (warm-blooded) and ectotherms (cold-blooded). Of course, there are exceptions to every rule and there are some animals that blur this line, but those aren't important here (this isn't a biology lesson, it's a hc demon biology lesson). Endotherms/warm-blooded animals, like humans and most mammals, rely on internal mechanisms to maintain their ideal body temperature. While they are still affected by the temperature of the environment, they are not dependent on the environment to regulate their own temperature. Instead, they achieve this by changing the amount of heat production and/or heat loss they experience. Ectotherms/cold-blooded animals, like reptiles and amphibians, on the other hand, have a dependent relationship between body temperature and the temperature of the environment. Meaning that not only do their body temperature change with the temperature of the environment, but they also rely on the environment to maintain their ideal body temperature. They regulate their body temperature, for example, through different behaviors such as basking in the sun (to raise their body temperature) or seeking shade (to lower their body temperature).

Demons are mostly considered endotherms/warm-blooded, because of how they regulate their body temperature. I did, however, once refer to them as "unorthodoxly cold-blooded" in an ask. This was because their relationship to the environment are more similar to ectotherms/cold-blooded animals (i.e. more dependent), despite the fact that they regulate their body temperature more in line with endotherms/warm-blooded animals (i.e. through internal mechanisms). So, yeah, demons are endotherms/warm-blooded, but not in the usual way. Now, this might sound a bit confusing, so let's take a closer look at what this means.

The biggest difference between demon and human thermoregulation (besides the ideal body temperature) is in how it is triggered. In humans, as you might know, the thermoregulation is triggered by changes in the body temperature itself. When a human is exposed to greater changes in the temperature of the environment, there is also a change in the body temperature (the body temperature is lowered in cold environments and raised in hot environments). These changes in the body temperature are detected by nerve cells called thermoreceptors. These thermoreceptors then send this information to the brain (specifically to the thermoregulatory center), which then responds with different mechanisms to either raise or lower the body temperature (depending on what is needed to maintain the ideal body temperature). In demons, on the other hand, the thermoregulation is triggered by changes in the temperature of the environment. These changes are detected by thermoreceptors located in the skin, which then (just like in humans) send information to the thermoregulatory center in the brain, which causes a response to change the body temperature through different mechanisms. Demon thermoregulation can, in other words, be described as preventative or counteractive. The demons' body temperature is raised or lowered in order to counteract the natural change in body temperature that occurs because of the temperature of the environment.

To give a concrete example: If a demon would go out into a colder environment, their thermoreceptors would warn their brain that the environment has gotten colder. Their body temperature would then be raised, through internal mechanisms, so that it would still end up at the ideal temperature when the body temperature is inevitably lowered by the coldness of the environment. In other words, the process would look the opposite to humans. A human's body temperature would go down (because of the temperature of the environment) and then back up (because of their thermoregulation), while a demon's body temperature would go up (because of their thermoregulation) and then back down (because of the temperature of the environment).

A lot of the mechanisms used in demon thermoregulation are similar to those in humans. These include: control of blood flow, metabolic activity, movements, and sweating. In order to raise the body temperature, demons restrict blood flow to the skin (to decrease heat loss to the environment), increase metabolic activity (to increase heat production), as well as experience behavioral changes like an increase in body movements (to increase heat production). In order to lower the body temperature, the opposite happens, demons increase blood flow to the skin (to increase heat loss), decrease metabolic activity (to decrease heat production), experience behavioral changes like more limited body movements (to decrease heat production), and sweat (to increase heat loss). However! Two things that do occur in humans but not in demons are shivering and goosebumps.

Demons don't shiver! (Is this part of the hc because the idea hit me and just wouldn't go away? Yes. But also-) Shivering, in humans, occurs as a reaction to a drop in body temperature and a need for more heat. One way to increase heat production is by increasing muscle activity, both voluntary (like rubbing one's hands together) and involuntary (like shivering). In other words, shivering is a means to raise the body temperature. But, since demon thermoregulation happens before the change in body temperature itself, shivering doesn't feel like it would be a really sustainable method for demons to raise their body temperature. I mean, they would be more or less constantly shivering whenever they're in colder-than-ideal environments. So, instead, they rely on other mechanisms to increase heat and raise the body temperature (see above), including voluntary muscle activity. Demons actually have a tendency to get hyperactive with their movements when in cold environments. How much movement, what kind, and how aware the demon themself is of these is also very individual.

Now, one could make a similar argument about sweating that I just made about shivering - and we have already established that demons do sweat - but I kinda disagree. I feel like there are more levels to sweating than there are to shivering. Meaning there would be less of a constant state of sweating and more of different levels of sweating that can be implemented in different situations, depending on the demon's current needs. Also demons are more used to adapting to hot environments and needing to lower their body temperature than they are to cold environments and needing to raise it (but more on this later). Furthermore, sweating in demons mostly occurs during the biggest changes in the temperature of the environment, and thus is used during situations that require a more rapid lowering of the body temperature. So, in other words, demons do sweat, but not as much as humans and just during specific circumstances. There are also differences between different types of demons, depending on what their respective ideal body temperatures are and what part(s) of the Demon Realm they live in.

Goosebumps! Just like shivering, goosebumps are also something demons don't experience. In humans, goosebumps are a (rather ineffective) attempt at trapping heat by raising the (very limited) body hair. A more effective example of trapping heat like this are birds fluffing their feathers. The same issues presented with shivering also apply to goosebumps. It just wouldn't be very sustainable (for most demons), considering how the demon thermoregulation works, that is, before the changes in body temperature itself. So, here as well, they rely on other mechanisms to raise their body temperature (again, see above). However, there are possibly some demons that do experience a raise of fur/hair or fluffing of feathers - but these demons would be ones with a much higher ideal body temperature, and wouldn't really be able to survive the colder winters in Britannia.

Why does it work like that? (need for heat)

Now that we've looked at the how, let's talk about the why. Like we've already established, demons, like other beings, have a need to maintain their body temperature within a certain range (to keep everything working properly). While there are differences between different demons, as a rule, the demons' ideal body temperature is higher than humans' (and the other races'). In other words, they also have a greater need for heat.

Okay, while this post isn't about headcanons about the Demon Realm's climate, I do wanna talk a bit about what kind of Demon Realm this hc is based upon (quick shout-out to @hihopelessromantics for discussing this with me <3). Because we know so little about this (the climate/temperature of the Demon Realm) in canon, but it plays a significant role in this hc. The Demon Realm is the demons' "natural habitat", meaning that their thermoregulation is adapted for that environment, and thus also works best under those conditions.

The Demon Realm is a hot environment. That is the basis of this hc, and also what I truly believe. I mean, we know of multiple demons who choose to walk around with little to no clothes in canon (and even if you could make the argument that their darkness might work as a substitute for clothes, some of them aren't wearing much of that either). So, yeah, the Demon Realm is hot. Of course, it is also a vast land, so it would only be natural to assume that there are some variations throughout the realm. Some parts are hotter, some are colder, but they can all be described as warm. And now comes the problem that "hot" and "warm" can also be subjective, depending on where you live and what kind of of climate/temperature you are used to - so, let's put it like this: the coldest parts of the Demon Realm are about the same temperature as a late spring/early fall in Britannia. And the hottest parts in the Demon Realm are volcanic and might be more or less inhabitable to your typical human.

Now, what does this "natural habitat" mean for the demons' thermoregulation? Well, for starters, it (and with it, their natural need for heat) means that the demons are more tolerant towards a rise in body temperature, rather than a drop in it. They can better handle hotter environments, and would have a less drastic reaction to the temperature of the environment going up (because they have less of a need to counter it). On the other hand, it also means that they are more sensitive to colder environments, especially environments that are colder than any found within the Demon Realm. These environments (like a full-blown Britannian winter) are not environments that demons would naturally encounter (although a lot of demons would/have visited Britannia), which means that they are prone to causing overreactions in their thermoregulation.

Exactly how sensitive a demon is to changes in temperature (and especially towards lower temperatures), and how high exactly they need to keep their body temperature, varies slightly between different types of demons and what part(s) of the Demon Realm they call home. Demons living strictly in the volcanic parts of the Demon Realm would have a higher need for heat and be more sensitive to a drop in temperature than demons who never set foot in those parts of the Demon Realm. By the same logic, demons who are adapted to and may visit more or all parts of the Demon Realm would be able to handle a wider range of temperatures.

What are the downsides? (cold environments)

Lastly, I wanna talk more about demons in cold environments. Like mentioned above, demons are more sensitive to lower temperatures and exposure to (particularly) cold environments may cause an overreaction in their thermoregulation. This happens because demons aren't used to handling these kinds of environments (due to the nature/climate of the Demon Realm) and their bodies don't fully know how to handle those temperature changes. When the demon's thermoregulatory center gets information of big drops in temperature, especially if those happen suddenly, you could say that it triggers a sort of panic - an oh shit, this might actually kill us kind of reaction. Of course, not every cold environment or (Britannian) winter causes an overreaction. But it tends to happen during sudden and/or prolonged exposure to cold temperatures, even more so the more intense/low those temperatures are.

The issue with environments that are colder than those in the Demon Realm is that the demons' thermoregulation doesn't always know quite when to stop. When there is a change in the temperature of the environment in the Demon Realm (regardless of if it's a raise or drop in temperature), the demon's thermoregulatory center knows which thermoregulatory mechanisms and how much of each is needed to counteract these changes in the temperature of the environment. Meaning, the ideal body temperature is maintained in the end, as it should. It might not be exactly the same body temperature in every environment (demons might be a bit warmer in cold environments and a bit colder in hot environments), but it stays within the acceptable range.

But in really cold environments (i.e. environments with lower temperatures than those in the Demon Realm), the demon's thermoregulatory center does not have the same basis or knowledge of what and how much is required to counter the change in temperature caused by the environment. Because of this an overreaction might occur; the ideal body temperature is not maintained. Instead the demon's body temperature is raised too much, beyond the acceptable range (because, again, the demon's thermoregulation doesn't know when to stop), and the demon risks overheating rather than freezing (as a human might risk in the same environment).

So, how do these overreactions present themselves in the demons, and how might the demon deal with them? Let's talk about a few things; starting with hyperactivity. Like mentioned before, demons have a tendency to become hyperactive with their body movements in cold environments (since muscle activity produces heat). Now how this hyperactivity might look varies. It can be anything from the smallest movements, like "vibrating" in place, to repeatedly rubbing their hands together, to bigger movements like continuously pacing around. These can also range from the demon being completely aware of them, choosing to do each movement, to these movements being done more or less unconsciously. For demons with less awareness of their movements they might even need someone else to help them realize they're doing them, and also, either by themselves or with help from others, be reminded to "calm down" or "stop moving".

Stopping an overreaction from happening or stopping one that is already happening, can be tricky. One way to do this is to lessen the thermoregulatory response happening, or at the very least the effect of it. This, of course, is a lot easier said than done, but one way to do it can be like mentioned above, that is trying to lessen the amount of movements the demon makes (less movements equals less heat production). Another way is to change the environment or the temperature of the environment. Striving to change the environment the demon is currently in is a basic need or goal for the demon. The overreaction happening is the demon's body telling them "this is dangerous, we need to get somewhere hotter". In other words, getting to a hotter environment or trying to make the current environment warmer is a way for the demon to stop the overreaction. A change to a hotter environment would change the information being sent to the thermoregulatory center and thus also the thermoregulation happening. A hotter environment would require a less drastic response, and might even fall within the kind of temperature change the demon's body is used to handling - in other words, the overreaction could be turned into a regular reaction.

The last thing I want to talk about today is the matter of clothes. The demon's clothes are a bit of a double-edged sword when it comes to cold environments. On one hand, removing clothes is a means for the demon to keep themself from overheating; because, as we all probably know, removing clothes makes us colder (wearing a layer of clothes reduces heat loss). But at the same time, removing clothes creates direct contact between the demon's skin and the temperature of the environment. Keeping a layer of clothing between the skin and the environment would lessen the input the thermoreceptors get, and thus also the information sent to the thermoregulatory center and the following thermoregulation response created. How a demon would tackle this clothing dilemma would vary between demons (and personalities) and also the situation at hand. One major factor of this could be whether or not an overreaction is happening. If keeping the clothes on would keep an overreaction from occurring then that might be the wisest decision for the demon. But if the demon could remove clothes without causing an overreaction then that could be their best course of action, since it would probably have the biggest effect on their current body temperature. In other words, there is no easy answer to whether or not removing their clothes would help or hurt their situation; it all depends.

Anyway! There is probably more stuff I could say about this headcanon, but this was all I had for this post. If you made it all to the end, congrats! I hope you liked it :)

#Cooold = HOT (whump-tastic!)#<- note i made while plotting this post lmao #these demons are imperfect little freaks (and i love that actually)#nnt headcanons #libra is rambling again surprise surprise #<- been a while since i used that tag lol (figured it was perfect opportunity to bring it back)#nanatsu no taizai #seven deadly sins #nnt #sds #nnt demons #nnt demon thermoregulation #nnt lore #uhhh idk what to tag this #meliodas #bc this hc was created to whump him <3

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