bucking the trend of mermaids I've decided to take a different approach with my mermaids. A long time ago a group of Australopithecus diverged from us taking to the sea. some characteristics of these pseudo-mermaids" are:

  • are 149.3cm (4.9ft) tall
  • are a grayish color
  • have a thick layer of blubber
  • have human level intelligence
  • have webbed hands and feet
  • have some type of echolocation but can communicate like humans (optional)
  • are omnivorous (but lean more to the carnivorous side)
  • have slit like noses (lacking a sense of smell)
  • thighs have started to become fused
  • can hold their breath for up to 15 minutes (but still need to resurface for air)

Given these characteristics could such a hominid realistically exist?

NOTE: magic does not exist in my story

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    $\begingroup$ Downvotes without comment won't ever improve questions, folks. $\endgroup$ Commented Feb 9, 2020 at 13:03
  • $\begingroup$ All of these attributes are basically mermaid/mermen. The last attribute seems to imply they are land-based and not fully underwater creatures. It is the only differentiator that says these creatures may not be mermaid/mermen. $\endgroup$
    – user72081
    Commented Feb 9, 2020 at 17:41
  • 1
    $\begingroup$ Why did you alter your question to a different one, one month after you got your answers? Just ask a new question instead. $\endgroup$
    – KeizerHarm
    Commented Mar 15, 2020 at 15:18
  • 1
    $\begingroup$ @KeizerHarm understood $\endgroup$
    – icewar1908
    Commented Mar 15, 2020 at 15:20

3 Answers 3


Your timescale seems pretty brief, but might be doable. Australopithicines diverged from the rest of the hominins about five to eight million years ago. Looking at the evolution of cetaceans, five million years is enough time to get from something that's basically a land-dwelling mammal that can dive for food to an obligate aquatic and unambiguously whale-like animal with all of the major physiological changes along the way that would require. Similarly, the ancestors of modern seals evolved from an otter-like Puijila to a very seal-like Pteronarctos over a similar timescale, though the changes weren't quite as dramatic as those that whales underwent.

Note though that the immediate predecessors to seals and whales were things already adapted to swimming and hunting in water. Proto-humans seem to have arisen and lived in quite different environments, which adds a non-trivial barrier in the way of the changes you'd like.

are a grayish seal like color

Seals are all different colours, both in terms of skin and fur. Cetaceans are also varied in colour. You can hand wave whatever colour you feel like, I'm sure.

have a thick layer of blubber

Seems fine... whales and seals independently evolved this from a land-dwelling mammalian predecessor, so it seems plausible that it could happen here, too.

have human level intelligence

That seems entirely like handwavium at this point, as only one species exhibits human-level intelligence and other intelligent humanoids are all dead, possibly as a result of the action of the direct ancestors of modern humans. You're the author though, so have at it.

have webbed hands and feet

Fine. Note though that there aren't a whole lot of diving predators who use their forelimbs for catching prey; those arms are not at all hydrodynamic and will impede their owner's ability to hunt. They make more sense in generalists, especially tool-using ones

have some type of echolocation (but can communicate like humans)

Dubious. Echolocation seems to have taken longer than 5 million years to arise in cetaceans, and required a lot of complex and specialised physiological changes. I think this is probably the least plausible thing you've requested (after human-level intelligence, perhaps) and it would be more likely that they've just got good underwater hearing, eyesight and other useful sensory modalities that aren't wildly different from their ancestors.

have sharp teeth (being carnivorous)

The forebears of seals and whales were already predators. The forebears of australopithecus, not so much. Human (and hominin) dentition and digestive systems seem best suited to an omnivorous lifestyle. Perhaps this, too, could have changed over time, but it doesn't seem entirely necessary and does seem a bit dubious. There's reasonable non-meat-based eating to be had around the shoreline, both above and below, especially for clever species.

have slit like noses (lacking a sense of smell)

Seals still generally have a good sense of smell on land. Remember that smell and taste are difficult to disentangle, and having a good sense of taste is handy for distinguishing toxic or otherwise unhealthy food from the good stuff.

thighs have started to fused

Seems fine.

can hold their breath for up to 20 minutes (but still need to resurface for air)

Also seems fine. Remember that breath holding times in marine mammals are related to the depth they need to dive to hunt. Deep dives require longer breath holds, but also substantially different respiratory physiology, not to mention the difficulty of locating and dispatching prey in deeper, darker water. Plenty of seals and other diving predators (like penguins) dive for only ten minutes or less, because that's all they really need. Still, longer dives don't seem unreasonable, so there's no reason you couldn't have them too.

As an example of a real-world primate that has some early adaptations to the water and can dive and swim, have a look at proboscis monkeys. They don't hunt or forage underwater, but eat fruit and leaves from trees near the water and use water as a handy escape route and take advantage of the open space is provides for group social interactions.

  • $\begingroup$ Just to add to the timescale part, here is a real life example of the type of evolution that would have went down: evolution.berkeley.edu/evolibrary/article/evograms_03 except that in addition to that, they will also have evolved human level intelligence. This means that over an evolutionary time scale, they will have had dominance over their habitat and an emphasis on the importance of social interactions (I'm sure there are more evolutionary pressures leading to high intelligence) One thing to note is that the mermaids will likely need to have big heads, same like humans. $\endgroup$
    – doe
    Commented Feb 19, 2020 at 2:31
  • $\begingroup$ A really well thought out answer, but there are two thoughts I think worth considering. 1: Many non-human hominids actually were tool using, and cranial structures imply even greater than human intelligence in some. (being the best at genocide does not make us the smartest). 2: Many anthropologists have suggested that human ancestors may have been semi-amphibious based on reduced hair and digit wrinkle responses to water. $\endgroup$
    – Nosajimiki
    Commented Feb 19, 2020 at 3:00
  • $\begingroup$ Nothing dubious in echolocation. Humans can do it (at least on land) and is a skill that can be learned: google.com/search?q=echolocation+blind+people (you'll even find movie clips). Imagine it as a skill exercised in everyday life as frequent as speech and does no longer sound that dubious. $\endgroup$ Commented Feb 21, 2020 at 5:55

Ever heard of Dugongs?

Dugongs are mammals that have gone back to the oceans, and share a lot of the attributes that you describe in your question. They even look from some angles to have commonalities with humans and are thought in some circles to be the origin of the mermaid myths.

enter image description here

Ultimately, the primary difference between these creatures and the one you describe is the level of intelligence. The fins as opposed to webbed hands is likely a by-product of not being a tool using species before returning to the oceans, but I would imagine that if the species that DID return had tool building skills, they wouldn't have hands that evolve back to fins as opposed to being webbed.

What is more difficult to understand is WHY a creature with intelligence would make this change. Arguably, one reason might be climate change (a warm blooded creature would find it easier to maintain comfort in water than on land during a sustained heat wave) but it would also lose a lot of the advantages that life on land gives it in the first place when coupled with intelligence; cover from predators, resources for tools, etc.

Is it possible? Sure, and the Dugong proves it. Likely? Well, that is a whole other matter and one would argue that the prevailing environment in which this is likely to happen is going to be rather specific.


The only thing that bothers me in the picture is intelligence in species adapted to an aquatic life style.

There need to be an evolutionary pressure from the environ to develop it - if a species can live without intelligence, it will. Maybe similar with the transition from jungle to savanna - not enough food to forage (is all seaweed toxic?), all the prey is large or agile enough to require hunting in groups (require communication/coordination) and the use of weapons or traps to kill it.

The impossibility of manipulating fire in aquatic life conditions is a serious impediment for the evolution of intelligence - no food transformations (some nutrients may have been beneficial in the the evolution of intelligence), no capability to preserve the food over longer periods (no causative temporal relations to favor the use of memory in cognitive processing).

Also, a watery environ is less likely to lead to technological development: advances in chemistry and metallurgy are hard without heat, no steam power, little chance to discover static electricity; batteries without access to metals and insulators... I doubt it.

  • $\begingroup$ Dolphins and octopuses are both highly intelligent aquatic animals, with dolphins being one of the few animals that pass all the tests about self awareness we can think of. There's no reason why being aquatic should preclude intelligence in any way. If anything, the pressures of aquatic ecosystems could end up driving the evolution of intelligence as animals have to be more creative to find food and evade predators. Now - whether the resulting intelligence is humanlike is another question. But sharing a common ancestor with humans should mean there's some basic similarities there. $\endgroup$
    – Nascence
    Commented Sep 1, 2022 at 2:48

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