If you’ve seen any of my previous questions about Algennon’s monsters, then you’ll be glad to know we’ve stopped talking about simple mollusk monsters. Now we can talk about cool monsters that have spines and limbs and stuff! This new monster is called a Simswine, and it looks like a tall boar which can stand on its hind legs, and has fingers on its upper limbs with large curved claws. It stands five feet tall and its eyes are blood red. Simswines mostly live in colder forests, dining on tree leaves and berries. But while the species only needs to eat plants for nourishment, they can’t survive on plants alone. Simswines need blood to create their reproductive cells. While any blood works, human blood can help the children born from that blood grow more strong and vicious. And one more cool thing about them: they can mimic sounds with great accuracy. So they lure young animals and humans by mimicking the sounds of their parents and drink their blood. It’s fun! But is it feasible, by the standards of Earth’s creatures? My question for the good people of Worldbuilding Stack Exchange: is the Simswine a creature that could feasibly exist? Please note that answers should not be based on fantasy biology. I’m asking about the Simswine’s feasibility, based on the biology of Earth and creatures that exist or have existed. The best answer will also include information about what would drive this creature’s evolution.

  • $\begingroup$ Is this mere spam or are you suggesting a Simswine creature could be feasible or what? $\endgroup$ Apr 1, 2023 at 20:23
  • $\begingroup$ Probably could be part of the Anatomically Correct series $\endgroup$ Apr 5, 2023 at 1:21

4 Answers 4


Needing others' blood to reproduce isn't so strange; mosquitoes do that.

From an evolutionary standpoint, you start from an omnivorous critter that requires energy, proteins etc. to reproduce - or maybe mature into a fertile adult - until a random mutation arises that greatly improves chances of successful reproduction if mammalian blood is consumed (not too different from mosquitoes). Lots of things in mammalian blood might do that; mosquitoes go for proteins, but several hormones could be the key component. Adrenalin, for example, or cortisol, or several steroids.

By selection and refinement, we arrive at the point where unaided reproduction becomes impossible - chances of miscarriage are too high. Any version of the animal that can reproduce without blood slowly extinguishes. The creature evolves into an occasional ambush predator.

Another mutation allows the creature to produce sounds similar to those of its preys. The better mimicry leads to more successful hunts, higher reproduction rate, and once again the "base" models get competed out and become extinct.

Where this stops working is the part whereby humans don't hunt down every single critter and drive them to extinction en masse. You'd need to have the simswine coevolve with, say, non-sentient, non-organized chimpanzees, the latter somehow evolving sounds resembling human speech, the former adapting. Then one day a real human comes along...

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    $\begingroup$ Yes. At the very least humans would teach their children to ask further questions and generally be careful when hearing their parents calling them in a forest. Imitating another creature's sounds works much better with non-sapient creatures. $\endgroup$ Apr 4, 2023 at 14:05
  • $\begingroup$ Amazing answer! Thanks a lot for including the parts about coevolving and the extinction of the base species. $\endgroup$ Apr 4, 2023 at 14:18

I'm going to say that it doesn't sound feasible really. Mostly that's because I cannot concieve of how the need for human blood to reproduce would be an advantage in this creature's evolutionary history. Some sort of blood... I guess.

Normally weird food preferences and needs, or weird breeding habits bring an animal an otherwise uncontested ecological niche (or it was once a very general niche but has become tiny). Because nothing else eats thistles, it's worthwhile if I only eat thistles! This doesn't seem to do that for the animal. The mimicing of voices, specifically their parents, demands a degree of cunning and hunting strategy that suggests it could get blood from a wide range of animals. It's so obtuse a reproductive strategy.

Again on humans, this suggests co-evolution. This creature must have evolved alongside humans for millions of years to evolve these highly specific and limiting behaviours. Human speech has evolved massively and very quickly (in evolutionary terms) so this beast would have been very well lucky to match that sophistication of sound making so well and so rapidly. This isn't like a parrot, this is a creature that can fool a child into beileving its own parents are calling it!

The only recourse on voice I can think of would be that it had very sophsticated vocal talents evolved earlier and independantly for hunting other animals, and has recently swapped to hunting humans for blood exclusively. How it chooses the right words and things, I'm not sure. I can't think of any creature with the right sort of vocal skills in nature.

So I think the bit I'm struggling with is the mythological horror aspect. The unworldly aspect. Besides that, I don't see why not. Sounds a lot like the giant lemurs and ground sloths we know used to exist. Give it weird bloodshot eyes for some reason and you're good. Biologically viable but just not something that's evolutionaryly credible in my view.

  • $\begingroup$ Good point. I have modified the Simswine so that it doesn’t prey exclusively on the blood of people, and doesn’t just mimic their voices. If it hadn’t been able to reproduce without humans, it would probably not have had enough time to evolve. $\endgroup$ Mar 30, 2023 at 18:10

Bear with Bird Best Friend

enter image description here

Art by Anni Betts

Bears cannot mimic human speech. Boars cannot mimic human speech. Birds can mimic speech super good. Your man-bear-pig needs a bird partner. A lyre bird specifically. The bird lures in unsuspecting people and the man-bear-pig devours them. The bird gets to eat the scraps from manbearpig's teeth. Everybody wins. No one knows it is not the pig monster making the sounds. Because those people all get eaten.

If you want to be slightly more creative, you can combine the bear and the bird into a single animal. Like an owlbear from D&D or a giant version of the real animal the kākāpō. These are football sized land-parrots that are unfortunately going the way of the dodo.

enter image description here

The blood stuff sounds unlikely. The flesh of the animal will provide far more sustenance than the blood. Perhaps by some fluke of biology, there is a hormone in human blood that activates manbearpig's breeding urges. The same way reindeer urine can be used as a recreational drug.


Since magic seems to exist in this world 🌍, the easiest explanation is that the Simswines get their prey to technically reproduce, then they use those souls, that are technically the children 🧑‍🍼 of the prey, to animate their blood offspring.

This can be easily explained as them having lost the ability to call their own children for some reason or another. This has the bonus of being horrifying for the story, especially once the humans realise they are technically killing their children. It also neatly explains the importance of human blood.

As for how how that niche works, the easiest comparison is gorillas or even better Chalicotheriinae which are basically the same thing as Simswines, but without supernatural effects.

How they evolved? A very simple explanation is they come from a land where sapient beings have been there for ages and thus speaking is useful. They could have been pets, gained that ability just to communicate with the human niche beings, or for extra horror points evolved from a sapient being (once the main lineage killed off all the animal competition leaving niches untapped).

Here is a situation that could lead to them evolving naturally:

There is a sapient race in this place. Let's call them the Pins. To start off:

The Pins have lost their ability to naturally have children of their own. They instead go through a rather complicated process where they use noxious chemicals somewhere or another to de-specialise the blood cells of other organisms then cause them to have children by giving up control of the blood cells to others.

They then move those souls to their reproductive cells. This causes non-sapient children to form from them, which are false humans, with a sapient race's body, without the sapience.

Finally, they sometimes create their own children as pseudo-parasites within the otherwise false humans. These need the other souls as mindless drones to do monotonous life support things. They can do this at any time.

This system has a bunch of advantages:

  • The Pins can use the false humans as work animals to care for their real children, help around the house, help in monotonous industrial or office work, as easily expendable scouts, etc. They might care for them like humans do with dogs, or not, depending on how they are.
  • The real children of the Pins can be given bodies without the prebirth risks, making it easy to select a lovely new soul with a stellar new body
  • The Pin can rapidly colonise new land
  • The Pin are free to use their vast intellect for more useful endeavours

Now, sometimes the Pin, even with their cleverness, have outcasts. Additionally, sometimes the false humans end up in the wild due to random tragic events. This creates a wild, non-civilisation dwelling population of Pins and false humans.

After many generations, some of this wild population loses sapience and the structures for it entirely. They become part of the natural ecosystem.

They diversify into a myriad of different shapes and sizes, one of which is the Simswines.

Simiswines inherit the traits from their sapient ancestors. This includes:

  • The need for blood to reproduce
  • The ability to raise onto 2 feet
  • The sound making system to mimic human speech
  • The long lifespans
  • The dexterous forelimbs
  • Anything else they can use as an exaptation from their sapient ancestors.

The Pins are almost certainly still around, though they might have diversified themselves.

That sensibly explains everything about the Simswines.

  • $\begingroup$ Could you modify the Question? Isn't 'Which animals are closest to a large upright boar monster that can mimic human speech'? at best, strange? $\endgroup$ Apr 1, 2023 at 20:17
  • $\begingroup$ @RobbieGoodwin Not really in a supernatural heavy world 🌍. Natural things like evolution 🧬 would still happen, so it is important to check. $\endgroup$
    – Aseku Vena
    Apr 2, 2023 at 5:12

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