I'm writing a speculative story about a planet in another Solar System. On this planet, there are five types of reproduction strategies amongst the sapient species. There are androgenic, gynogenics, autogenic, homogenics, and heterogenics. Homogenic species are species that sexually reproduce within their species; this is what the vast majority of real life species do. Androgenics are an all-female species that require males of another species to sexually reproduce. Gynogenics are an all-male species that require females of another species to sexually reproduce. Autogenics are genderless species that asexually reproduce (generally by parthenogenesis). And finally, heterogenics are a species that has two or more genders, but both genders generally reproduce with members of other species.

There are already examples of homogenic and autogenic species in real life. But is it plausible for there to be a humanoid species of one sex that requires humanoids of another species to reproduce with?

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    $\begingroup$ A species that requires input from another species in order to complete its reproductive cycle is called a klepton. (From Greek kleptô, I steal.) A well-known klepton species is the edible frog Pelophylax kl. esculentus (formerly known as Rana esculenta). $\endgroup$
    – AlexP
    Commented Dec 18, 2023 at 22:21
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    $\begingroup$ Note that the way you framed your question does not rule out parasites. $\endgroup$
    – DKNguyen
    Commented Dec 18, 2023 at 23:48
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    $\begingroup$ Just to be clear, are you specifically suggesting that copulation and impregnation happens across species? There are plenty of examples of creatures using other species as artificial wombs, or in place of the albumen of an egg. You aren't talking about that, right? $\endgroup$ Commented Dec 19, 2023 at 1:48
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    $\begingroup$ To quote Wikipedia: "A species (pl. species) is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction." If the different species sexually reproduce as you describe, they are one species by common definition. $\endgroup$ Commented Dec 19, 2023 at 9:46
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    $\begingroup$ A number of plants require specific insects or birds to pollinate the seeds. When we wipe out those insects, then the plants can't reproduce. Right now, a number of fruit trees in China are being hand pollinated because of a lack of bees. $\endgroup$
    – David R
    Commented Dec 19, 2023 at 15:28

9 Answers 9


There are species that require another species to reproduce. For example spider wasps. These depend on spiders. They paralyse the spider and plant eggs in its body.

Then there are cuckoos, they depend on another species making a nest, then they lay eggs in that nest.

Now I can imagine a "womb parasite". A species that appears to have a male organ, but actually injects motile eggs into the host, through her vagina. Those eggs then swim through the cervix and implant in the womb, just as a normal blastocyst does. The baby is then essentially a cuckoo, it is born and raised but has no genetic material from the host.

Now, is this parasite a "male" or "female"? They appear male (they have what appears to be a penis etc) but they are actually laying eggs, not sperm, making them female.

This gives a species that appears male, but depends on a female from another species. What about the other way around? Men don't provide much, just a little DNA. Now a possible female tactic is to deceive a male of another species into thinking that he has sired your children, whereas in fact they only have your genetics. He then helps raise the children (doing the usual father activities) A more subtle type of parasitism.

Is this plausible? Probably not in the real world, but I think it can pass muster in a fantasy context.

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    $\begingroup$ You might want to consider that species evolve ways to counter these tactics. Cuckoo chicks can't mimic their 'parents' calls, and so don't get fed (this is a real one BTW). The offspring of a female unrelated to a male may not smell or look right or something. $\endgroup$
    – Monty Wild
    Commented Dec 19, 2023 at 0:19
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    $\begingroup$ Also, trees envelop their seeds inside fruits so that animals will eat the fruits and poop the seeds. Not to mention, flowers rely on bees and other insects to transport their pollen from their own anther to another flower's stigma. $\endgroup$
    – Stef
    Commented Dec 19, 2023 at 14:05
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    $\begingroup$ @MontyWild Of course other birds don't like breeding cuckoos and try to counter it but cuckoos aren't extinct, so it seems to work in the cuckoos favor often enough. $\endgroup$
    – quarague
    Commented Dec 19, 2023 at 14:46
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    $\begingroup$ It should be noted that broods of cuckoos that parasitised some bird species are thought to be extinct because of the host got too good at spotting and discarding cuckoo eggs. $\endgroup$
    – Pere
    Commented Dec 19, 2023 at 17:54
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    $\begingroup$ "but they are actually laying eggs, not sperm, making them female" - Not necessarily? The eggs are presumably diploid, or at least viable without any additional genetic material. Unless some prior interaction was needed to fertilize the eggs before injection, your "womb parasite" sounds sexless/asexual more than it sounds female. $\endgroup$
    – aroth
    Commented Dec 20, 2023 at 3:29

Yes, in a limited sense it actually exists

The Amazon Molly (Poecilia formosa) is an all female species of fish, but they must mate with a male with a male of a closely related fish in order to reproduce. However, none of the genetic material from this male is actually carried forth to the next generation. This is called gynogenesis.


This is a rare outcome, that appears to result from hybridisation and is likely not stable in the longer term. The reproduction here is a form of cloning, and has none of the benefits of sexual reproduction. And that's the underlying problem for all your unusual sexual mechanisms: either they aren't actually sexual reproduction or they aren't going to be species because they're blending their material with a different species.

You could have forms which are parasitic in various ways, for example an "Gynogenic" (btw, I think you've named those the wrong way round) species would need to have sperm that invades the eggs of the host species, destroying their genetic material, and then growing parasitically in the womb. That could be stable, after all Cuckoos and various other species successfully get other species to raise their offspring.

But actual sexual reproduction between species is just hybridisation.

"Autogenics" exist, but sex appears far too useful

There are, of course, many real species that use the various forms of asexual reproduction in the real world. However, all the examples of complex asexual species we know of appear to have evolved from the sexual species and aren't stable in evolutionary time. Sex is one of those things that has independently evolved multiple times, and thus can be expected to exist in all alien ecosystems.

Also I'm not sure why you feel the need to coin a new word for this, why not just use existing terminology?

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    $\begingroup$ If reading the sources, the gynogenesis of these fishes seems quite stable. Latest studies indicate they exist for over 500.000 generations - which is more than homo sapiens. So is might be a very rare condition, but completely viable even for hard scifi $\endgroup$
    – Falco
    Commented Dec 19, 2023 at 10:51
  • $\begingroup$ @Falco When I say unstable I mean over evolutionary time. It doesn't seem likely to be something that would create a diversity of forms, but rather a curiosity in the bewildering variety of nature. But, yeah, I agree it's a decent justification; it's up the OP to decide how strong a justification they need. $\endgroup$ Commented Dec 19, 2023 at 11:02
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    $\begingroup$ @Falco the reason they are stable is because they aren't actually 100% asexual. It's believed occasionally some of the male's DNA manages to get passed on to a child. It's very rare, but even rare sources of novel genes can go along way towards adding some of the adaptability required to survive changes in environment over a purely asexual species. $\endgroup$
    – dsollen
    Commented Dec 21, 2023 at 22:38
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    $\begingroup$ Iirc aother term that will get someone a lot of search hits for this is kleptogenic reproduction .. there are several real species that exist out there that are single sex species and parasitically mate with a member of a close species to reproduce while discarding any genetic input from their mating partner. $\endgroup$
    – Pelinore
    Commented Dec 24, 2023 at 15:23

I'm going to say yes, but with a bit of a twist.

Digesting your lover's gamete

Everything on earth pretty much has two methods of interacting with the genetic material of other creatures. Either you eat them or you breed with them. We're extremely flexible with the first, being able to break down most proteins and carbohydrates to make our building blocks. In contrast, our genetics is super-picky about what you can do the second with. Our interbreeding mechanism is simplistic compared to our eating mechanism, requiring the two sets of genetics to match up like a zipper.

Chemically speaking, though, it doesn't have to be an either/or proposition. A sophisticated gamete could cannibalize the genetics of another gamete, picking and choosing which parts it wants to make use of. It might not be as simple as breaking down the genetics in their entirety, possibly involving tens of thousands of viruses, each of which seeks out a chunk of the target genetics and delivers it to a mechanism that assembles it to spec.

Artificial limitations

For this to work, it would require that the target gamete have all of the required building blocks. This limits the options, and you have to ask why the creatures can't breed with their own species. The key to back-justifying this one is the essential nature of predation.

I think it would be a safe to use vitamins as a source of comparison. Humans don't make our own vitamin C. We lost that gene somewhere along the way, because it's more efficient to get it from the things we eat. Similarly, your "predator genetics" might just not be able to reproduce itself without additional source material.

So, overall, this is justifiable. Not likely, of course, but that would be arguing "irreducible complexity," which is always a losing bet against the anthropic principle.

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    $\begingroup$ "picking and choosing which parts it wants to make use of" -> this sounds suspiciously similar to analyzing a Turing machine, which leads me to think you'd run into some form of the halting problem. $\endgroup$
    – Rob Watts
    Commented Dec 19, 2023 at 20:46
  • $\begingroup$ @RobWatts, Maybe, yea. I think you have the right idea. That's how the Descolata virus works in Speaker For the Dead. I was actually thinking of having it splay out the genome in a relatively large space and setting a bunch of viruses free to match some chunk of it, using massively parallel chemical processing. $\endgroup$ Commented Dec 19, 2023 at 23:01

For a given value of reproduce...

Some fantasy games like Warcraft have "races" that are actually factions. And some fantasy RPG's define vampires and zombies as races rather than humanoids with a condition.

Following this train of thought, zombies are a species that reproduces by infecting members of other species (regardless of gender).

The aliens from the Aliens franchise also reproduce in this manner in a way... some might say that the people involved in the process are just hosts, and the aliens are parasites - but the resulting offspring has genes from the host, which is why aliens springing forth from predators are way stronger and more monstrous than those coming from humans.

And then there is the Asari race in Mass Effect, a race designed to cater to a teenage male audience. The race only has females, and will reproduce with anyone and anything in the universe. The official explanation is that they psionically rearrange their genes using whomever they are mating with as a template.

So... plenty of examples in sci-fi and fantasy. You need only look around a little bit and any idea anyone might have here has already been overelaborated in a book or game already ;)


Yes, for some meanings of "species" - because a lot of "species" definitions include co-reproductive abilities.

Nature has, in fact, more imagination than most people.

A real life example off my head:

Two "species" of birds - having different outlook, foraging practices, nesting periods, etc... share a common male population.

I could imagine a genetic setup and an evolution path leading to this. But only after the fact.

In short, whatever means of reproduction you think about, chances are that it is not only possible, but actually an established practice somewhere on Earth.

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    $\begingroup$ Could you provide a link for your quote? I'd like to read more. $\endgroup$
    – brendan
    Commented Dec 19, 2023 at 10:11

A salamander in the Great Lakes region of North America fits the description of Androgenics. They are usually called unisexual salamanders, as they only ever have female offspring.


Many members of the salamander genus Ambystoma are sexual creatures—by which we mean males drop sperm packets to fertilize female eggs, producing offspring with a set of genetic instructions from each of their two parents. But unisexual Ambystoma lizards do it better. These females pick up those packets, but they can gather more than one with which to fertilize their eggs. And once they do, it seems to be up to them to decide which parts of the genome—if any—they use from each of their mates.

The female salamanders seem to be able to dole out genes to their daughters in all sorts of configurations. Individuals are basically salamander hybrids made up of the DNA of a variety of species, unified by common mitochondrial DNA (which a mother passes directly to her children, with no male input) from an ancient ancestor. Some carry five unique genomes around in the nuclei of their cells. They appear to always carry at least one copy of the A. laterale genome (the blue-spotted salamander), even though this species doesn’t seem to be the one from which they all descend. Scientists still don’t know how a salamander “chooses” what genes to give her daughter, but they know that mom can basically make whatever kind of Franken-mander she desires.


Bees and flowers. Bees carry gametes from one flower to the other. No reason that the analogues to both couldn't be humanoid.

What's in it for the bee? Here on Earth, there's free food. On your planet it could be that, or something else.

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    $\begingroup$ Flowers need bees because they're immobile, and cannot just come over to another flower to pass gametes on their own. Being humanoid, imo, requires some ability of mobility. $\endgroup$
    – user28434
    Commented Dec 20, 2023 at 13:13
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    $\begingroup$ @user28434 But it doesn't need to be absolute. A Mermaid-like creature can work as a bridge between two different but landlocked creatures in different landmasses, for example. $\endgroup$
    – Mermaker
    Commented Dec 20, 2023 at 19:44

The obvious case is the literal virus, it's shed much of it's metabolism in favour of numerous cheap copies made with hijacked apparatus.

Viruses that infect other viruses also exist.


If by humanoid you mean humanoid intelligence then no I don't consider it plausible, at least not as a result of natural evolution.

While all kinds of parasitical and unusual mating systems have evolved the fact is a human level intellect would counter such parasites too effectively for them to spread and prosper.

Let me set a few presumptions, and explain why I make them, before getting to the main problem.

  1. If the host species has human level intellect the parasite must as well.

One can hardly use mimicry to prey on your host is you are not intellgent, females are gong to notice a man trying to have sex with them that's incapable of basic language or social interaction. Likewise forced copulation (aka rape) isn't going to be viable, intellect, weapons, and organized group based tactics gives too much of an advantage to have a stupid parasite realistically able to exist and overpower females.

Even more simply humans have a huge number of physical limitations counteracted only by our intellect. A humanoid bodytype only really makes sense in presence of intellect and tools. A non intelligent humanoid would struggle to compete and survive in the wild.

  1. This species must have had it's intellect prior to becoming parasitic.

Again a non intelligent parasite would not succeed against intelligent humans capable of identifying and actively erradicating a species targeting them. Furthermore one can't really survive with a humanoid body without human intellect.

Thus your parasites would have to be offshots of human, or other homo-x, species

  1. Clonal parasites would lose due to lack of adaptability

I see parasites coming in two forms. One being a species that basically clones itself and ignores the other species DNA, much like many of the species your listed. This would have the advantage of bein hard to detect, allowing one to use mimickry to hide your clonal nature and spread your DNA.

However sex is super important, clonal species would lack the ability to adapt to their environment. To give one example pre-modern humans suffered significantly from diseases once they moved into larger cities. this clonal species would basically end up being eradicated by disease as soon as they tried to create or move towards a city. For that matter once a disease was known to erradicate them it's likely humans would intentionally spread a disease that was annoying but not life threatening to them - like chickenpox - just to eradicate the parasitic species.*

This lack of adaptability would also mean all of their species would look the same, which eventually would result in humans recognizing other humanoids with this species physical characteristics and shunning them, driving them out so they can't parasite them.*

* note in both of these cases I'm not necessarily saying it's a well thought out complex plan. Society has time and time again evolved counter to regular threats humans faced even without humans fully understanding the importance or even why they were doing the things they were doing. Most people wouldn't know why people with these facial traits were bad or why catching the flu was considered a good thing, and yet despite this cultural adaptations like this can work. In a sense it's a form of cultural evolution, cultures that had the appropriate mechanism to shun or drive out parasites thrived and so passed on their culture creating a unique type of evolutionary adaptation.

  1. Non-clonal humanoids would be easy to notice as engaging in parasitic behaviors.

Now lets say these parasites engage in sex, and then parasite another species afterwards. This gains them the advantage of sexual adaptation, but it hurts them in terms of mimickry. They would be having sex twice, once to share gamits, and once to parasite another. This makes it easier to detect them since their sexual behaviors are different.

In this case the humans can combat them even easier, notice the ones engaging in whatever mechnisms are necessary to copulate and then parasite someone else, and shun or attack them. This will be done so quickly that the species will be erradicated before it could really establish itself as a species. Plus this sort of sexual parasitism is far less likely to evolve for other reasons...

  1. boring trump card: parasites don't have time to evolve anyways.

While reproductive parasites have evolved plenty of times they are uncommon relative to other species because the odds of mutations lining up to allow parasitism of this sort are rare, and I'd argue their significantly rarer with mammals since it's harder to parasite a womb then it is an egg.

By comparison the length of time between when the first assorted homo-x species started to develop enough intellect to manage things like speech and tool use and today is no real time at all. Our technology evolved so rapidly that it was barely a blink of an eye from an evolutionary stand point. And that means there frankly isn't enough time for such an unlikely combination of mutations to develop to allow such parasitism to occur before you reach modern day humans.

But wait, there is still an option

All this assumes natural evolution. Guided or manipulated evolution is different. If you throw in genetic engineering, or even some sort of magically driven mutation or adaptation, things are different. You could make a parasitic species in sufficient numbers and with enough culture and intellect to have a chance of parasiting off of humans even if they couldn't evolve naturally.

In this case the species would likely be clonal and lack any kind of genetic diversity (that's far more likely to evolve then a non-clonal species). In the long term this species likely would risk being wiped out by humans due to lack of genetic diversity. But if they only popped up a few hundred or thousand of years ago, well their lack of genetic diversity is unlikely to do them in that rapidly.

So in short, magic made your goblins that prey on women and sure their die out eventually, but that doesn't make them less of a problem to you today!


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