A while ago, I asked a bunch of questions about my alternate Earth timeline, which contains plausible fantasy creatures. One of the concepts I've devised more recently is a solution for mermaids (Most people make them aquatic primates) - seals.

Specifically, descendants of phocid seals. My premise is that mermaids are an intelligent race of derived seals, which - preferrably - have at least basic technology. I'd like them to use their flippers to make tools, so, the question is as follows:

Is there any way that the flippers of seals could evolve to be able to manipulate, make tools and use tools? If you're wondering what kind of tools I'm thinking of, think Paleolithic-level.

  • $\begingroup$ Just to compare what others have concocted in their worlds - Phil Pullmans Dark Materials (also a movie Golden Compass) has intelligent polar bears forging armor and weapons, Was a young adult book though... $\endgroup$ Sep 6, 2018 at 18:07
  • $\begingroup$ @RonJohn one idea I had was some kind of extended dew claw, turning the flippers into "mittens" - they wouldn't be nearly as dexterous as hands, but might do the job. As for your question, as long as they have seal-like heads, sleek (main) bodies and hind flippers, with foreflippers that are in some way recognizable as being derived from flippers, they qualify. Also, it must be something that could have occurred within Phocidae's lifespan (Early Miocene to present). $\endgroup$
    – SealBoi
    Sep 6, 2018 at 18:27
  • $\begingroup$ @CongenitalOptimist did the writer of that book describe in detail how the bears did it, or just take for granted that they did it, and let the reader continue disbelief? $\endgroup$
    – RonJohn
    Sep 6, 2018 at 18:59
  • $\begingroup$ @RonJohn Intelligence and tool use are not the same thing. Intelligence and the ability to control fire are not the same thing. Intelligence and opposable thumbs are not the same thing. I'll grant you, though, that tool use can be one indication of intelligence. There are many species which lack opposable thumbs, and which may or may not use tools, and which do not yield fire, yet are considered to varying degrees intelligent. Outside of primates, dolphins and ravens come to mind. $\endgroup$
    – user
    Sep 6, 2018 at 19:25
  • $\begingroup$ @MichaelKjörling you're right. I should have said, "cannot become tool makers" (as opposed to tool users, like bashing an oyster with a rock, or sticking a piece of stripped twig into a termite mound). $\endgroup$
    – RonJohn
    Sep 6, 2018 at 19:31

4 Answers 4


I'm not up on seal anatomy; but I think the main thing to evolve is some sort of grip on, for example, a stick or spear.

That does NOT require an opposable thumb. Our opposable thumb gives our grip strength, but I have known a man that lost his right thumb in an accident (stuck it into an exposed boat propeller, had it surgically amputated). Using four fingers he could still grip and hold things and write with a pen: He held the top part between his index and middle finger, and near the tip of the pen between his middle and ring finger. So the middle finger wrapped over the pen.

Just gripping a stick, one can break off branches to form a shaft, and rub it against rocks to sand one end down into a sharp point. Likewise, one can form thicker shafts used as levers, and sand flattened ends to use as shovels. Or, as paleo people seem to have done, attach handles to the shoulder blades of animals to make them shovels.

A grip likewise allows the winding of cordage, the application of natural tars or pitch. And you don't need an opposable thumb to hold a rock and knock chips off it, by striking it against a larger rock on the ground. It is possible that using their lips, seals could tie knots as well. And don't forget, if the seal can grip a handle, it can have fine-pointed and sharp tools for details with large handles on them; such as drills, or picks. In that way they can also finely carve bone to make tools.

It is an extremely anthropocentric and misguided view to think opposable thumbs are the be-all and end-all of tool production; it only shows a lack of imagination. Even birds make tools with just their beak, and sometimes feet (which are adapted to grip branches (the precursor of sticks)).

Intelligence is the key, if the seals can grip a stick, and have human levels of imagination and problem solving, I'd expect them to develop a wide repertoire of tools, furniture and shelters. I'd expect them o master fire. It won't look like a tool for a human hand, of course. Those are just an accident of our own development, we made stuff easy for us to use. They will make stuff easy for them to use, using one flipper, two flippers, and perhaps their lips, teeth and jaw. Heck, we humans still use our teeth to get a grip on some things our fingers cannot grab.

  • $\begingroup$ Sure it doesn't require opposable thumbs to be able to pick up something and use something, but your going to need opposable thumbs to have developed to a stage where you had intelligence, knowledge to build and use tools to survive. Weapon development was a pretty crucial stage, and not having that extra grip strength makes it very taxing to use a weapon efficiently. Go pick up something bigger and heavier.. like a broom without using your thumb and give it a good strong swing and stop it half way through the swing. Chances are its going to partially slip out of your hand. $\endgroup$
    – Shadowzee
    Sep 7, 2018 at 1:16
  • 1
    $\begingroup$ @Shadowzee I completely disagree; I believe intelligence comes first, and that, and only that, enables the ability to build mental models (generalizations) of how objects work, have properties that can be put to other uses. How a rock can be used as a hammer or weapon, how a stick could become sharpened and how a sharp stick could be intentionally used to injure a person or animal. THEN the intelligent animal will find a way to make and use tools. Opposable thumb primates existed 55 million years before intelligence; apes 30m. Thumbs do not cause tool use; intelligence causes tool use. $\endgroup$
    – Amadeus
    Sep 7, 2018 at 9:52

If they stay aquatic animals, they cannot lose the steering ability connected to their flippers.

Therefore, if you want to add advanced manipulation abilities, you probably need to add an inter-digital membrane, which allows proper interaction with the water.

flipper anatomy compared to hand anatomy

Since the anatomy of the flippers is not that different from the hand of a human, it "just" requires switching of some genes at the right moment during the embryo development. (source of the image)


It seems that whatever changes you make to the front limbs to alter their purpose, the rear limbs evolve accordingly to compensate. For instance, front limbs that resemble human arms are less efficient than flippers. This means the "seal" or mermaid cannot use them in the same way. It will extend its front arms forward in order to streamline the body. The rear limbs, on the other hand, will assume the shape of a dolphin's tail and the back muscles will provide a stronger propulsion. The back muscles undulate the spine. They create a "wavy" motion which sways the tail up and down in the same way a dolphin does.

Dolphin kick for swimmers is the same https://m.wikihow.com/Dolphin-Kick


that is plausible. Mermaids might have been inspired by marine mammals. Dugong literally means "lady of the sea", it has dolphin-style tail, and has finger bones that only get rigid with age: https://en.wikipedia.org/wiki/Dugong

Seals are a better starting since they are predators, and hunting requires more brainpower than grazing. And otters (another kind of aquatic carnivorous mammal) are known to use rocks to break seashells.

You are right that they could not advance beyond stone-age tools, unless they come on land to make fire and work metals. But they still have rocks, shells, corals, bones to be used as edges. Seaweed or animal materials for binding. Driftwood or Corals for handles.

Besides evolving fingers (with webbing between them), they will also need to get their hands long enough to hold an small object with both hands (to work on it, or to use a tool on it).

You cannot swing weapons or tools underwater, so no axes. And no bows. For hunting, they could make spears that they will ram into prey. For close combat, probably short knives.


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