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I am interested in creating a reality based version of a creature from Greek mythology called a Siren.

Sirens were believed to combine women and birds in various ways. In early Greek art, Sirens were represented as birds with large women's heads, bird feathers and scaly feet

These were supposedly women that had the bodies of large birds, and lured men to them with their beautiful voices. Once the men were caught off guard, they would be devoured.

How could a creature with the following traits evolve?

  1. Instead of making them human women, I am simply making them an all female species.
  2. Their voices only affect men.
  3. They only hunt one gender of a species, specifically male humans.

A list of all of the Anatomically Correct questions can be found here: Anatomically Correct Series

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  • $\begingroup$ for the second part, the charm could be done with beautifull text and not only beautifull voice, so only humans can be affected. Make it war-related song (or any other menly subject) to affect male humans. $\endgroup$ – Kepotx Jun 27 '18 at 11:44
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    $\begingroup$ They do not need to be "female". They only need to mimic a human female's looks - or most distinctive features. Like the plant that emits a "scent" of rotting meat to attract flies or insects that mimic plants. They don't even need to be sentient and it might not be their voices that attract men, but instead they emit pheromones or chemicals that affect the brain, except those cannot be smelled by witnesses and they explain it with the voice. $\endgroup$ – Real Subtle Jun 27 '18 at 11:52
  • $\begingroup$ @RealSubtle that looks like a possible answer to me(?) $\endgroup$ – dot_Sp0T Jun 27 '18 at 12:06
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    $\begingroup$ Similar (not dupe): worldbuilding.stackexchange.com/q/36722/10851 (Anatomically Correct Harpy) $\endgroup$ – cobaltduck Jun 27 '18 at 15:29
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The siren is simply a descendant of a salamander with a very specific reproduction system. Surprisingly, having them look like birds is the hard part of this question.

The sirens evolved to hunt male humans to fuel their reproduction system. They lure in the men during breeding season with their high pitched songs and use their sperm on the egg clutches in order to begin their reproduction cycle.


All female species: Parthenogenesis is a form of unisexual reproduction that will let this species be all female with few issues. It is seen amongst several waterbound species, particularly amphibians, so your sirens can even hangout in water and lure sailors to their doom.

Voices affect men: The beautiful songs of the siren attract men and repel women because women are more sensitive to certain high pitches than men are. This Skeptics StackExchange question goes over the differences in hearing sensitivity between men and women: essentially, women can naturally hear slightly higher pitches better than men, and men lose hearing acuity earlier on than women.

So, the beautiful siren songs are laced with high pitched shrieks than only women can properly hear, causing them discomfort while luring the men.

Only men are hunted: Remember parthenogenesis? There's a perfect version of it for your sirens: gynogenesis, as found in the mole salamander. This reproduction system operates much like parthenogenesis, except that it needs sperm present in order to begin the process, thus why men, and not women, are targeted by the sirens.

Bodies of a bird: Parthenogenesis is known to rarely occur in some birds, though the offspring generally don't develop properly so getting from a real bird to a siren is a bit tricky.

However, all the characteristics of a siren certainly exist in nature, so it's definitely possible for it to happen to birds to give you a true siren.

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    $\begingroup$ You misunderstood that answer on Skeptics. When it comes to the upper cut off frequency, there is a much, much bigger difference between young and old people, and between individuals, than any statistical difference between genders. So even while the latter difference may be statistically significant, it's actually still tiny compared to other relevant factors. $\endgroup$ – Nobody Jun 27 '18 at 23:01
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    $\begingroup$ By the way, parthenogenesis isn't very rare in reptiles such as varanids, so since birds are phylogenetically reptiles, it seems even more plausible with that in mind. $\endgroup$ – SealBoi Jun 30 '18 at 20:03
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If you are not used to story telling mode, read the summary below

In the dawn of the times, when the humans were powerful, there was a tradition called "motor competition", where males of the humans, enclosed into funny shaped metal cans, would go around a closed path for a certain number of times.

Many details of this tradition are lost in the centuries, but it is known that the winners would spray a sparkling and sticky liquid on the bystanders, and that a special variety of women, known as "umbrella girls" and renowned for their pleasant appearance, were dressed in skin tight revealing clothes and were assigned to assist the men before the start of the competition and at its very end, to receive the spraying liquid from the winner.

Then it came the war, where men fought over men, and survival was harsh on everybody. The tribe of the umbrella girl resorted to a common trick in those times: they used their physical attractiveness and their voices to lure men into their lair, offering food and company.

There they laid together for hours, drinking and fornicating until, when the man was exhausted from the mating and invariably felt asleep, the tribe would make meal of his body.

The lure was always chosen to be in her fertile period, so that the tribe could carry newborns. The female were kept, while the males were abandoned close to nearby villages.

These umbrella girls are said to have spread in small groups and being constantly on the move, always searching for unaware males, as their appetites cannot be quenched.

Beware the fire of thy desire, you man, if you care of living old!

Summary

They evolved from a subset of human female who were used to count on the attractiveness of their appearance. In time of extreme scarcity, they had to resort to cannibalism to ensure nutrition, and being able to attract human males thanks to their bodies and voices made the hunt easy for them.

Over time they solved the issue of reproduction by mating with the pray before eating it (a la spider or prayer mantis), and keeping with them only the female.

They stitched to a nomadic way of life in order to be able to rely on the surprise factor.

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    $\begingroup$ L.Dutch... just... wow... never going to look at pit/umbrella girls the same way again $\endgroup$ – Blade Wraith Jun 27 '18 at 13:00
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    $\begingroup$ This doesn't really answer the question, it just tells a story. $\endgroup$ – Pyritie Jun 27 '18 at 15:54
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    $\begingroup$ @Pyritie, yes, it's answering by telling the story $\endgroup$ – L.Dutch - Reinstate Monica Jun 27 '18 at 16:05
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    $\begingroup$ The question asks "how would these creatures evolve?", which this doesn't answer. $\endgroup$ – Pyritie Jun 27 '18 at 17:01
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    $\begingroup$ Funny answer, but I have to downvote. This does not answer the question in any way. $\endgroup$ – ell Jun 27 '18 at 18:43
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If you are going for realism here, and want more than a hand-waving, techno-babble explanation, then you will have to do some serious thinking to create a world where sirens are possible.

First of all, it unlikely that a bird would be able to evolve visual mimicry of a mammal. Convincing mimicry would have to be very good to be useful at all. The bird would have to pass through a very deep low-fitness valley before the mimicry became useful.

A song that attracts only men is emphatically not possible. There may be a slight statistical difference between men and women in the tones they can hear. But this is an average difference. Some men (and most children) will be able to hear the high notes. Some women (especially older ones) will not. There is no way the siren will be able to specifically target the adults of one gender. At best, the siren song might attract a few percent more men than women. There will be lots of false positives.

Then there is the issue of mind-control through music. Music of course has some emotional power over a person, but there is no way in hell a song will make someone walk off a cliff or into the arms of a flesh-eating bird. The story of Odysseus tying himself to the mast of his ship is mythology. If you are going for realism, you just can't have this.

Also, cross-species reproduction does not work. There are no biological examples of this. Hybrids between distant species (say mammals and reptiles), is also totally out. If you are going for realism, you will have to be creative.

OK, sorry for raining on your parade. But I have good news. You can make this work and your world will be richer for it. You will need to think back a long ways, all the way back to the Carboniferous 400 million years ago and to the common ancestor of mammals and dinosaurs. This is where your story will need to start.

Plodding through the Carboniferous swamps was a species of ugly tetropods called pederpes. In the real world this species eventually diverged into the sauropsids (the common ancestors of dinosaurs and birds) and synapsids (the common ancestor of mammals). But in this alternative world, this is where the first sirens appeared. One population of pederpes began to mimic the female mating calls of another population, lure males into their groups and then killing and eating them. This prevented the other males from taking their females, it also provided food. Gradually the populations of siren and non-sirens pederpes diverged until they could no longer interbreed (became distinct species). But they did not evolve independently afterwards. Instead the sirens evolved under the constraint that they must be able to mimic the appearance and song of their prey. The sirens continued to evolve and speciate in parallel to their prey retaining only a superficial similarity. Over the next 200 million years the sirens evolved into dinosaurs and birds and the non-sirens into mammals. Most of the siren's descendants lost the siren trait and began to evolve freely. But some retained the siren trait and continued to optimize their mimicry.

The sirens could not interbreed with the non-sirens. But they could mimic their mating calls, their pheromones, and their appearance. The sexual dimorphism of the sirens decreased to almost nothing, such that both siren males and females resemble the females of their prey. The sirens are still sexual. Becoming asexual would vastly decrease their evolutionary potential and would not be viable for the sirens, since they must constantly adapt to mimic their prey.

The sirens seduce the males, and have sex with them, lulling them into complacency. Just after the males climax is when they are at their weakest, and is when the sirens kill the male.

But killing the males that are vulnerable to your song is a bad evolutionary strategy. It will result in the males that are not vulnerable reproducing more, leading to the prey evolving resistance. The best strategy would be to domesticate the non-sirens. To use the semen of the sensitive males to fertilize the non-siren females. In this way, you can eat your male and his children too without them evolving resistance. Alternatively, the sirens might only target men who are beyond their reproductive prime.

Regardless of what you decide the sirens do with the semen, here is how your world looks. There are male and female sirens. Humans in your world mistakenly believe they are all women. Further, the sirens are not true hybrids or chimeras, they are as distant from humans as other birds. That they actually are fertilized when they have sex with a man is another misunderstanding. They either mix the semen into the gravy they serve the man with, or use it to fertilize their stock of human women. Also, there are several other species of sirens that mimic other animal species.

Sirens are rare in this world. Humans are smart and will rapidly adapt to the wiles of the siren if they become too familiar with them. The song of the siren is not magic. It is beautiful, and can easily attract the lonely traveler, but is not irresistible.

That the song is magic is a misconception. That the song only attracts men is a popular, but completely false, belief. The truth is, the sirens just don't sing for anyone and will only try to attract a man who they think is vulnerable (e.g. a lone traveler or small group). Since the sirens rely on sexual allure that is adapted to men, they don't often sing for women. But a woman would find their song just as beautiful.

Also the sirens don't have to eat human meat. They can eat any meat. They may be omnivorous as well (your choice). Depending on how intelligent they are (and you have a lot of leeway here also) some sirens may choose not to eat human meat at all. Generally eating members of highly-social apex predator species that glorifies war and vengeance is a bad survival strategy. The sirens would likely be able to integrate very well into the human world if they chose. Some might adapt their talents in brothels or become bards.

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  • $\begingroup$ Hello trepanger, and welcome to Worldbuilding. This is an excellent first answer! Please take our tour and visit the help center to learn more about the site. Have a nice day! $\endgroup$ – Gryphon - Reinstate Monica Jun 27 '18 at 20:18
  • $\begingroup$ Cross-species interbreeding happens regularly, the species just have to be really close genetically. Mules, zonkeys, ligers, hybrid camels, clymene dolphins, and even 'killer' bees are all the offspring of two different species. Depending on the species, the offspring may be sterile, but that doesn't they can't happen. $\endgroup$ – Austin Hemmelgarn Jun 28 '18 at 0:16
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    $\begingroup$ @AustinHemmelgarn Ah, right. I ought to qualify that. Although species are usually defined by the ability to produce fertile offspring. In any case, there are no examples, of distant species producing hybrids, and we are talking about birds and mammals. $\endgroup$ – trepanger Jun 28 '18 at 0:44
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"Beware the Sirens", said the wisewoman of the desert tribe to the young warriors around the fire. Her face was lined, her eyes were rheumy, but her voice was sharp with hatred.

"Beware the unclean ones, hateful to the Gods, with the voices of women but the bodies of birds. If they catch you alone, you will be devoured, and you will sire no children to strengthen the tribe, and you will be no support to your mothers in their old age."

Of course, this is true, but through the darkened lens of religion, myth and propaganda.

Sirens are a closely related subspecies of homo sapiens, who diverged during a population-density bottleneck only tens of thousands of years ago.

Parthenogenesis isn't particularly uncommon in the animal kingdom, and possibly could arise from only a single point mutation, such that mitosis begins in the ova without fertilisation. The offspring would always be XX, and female. The effective inbreeding this causes is usually selected against, but under conditions where human population density is critically low (climate shift?) the fitness costs of parthenogenesis may be less than the fitness costs of not finding a mate. Its not impossible in mammals - https://www.ncbi.nlm.nih.gov/pubmed/3528971 https://en.wikipedia.org/wiki/Parthenogenesis

For the subspecies to survive as a distinct group, we need a barrier, preferably ecological.

Homo sapiens sirenus inhabits esturine salt marshes, with the desert on one side and the sea on the other. The technological toolkit and skills required to thrive in the marsh environment are very different to those required in the desert. Sirens hunt migrating waterbirds, among other things, and dress in the feathers of the birds. This is both a status display and a means of camouflage.

Various forms of parthenogenesis and sexual reproduction are not always clearly distinct in nature, and many species can use more than one. Sirens can reproduce through pure parthenogenesis, but fertility rates are very low. They more easily reproduce through Gynogenesis, where a sperm cell initiates mitosis but does not provide DNA.

Homo sapiens sapiens tribes live in the desert. Some low-status warriors wander, hunting, to the very edge of the marshlands. In the dense reeds and trees of the marshes, vocal communication is particularly important, and Sirens sing to each other. Sometimes human males hear them, are sexually attracted, and encounter the Siren. If she trusts him, he may be brought back to the hidden villages of the Sirens. This rarely happens to human females - they are usually not tempted by female voices.

For the human male, this seems like a great deal! Instant harem. His skills are useless in the marsh, but he is pampered and fed by his Sirens. It takes years to decades before the human male realises he has only daughters, and none of them look anything like him. He may repent, try to escape, and return to his desert tribe. The Sirens have cultural memories of this, and they cannot allow a remorseful human to return to his tribe, potentially leading a crusade back against their hidden village. So they hunt him and kill him. And then eat him. Because Sirens have a religion, too.

Either way, the human desert tribe has lost something. One of their sons that the humans invested in raising has been lost, passing on no DNA, and not supporting the tribe via his hunting and not guarding them against other human tribes from further out. Human tribes that do not strongly discourage their sons from seeing Sirens are weakened, and often overwhelmed by other desert raiders, losing their territory. Tribes that survive are those with a powerful prejudice against Sirens, usually expressed in religious and mythological terms.

Thousands of years have passed, and the populations of homo sapiens sapiens and homo sapiens sirenus have both spread into new territories. But the myth remains. Odysseus was very tow-y after months at sea without female company, but he remained true to his mother's teaching, and tied himself to the mast rather than join the Sirens.

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Sure, they need enough human in their DNA so that they can reproduce. Perhaps the fact that it's all females is because the semen from a single human can be used to fertilize a bunch of their eggs, just like in fish.

This could also explain why they prefer to sing in choir to allure their prey, so that at least one of them gets the prize -and in the process this could lead to some nasty fighting. it would also be a total deboner, but a sailor's report could explain why they turn really ugly just before mating.

After the deed is done, the temporary alpha who got to get her eggs fertilized would share the body of the hapless (dubiously happy?) stud with the losers who got only to look. A meal is served, while the female goes laying her eggs in safety and let the others hunt for more prey

EDIT: Additional info The sirens being hybrid would also explain why they need to lay a bunch of eggs for at least one of them to complete the process till hatching while the others 'abort'. And it would save the seas from becoming overpopulated by sirens!

As for bird-sirens:

This variety of siren could actually give birth like a regular mammal. This explains why they hunt in flocks: one of them has earned the pecking order to get to reproduce with the help of her sisters, and once the deed is done, meal (Hooray! -burp!-) and the flock will stop becoming a problem for the sailors, for it must keep watch of the pregnant alpha.

And if these creatures nest by the sea cliffs like the pigeons, it wouldn't be unusual that they lose the newborn to elements, sickness, rivals, etc, thus keeping an adequate culled number

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    $\begingroup$ en.wikipedia.org/wiki/Siren_(mythology) : Sirens were believed to combine women and birds in various ways. In early Greek art, Sirens were represented as birds with large women's heads, bird feathers and scaly feet $\endgroup$ – L.Dutch - Reinstate Monica Jun 27 '18 at 12:18
  • $\begingroup$ sigh I had checked with the Italian version, and OF COURSE it was totally incomplete! Sorry for this slip. Also, I see that despite the original representation, the tritonic model was the one who survived in folklore (and in fact it is the most known) $\endgroup$ – Valerio Pastore Jun 27 '18 at 12:25

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