In this hypothetical world, evolution occurs as it should. (Not to run afoul of any genetic diversity requirements of evolution; some simple viruses have aided in the genetic shifting process). But for various reasons, or for lack of various reasons; all eukaryotic species on the planet reproduce with some form of parthenogenesis instead of the dimorphism with which we are most familiar. Physiologically, you may assume the dominant bipedal intelligent species (Let's call them Parthans) is otherwise identical to humankind.

Perhaps coincidentally, Parthan society advances similarly if not almost identical to how Human society does with the obvious exception that there are no males, and all that this entails. Monogamous and polyamorous relationships are still formed, though like our society, poly relationships are not all too common. Certain achievements in the bedroom still result in pregnancy. Both parents may become pregnant, but the daughter only inherits direct DNA from her childbearing mother. Birth control drugs are still seen by some as 'unnatural'.

Fast forward a few centuries. By this point in the advancement of the species, Parthan-kind has developed a high-tech space-faring society. Though commercial and somewhat restrictive, travel to large Parthan colonies in nearby star systems is fairly common. It is at this point that a few ambitious Parthans decide to genetically engineer the concept of dimorphic reproduction.

To narrow it down a bit, let's say that their primary goal is to re-engineer their own species, and to ensure the procedure is safe and humane (parthane?), they first engineer various types of dimorphism in a few other species.

Assume the following:

  • An indefinite amount of time has passed in said universe, allowing the Parthen species to actually 'evolve' through viral DNA mutation; Assume they exist.
  • Males would not evolve genetically given any amount of time; Assume that sexual dimorphism is not obvious for cells, that relying upon an outside organism for reproduction is evolutionarily counterintuitive on the cellular level. Males don't exist elsewhere in the universe to provide inspiration.
  • It is considered unethical to engineer the race merely for purposes of genetic diversity.

What other specific reason or cause might fuel a group of Parthans to make this decision to engineer males within their own species?

  • 5
    $\begingroup$ This is a species that has reproductive sex without gene transfers? That might need more explanation, since it sounds like the kind of all-downside trait that evolution would stomp out in pretty short order. It's inconvenient and metabolically expensive - small prices to pay with the diversity payoff from sexual dimorphism, but just a waste without it. $\endgroup$
    – Toby Y.
    Commented Jul 18, 2015 at 0:31
  • $\begingroup$ You seems to think that there are only 2 sexes, your species might be tempering with science creating a variety of sexes including male and watch them fight each other to death in a colosseum, thumb down! $\endgroup$
    – user6760
    Commented Jul 18, 2015 at 2:01
  • 1
    $\begingroup$ @TobyY. Basically, with these women, any orgasm has a chance of causing pregnancy. This can happen to a Parthan on their own, but it's certainly easier and more fun with two! $\endgroup$
    – Ayelis
    Commented Jul 18, 2015 at 3:39
  • 4
    $\begingroup$ "the daughter only inherits direct DNA from her childbearing mother" – This seems to imply there's a way to inherent indirect DNA – what is it? Aside from this, I feel like Toby Y. is probably right about the evolutionary implausibility. $\endgroup$
    – zeta
    Commented Jul 18, 2015 at 7:20
  • 1
    $\begingroup$ Are these "males" capable of impregnating normal Parthens? If not, they are not males in any sense that we normally use. $\endgroup$ Commented Jul 20, 2015 at 16:35

14 Answers 14


As I understand it, your parthenogenetic species reproduces solely through cloning, since you said that "the daughter only inherits direct DNA from her childbearing mother." As it stands, this sounds a bit like bacterial reproduction, without any lateral gene transfers. It seems that the diversity of the species would be difficult to maintain solely through asexual reproduction. Perhaps evolution would have favored high mutation rates, or even guided mutation (favoring previously harmless mutations) at non-essential loci, so that parents frequently do not resemble their children. Example: the blue-eyed locus (if they have such a thing), might have a 10% chance of randomly mutating to brown. In any case, the genetic diversity issue should definitely be dealt with if Parthans are to look different, to start with.

There are two good reasons to introduce males: the benefits of sexual reproduction, or the benefits of sexual dimorphism. There several of each.

Benefits of sexual reproduction:

Population control:

Doug mentioned that the Parthans might want a group of people who could not get pregnant. All of his reasons are very good, but I can think of another: population control. If the Parthan population is growing too quickly, converting some of the newborn Parthan parthenogens into males ensures that they cannot reproduce with other males, and cannot reproduce asexually, thus cutting down on the birth rate.

Decreasing genetic diversity

Perhaps the Parthans are not willing to introduce males to increase the genetic diversity of the species. But what about to decrease it? This possibility was examined by Gorelick and Heng. Sexual reproduction, while allowing for higher rates of certain evolutionarily advantageous mutations, can reduce the rates of highly dangerous mutations, such as switching out entire chromosomes. If these sorts of drastic mutations are common among the Parthans, they might seek a more sustainable, less risky method of reproduction for the future.

Conserving genes

Sexual reproduction can also allow the conservation of genes that, while not currently beneficial, might be useful in future enviroments (particularly with regard to future parasites). This is essentially the famous Red Queen Hypothesis.. Perhaps the Parthans have been blindsided by lethal plagues many times, and have discovered that the Red Queen allows an out.

Genetic repair

The recombination that occurs during sexual reproduction is considered by some as a method of checking for errors. Recombination can repair two-strand damage to DNA. Perhaps the Parthans are plagued by low fertility due to frequent DNA damage.

Benefits of sexual dimorphism:

Separate ecological niches

Different sexes may have different biological needs. This could be an easy way of creating a subgroup capable of taking advantage of a certain biological niche, while ensuring that the mutations will not quickly be lost.

Different sex-specific talents

The different sexes may have different mental or physical attributes, not specialized to a certain ecological niche.

However, it seems to me that only the ones that hinge on the advantages of sexual reproduction are likely to be tried. If certain characteristics are needed in a species, it would make a lot more sense to try to introduce them directly, rather than producing a reproductively distinct group that has these characteristic. After all, in real systems, dimorphism generally follows differentiation. Only the advantages that hinge on the defining characteristic of a male--some reproductive difference--are worth the trouble of introducing precisely those differences, particularly when their emergence in the genome would be so unlikely to begin with. So one of the first four hypotheses seems most likely.

  • $\begingroup$ This is a well researched answer. Additionally, "Decreasing genetic diversity" was the last thing I'd have expected someone to say. Conservation of the gene pool makes a lot of sense, especially in a universe filled with extraplanetary and planetary sources of radiation and other mutagens. Good answer! $\endgroup$
    – Ayelis
    Commented Jul 23, 2015 at 17:44
  • $\begingroup$ "Decreasing genetic diversity" should be the main argument. Without it you won't get a single differentiated species but stemlines which are only related to each other depending on their last common ancestor. This may depend on how often genocides and other catastrophs happen. $\endgroup$
    – Henning M.
    Commented Dec 3, 2017 at 21:27

It seems impossible to me. To begin with, evolution without sex (even hermaphroditic) would be a much slower (at least on earth it was) and IMO there is bigger chance of sexual reproduction evolving than sentient species evolving without it. You assume also that the society would be similar to our. It won't. There is no chance for sexual intercourse evolving if there is no evolutionary profit from it. They will just have no sex at all and no idea it is even possible.

Even if it had existed inventing males is not obvious even on semantical level. What would "a male" of that species be? On earth it evolved among hermaphroditic species (and hermaphrodites reproduce sexually, just there is no dimorphism) as a result of the fact that either small eggs (consisting only DNA) and big ones (enough resources to feed growing organism) are evolutionary stable strategies while the in between state typical to hermaphrodites is not (i.e. half the resources from every parent). But if you assume there is no hermaphrodites and just parthenogenesis there is no obvious way for genders to differentiate. The specimens are not "females", but genderless asexual beings. To introduce genders they would need not only to genetically engineer the dimorphism, but also reenginer their genetics at cell level (introduce mechanisms like meiosis or at least crossing-over), so it would be probably easier for them to just feed the crossed embryos in-vitro.

Maybe after their culture accepts genetic modifications of themselves as something common it would eventually be engineered into their bodies. Assuming such a body is "female" we may call ones giving only their DNA a "male", but I fear it would be meaning very distant to what you expect.

  • $\begingroup$ Most hermaphrodites on earth, such as the earth worm still reproduce with other worms, both impregnate the other. $\endgroup$
    – bowlturner
    Commented Jul 20, 2015 at 16:21
  • $\begingroup$ I've added a few assumptions that I was making, but perhaps neglected to add to the question; Primarily, that Parthens actually do exist, and secondarily, not only that males have not yet evolved but would not have evolved at any time before Parthens exist at this technological level, or indeed, ever. I guess I'd thought that the question and assumptions section implied both of these, but I've now reiterated this in the assumptions section. $\endgroup$
    – Ayelis
    Commented Jul 20, 2015 at 16:33
  • $\begingroup$ I mean, sure, I admit there are things I don't know, and the reasons cells have for evolving how they do is certainly one of them, and this is just for a storyline on which I'm working, and I'm not trying to pick on you... But how can something so obvious to 'micro-psychology' be completely obscure to macro-psychology? Especially to a creature that stands the risk of getting pregnant whenever it has an erotic dream. I'd think genetic engineering would be one of the first sciences they invent. ;) $\endgroup$
    – Ayelis
    Commented Jul 20, 2015 at 17:24
  • $\begingroup$ Maybe the Parthans would re-engineer their genetics at cellular level first; Perhaps originally, they would always gestate after a short bout of non-pregnancy (the way Obligate parthenogenetics do). They would prefer to only bear young when a certain semi-controllable trigger occurred to keep from having babies constantly, so they engineer such hermaphrodites into their species. From there, separating out 'males' from 'females' would be a simple process of ensuring only one gonad type grows in the presence of a certain gestational hormone. Almost everything else could happen mechanically. $\endgroup$
    – Ayelis
    Commented Jul 20, 2015 at 18:10

these premises are hard to work with, which is not a complaint about the question exactly. I think that there is allot of interesting things that could come out of this question, but without more back-and-forth discussion it's hard to know where to focus my answers.

I will therefore try to do two things. First, I'll give a simple answer with the presumptions you have written. However, I will then elaborate more on why such an answer is so difficult to give, and why I feel it's partially a lie.

To answer your question, with the premises as stated and assuming otherwise identical to humans, I would imagine males would not be the original target of the process. In fact I doubt 'males' would occur, but hermaphrodites definitely could. I could see the chain of events going something like this:

  1. develop methods to treat birth defects and genetic abnormalities prior to child being conceived. This would happen far faster then it does with humans. Because the mother's DNA is (almost, see below) exactly copied into the child if a mother has a genetic defect the child WILL HAVE the defect, inevitable, except for cases when mutation happens to fix said defect; which is unlikely. Thus, a means to conceive without specific defects the mother has (due to mutation) will be desired

  2. The easiest approach turns out to be to copy DNA from another Pathon, likely a close relative, into the offending mutated area of the DNA of a new 'embryo' in a process similar to IVF & designer babies. Since close relatives would have almost exactly the same DNA (I'm assuming some mutation still occurs each generation, see below, but not enough to invalidate this presumption) they would be safe examples of what the DNA strand should look like. Thus asking mother's and sisters to provide DNA to fix abnormalities you don't want to pass on to your children becomes common.

  3. People decide that they don't want to settle on fixing current abnormalities. They notice that another Pathon has a cool mutation they like and wish they could have that mutation. Thus they start asking less closely related Pathons to provide DNA (or the Pathon equivalent) to get those copies.

  4. Assume that Pathons lack the ability to pull out specific traits (not at all hard to believe, DNA is not that simple). Perhaps the Pathon's version of DNA is even harder to mess with, and you need to copy large portions of DNA from one Pathon to the other. Then copying a Pathon's DNA would require less surgical precision and more of a replacement of large portion of the Mother's DNA. (with the original step 2 the close relatives DNA is so close to the mother's that even a large swap of DNA doesn't mean much, the two Pathons are nearly identical genetically so they are replacing DNA with exact copies of it).

  5. Eventually as this becomes more common the Pathons start to see how positive the genetic diversity provided by such methods are. It becomes common for them to find 'mates' and trade DNA for their children. This starts to become the norm, due to the advantages and ability to lower cultural stigmas (see below).

  6. Eventually you have a defacto hermaphrodite race that usually has young with another mate. Only in this case they may have multiple mates instead of just one. You could then have them force evolution of physical means to make this easier (ie sex, and your 'males'); however, this seems less likely. To reach this point they are good enough at having children via uterine replicator and/or IVF, and would prefer these methods since it's safer for the child and can filter out negative mutations. At this point going 'backwards' to traditional sex seems unneeded, technology does it better. There is a massive expense and difficulty in trying to genetically make a new sex, I can't begin to express how hard this is or how long it would take (good luck getting everyone to keep working towards this goal over hundreds of generations). It's just easier to stick to uterine replicators and doing the DNA exchange via doctors and technology then to change your physical structure.

If you mush have an actual sex you can claim that some eventually focused on providing DNA rather then carrying themselves. Eventually some traits became so common in provider of DNA that they got treated as effective males, and a sort of specialization (sexalization?) occurred. However, it seems unlikely in the presence of modern technology for various reasons. I would need a whole different question with it's own mulch-paragraph answer to go into how to justify going from step 6 to physical change into different species. I do have ideas of how to justify it, but the require allot of justification to make them the least bit plausible.

For this process to work your need a few things.

  1. the ability to genetically transfer DNA from one pathon to another, but not to cherry pick specific DNA subsets. An all-or-nothing approach. This isn't too hard actually, since this species isn't from Earth. Just say their version of DNA encodes differently, and makes it such that you have to transfer huge portions of the DNA to transfer any of it.

  2. The Mother's will not, as a whole, accept having their child contain a fraction of their DNA for no cost, if they did then less of their DNA would transfer to the next generation, and the ones genetically/psychologically inclined to refuse accepting others' DNA would 'win' the genetic race in the end. The easy way to avoid this problem is have the mother's share DNA. If mother A asks for DNA from mother B it will be a quid-pro-Que relationship, where both mothers agree to have a child that will contain some of the other mother's DNA. That way the total amount of their DNA will be be passed on to the next generation, even as they benefit from added genetic diversity. This may result in mother's raising their shared children together

  3. You need to decide how much DNA a 'transfer' between two mother's requires. can a mother accept only 1/10 of DNA? If so why do they accept 1/2 of the DNA, they would be inclined to have their child carry more of their DNA. The easy answer is to work off of point 2 above. Maybe as little as 1/10 of DNA could be transferred at a time, but culturally the norm becomes to have two mother's carry children together and each child carry half the DNA, so that they have shared investment in each child. It may be that other permutations are possible though. Maybe sometimes 3 mother's will get together and agree that each of the three will have a child that contains 1/3 of each mother's DNA etc. The point is I would say that a large, but no where near half, percentage of DNA must be transferred for this trick to work; to justify step 2 & 3 of evolution above occurring, which works better if the child still contains most of your DNA after a transfer), and have the tendency for parents to have a 50/50 split be due to cultural convention and agreement to maximize genetic diversity while still ensuring the same total amount of DNA is spread from each mother to next generation.

Now, lets get into the reasons this answer is not enough to address the premise. There are some issues with the premise itself that I would suggest hammering out first before digging into things like my above answer.

First, despite being a huge fan of evolution and being fully aware of how imperative sex is to facilitate the process, I think it's possible for a sapient species without males to evolve. However, doing so requires extensive world (and species) building to not just justify, but extrapolate from. The species will be different from humans, in many important ways. I can't answer the question as to why males would be desired without first discussing the culture, psychology, and physiology of your species.

To make this species work at all you need some form of added genetic diversity. If it doesn't come from Sex something else must provide it. An actual virus, as you mentioned, wouldn't do this, because there would be no benefit to the virus; it doesn't spread it's own DNA by triggering random mutations in others.

lets consider a somewhat related idea though. presume the parents themselves have evolved some tendency to intentionally trigger mutations in some controlled manner. Since mutations can be the root to long term adaptation and short term survival a form of controlled mutation to help with adaptability may not be harmful. You would risk the possibility of these controlled mutations leading to lots of harmful birth defects though; most mutations are bad after all. However, maybe the species developed a way to control mutations so they only occurred in limited areas of their DNA, combined with some sort of 'DNA verifier" that would quickly exclude bad DNA. Perhaps the mother's get pregnant often, but are prone to early miscarriages as their body realizes this pregnancy has a dangerous mutation and won't survive (human actually do this already, but this species would presumably do it far more often). This can be justified by assuming an enviroment that puts heavy strain on pathogenic species; for instances a huge array of viruses and bacteria which likes to evolve for a specific pathogenic sub-species and attack it viciously; forcing adaptations to be mandatory to survive disease.

This could work, but it brings up a major problem. The Pathons would not be the same. These mutations would change them, but nothing would control the genetic drift; meaning Pathons would become more and more different from each other with each generation. To give an example imagine each generation each child is 1% different from the mother, and that each mother has 2 children.

First generation each child is 2% different from each other. Next generation you have children that are each 2% different from their grandmother, and 4% different from their cousins (almost, it's minutely less technically). By the 10th generation they share 90% of the original parent's genetics, and are only 80% matches to their most distant cousins. by the 30th generation they share only half of their DNA with their cousins. This grows experimentally worse from there. 30 generations is not long on evolutionary scales, but it's enough to have effectively created different species.

You could use approaches to limit this effect, but in the end all the Pathons will be different based off of their parents. Some will be smarter, some stronger, some faster, and some just able to pop out more kids. You will have 50 different 'races' where 'races' actually are different. Now think back to all our racism in the past, and imagine how much worse it would be when there was undeniable proof that the races were different AND a (much stronger) biological imperative to support your own 'race' above all other races. You get racial battles of the most extreme type, and a desire to keep your DNA as close to your mother 'race' as possible which would make one wish to avoid sexual reproduction and getting DNA from a third party.

Put the above idea aside for a second, I'll come back to it, lets address a separate issue. specifically they won't have romance! There is no need for romance, sex, or pare bonding without...sex. Each will have their own child without partners. Their family will be imperative to them, sharing 99% of the same DNA, but that will be a familiar bond, not romantic.

Sex will definitely not be required for pregnancy, as you suggested. Yes there are a few creatures today that reproduce via pathogenesis that still require sex, but that's because they evolved as sexual creatures who only later adapted to be pathogenic, and haven't yet gotten around to removing the need for sex entirely. Without a sexual species existing at all (as you state in your premise above) there is no need to evolve a system where you need a partner to get pregnant.

However, there is an option to address the genetic drift (and racism) issue and lack of romance in one go. Suggest a method in which DNA is swapped between these species, but in a less controlled method then sex. Perhaps regular interaction with another can result in picking up some of their DNA, perhaps even via viruses as you said (though justifying how this is evolutionarily advantageous to the virus takes some work in itself). This would potentially be advantageous as it can help allow genetic mutation to be shared across a community, rather then each mother having to try (and most often fail) at genetic mutations until they found one that 'worked'. It would also limit the genetic drift.

However, this would make the need of the evolution I suggested above a bit harder. It also suggests extreme racial wars between communities that haven't had this 'virus' help them share genetics.

Then again, if you assumed a more controlled and intentional way of sharing genetics without sex you could go from that one to creating sexual creatures with a male...

Meanwhile, we still have the problem that any of the possible species above, other then the last one with it's own evolved intentional genetic exchange method, would most likely evolve males or other intentional means to exchange DNA eventually. It's a powerful evolutionary advantage, someone will stumble upon it.

I'll stop here, because I think I made my point. For me to really suggest a proper evolution we would first need a few species building questions just to hammer out how the species evolved and what it looks like now before I can go into detail about how they would further adapt to creating males.

  • $\begingroup$ I think it's great that you pointed out the flaws in my suggestion. However, your model is problematic, because it assumes a constant genetic difference between each generation. If any gene can successfully mutate, then the extreme divergence that you predict will occur. But even in bacteria, even in situations with minimal gene transfer, it does not, because a large percentage of the genes are nearly essential. There will be heavy variations in hair color, or toenail growth rate, or whatever, but too many genes are essential for there to be 50% divergence after 30 generations. $\endgroup$
    – Obie 2.0
    Commented Jul 20, 2015 at 22:55
  • $\begingroup$ The problem is this. A 2% genetic difference is already all that separates humans from chimpanzees. So by mutating 2% of the genes, you can go from humans to chimpanzees. But it has to be exactly the right 2%! The low odds of the right 2% of genes mutating is precisely why a 1% difference each generation doesn't work. With any finite, compounding difference, eventually we get to a point when most combinations of mutations are simply fatal. Even bacteria have this problem. $\endgroup$
    – Obie 2.0
    Commented Jul 20, 2015 at 23:00
  • 1
    $\begingroup$ What might happen is this: the unessential genes, specifically the same ones that vary frequently in humans (which is much less than 1 percent) would occasionally mutate the first generation. But the next generation, the SAME genes would mutate, not additional ones. This would be selected for by evolution, because Parthans with frequent mutations in the same sorts of genes that cause variations in humans would be more fit than both Parthans with little variation (because they could not adapt) and Parthans with variation everywhere (because even the best error-checking could not keep up). $\endgroup$
    – Obie 2.0
    Commented Jul 20, 2015 at 23:05
  • $\begingroup$ Jonah, I agree...and disagree with you. I had throught of the same issue, didn't address it due to the answer already being too long. For mutation to actually lead to adaptation the mutation can not be exclusilvy limited to 'safe' genes, it must include more life-critical genes. Some 'safer' genes may be adpated to be more prone to mutate, but all genes must be on the potential chopping block or you don't change species. It's those mutations that are random, and unlikely to mutate back due to the pure size of genome relative to the one tiny gene that's it's unlikely it will mutate ... $\endgroup$
    – dsollen
    Commented Jul 21, 2015 at 12:28
  • 1
    $\begingroup$ This detailed answer spawned a conversation that paid the topic more than enough attention, and even helped me build out my world a bit more. This is what Worldbuilding SE is about. Thanks, all! $\endgroup$
    – Ayelis
    Commented Jul 23, 2015 at 17:35

For "entertainment".

WARNING: possibly offensive material ahead - read at your own risk. (I've tried my best to keep the wording safe but sometimes it just doesn't work!)

Because if it is as you say, and the Parthans are "otherwise identical to humankind", it's likely that for them, using plastic/metal/wood/whatnot as entertainment is probably not enough to satisfy at least one part of the population.

Some mad Parthan scientist is bound to start engineering biological "toys" which could end up feeling a lot better and result in more advanced biological toys (which eventually turn into males).

This could easily spread - the first biological toy (which from hereon shall be deemed "D1") was used by only that scientist - then her friends decided to borrow D1 for a party or something (Humans do like to party) which turned into research grants and papers being published about biological toys. D1 may have just been a lab experiment, but it quickly turns into D1.1, D1.2, D1.3, with more functions, shapes, sizes and colors.

Eventually, we have D2. D2 consists of what looks like a human hip + D1, and includes some autonomous piston action. Various fetishes and ideas turn into different functions which just so happen to require various organs/bone/muscle. Perhaps D4.3 involves abdomen muscles and thighs in order to provide better "angling". Perhaps D6.3 happened to require a ________ system to satisfy ____ fetish - you get the idea.

The cycle continues until eventually you have your first male, which only has one purpose - to lay there and look sexy and provide "entertainment".

It just so happens to turn out that these bodies that are laying there are taking up a lot of resources and doing nothing and using valuable space. So the Parthan group decides to put them to use, and finally give it sentience. Voila! Your first male!

TL;DR and for those who still don't understand what I'm referring to: Males can come about as a result of sexual needs - a need most humans love to satisfy (usually via sex)

Note: I saw answer(s) that focused on the validity and the possibility of the OP's scenario. I'm explicitly choosing to ignore all that, and actually answer the question posted (Which is actually "What other specific reason or cause might fuel a group of Parthans to make this decision to engineer males within their own species?", and not "Is this possible/likely to happen", and certainly not "How would this process work?")

  • 4
    $\begingroup$ Yes, I also have found that if you want to give a plausible reason for an otherwise intelligent person to do something weird and, frankly, against their own interests, that reason usually ends up being "for sex". $\endgroup$ Commented Jul 20, 2015 at 16:40

They need a section of society that is expendable, but are not willing to create clones just to do [insert-dangerous-job-here].

Ruling out the genetic diversity benefits, the most obvious advantage that males have is that they are (biologically) expendable. You can kill off the majority of the adult males in a group and, assuming that there are enough male children/pregnant women/polygynous families, the population can recover within a few generations without changing the birth-rate.

If the Parthans find themselves with a pressing need for soldiers, unobtanium miners, direbeast hunters, or people to fill some other highly dangerous role, they might feel that engineering this form of dimorphism is the best solution.

Cloning or conscription are other options, of course, but both of those have a very real risk of creating a group of second-class citizens - reducing the people forced to do the job in question to 'not really real people'. Engineering males still results in creating a group whose social role is to spend their lives filling some dangerous job, but has some advantages that might make them decide that it's a more ethical alternative:

  • Allowing them to produce genetically-related offspring without needing to bear the child themselves helps with a live-fast-die-young lifestyle, and might make it easier to give them an acceptable quality of life despite their short life-expectancy.
  • Making them required for the rest of society to reproduce provides insurance against their being reduced to the kind of 'not a real person' status that clones/androids so often suffer in science fiction - everyone will have fathers and brothers and sons, so they can't be split off into a group of 'others' and departhanised.

It doesn't seem likely that a parthenogenetic species could develop the sociality to achieve the necessarily cooperative technological advances you say they have. All parthenogenetic species on Earth are loners. Asexual speciation divergence is likely for the time spans you suggest so rather than "Parthans" you'd have a cluster of very similar species.

To answer Why Invent Males? there are two likely intertwined reasons.

  1. They decide that divergence is becoming a problem and attempt hybridogenesis (good article on sciencedirect here) which can come in many flavors but also many dead ends genetically (sterile offspring) and
  2. They discover that they had arisen that way originally and was the basis for their cooperative society and maybe they were losing that through a very long time of parthenogenetic reproduction.

Eusociality is what EO Wilson describes as the primary strength of humans: cooperation. There's plenty of debate on how to define it lots of other terms come into play and loads of yakety-yak debate. But without some basic organizational mechanism down at the genetic level there is no way we could have built cities and technology much less a need for language or any conceptual communication (beyond grunting at each other).

Story-wise, even if (as several commenters suggest) there was a role hierarchy going on based on lineage, from one line a "queen" is born. A freak occurrence that allows all their potential genes to be unlocked but they need a separate mate to accomplish this. Or another "queen" is born in another parthenogenetic line, maybe a third, fourth; then a true threat of the Parthans becoming separate species capable of creating their own castes would threaten their collective future presaging a time of competition and warfare. The queens are discovered to have the ability to produce a male, allowing genetic mixing between the current lines and thus avoid all that trouble.


The society you describe sounds rather individualistic, but if they were redesigning their race for the purposes of maximizing the quality of the race, they might find a desire to create two phenotypically different types of Parthanes. Perhaps one might be optimized to deal with situations where raw force is required, and the other optimized to deal with situations which call for more finesse.

In many cases, this decision can be made late in the game. Perhaps during childhood a Pathane is given a chance to select an approach, or it might even be more like working out, where the Parthane's body adapts to what it is expected to do. However, some physical structures are very hard to make after the fact. For a real life example, read up on the insane process our embryos go through to connect our optic nerve to our brains... its hard to do when the fetus is the size of a small fruit, much less attempting it after birth.

It would be good design to provide a mechanism for this differentiation. Once the huge decision to differentiate the sexes is in place, it is a much smaller decision to explore mating patterns and other things which relate to the sexes. The division of the species is the big part.

  • $\begingroup$ Genetics is hard. Why would they have access to genetic engineering but not machinery capable of far more raw force? $\endgroup$
    – Rob Watts
    Commented Jul 22, 2015 at 21:22
  • $\begingroup$ @RobWatts True. That gets into a bit more philosophy than I wanted to leak into it. However, I can point to the Bene Geserrit from Frank Herber's Dune as an example of a fictional group undergoing genetic optimization in an era of extreme technology. The group had its own reasons for doing so (I won't spoil the book). $\endgroup$
    – Cort Ammon
    Commented Jul 22, 2015 at 22:50

TL;DR: because males are evolved risk-takers whereas females are evolved risk-avoiders. And as a species (especially intelligent one), sometimes you DO need to take risks, to evolve, develop, and survive.

So, your species wants a new sub-species of explorers, daredevils, soldiers, startup founders, and other professions that require out of the norm risk-taking abilities - and perhaps it has a couple of individuals wise enough to recognize both the need, AND the reason why the need exists (lack of evolved risk taking demographics) and the solution is a sub-species which is designed to be risk-takers. They call them... "males".

Let's unpack this in detail:

I must agree with some other posters that the species you describe is extremely unlikely to be even remotely close to humans, including - and especially - culturally.


Because sexual dimorphism does not merely serve as an evolutionary reason to have sex. It also (leaving aside genetic diversity angles), results in the male of the species being a risk-taker, according to most recent genetic and evolutionary and psychological research (src1, src2, src3)

At a high level, this makes sense: the whole biological definition of male/female sexual dimorphism (in non-isogamous species) that ova are much larger, immobile, and require higher biological resources to generate - and therefore, a risk/reward scenario is highly different for a male and female of the species. In layman's terms, males can afford to take risks since both the individual and the species has "less to lose" if the risk-taking - genetic or cultural - doesn't work favorably to the individual. And in turn, male risk taking increases the species fitness due to higher payoffs for those risks.

As such, your Parthan society would evolve to be extremely risk averse, and likely find it far harder to achieve higher technological level, or even spread out much (note how in humans, it's typically males who go out a-exploring for walkabouts).

  • $\begingroup$ I deliberately ignored isogamy in this answer, since there are virtually no multicellural isogamous organisms on Earth, presumably, for a good evolutionary reason. $\endgroup$ Commented Jul 18, 2015 at 19:05
  • $\begingroup$ This seems like a peculiar reason to introduce an entirely new sex. How do we know that the existing variation in risk-taking behaviors within the parthenogenetic species is not sufficient for diversity purposes? Remember, evolution does not seek global minima, but local ones. The most efficient way of getting enough risk-takers is to do it directly. There are many less efficient ways of doing it, of which males are a particularly inefficient one. They likely evolved for diversity purposes foremost in any case, which makes the side-effect of rashness even less likely to be optimal. $\endgroup$
    – Obie 2.0
    Commented Jul 20, 2015 at 3:48
  • $\begingroup$ Put another way: The existing variation in risk behaviors in women is probably sufficient to ensure good risk/reward tradeoffs. Is there research showing a species with men to be more optimal? I am not aware of any, but perhaps there is. In addition, the Parthans would have evolved risk avoidance based on countless factors. If the Parthans can reproduce individually and rapidly, they might be even bolder than human males or females--think bacteria. Environmental and historical social characteristics might also affect the level of risk-taking. Of course, $\endgroup$
    – Obie 2.0
    Commented Jul 20, 2015 at 3:55
  • $\begingroup$ @Jonah - the ESS for bacteria is WAY different than for a r-strategist species with ova (I'm assuming Parthans are r-strategists, admittedly). $\endgroup$ Commented Jul 21, 2015 at 19:49
  • $\begingroup$ If you are using ESS (evolutionarily stable strategy) in a broad sense, rather than a strict game-theoretic sense of a pure strategy, there is not a discrete spectrum of stereotyped ESS's which dominate. You are unlikely to see a single strategy being used to the exclusion of others in an intelligent species. For example, humans exhibit altruism, tit-for-tat, and defection in varying proportions: a mixed strategy, and one that varies between individuals. If you are using it in the strict sense, you might be aware that a rigorously defined ESS does not always dominate in an ecological system. $\endgroup$
    – Obie 2.0
    Commented Jul 22, 2015 at 2:59

Maybe someone decides there's a need to create a group of people that everyone knows will never be pregnant? Pregnancy tends to complicate things, after all. Maybe there's dangerous things to be done, and everyone would sleep easier if there weren't a bunch of gestating fetuses in the line of fire? Or maybe they decide to send a starship on a decade-long mission across the galaxy, and nobody wants a bunch of babies cluttering up the works along the way?

I'd probably recommend contraception over engineering a whole new gender, but apparently they consider birth control "unnatural", so maybe this is "easier" for them. Even in that case, I'd still recommend they just use sterile individuals, but who knows, maybe they grind sterile people up into soylent green.

A super-long-term thinker might also try to introduce sexual dimorphism because it greatly speeds up evolution. Maybe they anticipate the collapse of their advanced spacefaring society at some point, and they want the survivors to be able to adapt rapidly to the aftermath.


All right, so let's say you have this spacefaring race. They've been expanding, getting themselves into new environments, and having babies on completely new planets. The only problem is that some of these babies don't develop too well in these new environments; some are stillborn, some deformed, and some are just straight up missing things. One of these things is the Parthen version of a uterus.

For the latter deformed babies, the future looks pretty grim; without the possibility of bearing children, they'll look to other ways of attaining lasting happiness and satisfaction. Some may become doctors and biologists, and in their hi-tech world, they may seek answers as to how to solve their infertility.

Finally, after decades of research, a solution is devised: they can't repair the uterus, and it's too late to clone and insert a new one, but what they can do is hijack the uterus of a surrogate mother, splicing DNA from both parties to create a hybrid baby. And since the baby is getting genetic material from both mothers, it's got a fifty-fifty chance of having the same deformity, and needing to use the same process to have its own children.

I think you said somewhere that some of your Parthans already couldn't reproduce on their own; this solution could work for them too.

What I'm imagining is some sort of cyborg-genitals (never thought I'd say that), but given an advanced enough species I guess it's possible that they could just use some other parts of Parthan anatomy to get the job done. Perhaps the baby would get all of the 'father' DNA, instead of a split; that would make more sense to me, but may not work in your story. Also, with more of a biological solution, there could be more drastic physical changes due to hormones, leading to a more 'masculine' appearance (rather than a woman with a baby-making attachment strapped on).

After a while, this solution might not be the best one (that is, the original problem may have been solved in a more satisfactory fashion), but by then there would be enough 'men' around to sustain a viable population. Plus, by then the Parthans might have found more uses for them, such as the ones other answerers have mentioned.

What I'd like to stress with this answer is that it sounds quick and dirty, but that's exactly why it makes sense: people will go to great lengths to ensure the survival of their genes. The solution may not be the best, but given the direness of the problem, some concessions can be made.


Advantages of being male:

  • Don't have to carry around or maintain female organs.
  • You don't have to expend energy on pregnancies.
  • Paternal instincts possibly weaker (less obstructive) than maternal instincts


  • Cannot reproduce without the aid of a consenting female. (but not true in reverse in this case.)

I think that the purpose of engineering males would be to create a workforce or army of slaves. Slaves who would die childless of old age if they escaped. Slaves that have no access to their own offspring. Slaves that are indoctrinated from birth by their own mothers. Slaves with no possibility of leaving a legacy to the world. Slaves who's population can easily be controlled by females.

  • $\begingroup$ Periods don't exist for Obligate Parthenogenetics. Instead of estrus, they have pregnancies. $\endgroup$
    – Ayelis
    Commented Jul 22, 2015 at 23:30
  • $\begingroup$ Slavery is certainly a unique idea. If the whole testosterone thing is a requirement of maleness, and it also causes the slaves to be stronger than the slave-drivers, it's sort of a double-edged sword... But you work with what you've got, I guess. $\endgroup$
    – Ayelis
    Commented Jul 22, 2015 at 23:32
  • 1
    $\begingroup$ Most slaves are stronger than their slave drivers in our world too, due to extra exercise. Usually slaves do not have access to military weapons. However, they usually require surprisingly little physical discipline or threats to keep them in line. Keep in mind that they have no other home or society to flee to. They are not allowed to broadcast their opinions in open forums. Uprisings would be local in scope and minimal destruction, if they happened at all. $\endgroup$ Commented Jul 22, 2015 at 23:45
  • $\begingroup$ Technically males can reproduce without the aid of a consenting female, but it's a horrible crime when it occurs, and seems like it'd be rare in the proposed setting. $\endgroup$
    – user867
    Commented Dec 13, 2015 at 0:07

How's this:

Your Parthan scientists originally create dimorphism in other species, as you said, only to see if they can. it is a pure experiment. In fact, in this case, they don't really create males, they simply induce a version of meiosis in a test tube using two, or many more (what the heck), ovum from many doners.

Their experimenting shows them that a not insignificant portion of such creatures evolve/develop solutions to environmental challenges that the standard parthonegenic (sorry) fauna do not.

Next step...bio-weapon of course. Or, if the Parthans are not so warlike, experimental error and escape on a grand scale?? Soon a scourge of fast evolving, fast adapting micro and macro bio-weapons are replacing the natural fauna of the universe. The only choice left to the Parthans, find a way to adapt as fast as the new competition, or face extinction.


May I suggest a social drive?

In a Parthenogenetic society that otherwise develops similar to a real life society, who is in charge?

I postulate that eventually certain families would consolidate and perpetuate power. If this society is capable of genetic modification on the scale you propose, perhaps some cultures would use a form of genetic primacy to establish the right to rule. Especially since parthenogenetic reproduction does not allow much variance normally. This could affect all aspects of social organization, possibly leading to a very stratified society.

Stealing and incorporating genetic material into ones own line to allow offspring to pass the governmental or educational entry tests is one social possibility. A less savory social aspect of this concept could eventually lead to the idea of mixing certain "lesser" lines of genetics into the ruling lines, thus diluting them; causing them to become less pure, or in effect, to lose power. Males might be a potentially ideal delivery mechanism. Sabatoge via seduction.


Why would they invent males ?

There is no logical reason to do so.

1) They lack the concept of sexual dimorphism. What would be a male for them? Same if someone never sees a different sex or hear about it for their entire life, how can they realize a different sex is possible and real? It happens in real life too, Nobody is willing to recognize the existence of the 6 biological different sexes until they see them. After all we only know our sex after noticing there's a difference(why would you need to label yourself differently from something you ignore?) sometimes even after people see there are other 4 biological sexes after the two famous ones, they don't believe it for moral and religious reasons. Example: God made us this way, anything different is Satanic/Nature made us this way, anything different is sickness

Or because they are the minority and minorities either can't exist or have to be crushed down. Even individuals of different sex from male or female refuse it because being different it's humiliating.

Same happens with this modern ideology of gender used by teenagers, once people realize there can exist an endless amount of genders, they either start to create their owns out of fantasy or identify with some other new abstract genders.

2) For reproduction females would be more useful given sexual reproduction is even possible, Females or Intersex individuals have to be compatible with the received sperm, Males or Parthans don't therefore reproduction with male x parthan would be harder than intersex/female x parthan.

3) They reproduce by cloning, this slows down evolution and if they are like us humans then they don't want to evolve. Why would they take the risk to evolve into a mosquito and lose everything they have ? Evolution happens only when there's immense environmental stress and can transform organisms in almost anything. We were just worms at the begin,then fish.. then lizards, then rats and only lately monkeys. In a society like ours they would really have no reason to abandon the easy life and risk everything cause evolution doesn't care what you enjoy, but about what could make your offspring reproduce more than you did. I mean, do you see anyone who wants to evolve, to change? They say so but every time someone is born with tails,fins,fur or scaled skin it's called a sickness not evolution.

4) Males as we know them are more likely to die.

-Social threat. Every society abuses/murders/tortures/sacrifices 3 times more males than females, even in countries where sexism female oppression is holy like Middle-East, males are still being killed more.

-Social stress. Boys are pushed with force from society to be Strong, Big , Rich, Courageous and sexually dominant. Reason for men to suicide twice more than women.

-Nature. Men are biologically supposed and required by the ecosystem to die younger and in massive quantities every year, Having as much females as males or even more males than females would be dangerous for the specie, if men lived globally as much as females and had their same safety then Humanity would be probably doomed or evolution would resolve the problem again by increasing the dangers for men even more, like lesser lifespan and weaker immune system or females with bacteria that kill most male sperm cells.

5) It's simply not feasible they would need to change the genetics of every existing Phartan to make them able to reproduce with the male ones. It would be easier to create a new specie with different sexes but they would need to get the idea of how the hell would every sex look like from other animals.

In the end the only reason they would have to create another organism compatible to their specie but with different characteristics would be to use it as slave.

This organism would need to be stronger or smarter than the rest and willing to be dominated, it will lack any sex because it wouldn't be needed. It will be a cheap organism with short lifespan that clones itself in great quantities, would be the perfect tool for everything.


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