Rethinking Merfolk

[Andrian]

I recently watched this video on what medieval weapons merfolk would use, and it got me thinking about things. One of the things the creator of the video mentions is the use of swords underwater, and it occurred to me that merfolk would have a very hard time making swords and an even harder time keeping them in working condition, as salt water doesn't like heat or metal very much. This led me to consider what sorts of materials merfolk might actually be able to use for weapons and what sorts of weapons would work best when made of those materials, which has since led me down a huge rabbit hole of trying to figure out what merfolk would really be like. I would like to explore some of this and share my thoughts.

For the purposes of this discussion, I will be assuming that magic does not exist, or at the very least that it is unavailable to merfolk. I will be discussing their biology and evolution, as well as their technology and culture as I think it might develop.

Let's start at the very beginning - the origins of merfolk. Humans developed technology as they evolved, and I think the same would probably be true of merfolk. Hence, let us consider how we might arrive at something resembling a merfolk in the first place. I think the way merfolk would be most likely to evolve would be much the same way that whales evolved - with a population of land-dwelling mammals returning to the sea. However, unlike whales, merfolk would probably have evolved from a primate, as they clearly exhibit the classic features of primates, such as hands with opposable thumbs, downward-facing nostrils, large brains, and flattened faces with a wide field of binocular vision. Hence, the ancestors of merfolk were probably primates who lived along the coast, probably exploiting food sources from the water and possibly entering it to escape predators. As they became more and more dependent on the water, they would start to get adaptations to help them survive in the water, such as losing their hair, having their hind legs be more adapted to swimming and probably developing a protective layer of fat to help insulate them. However, unlike whales, whose hand bones fused into flippers, these proto-merfolk must have found that their hands were more useful for manipulating objects than they were as mere aids to swimming. This suggests that merfolk may have been using tools before they entered the water, possibly even shaped tools. This suggests that the ancestors of merfolk may very well have been bipedal before entering the water, and for wading creatures, bipedalism would be a pretty big advantage, allowing them to wade deeper than they could if they had a different posture.

Realistically, merfolk would probably not have hair on their heads. Maybe they would have it as a result of sexual selection, but more likely they would develop other kinds of displays there, such as colorful skin patterns or raised fins or something. Merfolk would also be unlikely to have external ears unless they were largely amphibious, in which case ears that could fold flat against the head would probably be selected for, as this would reduce drag in the water. Realistic merfolk would probably develop blue-gray skin to help hide them from predators and prey, and would probably have counter-shading (a lighter belly and a darker back), as this would further add to their camouflage. Merfolk would also need to develop adaptations to deal with increased water pressure for deeper dives, and increase their ability to hold their breath underwater. They might develop some way to breathe underwater, but as neither birds nor mammals that have returned to the sea have yet to develop such an ability, I think it's safer to assume that merfolk would have to surface from time to time in order to breathe. Merfolk would probably have developed some way to eat underwater, as it would be safer and more convenient than having to surface in order to eat. There's probably more adaptations that merfolk would need to develop, but these are all the ones I can think of right now.

Now on to technology. As I said, merfolk probably used tools before entering the water. These would probably be simple tools - at most, knapped stone. Now, a marine environment provides a lot of challenges for developing technology. For one thing, water dissipates heat very quickly and limits the maximum temperature that can be achieved underwater to its boiling point. This makes fire a virtually worthless technology for merfolk, unless they remain largely amphibious, in which case they might develop fire. However, I feel as though the advantages fire would bestow to merfolk would provide evolutionary pressure toward leaving the water - easier thermoregulation and cooking food to improve its nutritional value would be big evolutionary advantages. I think if we want anything close to traditional merfolk, we're going to have to assume that they did not develop fire early on. Stone knapping, on the other hand, could probably still be accomplished underwater, or at the surface without leaving the water, and it would provide a significant benefit in the form of sharp tools for cutting and piercing. These blades could help them open shells and harvest seaweed, as well as help protect them from predators.

Another challenge that merfolk would face in developing technology would be water's tendency to speed up the decay of materials. Salt water is especially bad about this. Plant and animal material would rot and disintegrate. Metal would rust and corrode. Many preservation techniques, such as drying and tanning, would require doing things above the water. Glass, ceramics, and metalworking would be all but impossible, and would certainly require a lot of time on land to use and develop. This means that merfolk would need to constantly gather fresh materials and repair or replace things. For example, merfolk might use kelp or seaweed to make cordage (that is, ropes, strings, thread, etc.) and wicker, but unless they were able to find some way to prevent those plants from rotting away once they're harvested, anything they make from them probably would not last long. About the only things merfolk could count on to last would be hard stone, corals, shells, teeth, and bones. As a result, I think that merfolk technology would tend to favor these materials.

One thing that is a benefit and a detriment to merfolk technology all at once is the physics of water. Unlike the firm ground, water does not provide much of a way to overcome the negative effects of Newton's Third Law of Motion. On land, if you push against something, the friction with the ground helps transfer more of the force into moving the object. In the water, however, there's no easily-available source of friction, meaning that moving objects requires more effort. However, since water is significantly denser than air, it is easy to take advantage of buoyancy to aid in lifting heavy loads. Instead of developing the wheel to overcome friction with the ground, I think merfolk would develop air bladders to assist them in lifting and moving heavy objects. These could be harvested from kelp forests or invented using animal parts.

Agriculture might actually be quite easy for merfolk to develop. They could farm seaweed or shellfish like mussels and oysters, allowing them to have more control over their food supply. Food storage would probably be a problem, though, so merfolk might need to migrate or develop crop rotation in order to ensure they were able to survive, as the life cycles of their food sources would probably wax and wane at regular intervals. Alternatively, they might build up large fat stores, as many marine animals do, to help safeguard against leaner times. This would probably mean they would gorge themselves during times of plenty. Which strategy would be most effective would probably depend on local conditions. They might also find some sea life which they could domesticate. Seals come to mind as animals which might fit well, as they have social hierarchies and relatively short breeding cycles, and they would be an excellent source of food. They might also be trained to assist in hunting or other tasks, much like dogs. Seal skin, should merfolk learn how to properly preserve it, might also work as a more durable, waterproof material. I doubt that merfolk would be able to domesticate dolphins, though the two species might form a symbiotic relationship of some kind. This is mostly due to the fact that dolphins take too long to reach sexual maturity, and as such would take much longer to properly domesticate than other creatures with shorter reproductive cycles and lifespans.

Regarding tools and weapons, the materials of choice would probably be shell, stone, coral, tooth, and bone. Large, thick shells could be used as containers or digging implements. Their edges might also be sharpened for some cutting purposes. Bivalve shells would probably be the most useful for such purposes. Stone would be readily available, especially along certain coastlines. They might have access to just about any type of stone, though the harder stones would probably be the most useful. Flint and obsidian would be most valuable for making blades, while pumice could be used like sandpaper. Stones could also be used to anchor things down and prevent them from drifting away, and as such stone might be an ideal building material should they be able to ensure its stability. Coral comes in a number of different shapes which might be refined and specialized for specific tools. Tooth would be ideal for cutting or piercing. This could be anything from the tusks of walruses or narwhals to shark or whale teeth. The teeth of sperm whales would probably make excellent weapons - particularly spear heads, as they are pointy and conical. Bone could be used in a number of different ways, as bones come in many shapes and sizes. Small bones could be used for fine tools, while large bones could be used in structures or as the shafts of tools or weapons. Bone can also be sharpened into blades and points, making it a highly useful and versatile material for merfolk. Spears and knives would probably be the most useful weapons for merfolk, as they would be easy to make and easy to wield underwater.

Merfolk might also develop drugs and medicine to some degree. Dolphins have been known to play with puffer fish in order to get low doses of the venom for recreational purposes. Merfolk would be likely to make similar discoveries, and might develop drugs for reducing pain, healing various conditions, and recreational or religious purposes.

When merfolk come in contact with humans (or other land-dwelling humanoids), they would suddenly have access to a lot more things, and there would certainly be a cultural exchange of some sort. Sunken ships would provide merfolk with all sorts of treasures - particularly in the form of new materials, but also possibly in the form of ready-built homes. I could easily imagine a community of merfolk living in a ship's graveyard (and possibly intentionally sinking any ships that come around), scavenging them for valuable items. Should merfolk and humans have disagreements, things could get very nasty. In the water, merfolk would have significant advantages. They could dive under boats and sabotage them from beneath, or pull sailors into the water to drown them. Humans would have ways of fighting back, though, especially if they were able to deploy large nets to trap and entangle the merfolk. In shallow water or on land, of course, merfolk would be at more of a disadvantage, but as these would not really be the territory of merfolk, I don't see that they would be likely to attempt any hostile action in such areas. However, cultural exchange might also be more friendly, with coastal peoples and merfolk working together for mutual benefit. I imagine that trade between the two species could be quite lucrative for both of them. Merfolk would probably highly value pottery and glass, and could exchange pearls, coral, and food for such commodities. Merfolk might also be able to provide services to coastal peoples, such as guiding ships through dangerous waters or protecting them from marine predators.

Merfolk culture would probably be quite diverse, and would likely vary with the area in which they live. Multiple species of merfolk might develop, each suited to a different environment. Coastal merfolk might be more inclined toward farming and staying in one place - especially in areas with fairly consistent conditions year-round. In areas where conditions change regularly, merfolk would probably be nomadic, moving from one food source to another with the seasons. Open ocean merfolk would probably be more physically imposing and rely more on hunting to obtain their food. They would probably need to dive to great depths and have some way of navigating and finding prey in the dark. Such merfolk would probably have large territories. Merfolk would probably not wear clothing, as clothing would slow them down, provide little benefit, and degrade quickly. They would probably employ ornamentation of some kind, however, using the materials available to them. Pearls, mother of pearl, bits of shell, stone, bone, tooth, and coral could all be used for piercings and other jewelry. Merfolk might develop practices like singing, dancing, and storytelling, which could fulfill many cultural roles. Musical instruments might also be developed, though their selection would probably be more limited. The only kind of instrument I can think of that would work underwater would be percussion.

That's about all I can think of regarding merfolk right now. I'd be really interested to see what others have to say on this topic. Do you think I got something wrong? Is there something you'd like to add?

[Zorku]

You tend not to see re-evolution of gills because the potential oxygen content of water is so low compared to air that the high blood pressure land lubbers just can't sustain themselves breathing water. The diving species eventually learn how to regulate their metabolism to slow way down a lot of the time, but by that point they're find just taking a deep breath and subsisting on that for a damn long time.

Although copper does corrode underwater, it's slowish, and slower still the less salt it is exposed to. Salt concentration is highest at the surface of the water, so as long as they kept these tools to lower depths they could get some decent lifetime out of them. Throw in a habit of burying the tools between uses and these things would actually last quite awhile. If they can somehow get their hands on the stuff, various bronze alloys are even more resistant to salt water corrosion, though without fire I'm not quite sure how they'd figure that out in the first place.

Once you get the human trade situation sorted out there's a fairly obvious synergy for metal tools. Quite a lot of clay mining was done by slaves crawling down long tunnels and running just terrible water pump systems to keep from drowning, and then a lot of the time those tunnels would collapse. Merfolk could much more easily mine the clay, and then in turn the humans could use that to make more casings for pouring metals into. Because of the corrosion issue I don't think the mermaids would be a great source of copper ore, but that stuff is fairly plentiful on land anyway. Tin on the other hand, is pretty much unaffected by sea water (it technically oxidizes, but the surface layer seems to prevent deeper oxidation.) I'm not entirely sure how easily a mermaid could find a nice vein of tin to mine, but it seems plausible enough, and where tin is usually the limiting ingredient in how much bronze a civilization can produce, that could be very beneficial for both parties.

[Andrian]

Thanks for that information, Zorku! That's actually quite helpful to know! If merfolk were able to get their hands on metal tools that wouldn't corrode, more advanced stone work and mining would be opened up to them.

Another thing I realized I'd forgotten was writing. I think it would be very difficult for merfolk to develop any kind of advanced writing, as I can't think of any equivalents to ink and paper that merfolk could use. They could, of course, carve stone tablets, but those are large, heavy, and require a lot of effort and skill to create, as well as tools capable of carving the rock in the first place. For temporary messages, sand would of course work, but it would be hard to create messages that would last. One advantage of books and scrolls is that you can store a lot of information in a small space and easily transport them, but I don't think merfolk would be able to develop an analogous technology. This would probably limit their ability for cultural exchange and development of technology, as they would be restricted to an oral culture.

[Mechalich]

There's a lot here, most of it pretty good.

Regarding the evolution of merfolk, that is indeed a tricky one, given that traditional merfolk are a tauric amalgamation of fish and mammals that makes no real sense. It's much easier to think about the evolution of something like Sahuagin or Locathah - fish to fish-person - rather than a means to get merfolk. Primates returning to the sea is one approach, the alternative is to have a marine mammal evolve hands (or actually, revert towards more traditional limbs and then develop primate-style hands) in which case your best candidate is probably sea otters followed by sea lions. If you go with the primates who return to the sea approach its helpful to note that limbs and fingers actually evolved in water first, not on land, so your best bet for retention of hands is that these proto-merfolk lived in a similar environment. Namely murky waters with thick vegetation where digging, grasping, and pulling provided a useful mobility advantage. In this scenario the proto-merfolk ancestors might have evolved in a riverine environment or in mangroves. The proboscis monkey - which swims well and has partially webbed fingers and toes - serves as a model you could start from. In this scenario merfolk would be creatures of the coast inhabiting rivers, swamps, mangroves bays, and shallow environments such as coral reefs, not the open ocean. They would most likely not be particularly powerful swimmers - especially if they remained partially herbivorous. Sirenians, which are often considered the inspiration for mermaids are among the only herbivorous marine mammals (and so far as is known among the only large bodied herbivorous marine creatures period, most big things in the ocean eat other animals) are not powerful swimmers and generally avoid pelagic environments. They could even retain hindlimbs and the ability to move about, with some difficulty, on land as seals and sea lions do. Depends on what you want.

Developing technology underwater is indeed a problem. Without the ability to move about on land merfolk are going to be limited to stone and other naturally available materials such as bone, coral, shell, shark and whale teeth (and exotic marine reptile teeth if your setting includes beings out of time), and so forth. That is sufficient to make capable weapons for dealing with aquatic wildlife, but not very effective against armored opponents. Other technologies depend on whether your merfolk have any access to land at all. Even if they can do nothing more than haul themselves onto beaches that dramatically increases technological capabilities. Tanning, for example, becomes possible once you have any sort of land access at all, and that gets you at least some measure of armor (fish scale and sharkskin).

Food storage is a problem - there's no real good way to preserve food while in an aquatic environment, it will either rot or something will come and eat it. You can't even butcher anything sizeable without attracting a whole bunch of predators and scavengers. That means whatever crops/livestock merfolk possess have to be kept alive full time and somehow confined. That works well for stationary mollusks, but gets awfully challenging for almost everything else. This makes living in a tropical area much easier than in temperate zones with seasonality, unless the merfolk are migratory, which is potentially a good source of division into varieties.

Without any ability to develop the equivalent of granaries or any real means to effectively transport food across distances, merfolk civilization is probably going to stabilize at a fairly low level since they won't be able to concentrate in especially large numbers and they really won't have much of a need to build structures at all - though if they can haul out on land there's probably competition for limited beach resources on secure islands and atolls, which is a potential source of social stratification and resource monopolies leading to the development of complex government.

[Andrian]

Thanks for your input, Mechalich! Those are all very good points! I was thinking much along the same lines with regards to merfolk civilization being stuck at relatively primitive levels.

One thing I forgot to mention is that merfolk would need to evolve in a way that allows for big, human-like brains. Some scholars suggest that cooking preceeded our large brains, and that the improved access to nutrients is what allowed our brains to get so large. This is not necessary for developing a large brain, however, as dolphins, with their complex social structure and methods for hunting a wide variety of prey, have also developed very large brains. I think that an abundant source of high-quality food would probably be necessary for the development of the merfolk brain, however. I think that this food would probably not have come from a single source, but rather a variety of sources, each of which required a different method for obtaining it. This would provide selective pressure to develop large, complex brains in order to exploit these food sources while also providing the excess of nutrients necessary to support brain growth over successive generations.

[Trekkin]

I think the biological options for merfolk evolution have been pretty much covered, but I think there's a credible case to be made for merfolk metallurgy, glassmaking, and other processes that require heat, as well as writing.

Fire doesn't work underwater, but lava does, and submarine volcanoes are a ready source of volcanic glass already. Fabricating some kind of macuahuitl (or some kind of spear equivalent) would take nothing more than the ability to knap that glass and slot it into a piece of driftwood or a suitably shaped (lightish) rock, perhaps wrapped in seaweed to help stop it shattering. So, at minimum, they've got glass blades -- and, more importantly, a reason to acquire enough familiarity with volcanoes to understand in broad terms how they work and where the heat goes, which is enough to make cooking via hydrothermal vent possible. Luckily, hydrothermal vents are often found around submarine volcanoes. So they can at least cook their fish.

This understanding of volcanology is important because water only boils below a certain pressure, above which it will become a supercritical fluid; that pressure corresponds to a water column of about 2200 meters in depth, which is well within the depths to which several cetaceans are known to dive. This makes very high temperatures accessible, at least transiently, without the disruptive effects of boiling. Inhibiting the flow of supercritical water upward (perhaps a stone covering?) would only help matters. At any rate, that's enough to enable ceramics to be made by firing pelagic clay, which in turn can allow written messages to be stored long-term. Having an industrial base centered on volcanoes is also an excellent reason to write things down to track their eruptions -- and to develop the mathematics required to predict them. Oh, and you can cook clay-wrapped food to store it long-term, too. This heat could also be enough to allow a quantity of ore to be suspended above a clay mold so that the metal drips down and can be freed of the mold (and the rock) once the lava has cooled. That won't be good enough for swords (which need to be forged) but it can at least enable cast iron articles and lead shot and so forth.

There are probably ways to design what is in effect a wattle-and-daub geothermal smelter, but I'd need more time to design one.

At any rate, the idea of merfolk with macuahuitls and atlatls writing descriptions of principal component analysis in cuneiform on tablets of pelagic clay amuses me greatly.

[LudicSavant]

Extreme heat *is* available underwater, via thermal vents. You could probably build a crucible with that.

Electrolysis would also be available to merfolk, I'd think. Electroplating and electroforming should also work. As would use of airtight spaces and pumps.

[Andrian]

I didn't know about supercritical liquids. That's very interesting and valuable! It would require merfolk to evolve to be able to make long dives to great depths, but at least it's possible. Question is, what metals could they use? I think glass and ceramics would be more useful, though my concern would be whether they could get clay to hold its shape underwater long enough to fire it.

Another concern would be the merfolk themselves surviving the temperatures. Unlike fire, you can't turn off a volcano, and I imagine the heat would radiate a good distance from the vents.

Another thing I'm unsure about is whether it's possible to build a battery underwater using only materials found in the ocean. Obviously they might build batteries on the coast, which might solve the one problem, but I'm still not sure how easy it would be to find appropriate materials. I think naive south American cultures developed primitive batteries, so it's definitely plausible that electricity might be harnessed by merfolk.

[LudicSavant]

I didn't know about supercritical liquids. That's very interesting and valuable! It would require merfolk to evolve to be able to make long dives to great depths, but at least it's possible. Question is, what metals could they use? I think glass and ceramics would be more useful, though my concern would be whether they could get clay to hold its shape underwater long enough to fire it.

Another concern would be the merfolk themselves surviving the temperatures. Unlike fire, you can't turn off a volcano, and I imagine the heat would radiate a good distance from the vents.

Another thing I'm unsure about is whether it's possible to build a battery underwater using only materials found in the ocean. Obviously they might build batteries on the coast, which might solve the one problem, but I'm still not sure how easy it would be to find appropriate materials. I think naive south American cultures developed primitive batteries, so it's definitely plausible that electricity might be harnessed by merfolk.

Sources of electricity for merfolk:

- Primitive sources from the real world.
- Bioelectricity, generally more available underwater (and moreso in a fantasy setting).
- About a bajillion ways via D&D magic.

That said you also have to worry about many kinds of metal oxidizing underwater.

[Trekkin]

I didn't know about supercritical liquids. That's very interesting and valuable! It would require merfolk to evolve to be able to make long dives to great depths, but at least it's possible. Question is, what metals could they use? I think glass and ceramics would be more useful, though my concern would be whether they could get clay to hold its shape underwater long enough to fire it.

Another concern would be the merfolk themselves surviving the temperatures. Unlike fire, you can't turn off a volcano, and I imagine the heat would radiate a good distance from the vents.

Another thing I'm unsure about is whether it's possible to build a battery underwater using only materials found in the ocean. Obviously they might build batteries on the coast, which might solve the one problem, but I'm still not sure how easy it would be to find appropriate materials. I think naive south American cultures developed primitive batteries, so it's definitely plausible that electricity might be harnessed by merfolk.

Well, there are potato-sized chunks of what is essentially low-carbon mangalloy ore literally lying around on the floor, so they would probably start there. It's also reasonably resistant to corrosion. Gold would be better and easier to work.

As for safety, that's why I suggested having them start harvesting volcanic glass early in their history: to develop a process for gauging and predicting where the heat is going to go during an eruption, so they can leave stuff to be heated, get out, and retrieve it later once the eruption has stopped. Supercritical fluids make this process more predictable, too; absent boiling, flows are more laminar and stable.

They're also more useful as a source of kinetic energy, which is where I'm going to disagree with LudicSavant and suggest they're likely to develop generators as an outgrowth of hydrothermal vent-driven waterwheels rather than bioelectric cells. Affix magnets to the shaft, surround it with a conductive coil, and suddenly electricity. It's not hard to build in a rotation-sensitive switch to act as a rectifier, either.

[LudicSavant]

They're also more useful as a source of kinetic energy, which is where I'm going to disagree with LudicSavant and suggest they're likely to develop generators as an outgrowth of hydrothermal vent-driven waterwheels rather than bioelectric cells. Affix magnets to the shaft, surround it with a conductive coil, and suddenly electricity. It's not hard to build in a rotation-sensitive switch to act as a rectifier, either.

Wasn't this the very first thing I suggested?

[Trekkin]

Wasn't this the very first thing I suggested?

Much like thermal vents were the first thing I mentioned above, yes.

That said, for an extremely loose definition of "primitive", perhaps, although since we use generators based on exactly the same principle now, I certainly wouldn't call them so. Electrostatic machines would probably qualify as primitive, as might even voltaic piles. Electromagnetic generators, not so much.

Sorry if I misunderstood, though.

[Andrian]

Yeah, I mean, so far as I know, voltaic piles were about all that was used in early history, and they're super easy to build, at least above land. I think the ones I read about were thought to perhaps be used for electroplating gold. If such things could be manufactured and used underwater, I think that's where merfolk electrical engineering must have started.

Making generators would be easy once they knew how to make that work, though personally I'd prefer wave generators anchored to the continental shelf to something hundreds of feat under the surface. Those are basically buoys that convert the kinetic energy of waves, (which should be pretty much a constant almost everywhere in the ocean) into electrical energy. I'm not sure exactly how they work, but I think it's kinda like a shake weight, with an inner magnetic core that moves freely through a coil of wires. An advanced merfolk society would be highly likely to develop them, as they would probably already have a keen understanding of buoyancy, and the waves would be an ubiquitous part of merfolk life.

Now, before I forget, I wanted to point out another interesting thing about merfolk biology - very likely they wouldn't be able to see the color red. Few primates can distinguish red from green, and, since red light is the first to be filtered out underwater, few aquatic creatures can distinguish red from blue. This is so pronounced in deeper parts of the ocean that many deep sea creatures are bright red. Now, perhaps an argument could be made that if merfolk could see red, they would have an advantage, but that would probably only be the case if they had an easy source of white or red light that they could carry with them due to the light filtering washing out red colors. I don't really see an evolutionary advantage to aquatic primates being able to see the color red until the point that they can produce red light somehow, so unless merfolk are descended from Ruldolf the Red-nosed Proboscis Monkey, I don't think it's likely that they'd be able to distinguish reds. Still merfolk with red bioluminescence could be a pretty interesting concept for a setting!

[Trekkin]

Wave energy converters are definitely among the more sustainable options for merfolk, of which those buoys are one and Salter's ducks are another. I simply feel that sticking a paddle wheel in the big column of hot fluid is a more immediately obvious source of rotary power, at least for a society that's pre-electrical, since the rotating shaft stays put. Most wave energy converters need to move too much to handle a rigid connection to something like a mill wheel, and the stationary currents they could harness move rather too slowly.

As for batteries, they're going to be tricky, since liquid electrolytes aren't an option in water and the whole thing will need to be insulated anyway. I'm not sure why they would think to insulate something like an electrical pile before they knew what electricity was, especially since they can't start with static electricity as we did. Magnetism seems to me to be a more likely route to an aquatic understanding of electric currents, since their environment can at least support magnetism -- and they'd likely learn about degaussing rather soon after ironworking, at least if they carried a large enough amount a long enough way.

[Mechalich]

This understanding of volcanology is important because water only boils below a certain pressure, above which it will become a supercritical fluid; that pressure corresponds to a water column of about 2200 meters in depth, which is well within the depths to which several cetaceans are known to dive.

None of the relevant cetaceans (mostly beaked whales) have hands, and they aren't exactly able to remain at depth for a particularly lengthy period of time. An air-breathing species successfully locating and utilizing hydrothermal vents for anything without some magical assistance to start with is pushing the bounds of believability. This is especially true given that hydrothermal vents are widely dispersed and fairly short lived (decades according to most current estimates). If your merfolk are utilizing deep water or seafloor resources of any kind you really need to be thinking about something with gills. Perhaps merfolk trade with or compete against a deep water species of fishfolk that has greater technological capabilities but reduced numbers.

[Vogie]

You could also go the opposite of the normal route, and instead of having the merfolk figure out how to create ceramics/metallurgy/architecture, perhaps make them be more in the bio-hacker route. They breed certain types of fish/sharks/whales for sharper teeth and stronger bones, breed coral for diverse types of fish in reefs to eat as well as for shelter, and have algae farms. I like the idea of using volcanic glass as a basic version of a knife, and there main weapon for hunting is a net - presumably made from algae and other underwater plants, similar to how mankind's early nets were also based off grasses and fibers, or something like shark- or whaleskin. Armor would likely start off crustation-based, and also need to be grown like ironwood. Ranged combat really isn't a thing in an underwater environment, both due to drag and that everyone moves in 3 dimensions by default, so the only martial application of weaponry would be throwing bone-spears at those above the water line.

They grow their habitats, their most basic magic would likely be water manipulation and creature-based, using things like octopi as a reference of something that is likely to be emulated first (self healing, camouflage, ink as a distraction, et cetera).

Basically, make them more like elves, just under the sea, instead of in the forest. This makes significantly more sense than basing them off humans, which would make these questions like "how to they make metal weapons" and "what do their chariots look like" come to be. They're almost more like the Zerg, in a sense, where they modify and grow their creations instead of taking inert things and putting them together.

[Andrian]

I'm unsure of whether merfolk would be capable of any significant amount of biological engineering without the aid of magic, which was the original assumption that I was working with. Obviously, if magic is involved, just about anything is possible, depending on the magic available to them. If, for example, they had magic to preserve materials, that would open up a lot of options for them. If they could use magic to create pockets of air underwater, that would also help them immensely. However, as we don't have a benchmark for determining what magic merfolk should have access to, we simply can't know how magic would affect them. We'd basically have to just decide it by fiat, which is fine, but there would be no reason for anyone else to make the same assumptions regarding magic. A zero-magic baseline, however, is helpful for determining where magic might be needed, and how things would be in the absence of a magical solution to any given problem.

[Zorku]

Thanks for that information, Zorku! That's actually quite helpful to know! If merfolk were able to get their hands on metal tools that wouldn't corrode, more advanced stone work and mining would be opened up to them.

Just to be clear, it's not that these things wouldn't corrode, just that they would do it much slower while in use, and that they could easily enough be stored in a way that they would suffer very little corrosion.

As for writing... this is kind of a stretch, but if you were to skin an octopus or any of their relatives, you might be able to write on that hide. The whole color change thing that they do has these muscular structures loaded with pigment contract into a little point (no ink) or fan out wide (ink in a variety of colors.) I don't think you can just make this happen with mere pressure, but using something like jellyfish tentacles to sting it could potentially tweak which colors showed up or hid themselves. This is all organic, so you'd have to do your writing pretty quick before rigor mortis and such settled in, but if you skip over the early days and have them farming octopi with broad flat tentacles then they could just pluck a tentacle off every so often and then tent to the flock until the arm regenerated, and produce a lot of this leather-paper in that way.

I know next to nothing about tanning hide, but if you could expect to lock the skin pigment orientation during that process then you've potentially got this multi-layer parchment. If their eyes work in certain ways then that means tons of information on a page, but more likely this means you need to know how deep into the water and the time of day that you should try and read certain messages, which is kind of bad ass for a language.

One thing I forgot to mention is that merfolk would need to evolve in a way that allows for big, human-like brains.

The professor that strung the following story together was a bit of a crank, but it's neat for thinking about human evolution.

Most land mammals have this nasty limitation. Having your muscle concentrated up near your core is really good for efficiency (think Kenyan runners.) Having the muscle concentrated further out is more useful for grappling, where you need to rapidly overpower an opponent. With this in mind, male competition tends to doom species, such that they have fairly low stamina, and this restricts how far they can range. There's a strong exception to this rule any time the males fight in some way other than swinging their arms and legs around. Basically every species with a big rack... of horn sticking off the top of their head. These species all get to have efficient locomotion, without it getting in the way of males showing off. Humans don't have horns, but we do have these useful hands. Chimps have these long fingers that prevent them from making a fist, but humans have just the right proportions to do that. Chimps have to open hand slap each other, and you can only do that so hard without breaking your fingers, but you can punch somebody as hard as you want with very little risk of broken fingers. (In reality no human instinctively makes a proper fist, but hey, I warned you about this kind of thing going into this story.) Normally grappling also favors someone with a very low center of gravity, but once we break the old rules humans are free to develop long, efficient legs.

As we start walking upright, a lot of the time we don't even have to directly fight a lot of our prey, we can just chase it until it collapses and practically has heat stroke. We start to win via endurance. This works pretty well, but figuring out that we can use our hands for tool drives significantly larger brains over time, and as we start to actually figure out basic weapons, we kind of become kings of the world. Sure some tiger might still kill us in a dumb situation, but we've learned so much about the animals around us that they aren't really the same kind of threat that they once were, and we learn like this about every threat until nature can't normally throw anything at us that we can't handle.

Nature does throw a really mean curve ball though. Turns out there is actually something extremely dangerous in our environment: Us. Chimps go to war with each other and eventually wipe out opposing clans via lots of underhanded sneak attacks. That just gets so much worse when they're armed with axes and spears and they can sneak up in the middle of the night. Well, at this point we add sexual selection to the list of factors that keeps making our brains bigger. The women want their babies to survive, and the only chance you have against other humans is to be smarter than them. The women want smart men, our lineage of primates is pretty low on the sexual dimorphism, and even lower since we diverged from chimps, so the women get big brains at the same time, and that pretty much brings us to today.

-

Although that one's kind of kooky in places, there's another noteworthy story in this that should impact our Mermaids quite a bit. In most species the newborns can kind of walk around and tag along with mom pretty quick after birth, but because humans are bipedal we've got a physical constraint on hip width, and those damn big brains would crack a pelvis. Instead of that, we front poop out the kid when their brain is way premature. Related: in most species menopause and death of old age happen at the same time. Humans seem to be an exception to this, because our damn babies can't just hang on to mom's back on their own, but instead blubber about and demand that she uses her own damn arms to carry them. This puts a real wrench into any other work that mom wanted to do for most of the day. Dad sticks around a lot closer to provide for these energetically expensive helpless roly poly little vessels for carrying genes into the next generation, but it's still pretty damn hard to feed several mouths while also carrying so much dead weight for years, and they don't become that much easier to tend to once they can walk around on their own. Thanks to all of this, there's something really useful that grandma and grandpa can do to propel their genes into future generations. They don't eat so much anymore anyway, so they can hold onto a couple of kids while mom and dad go scrounge up enough ripe fruit to keep themselves and their kids from starving to death.

Due to buoyancy and it being really weird to picture a fish thing that can't just float there by itself, I don't think the mermaids would need the grandparents to tend their kids like this.

-

One more interesting narrative for big brains. We tend to think of genes are good or bad, but sometimes you have to think about who they are good for. Dad doesn't have to grow this in his own abdomen, so it benefits him to pass along a few genes that make the baby as big as possible. Mom probably wants to get at least a few uses out of her womb, so it benefits her to pass along a few genes that will slow down the growth to something more manageable. If you look up epigenetic disorders, you can kind of see this history of dad's genes making the kids too big and mom's genes reigning them back in. Now a weirder relationship: regardless of gender, the kid benefits from being born bigger, while mom has to also fight them to try and keep her womb from being wrecked after each kid.

Menstruation is pretty uncommon in the animal kingdom. Most species just slough off the lining and then reabsorb it. Why don't humans reabsorb it though? Well, that part of the equation still works just fine, but the trouble is that the lining is freaking huge.

So, egg and sperm meet up, implant on the uterine wall, grow a nice placenta for blood content exchange, then do the pregnancy thing. There are a couple of ways that placenta can work, but for most animals the blood vessels in it just get close to mom's blood vessels and stuff diffuses back and forth. Not so with humans. Baby just hooks those blood vessels right up to mom's circulatory system. With the diffusion deal mom's hormones can control her blood sugar and limit blood flow to what best suits her. The way humans do it... well, that placenta can just dump insulin into the blood if it wants more sugar, and after a certain size it can just take as much as it wants when it wants (for further reading, look up gestational diabetes.) All of this is relatively traumatic for mom's body in general, but it's especially rough on the womb. Usually an animal could throttle all of this and build up a thicker lining once the embryo had implanted, but for humans your organs are wrecked if you wait that long, so instead we grow it ahead of time just to try and brace for the shock of this little parasite growing out of control in whatever runaway cascade of adaptation created this mess.

-

It might be that all of these stories are not the way that humans evolved, and identify the wrong factors that lead us here, but for a fictional species any number of these can apply simply because the conditions were different and we're making up their history.

[Mechalich]

As for writing... this is kind of a stretch, but if you were to skin an octopus or any of their relatives, you might be able to write on that hide. The whole color change thing that they do has these muscular structures loaded with pigment contract into a little point (no ink) or fan out wide (ink in a variety of colors.) I don't think you can just make this happen with mere pressure, but using something like jellyfish tentacles to sting it could potentially tweak which colors showed up or hid themselves. This is all organic, so you'd have to do your writing pretty quick before rigor mortis and such settled in, but if you skip over the early days and have them farming octopi with broad flat tentacles then they could just pluck a tentacle off every so often and then tent to the flock until the arm regenerated, and produce a lot of this leather-paper in that way.

For undersea writing, I think you'd want to avoid using pigments and ink at all and write by using cutouts or carving. Symbols can be cut into bone, marked or chiseled into stone, inscribed on shell, or potentially cut into dried skins of seals, sharks, or rays. Turtle shell would also work, as in oracle bone inscription.

If pencil-grade graphite is available - natural deposits are quite rare and the technology necessary to reconstitute powdered graphite fairly advanced - then you can write underwater just fine using pencil.

[Trekkin]

For undersea writing, I think you'd want to avoid using pigments and ink at all and write by using cutouts or carving. Symbols can be cut into bone, marked or chiseled into stone, inscribed on shell, or potentially cut into dried skins of seals, sharks, or rays. Turtle shell would also work, as in oracle bone inscription.

If pencil-grade graphite is available - natural deposits are quite rare and the technology necessary to reconstitute powdered graphite fairly advanced - then you can write underwater just fine using pencil.

There's some utility to having the ability to erase, too. If the merfolk could manage a flat plate of shell with a layer of spermaceti over it, they could essentially have a reusable notebook, which makes it easier to develop a system of writing.

[Mechalich]

There's some utility to having the ability to erase, too. If the merfolk could manage a flat plate of shell with a layer of spermaceti over it, they could essentially have a reusable notebook, which makes it easier to develop a system of writing.

For temporary purposes, you can always write in sand or mud. You might even be able to make a sort of 'mud slate' using a large shall as a frame.

[Andrian]

I've wondered about graphite or chalk (chalk probably being more accessible to merfolk) as a writing tool. My concern is smudging. Not a total dealbreaker, but definitely something to keep in mind.

[Trekkin]

For temporary purposes, you can always write in sand or mud. You might even be able to make a sort of 'mud slate' using a large shall as a frame.

Only horizontally, only if you're going to keep them still. and only if you don't need much precision; water messes with sand's angle of repose, and of course mud is just smaller sand. You could use them for tally marks, but I think a path to actual writing as we understand it, with proper lexemes and a syntax and so forth, would need a way to write things down rapidly, persistently and movably with minimal effort, much like our own clay tablets. Ideograms are suitable for carving into turtle shells, yes, but if all you want to do is keep accounts and records (and thus develop a system of writing down numbers and arithmetic and a sense of the passage of time for verb tenses and so on) carving receipts into stone is overkill; the record would cost more than some of the transactions, and certainly take longer.

Clay is an option, but pelagic clay has the same problems as hydrothermal vents with whales not having hands and so forth. Absent clay, wax can serve.

Chalk could also work, given something of suitable texture to serve as a dive slate.

[Zorku]

For undersea writing, I think you'd want to avoid using pigments and ink at all and write by using cutouts or carving. Symbols can be cut into bone, marked or chiseled into stone, inscribed on shell, or potentially cut into dried skins of seals, sharks, or rays. Turtle shell would also work, as in oracle bone inscription.

If pencil-grade graphite is available - natural deposits are quite rare and the technology necessary to reconstitute powdered graphite fairly advanced - then you can write underwater just fine using pencil.

Shoot, maybe I should have described this better. Cephalopod skin comes preloaded with pigments, so you don't actually have to draw on them so much as coax the cells into taking on the configuration you want and then lock that in place.

[Mechalich]

Shoot, maybe I should have described this better. Cephalopod skin comes preloaded with pigments, so you don't actually have to draw on them so much as coax the cells into taking on the configuration you want and then lock that in place.

Right, but good luck actually doing that. That's a high-tech and/or high-magic solution to a low tech problem. I mean, you can write under water easily using a magna doodle too, but that's not really a viable solution for a pre-industrial merfolk society.

[Grim Portent]

Merfolk would make most sense as a race of very low tech hunter gatherers living in coastal shallows in the tropics. No metal gear because they can't smelt it without tech that needs already processed metal to work, no leather since it doesn't cope well with salt water and can't be cured properly down there anyway, little if any farming because the ocean isn't kind to that sort of thing outside very specific places where the water is usually calm.

I would see them as living somewhere like the Great Barrier Reef in Australia. Lots of vibrant fish and plant populations, a few still lagoons inhabited by large herbivores, warm, fertile water. Tropical rivers like the Amazon or the Ganges would also work, or areas like the Gulf of Mexico. Those kind of climates and biospheres seem appropriate.

I'd expect stone/bone tools, woven plant fibres to make pouches and the like, probably no shelters of any kind beyond burrows and natural caves. No writing beyond carving on rocks and shells. Maybe domesticated grazing animals like dugongs used as livestock and pack animals, though the water makes them impractical for a few reasons.

I wouldn't expect much by way of population density, a few dozen for every few square miles maybe unless the area can provide for a lot of decent sized omnivores. In a river I'd expect a lot of seasonal foods like fallen fruit to be used to supplement their diet, and would probably coincide with a breeding season, a tropical ocean would probably be more static year round unless migratory whales enter their territory or there's a seasonal bloom in life.

Obviously any meat would be eaten fresh and raw, because trying to keep it fresh and uneaten in the sea is a losing game.

[Zorku]

Right, but good luck actually doing that. That's a high-tech and/or high-magic solution to a low tech problem. I mean, you can write under water easily using a magna doodle too, but that's not really a viable solution for a pre-industrial merfolk society.

Except that it's low tech. You need to raise your octo-cattle, skin them, then perturb the skin in a certain way to get it to change to the color you want. The only bit that might not be plausible is locking that into place.

If you wanted to go magic with it they'd make the leather strips, bind them, and then be able to write or erase them indefinitely, and when they got fancy you'd have to speak a password or something to get the page to switch over to some previously recorded writing.

[Grim Portent]

Except that it's low tech. You need to raise your octo-cattle, skin them, then perturb the skin in a certain way to get it to change to the color you want. The only bit that might not be plausible is locking that into place.

If you wanted to go magic with it they'd make the leather strips, bind them, and then be able to write or erase them indefinitely, and when they got fancy you'd have to speak a password or something to get the page to switch over to some previously recorded writing.

It would be borderline impossible to preserve octopus skin underwater. It's very soft, rots quite quickly and would be nibbled to nothing by small fish and invertebrates. Not to mention if you tan it the chromatophores would stop working. Leather in general is a no go underwater.

Chromatophores work with tiny muscles that expand and contract their pigment pockets. These start firing randomly after the creature dies for a while.

The only way to force a chromatophore to work would be electrocution to the muscles that control the cells, which doesn't work underwater and wouldn't work on preserved tissue.

Cuttlefish or squid mantle is closer in texture to what would be needed, but would still degrade very fast and would need electrocution to change colour.

It would be far easier to just carve messages on large seashells or flat rocks.

[Andrian]

Large bivalve shells are actually a pretty good idea as a paper substitute. Obviously you can't get much information density with shells, but you could record longer messages and string them together like a necklace if you could drill a hole in one corner. They'd probably carve pretty easily if you could find an appropriate type of stone that would be hard enough to scrape away calcium carbonate and that could also be knapped to a fine point. It's definitely not as convenient as pen and ink, though.

One thing that might work really well as a needle and a carving tool would be the radula of certain predatory mollusks, like the cone snail, which basically has a hypodermic needle that it uses like a venomous harpoon. I know the moon snail bores very nice neat holes in mollusk . Though it doesn't have radula that would be suitable as a tool, the snail itself might be a tool for drilling holes in shells - just plop it on the shell you want to drill, and it'll think it's found lunch!

I do like the idea of a merfolk scholar that wears a lot of shell necklaces. Double points if that scholar is a wizard and the necklaces are his spell book.

[Mechalich]

I wouldn't expect much by way of population density, a few dozen for every few square miles maybe unless the area can provide for a lot of decent sized omnivores. In a river I'd expect a lot of seasonal foods like fallen fruit to be used to supplement their diet, and would probably coincide with a breeding season, a tropical ocean would probably be more static year round unless migratory whales enter their territory or there's a seasonal bloom in life.

I think you can actually get a fairly high population density with merfolk, it would just be very spotty and might be seasonal. Many aquatic ecosystems - especially relatively pristine ones that haven't been hacked to h*** and back by human activity (a major rarity these days, to the point that our very idea of the baseline is nebulous) are predator-mediated with a really high proportion of the vertebrate biomass being represented by fairly large-bodied predators such as sharks or pinnipeds. If a merfolk colony basically clears out all the sharks or seals and replaces them, you could have some pretty big colonies in highly fertile locations around islands or seamounts. Sea lions - which represent a reasonably close comparison in terms of probable nutrient requirements, congregate in large numbers at breeding colonies and haul-out locations. Merfolk could do something similar if they build underwater structures for protection - even simple stone and net enclosures would be useful for that purpose. So you'd have a sort of 'home-base' setup where though the population has a vast hunting range, the bulk of the people would live and sleep in a concentrated protected zone.