The traditional description of the mermaid is half-girl and half-fish. That, both biologically and dramatically, is just ridiculous. If the mermaid were half-fish, then why does she move her tail up and down and not side-to-side as fish should? No, my first proposal is to make the mer (the whole race, not just the females), half human and half dolphin (or porpoise).

Now the first issue to address is hair. In classic literature, the girl half of the mermaid has long, flowing hair. Not only is this too clear-cut, which is biologically impossible, but it would create way too much drag. So my proposal is this--either make the mer short-haired (think "pixie cuts") or all-out bald. Either choice would reduce drag substantially.

As for the face itself, my original proposal is to reduce the nose into flat nostril slits, since smell is of no use to an air-breathing mammal that spends its entire life underwater. But my proposal to keep the human face is way more interesting, and here's how--How to Breathe Both on Land and Under the SEA

Of course, the proposal for tetrachromacy (having four color receptors) is valid here, too. Also, if one wants to tackle the Amazonian legend of the Boto, we'd might as well give the mers the tapetum lucidum, a layer of tissue behind the retina that reflects light, increasing the availability to photoreceptors, though at the risk of losing detail. (However, tetrachromacy might be a way around this problem.)

How would a mer vocalize to attract a mate--be it mer or human? Would it echolocate using the melon, as cetaceans do? Or maybe something less front-heavy--an enlarged vocal sac, just like frogs or gibbons?

The final issue to address is coloring. Unlike the centaur, the mer's transition between two species is smooth and natural, but they are still colored separately. My proposal is to give both halves one color scheme, based on the following cetaceans:

  • Orca
  • Atlantic Spotted Dolphin
  • Pacific White-Side Dolphin
  • Bottlenose Dolphin
  • False Killer Whale

Are any of my proposals listed above sound, or have I created some unintentional side effects to the mer body?

  • $\begingroup$ Comments are not for extended discussion; the conversation about hair, drag, evolution, and the "anatomically correct" series has been moved to chat. Please use comments to improve the question (such as by seeking clarification). $\endgroup$ Sep 25, 2016 at 19:49

2 Answers 2


And your question is...

I'm not quite sure what the exact thrust of your intended question is. It seems to be about how to go about making the concept of a merfolk more realistic? And also if your existing suggestions are realistic?

Assuming that is the case:

Point one: Tail movement

It will be noticed that, most, if not all ocean mammals move their tails up and down, not side to side, while non-mammalian fishes again most, if not all, move their tails side to side. As such, it only makes biological sense for a mer to move their tail up and down, as they are (being half "human") presumably mammalian.

It is indeed odd that mer tend to be called out specifically as "half-fish". Perhaps this notation stems from taxonomically ignorant origins, people who in their time and era called anything and everything that swam in the ocean a "fish" and were not aware of the differences between mammalian and non-mammalian ocean creatures. (Not to mention that mythology does not always make sense, even if there was awareness of the differences back then.) As such, there should be no issues with, and indeed should likely be more genetically possible to have mer be half-human and half-mammalian ocean creature instead.

Point two: Hair

Hair is ascetically pleasing to a human, but seems rather unnecessary in an amphibian or purely water-breathing species. As pointed out, it would produce drag, and seemingly serves no other purpose than the ascetic.

Here, the origin would become critical. If the mer are augmented or altered creatures using humans as a base, and if the initial tweaking did not remove the hair, then the mer would still have hair from their human heritage, useless as it may be.

It would seem quite the disadvantage to have hair underwater, unless it was replaced with some sort of sensory boosting appendages that superficially resemble hair and are less drag-producing that traditional hair. Of course, if they are amphibious, and not purely water breathers, then perhaps the hair would be left in place for their above-water times. The above-suggested short-length hair would seems a more viable option in such cases. Another option is to replace the hair with an analogue, fins or some other mechanism for display or ascetics.

Given the mythical stories and origins of the mer: namely, that they were a species that hunted men specifically, luring them to death and/or doom, it actually makes sense for them to have hair for those purposes, noting again that hair is considered attractive to humans.

For a realistic and viable race of mer, with both male and female, and assuming that they don't need to hunt human males for some reason (such as an all female race or something) then it would make more sense for them to not have hair - barring the above mentioned [possibility of sensory appendages. Another slightly more far fetched justification for hair would be harvesting and using hair as a tool - weaving it into water resistant fabrics and ropes. Given that forging is going to be problematic underwater, tool development and usage will be somewhat more challenging.

Point Three: Nose

This will again depend upon amphibious versus pure water-breathing. In either case (and I was going to suggest chest-gills myself, but I see that it was covered in the question referenced) the nose would likely be streamlined and on the small end of the spectrum for the amphibious mer, if not flattened or removed entirely for a pure water-breathing mer.

Given the comments about oxygenation, it would seem the amphibious version would have more potential realism.

Point Four: Senses - Visual and Auditory

Visual adaptations for low light would seem critical given that so much of the ocean is little to no light whatsoever. Also, a nictitating membrane would seem critical for eye protection (given the amount of debris floating around).

However, more of the ocean is dark than lit. Fortunately, human echolocation is a real thing, with the more extremely talented examples being able to walk or bike around town, skateboard, even playing video games(!) solely using echolocation. (Ben Underwood and Daniel Kish are a couple of the more famous examples.) For an ocean-going (amphibious or not) creature, it would seem that honing and developing this ability would become critical for navigation and creature recognition, and perhaps some more robust vocal cords might be in order.

I imagine that singing, above or below water, could become the mate attraction of choice. Recall also the possible hair analogue suggested previously for display purposes.

Point Five: Coloration and Skin

Depending on the target dwelling and intended travel regions and areas, the skin becomes quite important. A shallows dwelling creature will have different composition to the skin than a more widely-ranging ocean-going type, notably, the fatty tissues directly underneath the skin.

An ocean-going type mer would need to be able to withstand the cold and potentially the crushing depths of the oceans, needing a much thicker layer of blubber, and some other internal structural differences for long / deep cruising. Especially the deep dives.

Having a coloration and body shape that can blend in with or mimic other creatures would be a potential advantage in cohabiting and/or cooperating with native ocean creatures, as well as times when hiding amongst the crowd has benefit. On the other hand, it could also get them mistaken for valid prey by certain creatures.

A chromatophoric integument would have certain advantages as well. Not only could mer pull off the above mentioned tactics, they could also hide against objects and the sea bottom. In areas with light, it could also serve as a non-auditory form of communication. Combine with the optional ability to fluoresce, and you have signalling capabilities even in the depths. (And a possible method to lure prey (or mates) to themselves!)

Finally, in a natural or survivability-designed mer race, streamlined skin would be the ideal and most advantageous, as such while the chest cavity would likely be rather large (see oxygenation comment above), female mer would tend towards (ahem) smaller mammalian organs. Anything else would produce considerable drag during water maneuvers. I will decline to comment on mer designed for purposes other than survival.

In Conclusion...

Most of the comments and suggestions made in the original question seem to on the whole support the survival and prosperity of an amphibious race of mer. I hope my additions are helpful.

  • $\begingroup$ "the nose would likely be streamlined and on the small end of the spectrum". Which means? $\endgroup$ Sep 25, 2016 at 16:12
  • $\begingroup$ If the nose still exists as a structure (likely only in an amphibious mer) it would likely be designed to reduce drag. Perhaps a combination of the "button nose" / snub nose, and the straight blade of a nose, or perhaps only the "button nose". Come to think of it, that might be a good location for an electro-sensory apparatus to be housed (much like the platypus, another mammal), and/or an extra sonar-sensitive location on the skin. Out of curiosity, would the mere give live birth or be a monotreme mammal? $\endgroup$
    – nijineko
    Sep 25, 2016 at 16:20
  • $\begingroup$ Oh, no, calving is still a thing. $\endgroup$ Sep 25, 2016 at 16:22
  • $\begingroup$ Out of MY curiosity, do you mean "chromatophoric", like an octopus or cuttlefish? $\endgroup$ Sep 25, 2016 at 16:22
  • 1
    $\begingroup$ For many reasons the hair should be tentacles. $\endgroup$
    – RedSonja
    Jan 17, 2017 at 12:22


  • pixie cuts for females if you like these, buzz cut for women if you liked Segourney Weaver in Aliens or Demi Moore in G.I. Jane
  • for men it could short or buzzed or bald or even long if they don't want a dagum hair cut and don't care about the drag, suppose the same could be true for females as well
  • dolphins are actually born with whiskers, I didn't know that before I just looked it up, apparently all mammals have hair


Not to step too far forward, but if I were to have a romance with a mermaid, language would certainly help. However, if she could see in the dark, could notice my vulnerability and helplessness in a very low light setting, that would make me depend on her more in those situations and, particularly, it would reveal a part of me to her. This could serve to strengthen the relationship and it could also serve to create tension upon first meeting her. And I wouldn't mind the glowing eyes. That would actually lend a more wild aspect to her, making her seem more exotic to me than she already is.

Not sure if it matters whether she can see colors, but as you say, if it helps her to see higher resolution, and therefor greater distance out of water, then it is perhaps for the better from a purely evolutionary standpoint, i.e. spoting trouble from a distance, remaining undetected etc. However, and I'm getting gushy here, but I want my mermaid to be bad-ass, top-notch and well equipt in all aspects of survival and ready to fight and not just run away at the first sign of danger. Seeing well is also a predatory advantage, spotting seals on the rocks for example before they can see what is approaching.


Well, as I mentioned above, language helps with human interaction and a human like voice is obviously preferable to that end, but it isn't strictly necessary - nor are vocal chords. For example in Jean Auel's Clan of the Cave Bear, the Neadertals are described as having vocal chords, but they are less well formed for speaking and the faces have less expressive features and as a result the communications with voice and lips are mostly grunts, whoops and simple sounds, but the language of the Neandertal in the book is a very rich and nuanced sign language which involves the whole body, not jus the hands. This sign language comes in a colloquial dialect as well as a formal/inter-regional dialect. If you go without smooth tones for the voice then perhaps a rolling burble or intricate sort of purring like muscular contraction like the sound that frogs make but less projected for close or quiet conversations, otherwise belting, screeching groans when a high volume is required - for example like the mating sound of the Southern toad or this cicada call, but overall perhaps with a more variable/deeper tone. I don't know that squawking, clicking and chirping is as personable as something more like burbling would be, something in between the lion rumbling and the aligator growling - but I suppose that as well is a matter of taste.


Anything from gray to white to cream-colored to brown or black I would think is fine. I'm assuming you're not after the blues and greens of peacock feathers. They could be different colors like animals and people - what a concept! I personally wouldn't make them too distinctly marked other than overall tone because I want to get to know them personally to understand their individual differences, but there is nothing preventing any choice you make in that regard. Natrually speaking they would probably be predators/hunters so they would need camouflage to hide and ambush or they would need eyesight and speed to rush. But they could in theory also graze on kelp forests. Maybe they have no natrual predators and are smart enough to capture or kill any kind of prey they wish so would have less need for camouflage. If they are smart they could make their own camouflage if need be.

  • $\begingroup$ Why just "her"? $\endgroup$ Sep 25, 2016 at 13:33
  • $\begingroup$ Have you not noticed that I mentioned BOTH sexes? $\endgroup$ Sep 25, 2016 at 14:15
  • $\begingroup$ @JohnWDailey I did notice that you mention both sexes. I can expand on the answer more when I get home from work. $\endgroup$
    – Nolo
    Sep 25, 2016 at 17:49

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .