My brothers and I grew up on an island in the Philippines (Cagayan de Sulu) and one day when he was about 12 (I was 10 or 11), my older brother came home one day from fishing with a buddy out in a canoe, saying he’d seen a “galap”, the local term for merperson. His description was rather close to the story of the creature described by the Iranians above. He’s never been one to tell whoppers, and all these years he’s stuck by his story. Day before yesterday, he spent the night, and my younger brother brought up the incident and asked him to tell us about it again. I’ll recount what he said, which, by the way, is the same as it was when he first told it. He and his buddy were sitting in the canoe back to back, fishing in not too deep water, but not super shallow either. He heard a splash, and turned to look… There coming up out of the water (I forget if it was only feet or maybe some yards away-but quite close) in an arc was a pale white creature with its arms in a forward position like a diver, whose head was bald of hair; its head was turned to look at them. What he saw in that brief moment were eyes that looked large, black, almost diamond shaped, and same of the mouth. He said nothing about the nose or ears. As to the lower half, I think he said it looked pretty human; though he couldn’t say for sure about the feet, he said if they WERE feet they were together. After reading these accounts above, I’d like to question him more closely sometime, though his details are understandably sketchy due to it being such a short glimpse. What I do know is that he was convinced it was not human. It wouldn’t have been a joke by anyone, because it did not resurface, and for another thing, our family were the only white people around. And we don’t have huge black eyes and mouths either. His friend did not see it, but when he told his friend about it, rather than disbelief, the friend said, “let’s get out of here!” and he readily agreed and they paddled quickly away from there.
I always believed my brother, and after this recent reminder, thought it would be fun to look and see if similar accounts were out there. Sure enough.
Thanks for reading.

(The oldest known whale ancestor looks more like a coyote than it does a whale.)

Much appreciated, and makes total sense. Thanks!

Being now three or four more years than sixty,
I have seen strange things in my time. I have seen a
merman standing waist-deep in the ocean off my rock shore.

Unmistakeably human and unmistakeably a sea-beast: he
sumerged and never came up again,
While we stood watching. I do not know what he was,
and I have no theory: but this was the least of wonders.

———
Robinson Jeffers, “The World’s Wonders” (1951),
first verses in Selected Poems
(NYC: Vintage Books, 1965), p. 75.

What I have a problem with is the idea of a fully aquatic animal that has diverged from the evolutionary path humans took developing a tail like a dolphin, yet having an upper body virtually indistinguishable from a modern human in all other respects.

That’s why I am more interested in the bottom two illustrations here when entertaining the thought that they are real biological creatures, rather than the more classical depictions of mermaids.

Do these last two posts answer your question at all? I hope so, even though I’ve perhaps been a little long winded.

First of all, before I start, keep in mind that I am referring to the traditional image of mermaids as a human body or that of a maiden atop a fish like tail. I also am thinking of this from a biological and evolutionary perpective, so I won’t be mentioning magical or divine transformations from human to fish.

How plausible the idea of mermaids are really depends on the viewpoint you are taking towards these creatures’ origins and physiology. Do you think they evolved from fish or some other aquatic creature? Do you suppose they are air breathers or water “breathers”(of course fish don’t really “breather water, but rather extract oxygen from it, but bear with me. )? Do you actually think they are creatures that are literally half mammal, and half fish? Since you mentioned dolphins, seals, and manatess, I’ll assume you are considering the most plausible scenario, which is that mermaids would likely have descended from terrestrial animals and then evolved towards an aquatic life. This is the more rational possibility and it is what I’d like to explore here.

Yes, we have seals, dolphins, otters, and manatees. This is an indisputable fact. However, how many types of seals, dolphins, or manatees do you know of with long flowing manes of hair, long arms with manipulative digits and opposable thumbs, or even pendulous breasts for that matter?

If you look at pelagic aquatic animals (that basically means animals that live in open water), you will see certain trends in the adaptations they exhibit. You will notice that they have a more or less streamlined shape, and that they have pectoral fins and often dorsal fins as well. Even animals with very different origins, such as sharks and dolphins, have these basic characteristics, and this is due to a concept known as convergent evolution. I am sure you are aware of what this is, but for those who do not, it basically means that certain unrelated animals will develop similar adaptations for dealing with the same types of environmental pressures. These animals have evolved to live in and swim through the water and certain adaptations are more conducive to this way of life. You can see certain trends that are similar in a wide range of aquatic animals of this nature.

All of this isn’t for show. Things like pectoral and dorsal fins serve a very important purpose. They allow the animals to maintain equilibrium in the water and swim in a straight line. Fins are a good way to do this, and so you see fish, sharks, dolphins, and a wide range of pelagic animals with fins. Nature tends to stick with what works. The same goes for a streamlined form that allows the animal to minimize the effort needed to move through its liquid environment.

Some features of traditional mermaids just don’t fit in with a creature which has already developed the adaptation of a full tail for travel through the water. This indicates that the creatures would have had quite a long time to evolve to this element. So for instance, with something like the hair I mentioned, why would this kind of creature have a full head of hair? A long, flowing mane of hair does not make much sense for this type of animal as this would create drag when swimming through the water and thus increase the amount of energy needed to do so. Even when humans want to swim fast, they wear swim caps in order to reduce this drag. The human body in general is not exactly well adapted to swimming and moving through the water.

Let’s look at the human form here for a moment. We have evolved in a terrestrial environment and much of our physiology is testament to this fact. For instance, our head is situated upon our spinal column in such a way as to be best suited to our upright posture and bipedal nature. We were able to evolve tool using hands because we didn’t need them for swimming or maintaining our bearings underwater, and our bipedal nature allowed our hands to remain free to become the appendages they are today. These sorts of adaptations make sense for us, but not so much for an animal evolved over millions of years to living in an aquatic environment.

We humans have undergone millions of years of adapting to a terrestrial lifestyle. If mermaids were real, they would have had to have branched off from us quite early for them to have evolved aquatic tails along the lines of dolphins, whales, and manatees. In that time, even our terrestrial ancestors have changed dramatically in form and appearance. Modern humans look quite different than many of our early ancestors from even a fairly recent time frame. So what I wouldn’t expect is for a creature that diverged so early, and spent such a long span of time adapting to a completely different environment with completely different demands, to end up with an upper body that looks exactly like that of a modern human being.

That just does not seem very plausible to me.

If mermaids have evolved separate from early human ancestors that looked different from us to begin with, and then spent that time in a totally different element, I would not expect they would look all that much like us. There will have been changes, adaptations in form and function that would be the result of evolving with quite different environmental pressures and needs than what we had to deal with. I suspect their appearance would be notably distinct in many ways from our own.

So a creature with a tail like a fish or dolphin, yet a perfectly modern human body complete with full head of hair, breasts, and tool using hands just does not seem feasible in my opinion. Hands could have developed, I suppose, but the arms would likely be shorter to reduce drag, and I don’t think they would necessarily look just like human arms and hands.

I do keep open the possibility of some sort of unknown creature that may have been mistaken for a maiden with a fish tail, or an animal that has a few characteristics along those lines. But no, I do not see the biological liklihood of a completely human looking creature with a fish-like tail.