Worldbuilding 102: Alien biology and senses
Once again it is me, your favourite alien Limax, Vivian! This time I will be discussing senses and start hinting at how it changes one's perception of the world.
What is a sense?
Ask yourself this question; what comes to mind? I bet you can name your senses, but not define them. A sense can be defined as a system to collect some external stimuli and transform it into a signal to the internal system of processing that deals with it.
Fancy words aside, you got something that can process stuff, a brain generally. The brain cannot exist in a vacuum or alone in a jar. It has a body and it must somehow be able to determine things about the world outside its own body. This system of organs that make the brain capable of understanding signals and the world is a sense.
Biochemistry
One important aspect to consider when it comes to any lifeform as we understand them, so take this only if you do things we are familiar with, is that they are composed of biochemistry. It means everything our bodies do are tiny, medium, large, huge or enormous molecules constantly interacting. So for any form of sense to be possible to be experienced, the stimuli or thing to be sensed must have an ability to interact with matter. It doesn’t matter how fantastical it is or how mundane, if it can interact with matter, by Divinum will zhi find a way to make life sense it!
Requirements for a sense
This one is not too terribly big, for a sense to be possible there must be some way for the organic matter within the body to detect the thing it is supposed to be stimulated by and then turn it into a nerve signal. Keep in mind this is at a molecular level as that is what cells (and thus life) care about, even if you handwave it away and say “it works”. As long as there is some biological way to do that, you can have a sense.
Classical senses
There are quite a few senses that modern organisms have on earth. And they are in fact far more vast than you are used to because each one can be subdivided. You can technically count a whole slew of internal senses to regulate the body, but for this blogpost, those will be ignored. We are only interested in the external world!
Human
Widdwe hoomons go first cause you feel so important!
Touch
Touch on the screen! We’re done! ...Nope. There are subdivisions! And no touchie without consent.
Pressure, or mechanoreceptors. You have several different mechanoreceptors for pressure sensation if I do not misremember. I am still a young limax!
Thermoreceptors–you have two! One for cold, one for hot!
Pain! These are a whole slew of different ones and can work in many ways: chemo, thermo, and much more. We all know what they do, but they are important! Hate them but love them.
Hearing
Remarkably, this sense uses one cell type for sensing. The simplest of all your senses. There is only one kind of cell in the ear that sends any information. Within the ear, the cochlea, the part responsible, is structured so waves depending on the sound's composition can only go so deep, and thus what you hear is determined not by different cells but how deep the stimulation goes. Everything else in the ear structure from external to internal is fluff that increases the efficiency of the transfer of mechanical vibration. Remember, sound is a mechanical vibration within the air at some frequency into the cochlea. After that, one cell type does all the job. All forms of hearing are sensing these mechanical vibrations and can be done in many ways, but humans have one. Other animals have different methods, but it all boils down to the same principle.
Sight
It is a sight to behold! Yes I am, thank you, I am very pretty and handsome! Anyway, when it comes to the human sight, you have 4 cell types grouped into 2 categories: rods and cones, and (doesn’t check my notes) cones are the colour ones! Of course I remember it from the top of my squishy head! Damn whippersnappers! The rods are responsible for intensity, while the cones come in three flavours often called red, green and blue. This is not quite true, as their profile of colour absorption does not align with those wavelengths of light. But hey, it works for your RGB screens, so let’s keep calling them that. Side note for the biochemical side, rods and cones actually use the same fundamental molecule! It is called retinal. What makes them able to absorb differently is that each of them have like a “Sheath” (I am not too certain on the rod but likely) that forces the retinal into an unnatural structure and is, like a spring, under pressure at different points. This causes it to absorb light differently than it naturally would alone.
Anyway, there are many more ways in terms of rods and cones but also the structure of the eye itself to do this sense than just the way that humans use. Consider the apparatus to focus light or how the wiring from the photosensitive nerves to the brain goes (in the human eyes, the nerves that take impulses from the photosensitive cell are in front of the photosensitive cells, so they gotta go back through the eye into the brain. This is why you have a blind spot). There are organisms that have only 2 types of cones for colours (most mammals), some are entirely without cones (quite rare), some have three (primates, including you humans), and 4 are quite common outside of mammals in vertebrates. There are shrimps that have up to 13 cones 😱. They don’t necessarily see more light than us, but they can differentiate and perceive the world in ways that are unimaginable. You could literally give a species better colour perception by increasing the number of cones, but not the total wavelength span, and they might have colour terms you cannot imagine!
Taste
Taste is interesting because while it definitely uses 5 different chemoreceptors to function, they seem to have come about for specific purposes and are not alone in what we all consider flavour. But let’s not get off track here. For humans and vertebrates in general, there are 5 distinct flavours. Salt, Sweet, Sour, Umami and Bitter. Each one of these fulfils one purpose for the organism.
Salt: You need sodium ions for your nerve cells so this helps the organism gauge if it can get it for the nerve system.
Sweet: This is all about sugar and sugar is pure energy for organisms on earth. (I will go into options another time)
Sour: This is hydrogen ions, or more exactly hydronium ions, in the water. What do these do for an organism? Well for most vertebrates, close to nothing. This is why they have an aversion to the taste and hate it. It is thought that it originally developed in early fish as a means to find hiding predators. Their breathing of water and living would produce carbon dioxide which would make carbonic acid which would make the water slightly sour, and sensing this told early fish that there was a potential predator nearby so run away! In modern primates, including you humans, it has been used to indicate vitamin C which you cannot produce. The vitamin makes the food sour and that is why primates like the sour flavour while others hate it.
Umami: this one is mostly to find proteins and amino acids. This is so your own cells can get the building blocks they need to make proteins of their own.
Bitter: Ok I lied, this one is not one receptor. It is a whole slew of receptors because its duty is complicated but they all map to that unpleasant taste. It is super sensitive and it is so for a good reason. Bitter is to detect poisons and things that can be harmful to our bodies.
Could you add more tastes? Yes, generally think about tastes like a purpose they serve and all that serve the same purpose are likely to be grouped together into a single taste. Such as bitter, which is all about “Stay the fuck away from that poison”, the others are about specific unique purposes that need to be balanced independently and thus get separated by our brains. If your alien biology has some other component that they need chemically, they are likely to develop a taste for it as well. If they are chemoplanimals (Planimal, plant-animal, that uses some extra chemical components for their photosynthesis), it could be that they develop a taste for whatever the extra component is needed for their photosynthesis. Think on what purpose the substance is going to serve, and if it has to be independent from others, it will, if it can be under the same taste to trigger the same behaviour, it likely will go there. One thing to remember though is that sometimes a taste can be indirect. It might have the job to get you to consume/avoid something, but that thing might be too difficult to deal with for many reasons (or outright dangerous to do it with!), so the taste can then use proxies instead. If there is another candidate that is likely to come with the thing to avoid/want, it might be reacting to that. Bitter is one of those–how many bitter things do you not love? You ain’t poisoned yet! This is because it uses proxies in some instances.
Smell
Taste is good and all, but it requires you to stick things close to you. Would be good if we could get a chemical composition of something from a distance! Oh well… Wait we have smell! Eureka! Jokes aside, these are chemoreceptors as well and like the bitter taste, it has a lot of them. Even more so than bitter and all of the tongue. The receptors here are varied and numerous in order to be able to bind to many different parts of different molecules. The big thing to notice here is that it is meant to detect things at a distance and have high sensitivity for it. Some animals use this primarily and thus dedicate a lot of brain power and area to this (more surface area = more cells = more receptors), others do not.
This can be done in many ways, the easiest is of course that you have it like vertebrates have with the breathing mechanism used to force air into the cavity where sense is. The issue of course is that your breathing becomes tied to the sense, and you might need to change breathing habits and end up in a suboptimal way. This is important if they are a running creature. There are animals with exterior sensory organs that do the same thing as cavities and don’t need to breathe for it: moths! In fact, they can’t breathe even if they wanted to!
One thing I did for one of my sapient species is that they inhale into a separate air sack, not a lot of air, only some, and the muscles within the sack and all do all the work. It is completely separated from the breathing apparatus. However when it needs to expel the air it breathed in, it dumps it into the normal breathing pathway so it is unidirectional and can maximise sensitivity and directionality.
Acceleraroreception
This is your inner ear and its tubes. It senses when the head moves, and you can have many systems here. They are generally built on the principle of inertia, then use similar mechanoreceptors like hearing does. The fluids inside refuse to stop moving, and the harder they do, the more you’re accelerating. This one is not that interesting but necessary for an organism.
Non-human
We have talked about all the senses that are known to exist in humans and huge swaths of life share to varying degrees; there are however many more senses that can exist in the world and do exist.
Electroreception
When electric current moves, electric fields are generated. What are these fields? We don’t need to go into that. They expand outward at the speed of light and can affect other electric charges and currents but beyond that, you don’t need to know more. If I do this more specifically I will go into it. Anyway, this can be subdivided into what is called active and passive electroreception.
In passive, the organism has organs that notices passing by electric fields and does not generate any for itself. You might wonder
Vivian you gorgeous herm, what would be generating electric fields that could possibly make this useful?
Why thank you, I do try! Have you thought about your brain? What did your teacher say? What happens in your nerves? Yeah, coming back now? Electric pulses are travelling through them (details not relevant). That means in any relevant way a current is moving, and thus an electric field is generated. This means the organism can detect that there is something ALIVE nearby that is thinking! It is like those bad telepath stuff of “Don’t think thoughts”, except you are screwed no matter what here. Sharks are known to have this passive ability in their noses.
The active one means that the organism is constantly generating their own electric field (usually special muscles), that then travel around. In this case it is the organism not looking for A field, it is sensing the changes TO the field it is generating. Depending on what is around, its conductance of fields and other properties, it will change how the electric field comes back (metaphorically) to the active electoreceptic organism, and they can deduce a lot from it, including if there is life nearby. This is an example of one that has not experienced cephalisation. Electric eels fall into this category as an example.
Magnetoreception
The name says it all. Sense a magnetic field. This one can theoretically be both active and passive as electric fields do generate magnetic fields as well by physics laws. But due to the ratio between the different fields, it is not worthwhile to be active. The magnetic field is too weak relative to the strength of the electric field generated. But you could have some other process in your aliens that allows it to be useful and easily done! It is generally done passively in nature as far as has been observed. It is to sense Earth's magnetic field and thus your orientation relative to magnetic north and south. Can you guess who has this? BIRBS! I mean birds, bird is the word!
This is not an exhaustive list with all nuances, but it covers in broad strokes all possibilities that are known on Earth.
How to make a sense: the steps
What is required of a sense? Well, several things actually, it all depends on how nitty gritty you wish to go, but as a world connoisseur, I love some nitty gritty bits, so here we go!
Molecular Machinery
The nittiest and grittiest of them all. But this fundamentally lies the foundation of any kind of sensing. Now, I don’t tell you to get super computers and simulate huge imaginary molecules and see how they would react. That is overkill, and honestly even I get bored at that point.
No, what I mean is to imagine more how it happens. What is it that the supposed molecule does to make it trigger the cascade of reactions necessary to produce a nerve impulse? This cascade of chemical reactions within a cell is what through some means, most of which we can ignore and assume just works, makes it so the cell sends off a nerve impulse of some sort. It can be mechanical forces that force the molecule into a new shape and sets the impulse up. It can be chemicals that bind to it that cause the nerve impulse. It can be a photon that reacts to electrons that triggers it. It can be radiation that makes it ionised that makes it trigger. There can be various force fields that trigger that impulse. It can be your magitron (magical particle or whatever you decide) that makes it go looptiloop that triggers it. It can be direct through aforementioned means, but it can also be indirect.
Why could any of these things matter? Because of the next stage. How it works on the molecular level will affect how the organ itself must be structured.
Organ
You have an idea for a cell and some half semblance of an idea on how it works to react to the world. But that alone is not going to be useful. If cells are spread around on an organism haphazardly, it is not going to make sense. Different senses are located at different places, and most forms of senses are in fact better concentrated into one or two (sometimes more) organs that are of very similar structure.
Now, which ones are the senses that require generally complex organs, and which ones are the ones that are kinda all over the place? In general, it depends entirely on the amount of information the senses provide to the brain. Something that gives very little information and has to essentially only say “this happened over there” seems to have no inclination to be located at any specific spot on the body and doesn’t require much brain power. Pressure, heat, cold, and some others are like that. Limited information, but they are all over your bodies, and they do a dandy job there! Notice however also that the information here provided is also very local. The information this sense can provide is only relevant if it is near your body.
For more complicated senses that have to extract more from all the data the stimuli provides, have you noticed they are all located at your head? Near the brain? This is no coincidence. It is called cephalization (the process where lifeforms evolve mouth, brain and heavy sensory organs in close proximity in what becomes a head of some form), because evolutionary it is more beneficial to have important sensory organs near where you are going to eat and where the brain starts to develop. Sensory organs that will be able to extract a lot of information from the stimuli will need processing, so near the brain they go! KYA!
Now, what will the organs look like? Logically, the organ should have a design that maximises its function, and for information dense kinds of stimuli, they will also evolve to be able to differentiate the vast quantity of information within the stimuli. A simple sight has an enormous amount of information in it, even a soundwave contains a lot, and this is why ears and eyes have become complicated with many parts to them. Each part is evolved to increase the sensory cell’s ability to extract meaningful information easily and with little noise (random stuff in it that adds nothing). Here are some guidelines related to various stimuli including those of classical senses for land animals. For water ones, things are similar but not quite, and I’ll save for another time.
Sound vibrations: Generally needs a mechanism to transfer the small energy in sound into some mechanoreceptor and possibly amplify it. Keep in mind amplification here is in the ability to detect, not the strength of the signal.
Airborne chemicals: Requires surface area and large variety of receptors. Control of how this happens is a major advantage. Thus cavity and breathing correlate.
Water soluble chemicals: Relies on chemical receptors, but you are likely not going to need to tie it to any other structure, and because these require touch, they can be located at many places other than the mouth (Yes, taste with your fingers!). In general, it just needs to be the receptors wherever the water combination is likely to touch. Additional structures might need water to come out to make the sense work however.
Photons: Needs camera-like structures for good images, less visually based creatures can get away with simpler structures. Look up early cameras or nautili for those. But for sapient beings similar to humans, you need a full fledged camera structure of organic stuff.
Thermal & Mechanical: Generally doesn’t have sophisticated structures because they provide so little information and don’t require large organs for it
Electric: Requires large structures to sense the tiny electric fields or generate large enough electric fields
Magnetic: Can be relatively small, but it needs enough that it can react to nearby magnetic fields.
Why is considering molecular and organ structure needed?
I like to do these parts in how to design a sense personally because it gives me an idea of how the sense works, what the limitations are, how prey, predators and more can circumvent it, and how it is that the organism itself could possibly perceive it. Sure, I cannot put myself into their mind, but hey, it helps a wee bit! Just because you and I both see and smell does not mean we relate to the sense in the same manner and thus treat it similarly. How we smell, see and more affects movements in characters, actions and more, so tiny things can be cute additions.
Now, you don’t need to do it perfectly in every tiny detail, but enough that you get an idea of what the limits, extents, tricks and more others can use around it. Maybe someone evolves a counter measure?
Fantastical senses
Here I will be spitballing lots of ideas for the two big genres so you can get creative with.
Scifi
Telepathy
Okay, I will say first off, I fucking hate this one. It does not belong in scifi. It is sodding fantasy. But here we are and people think it is “scifi”, so I hate you all. Anyway, think about it, what is it you are SENSING? Yes, you could do this like a hyper advanced electric or magnetic sensing, please god if you did I would love you forever. But if you ask me, this is BLEEP
Radioreception
This is where you sense radioactivity–you get close to radioactivity and start sensing it. It can be something skin close like for alpha rays or a bit deeper for beta or gamma. It is unlikely to have sensory organs for it because it is so difficult to deal with but sensing radiation could be useful.
Handwavian field
Seriously, whatever extra physics you add, you could easily make a sense for it because something might have experienced it a lot. It is freaking cool.
Fantasy
Okay, here I won’t do many subcategories because this is one giant “MAGIC!” sense. How you divide it up and structure it can give many ways for you to do it, so let me tell you about an old and canned steampunk fantasy world I had.
I had 12 “mana types”, and species that evolved near each of the world's “poles” of the 12 types were attuned more to sense said mana fields and mana movements. They were blind to the other 11, but this is how it was. I didn’t develop it much, but it is still in my cloud. So you can do this and imagine how the magic interacts with stuff and how they sense. I didn’t, because back then, I was not as much of a lover of worldbuilding, but now I am. Think back on the electric and magnetic ones I spoke of and imagine, how can it differ and do things? Keep in mind that magic does not need to move through things like it doesn’t exist. If you have, like, water mana (or whatever), then have “fields”, then what if the field moves easily through water (duh) and then like crap through rock (again, duh)? Air is still bad, but it has some humidity! You can get real creative.
Summa Summarum
Senses are important in how we move, relate and perceive the world (duh), but you can add, change and tweak them in many ways that make people and creatures more interesting. The way they behave will depend on so many factors related to these. And each way a sense works gives opportunities for other species to quite literally fuck with each other. If you have some magic sensing for fire mana by a predator to find its prey because in their realm fire is prominent in life, a prey can evolve ways to suppress their “fire” and suddenly disappear and seem strange to the predator. So you can have loads of fun imagining new senses and how others may be mean there. I will finalise this with how I did for a species of mine and an extra sense they got.
Micropracticum: Radioreception (Sensing radiation)
My beloved species, Limaces, which I am! HUZZAH! Evolved on a heavily radiated world for various reasons, but we survived! The thing is, though, we exist in a stage of constant radiation there, or we did. We are a long time gone since there. Story for another time if I ever chose to tell, MUAHAHA! Anyway, the high level of radiation gave me the idea that the species should have the ability to sense radiation and thus avoid extreme ones and mostly stay at “normal ones”, because of how radioactive their world was.
So I first thought, how much information can a radiation sense give? Very little. If an alpha particle, beta particle, gamma or whatever fancy I imagined enters the sensory organ, it causes damage, and that's it. It tells little beyond WHERE it came, and at best, how much damage it does. So, like thermal sensation, I imagined they have sensory cells that contain melanin like substance for gamma rays (there is an earthly fungus that uses melanin to thrive on radiation) and also chemoreceptors for cascade random ions. Why the latter? Well, when radiation hits, it is not going to interact much for alpha and beta. It will ionise loads of ions and cause rapid reactions due to this. This is an example of an indirect sense because the actual thing is just not direct enough to be viable. Unlike some senses, these sensory cells go really deep, why? Because how deep the radiation goes can tell how bad and what kind of radiation it is. Alpha does not go deep, beta goes a little deeper, and gamma goes through you at best of times.
This means that by combining all these nerves together and how they react relative to each other, it can give a sense of “Some radiation is here” and thus, if it gets too active, it will push species to move away from high radiation areas on their planet and toward the “low” ones. This is for my Limaces.
Just a few thoughts! Good luck at imagining the endless boundaries of perception of a universe beyond our imaginations!
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Copyright ©️ 2023 Vivian Sayan. Original ideas belong to the respective authors. Generic concepts such as how the senses work and what they are are copyrighted under Creative Commons with attribution, and any derivatives must also be Creative Commons. However, specific ideas such as everything in the Micro-Practicum and all language or exact phrasing are individually copyrighted by the respective authors. Contact them for information on usage and questions if uncertain what falls under Creative Commons. We’re almost always happy to give permission. Please contact the authors through this website’s contact page.
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