Fishful Thinking: Five Reasons why Mermaids Can’t Physically Exist

This guest post is brought to you by Sheanna Steingass.  Shea is a graduate student at Oregon State University’s Marine Mammal Institute studying the behavioral ecology of pinnipeds. She is also author of,  a marine debris blog focusing on the Pacific Northwest.

“Mermaids are real- I saw it on Animal Planet!”

No, you didn’t.  That ‘documentary’ was in fact a new generation of fictional media called a ‘mockumentary’, or as Animal Planet puts it, ‘docudrama.’  It’s like “This is Spinal Tap” for marine biology.  And they admit that.  However, people took the show so seriously that in order to deal with massive amounts of inquiries, NOAA had to issue an official statement that, to their knowledge, mermaids aren’t real.

Mermaids were probably a lot more rooted in lonely sailors’ imaginations than the physical world. [WikiCommons]
A critical look at the Animal Planet ‘docudrama’ reveals abominable (excuse the pun) CGI, combined with scripted interviews with actors. And who can blame them? People love mermaids, they delivered, and they made a ton of money. In fact, it worked so well that they produced another fictional (FICTIONAL!) docudrama, “Megalodon” for Shark Week.

Most scientists wouldn’t touch the subject of mermaids with a ten foot pole- I am going full contact.

Why couldn’t mermaids exist? Here are 5 reasons.

It takes waters much above 70 degrees to maintain an individual (especially a lean one) for a prolonged period of time in the water without dying. (Cold Water Boot Camp/ US Coast Guard)

1: They would freeze to death.  Quickly, and matter what ocean. Especially those skinny Ariel/Disney types. The truth is, the human-like body form is not made for surviving long periods in the water.  Check this out:

Sure, there are areas of the ocean that are above 70 degrees- on the SURFACE. Assuming mermaids would want to live out in the bottom of the open ocean, it is just too cold for them.  And, once you get down a few meters, water temperature drops dramatically. 

[Thermocline graphic] Oceanic water temperature drops quickly below the surface- no matter what climate. {}
Oceanic water temperature drops quickly below the surface- no matter what climate. {}
So what would a cold-hardy mermaid look like?  1: really hairy, or 2: really fat. Or: 3: both.

The first option would to look like a marine mammals, whose thick blubber layers protect them from cold, dark waters.   What of smaller animals? The second option for thermoregulation is a thick coat of hair- such as that of Enhydra lutra¸ or the sea otter.  The sea otter has more than 900,000 hairs per square inch (Kuhn et al. 2010). The problem? Otters have to groom themselves often to keep their hair filled with air, and not with water (Fish et al. 2002).  Very inconvenient if you are an elusive denizen of the deep.

And those long slender arms? They would freeze off.   Marine mammals have fusiform bodies (reducing surface area-to- volume ratio) and short appendages that can withstand reduced bloodflow and heat.

So, essentially, you would end up with a very hairy or obese mermaid with stubby arms.

2: You can’t pick and choose…body parts Picture your typical mermaid- a graceful female with the scaled tail of a fish. Mammals are defined by being warm-blooded and having hair; fish do not.  An animal cannot have both human and fish-defining characteristics- it’s just all wrong, evolutionarily speaking.  The human line of evolution is fairly well-mapped.  Prior to the development of hominids, humans and fish are so far branching down the evolutionary tree that the first marsupial mammals appeared during the Jurassic period 173 million years ago (Kumar and Hedges 1998).

Additionally, the idea that somehow a human bred with a fish and produced viable, virile offspring is just ridiculous.   Which brings us to the next point… 

[Megazostrodon photo] No mermaids here! Photo: London Natural History Museum, WikiCommons
[Megazostrodon photo] No mermaids here! Photo: London Natural History Museum, WikiCommons
3: They would go extinct.  How do mermaids reproduce?  They are human down to the waist, after all.   Well, there are two options for that.  First, they could do it human-style.  Which means that they’d have to get it on the mammalian way- with internal fertilization.  But what if you have fish parts down there?  Most fish reproduce externally- with females depositing eggs in the environment and males fertilizing them.

Could mermaids lay eggs? Think again!  The only mammals that produce eggs are the echidna and platypus- the monotremes of the class Mammalia.  And these guys don’t have any teeth, look nothing like a human, and really would make a poor excuse for a mermaid.

Oh, and don’t even get me started on sex ratio.  As far as I can tell, there are waaaay more mermaids than mermen.

4: They would be constipated. While we’re talking about plumbing, the fish and mammal digestive processes are so very different, they cannot jive.  Mammals digest food via complex digestive tracts, which produce solid waste and urine- a sterile byproduct composed mostly of water and waste, salts, and proteins.  Fish kidneys produce ammonia- which is expelled via their gills.  Yep, they essentially pee through their gills. (

As for digesting food, where humans have well-developed large and small intestines, fish have one simple intestine.

So really, you can’t have an animal with a mammalian digestive tract and a fish-designed hind end.  Even more tellingly- can you point out the butt on a mermaid? Didn’t think so.

5: We have no physical evidence.  Really.  If the existence of such a creature were true, it would literally change the face of science- and why would it be covered up if it were a real animal?  That makes for a good plotline, but doesn’t make any logical sense- what global conspiracy would cover these things up? If mermaids existed, the scientific world would be studying them endlessly, and grant money would fall like rain during monsoon season. The world would know.

So there you have it- mermaids would be very cold, sterile, constipated, and probably extinct, which seems pretty miserable to me. So the next time you see something you think looks too good to be real, think again – because it probably is.


Literature Cited

Kumar, S., and S. B. Hedges. 1998. A molecular timescale for vertebrate evolution. Nature 392:917-920.

Fish, F. E., Smelstoys, J., Baudinette, R. V., & Reynolds, P. S. (2002). Fur doesn’t fly, it floats: buoyancy of pelage in semi-aquatic mammals. Aquatic Mammals, 28(2), 103-112.


57 Replies to “Fishful Thinking: Five Reasons why Mermaids Can’t Physically Exist”

  1. You consider only “fish” parts, but what about cetacea parts ? We’re sure they are mammals as they have breast and hairs. Let’s just forget about the scales ! (even if they still could be a mammal apomorphy, just like pangolins).
    This would answer to your points n°2-3-4.
    And creatures such as Hydrodamalis gigas could prove point n°5 wrong too : we are still far from having discovered all big marine animals, all the more if they are elusive and living in tiny, isolated populations in remote areas.

    But another problem could be hydrodynamism : even with a dolphin tail, what underwater speed could a long-haired human reach ? Probably not enough to catch fish, or to escape from a marine predator… And no way to protect the babies from predators too, which could jeopardize the population (even with such a sex-ratio !).

    Anyway, this is a funny and beautiful post, thanks a lot and congrats !

  2. Haters!! ;)

    I will turn 48, next week, yet I still hold fast to my beliefs in fairies, UFOs, ghosts, Nessie, and Atlantis. There is room for a fanciful dream of mermaids in there as well. With a few mermaid movies slated for release in 2014, you folks may want to bookmark this page – you’re going to need it. Fins are the new fangs.

    Aeolius, a.k.a. Merman Dan

  3. Shea, your friends from Wyoming are cheering. Love the smarts, love the fun, and love the correct hyphenation of complex adjectives.

  4. So, not that I believe in mermaids, but just to play devil’s advocate, what if they were dolphins from the waist down (or manatees for that matter).

    Reasons 1, 2, and 5 would be unchanged I think, but reproduction and waste elimination could be addressed that way right? Since dolphins are technically mammals even if they are a fairly distant offshoot from people.

    If I believed that mermaids were real, then it would be a small leap to assume that previous sightings were mistaken in assuming they had fish-like tails instead of more mammalian ones.


  5. Great Read! I love the “sarcastic” truth about the scientific breakdowns. great job.

    BTW the “Show” about mermaids on animal planet or what not was a total fake for entertainment.

  6. Well as a mermaid I feel offended, I exist and I’m a mammal. Most merfolk are mammilian some are fish like true but there are many offerent species as there are humans. We give birth to live merbabies we are warm blooded have hair breath air but have a gill like feature on our bodies that allows us to extract oxygen from water if need be (like bettas)

  7. Great article. I am a professional mermaid performer, and while I love fantasy and imagination, I’m also a teacher too. It really bothered me just how far Animal Planet went to try and pull one over on everyone. I don’t think it’s fair to do something untruthful like that in the context of education. :/ I wasn’t impressed. I love my fans, but when they send me links about it I always want to pull my hair out. Yes I saw it. No, it’s not real.

  8. As a writer on the odd corners of zoology, I thought this was a lot of fun as well as (hopefully) educational. I fear, though, that the people who believed the TV show are not likely to read Deep Sea News. It is interesting to speculate that some line of primates, perhaps the monkeys, could theoretically evolve a coastal aquatic species. I suspect it would, over time, develop to look less like a monkey and more like a seal. Alas, long flowing hair seems unlikely.

  9. 1. Fat hairy Mermaids? Hellz yeah! Though… a blonde/fair coat would create a situation where the girl would be human looking…. somewhat. Darker coats would create for other skin colour appearances. Mostly would be about having it at a length to deal with.

    Also: Volcano vents.

    But Fat Hairy Mermaids… seriously… I like this. This needs to be a thing.

    2. In order to handle this one… you must also handle the Legendary Fur Bearing Trout. It could, thanks to this comment, be suggested that the Fur Bearing Trout holds a similar ancestor as the Mermaids.

    As per how it would come about… you are aware of how the Samurai Crab was created via unnatural selections, right? Let me suggest an experiment involving Sea Cows… several decades worth of breeding in an effort to make a Sea Cow breed that looks aesthetically very close to human.

    I mean, if we do not simply use the Fur Bearing Trout’s divine wisdom on the matter, as reason to have Mermaids.

    3/4 Nobody has actually gone over what their genitals and digestive systems work like. There are very few classic images of these creatures being cut open. There are ones that currently exist, with their guts and internals being very fish like in nature.

    The Monster Girl fandom usually has their reproduction done in the fish style. As the Monster Girl fandom is fucked like that. The Monster Girl fandom also has cloacas show up on their girls, and various other styles of genitals.

    They cannot agree either. For example, Lamia (that is snake lower half, female top half, and often having frilled shark and/or dragon-like traits) has shown up giving live births, egg laying and aplacental viviparity.

    The Monster Girl fandom does the mismatch of parts in some areas… while other parts have them looking biologically accurate–as biological accuracy is freaky enough to get people off, or scare them… or it is the Monster Girl fandom, half the fun is messing with people.

    What is more, there has been suggestions that male mermaids look just like female ones… and that it is hateful to say they all look alike. Seriously… what kind of hateful discriminatory person did you mother raise, to not be able to tell them apart. This notion was taken further in the game series Tales of Monkey Island, where the mermaids are all a single gender–and sex involves at least five of them, and a cocktail party involved.

    Which… I… uh… am yeah, part of the Monster Girl fandom… just FYI.

    5. On there being no evidence… you are correct. We’d have seen a half eaten skeleton in a shark, We’d have seen one wash up on the beach strangled by six pack rings, or one in a bunch of washed up HIV+/HEP-C+ filled medical waste.

    These depictions are also the sorts of things the Monster Girl fandom does post and make. Usually in tandem with horror, vore and gorn type images. As well… sure a monster is scary… but it is more scary to see a monster laying dead washing up in amongst medical waste on a beach. Tell me a monster, and explain to me, why it isn’t more scary to see it dead in amongst medical waste. You cannot do that. Freddie Krugar, Jason DeVoyerse, Chuckie, Slender Man, Jeff the Killer, the Jersey Devil, Baba Yaga, C’thulhu, Nyarlothotep, Dr. Frankenstien’s Creation, various Tulpas, BEN DROWNED, Those creepy kids from The Village of the Damned, Jigsaw, Okiku (and her nine plates), Lilith, Plant Girl, Octomaiden, Dullahan, Skriker, Banshee, Harpie, etc., etc. all look EVEN scarier washed up on a beach, dead in a pile of medical waste. Which is why images like that show up in the fandom.

    That… and some of us don’t much care for mermaids, and will draw then strangling in pop can rings.

    Even taking into account cartilage skeletal systems, like the one depicted forming in the girl in the 2008 movie Teeth… which would be implied by suggesting Lamia, Mermaids, Shark Girls and the Fur Bearing Trout all share a common ancestor… the skeleton would not go away right away, and there would be fossilised traces. If the skeleton were designed to disintegrate upon death… there would need to be a system in place to keep the skeleton from disintegrating while the creature was still alive. Implying either an insanely high regeneration capacity (requiring a LARGE amount of food). Though constantly repairing a cartilage system would likely create enough body heat to counteract the cold depths… I have issues thinking such a concept would come to and be a thing.

    Though nice article… I often enjoy reading and looking up biology to figure out possible solutions to make things even weirder in my monster girl depictions.

  10. Mermaids are real. Why all the secrecy? Marsupial some egg laying koi, carp, salmon. Others polywogs.
    They migrate to warm waters even island keyholes. My daughters have to leave the water 35 min due to waterlogging. Men with vasectomies cutting themselves cleaning fish are biggest producers of new lines.
    All females risk etopic pregnancy swimming with fish pee. Why the secrecy and denial when everyone should be warned of hazards. Some perochial schools still educate some. Here they are still kept hidden underground housing-why? In the sixtys they attended public schools. Why the segregation? Why the secrecy? Why the mass hysterical denial? Mermaids w/out legs use wheelchairs on land. Large companies hire them. They own companies. “Dragon naturally speaking” was written by mermaids for mermaids. They hold admiral and captain officer ranks in us navy. Mermen signed declaration of independance (they expected equality). Why the apartheid? Why the secrecy?

  11. May be…they are a way of representing sailors’ sexual fantasies or their love of prostitutes at ports :D

  12. What about a mermaid with the top half fish and the bottom part sexy female human legs?

  13. Mermaids are magic- you don’t get to apply your silly science and logic to them!!! ;P
    I live with one!!! I know they’re real.

  14. Great points Fred! However, I would still argue that *if* they were marine mammal hybrids, those rules of fusiform, high blubber anatomies would very much hold true. Therefore, the ‘idealized’ mermaid is impossible physiologically. In addition, I would still argue that a primate-like mammal with a chimeric marine mammal hind end is very unlikely; they are from two very different evolutionary branches; marine mammals likely evolved from perissodactyls(think hippos and horses), and there is no evidence for a marine intermediate primate species.

  15. Thanks for your kind answer. Of course, in the northern Atlantic the comparison with mammals would increase the first point, with a probable plump figure, but could also restrict their area to warm waters : your figure stopped at 20°C, whereas many oceans are always warmer than 28°, in which humans can survive…
    So for me the main problem would be ecology : even with a strong dolphin tail, a maid-busted marine animal would probably not reach sufficient swim speed to catch fish or escape from predators. Then, to swim well they would need a fusiform body, no hair (but a seal-like fur would be OK), no prominent breast (sorry guys), fat hydrophobic skin, short and large arms, and maybe even a rostrum…

    But I don’t think that, with enough evolution, a marine primate would be “impossible” for all that : mosasaurs were lizards (squamata), which are supposed to be far less adapted to such an environment than monkeys… And look at what looked like the ancestors of current marine mammals ! They all came from a wide variety of primitive forms : don’t forget about pinnipeds, sea otters or even polar bears… Evolution can do anything from anything, so I think it is hard to say that something is definitely “impossible” (it was said too long about platypus).
    And remember the fancy “Aquatic Ape Hypothesis” !

    Anyway, thanks to you I finally got a scientific reference to help me in creating a section entitled “from a scientific point of view” in the “Siren” article on Wikipedia (French version) !

  16. And when the sailers got home and described these creatures nursing their young like a woman the artist went to work drawing a fish with the upper body of a woman. So there you have the mermaids. The artists did not see the manatees. They heard the story of the sailers.

  17. Fred- excellent points! I too wish I would have brought up the issues of *ahem* mammary glands in the context of mermaids. Not only would that external anatomy slow you down, but most aquatic creatures, mammals especially, have internal reproductive anatomy.

    So really, the point of the article (besides being a humorous look at the subject) is that mermaids AS THEY ARE PORTRAYED by popular media (and wishful thinkers), are not evolutionarily logical.

    This doesn’t mean it isn’t fun to entertain the idea of them as FICTIONAL creatures, that, for example, can personify our relationship and love for the ocean.

    Besides, you give a mermaid all the theoretical characteristics of a marine mammal, and what you end up with is… a marine mammal.

    Sounds great with Wikipedia!

  18. Great post, Craig. I don’t thinks ‘Splash’ would have been quite as popular if Daryl Hannah’s character was a 500-pound, armless blubber monster with constipation. Just saying …

  19. Well..
    People used the same word impossible about platipus..
    But eventually that turned out to be more than possible.
    According to science faries cant exist aswell..But..My word they do..believe me..
    Then again i believe that if ancient primates would be told about homo sapiens they would show the same impossible type reaction.
    Its up to the creature how it would adapt to its sorroundings..We cant imagine that sitting here..Lots of wierd unlikely charastaristics were seen among creatures that we woudnt actually believe..
    But your article is a good one..:)

  20. I love how there’s a mature scientific debate of hypothetical mermaids even though we’re already sure they don’t exist, and you’re both just debating purely for the thought-provoking fun of it.

    The mark of wisdom is the ability to entertain an idea without accepting it.

  21. Not that I think there are mermaids, but all these points aside from the fifth one are horrible lmao

  22. 1. humans can adapt over time in any environment. mermaids had billions of years to adapt to cold waters for example dolphins and sharks are mot fat or hairy and they do very well under deep water.

    2. evolutionary speaking we saw allot of babies be born very strange some with hair all over their bodies and some with snake skin. it is called mutation people and other creatures can be born differently or mutate over time.

    3. how do sharks and dolphins reproduce if you look at their bodies you don’t see any general areas so find out how they reproduce and you will get your answer.

    4. again internal mutation they can learn to do what sharks and dolphins and even whales they would learn not to leave their waste around.

    5. the government think that people would not be able to handle the thought of knowing of their existence. if people knew about them then they would really do go extinct because of the people who would want to catch them and kill them or worse sell them around like they do with some people around. if we knew we would kill them all.

  23. Seeing isn’t believing. Very good points, but since I am a fish breeder, I must disagree with point 3. Not all fish give birth to eggs, the fish molly gives birth to live free swimming fry, and have babies almost once a month.
    As for the cold water, the mermaids could have adapted to the cold water. Not by being obese or hairy, just by adapting to be cold resistant and not being slowed down. They couldn’t be fat and hairy, they wouldn’t be able to out swim sharks and other predators. Funny post, just a daily dose of fake for someone.

  24. If Mermaids are not real then how do you Explain how on the Animal Planets New Found Footage of Mermaids of that Russian equipment on the dept dept dept part of the ocean where no human can withstand . out of nowhere the fish gets speared then you see a big fish tale . watch the footage and it Explain it self . Self Explanatory. trump that!

  25. That was so awesome on that New found footage when there in that vessel under water and that mermaid puts it fin/hand on the window . i wonder if mermaids have felling sense like we do or radar sense like Dolpnins

  26. Although your theories and explanations are very valid and reasonable, why don’t we stop viewing the mermaid as half human and half fish, and as a whole mermaid. If we do that, we’d be able to say things like this. Who’s to say that mermaids aren’t completely warm (or cold) blooded? Also it would make sense that they only live in shallow waters, because that would explain all of the sightings. Maybe they can only dive deep for a small period of time. Also, who says that they have lungs? Until we actually find one (if they truly are real), who’s to claim that they don’t have gills just like fish? Now, if they did only reside in shallow waters, then they could be thin. Also the reproduction thing; maybe they have neither human or fish anatomy, and have their own way of repopulating. Also, with the constipated thing; perhaps they actually do have gills and expel ammonia just as fish do. Now, I’m not saying that I am a firm believer in the existence of mermaids or mermen, but I’m also saying that I don’t believe it’s completely and utterly a closed case yet. Until we can search the entire ocean, (which we cannot do) and find absolute proof that these creatures are all myth and no substance, well I’d have to say that there is still a possibility. I’m actually quite neutral on the subject of the matter, it’s just the points “proven” in this article seemed unimaginative, like they didn’t consider all things possible no matter what the probability of such things could be. Just like in court when people are innocent until proven guilty, I believe the subject of mermaids being real is possible until proven impossible. That is all…

  27. No offense but why do we always try to scientifically compare everything to human if mermaids are magical they could have ways of surviving. Their necessities of life could be different then ours. I’m not saying they’re real but that not everything works and functions the way our life form does. Like what if they don’ t need air and food. Plus there is no proof that they are mammals,or birds,or reptiles. It is unnessicary to compare e

  28. cling to your soul sir, for mermaids seem to take the rest. a bunch of the ocean remains undiscovered, so how are you going to tell me mermaids aren’t real ? there are thousands of species out there in the world (and ocean) that are, in fact, out there. considering the fact that you probably have not explored every inch of the ocean in your life, all of your points are invalidated. anything is possible you know.

  29. Mermaids are real pls stop breaking my 11 years old heart with mean articles like this one:(

  30. I appreciate the points made in this article however, we can’t assume they would freeze to death. They may be different then humans in this sense (maybe they can survive cold waters due to some type of evolution) which is something we can’t prove.

    It’s like those news stories where there is no evidence of life on others planets because there is not enough oxygen or water to sustain life on those planets. Well don’t those researcher ever presume that maybe other life forms survive on other resources and in other ways.

  31. when we talk about mermaid it means that we are talking about a thing which is exist or was exist other wise who really create this matter

  32. Science always have new frontiers to be explored. Logic sometimes cannot be applied because logic is based on our limit understanding in science. For example, what about presence of antifreeze in blood or bodily insulation that can withstand cold temp? How do flies and mosquitoes survive freezing winters? This comment is not to assert the presence of mermaids but for scientists to also realize that everyday there are new things discovered which pushes the frontier of our understandings. Be vigilant and analytic but never have a closed mind :) Why are there myths of dragons in almost every ancient cultures? All of them breathing fire yet we cannot find any evidence of them? Ancient civilizations thousands or millions of miles apart recording the existence of the same creature. How is that possible? Sharks can speed through thousands of feet and rising hundreds of meters quickly without getting the bends like our human divers. How is that possible? Forces of nature applies to all creatures big and small but some found ways of coping to survive. We should always keep our minds open.

  33. that is very true, like did u even watch it?! like I’m 12 and I’ve watched it and what u were saying sounds like u didn’t watch it. Hello? ever heard of adaption? and where were polar bears related from? bears to polar bears, they have different capabilities. It’s definitely possible then. You might say I’m too naive, I say your too skeptic. You said hair and average human and stuff. According to the show, they adapted to it, so there are different sides to evolution, either hair to adapt or SCALES like in the show. And adaption changes ways of living so people can stay in those temperatures if they adapt, they’ve got plenty of time this world IS old.


  35. took 60 years to find a panda. just couldnt seem to find out, thought to be a myth.

    all of your point are based off assumptions, that they are “human” on top. in this case yes your ideas would hold water, but “humans” have adapted to live int he conditions that surround them. we dont live under water there for cant not survive there, same goes for a fish on land. many animals (and some humans) have ways of producing heat to regulate their bodies even in the most rough conditions.

    “They would go extinct – they cant lay eggs because they are mammals. and they cant give live birth” because you know the layout of the plumbing of a mermaid….this alone discredits your article. making an assumption that because you have seen “The Little Mermaid” you know how they would mate. think out side the box. “life always finds a way”

  36. The whole thing was extremely insulting. I actually got invested and read up on it and then I realised it was fake. I feel like an idiot

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