This idea came to me after reading up on the relationships of the prairie vole and the research done into why monogamous pair-bonding occurs. What I'm looking for in my story is biologically enforced sexual monogamous pair-bonding, and how science could stop it. People in pair bonds do not have to be in love, and in fact being pair-bonded does not mean you will love your partner necessarily, only that you are only sexually attracted/can mate with them. (for more context on the worldbuilding, look to the end of the post)

The Research so far

So the closest animals I could find that were sexually and socially monogamous seem to be the prairie vole's. One article has this to say about biological reasons for what causes the pair bonding:

Several studies have now demonstrated that oxytocin plays a role in the development of the pair bond in the female prairie vole. Injections of an OT antagonist, a drug that blocks activation of the OT receptor, directly into the female prairie vole brain prior to cohabitation and mating inhibits the subsequent development of a partner preference (Insel and Hulihan, 1995). Some studies have suggested that OT's role in partner preference formation is specific only for females, while other studies have found similar effects in both sexes (Cho et al., 1999). However, in males there is clear evidence that the peptide arginine vasopressin (AVP) plays a significant role in the formation of the pair bond of the male for its mate.

I'm not a biologist so I don't really totally understand everything in the linked article, but essentially what I got out of it was that mating between two specific prairie voles lead to changes in their brain chemistry - the release of OT and AVP - while around their preferred partner. Essentially 'love is a drug' and this causes them to seek out that preferred partner who gives them more OT or AVP. This is more 'emotion based' than I am looking for, but I think it's a good start maybe?

I'm not sure if prairie voles can be considered entirely sexually monogamous, however, as there have been studies that prove the genetic offspring is sometimes fathered by a male outside the pair bond:

For biologists, monogamy implies selective (not exclusive) mating, a shared nesting area, and biparental care. In recent years, genetic analyses of offspring have provided evidence for extra-pair copulations even among species thought to mate exclusively monogamously.


The incidence of sexual monogamy appears quite rare in other parts of the animal kingdom. It is becoming clear that even animals that are overtly socially monogamous engage in extra-pair copulations. For example, while over 90% of birds are socially monogamous, "on average, 30 percent or more of the baby birds in any nest [are] sired by someone other than the resident male."

Based on this, I'm not even sure if there are any existing species that are entirely sexually and socially monogamous. If there are and I just haven't found them, please let me know (if there's research on it anyways) what allows them to be sexually and socially monogamous on a biological level. Additionally: how could such enforced monogamy be broken with science?

For more context, this is my worldbuilding that I'm trying to back up with science:

World has late Victorian/early Edwardian era level of technology and scientific advancement (if needed I could come up with some reason they have more advanced science though). The people are essentially humans except for the changes needed to be made for sexual monogamy/pair bonds to work (aka if I need to give them the ability to smell pheremones or something I will but otherwise they are just human). All men and women are thought to be 'incomplete' before they bond with someone, as the Creator made men and women together as two sides of the same coin/soul but seperated them at birth. Only once they become one once more are they 'whole.'

As soulmates are 'ordained by the creator' only the church can know who is truly meant for who, as they are the voice of the creator. In reality bondings are done for political or socio-economic reasons, though there is a lot of romanticisation of 'falling in love at first sight' like in our world. (fun fact: the church is always lead by a pair-bonded priest and priestess. They give up any children they have to the church to become men/women of the cloth where they are raised communally. There is no prohibition of sex or having children within the church.)

Bonding happens upon consummation of a union (sex/mating) and from that point on it is impossible for the two to have sex with anyone else - meaning they will not be sexually aroused by anyone else or physically attracted to someone else and cannot bond with someone else. It does not mean that they necessarily will be attracted to the other person, only that they can only be attracted to them. By this I mean that men can still have ED and women can still not have fun in the bedroom if their bonded sucks at sex. The only way for anyone to bond with someone else is for their bondmate to die.

The story is about a woman activist who finds herself in a very unhappy bonding and wishes to find some way to break it without killing her bondmate and going to jail for murder.


  • what biologically could cause complete sexual monogamy within a pair-bond? I'm not looking for cultural norms, but rather a biological reason for why a bonded pair would only be able to mate with one another after having sex.
  • what scientifically could break or reverse such a biological pair bond?

Bonus points for helping me with these questions too:

  • whether pair-bonding has to be tied to orgasm during mating.
  • how this biological pair bonding would affect sexual aggression.
  • how this biological pair bonding would apply to LGBTQ attraction.
  • $\begingroup$ Im unsure how one aspect of this works. At one level you want it biological - once bonded they are stuck with that as their only sexual partner, until that person dies. Then they find themselves able to bond with someone else. On another level, you want it that being bonded doesnt mean having sex or intimacy, so they can leave or separate any time, it just means they cant have sex with someone else until the bonded partner dies. So my question is, those seem to.contradict. How do you want it to work, if they are separated, or out of touch a while (whether separated or just away from home)? $\endgroup$
    – Stilez
    Aug 13, 2021 at 6:16
  • $\begingroup$ Example scenario: John and Jane are bonded but never ever touch, or even stay in the same house/room. They barely talk. John stays at home, Jane goes on a years cruise. John is in an accident 3 months into her cruise (while she's at sea) and brain dead in a coma; he dies a month later. Jane doesn't know, because she's separated and doesnt talk to him. On holiday, Jane meets a nice guy and finds herself wanting to have sex with him (whether in month 1, month 3 or 4, or month 12, or on her way home). At what point should she become able to do that, or bond with him, as you see it? ..... $\endgroup$
    – Stilez
    Aug 13, 2021 at 6:16
  • $\begingroup$ ... Would the answer change if she knew sooner? Or never heard? Or isnt it about when she hears? What happens if she believes him dead but miraculously he wasnt? $\endgroup$
    – Stilez
    Aug 13, 2021 at 6:39
  • $\begingroup$ You specify humans, but if you look at other species, all sorts of fun stuff happens. When a male angler fish mates with a female, it literally becomes part of her body. $\endgroup$
    – Cort Ammon
    Aug 14, 2021 at 18:37

7 Answers 7


Warring parasites in sexual fluids

Each person is host to a unique parasite on their genitals. When a couple has sex, the fluids transfer some of this parasite to their partner.

One male parasite and one female parasite (probably different species) will happily coexist. However, if a man hosting one female parasite is exposed to a different female parasite, the two engage in chemical warfare that produces intense genital pain for the man. And similarly for women. People learn very quickly not to cheat.

These parasites can’t live forever on the “wrong” host sex, though, so if your bonded partner dies, their parasites on you eventually die too (during the cultural mourning period), and then you’re free to bond with someone new.

Science addresses this with medication that kills the parasites, or at least reduces them to a population level that isn’t painful, allowing you to boff whomever you want.

Bonus questions:

  1. Orgasm means more/different fluids, or if you wanted orgasm to be mandatory for bonding, parasites are only transferred in those fluids, or there’s some reaction to OT/VAP that triggers them to stick around.
  2. If OT/VAP is needed for the new host to be attractive, then a male rapist would be bonded to his victim, but the victim wouldn’t be bonded in return, which seems fitting.
  3. LGTBQ bonds would require a much more complicated system, or perhaps changing from male/female parasites to a system of repeated exposure to make bonding happen: any two parasites will accept each other but will jointly fight a third.

If you want the church to control all bonding, then make the parasites attack any foreign parasite unless some special holy oil is present, which is applied by a priest to the genitals of a newly bonded couple before they consummate their bond. That would also solve the LGBTQ problem, but it rules out the parasites having evolved naturally along with the hosts.

  • $\begingroup$ How do you get infected with parasites? $\endgroup$
    – Otkin
    Aug 13, 2021 at 2:02
  • $\begingroup$ If you're bonded but not having sex, how do parasites "know" when to due off, when partner dies? $\endgroup$
    – Stilez
    Aug 13, 2021 at 6:00
  • $\begingroup$ @Otkin My basic idea is that the wild version of the parasite is ubiquitous in the water, and when a person with no parasite first bathes, they get infected and the parasite begins to adapt to their unique chemistry—and repels new infections from the wild variant. $\endgroup$
    – StephenS
    Aug 13, 2021 at 13:05
  • $\begingroup$ @Stilez If you go a year or more without sex, the relationship is dead, even if the people aren’t. $\endgroup$
    – StephenS
    Aug 13, 2021 at 13:08
  • $\begingroup$ Not at all, tons of relationships become platonic. Often happily so, over time, as dynamics and directions change, and quite often as a relationship deepens, not breaks. Of course in this world, who knows. But in the real world, thats pure inaccuracy $\endgroup$
    – Stilez
    Aug 13, 2021 at 13:27

Fluids and immunity

People can feel attracted sexually to anyone of the opposite sex, but only up to their 1st mating. They will then develop immunity to proteins in the fluids of each other.

After that, having sex with someone else is like exposing yourself to a variant of a virus that you've already develop immunity too. Fluids are as specific as the cell markers for bone marrow transplant. Mating with someone other than your spouse will get you sick, and possibly fatally, unless you had sex with their identical twin. Over time evolution favors the monogamous, so the drive to maintain a partner is instinctive and completely neural. Some people do fornicate outside the pair but they get sick and die.

Science resolves this with a broad spectrum vaccine (fluids from lots of people mixed in a vial for innoculation) which when applied prior to losing virginity maintains the ability to be attracted by multiple people. The church is going to flip when they find out.


It Always Hurts the First Time - Both Ways:

My solution sounds radical, but is completely plausible. Male gonads are detachable, and implant in the female. Unbonded males and females are sexually attracted to other singles, but once they have sex, the male gonads implant in the female and produce pheromones. Other males are repelled by these pheromones, but the male who's gonads are implanted find them irresistible. Females with implanted gonads only become aroused after sex starts, so they will only have sex with their specific male because he's the only one that finds her attractive, and she's unaroused by anyone before then (very Victorian).

The female doesn't need to have sex to have children anymore (she's got a set of male gonads in her), but the male stays with her protectively because of his compulsive attraction/arousal around her (assuring her survival and that of their offspring).

As to how this affects homosexual relations, it is up to you. It would be likely that prior to first mating, they could mate freely (depending on how it was handled - male on male prior to first mating might be strange). After mating, males and females with mates would be able to have sex with other people, but only in the presence of their mate (so threesomes and maybe foursomes would be possible). Again, depending on how exactly the female arousal worked, it might require insertion or not, and females would not be excited until they already had sex.

For Victorian technological levels, reversing this is complex but possible. Removing the male gonads from a female without sufficient surgical skill was lethal, but advances in medicine finally allow a female to be unfertilized (surgically or by the discovery of a drug that causes her immune system to reject the gonads). The female would thus stop repelling other males, and the gonads would stop suppressing her desires outside of sex. The male might regrow gonads after a sufficient time not having sex with his partner (to simulate a widower being able to remarry), or the gonads might be able to be sewn back on to the male. But in this case, the similar operation (call it a stitch-job) prevents the gonads from releasing into a new female, allowing the male to continue seeking a mate indefinitely.


Psychological imprinting

It’s no different than baby chicks that associate the first thing they see as their mother. The instinct is already there. I would probably go something like this; person one cuddles and shows signs of intimacy to person two. If person two reciprocates the action a switch is flipped in both of their brains that marks the other person as their partner for life. Once bonded the affected person can still like other people but can never feel a romantic or sexual love towards them. If the person tries for some reason they’ll feel intense disgust and be forced to stop. So basically the limbic system (emotional center of the brain) is affected and handles this like every other like and dislike matter.

The thing you’ll have freedom with is what happens if the two get separated in a way or another. Swans are famous for killing themselves out of depression when losing their partner or their eggs. So what would happen if a pair was appart for a long time and one was told the other was dead? Whatever suits the story, but you’ll probably want something that ups the stakes. There’s also the unexplored territory of what happens when someone severs the bond and goes on to be with someone else.

To forcibly disable the instinct I would suggest a form of risky chemotherapy to remove the marker from the limbic system. The risks may include many clinical manifestations, such as epilepsy, limbic encephalitis, dementia, anxiety disorder, schizophrenia, and autism.

  • $\begingroup$ This was my first idea, too. Psychological imprinting is the easiest explanation and all mechanisms already exist in reality. $\endgroup$
    – Otkin
    Aug 13, 2021 at 16:25

I can't give you the level of science you're looking for, but...

The relationship between the voles can be described as addictive. It's been seen before in SciFi: in Frank Herbert's Chapterhouse Dune. In that story the Honored Matres, a deriviative of the Bene Gesserit Sisterhood, come back from the great scattering. They've lost some of what the BGs had (and want it back!), but they've replaced it with other things. Among them, sexual enslavement.

Like all good writers, Frank Herbert didn't spend a lot of time on the biology of how the addictive relationship was formed. I'll be honest with you, unless you have the necessary college degrees to really understand a fully scientific answer, it won't really help you. You won't know how to use the information you've been given in a way that would help you sound any more credible when you write your story. I'm not trying to be mean! I'm just pointing out a reality. Unless you want to become an expert in the field, you should seriously consider what Frank Herbert did: not explain it and move forward.

Having said that...

What Herbert explained in his book was what that science article described about the voles... only on super steroids. If you think about it, he had to do that. Humans can reason their way into and out of pretty much anything. Take my grandfather (rest in peace!). He smoked every day of his life since he was a teen. In his late 80s he was told by a doctor he'd die in six months if he didn't stop. He stopped. Right then and there. And lived for years.

Humanity's divine gift of reason means no simple chemical bond will fully explain an entirely monogomous relationship. Or, said another way, those voles don't really have a lot of choice in their lives. It's not like there's newstands with vole porn on street corners and vole hookers on the other corners. A simple chemical addiction can keep them permanently pair bonded.

But humans can't... unless you introduce an idea like Herbert did. In his case, it was basically "super sex" so intense that the chemical wash resulting from orgasm caused an unbreakable addiction to the partner. You couldn't be satisfied with someone else. You had to go back, again and again.

What I recommend you do...

You have all the tools you need to solve your problem already in a wonderfully artistic way. When the time comes in your story to explain why the forced monogomy exists, use a "practiced in the art" medical professional to explain it to someone who is not practiced in the art (like a journalist) — and have that person literally say, "you know, it's something like what you find in voles... the bonding experience uses a natural form of oxycotin that creates an addicted co-dependency that forces the pair together. It's a lot more complex in [our species], but it's basically the same thing."

And when the time comes that you explain how the dependency is broken, you can reverse the explanation by describing how people become unhooked from drug addiction.

That might not be the answer you were looking for, but considering how few of your readers will appreciate any greater detail (indeed, considering how many would become bored reading any greater detail...), I'd like to think it's good advice.

  • $\begingroup$ I get what you mean by not over-explaining in detail, but I also think it has to be a bit more complicated than just 'it's an addiction' and 'withdrawal' as a solution to break the bond. The reason being that it'd be very, very easy to realize that the bonding is not actually permanent/given by god every time men went to war or away for long periods of time, as it would 'break' the bond through withdrawal. $\endgroup$ Aug 12, 2021 at 22:30
  • $\begingroup$ @TeannaSchmaeh Worked for Frank Herbert... next reboot of Dune coming out this year. I'm just sayin'. :-) $\endgroup$ Aug 12, 2021 at 22:36

It's all in the mind...

Let's start with :

whether pair-bonding has to be tied to orgasm during mating.

Psychological bonding without any sexual intimacy is arguably stronger than any sexually-based bonding. People can be made to be extraordinarily loyal to another person and this fact is often used by the more manipulative people in society to keep people loyal to them, including their mates. We also see this happen with cults as well. Sex is used to augment/compliment psychological bonding in this context.

People can have quite miserable and downright unpleasant sexual couplings with a partner they are otherwise devoted to. It just isn't as simple as sex cures all, and I would suggest it's often the case that sex can break a relationship, not make it.

how this biological pair bonding would affect sexual aggression.

Hard to know what you mean by "aggression" here. If you mean aggressive sexual behavior then some people engage in that and it it does not necessarily improve or damage a relationship - it is very dependent on the details of the people involved. Nothing really changes in the context of "chemically" bonded people, except that it could result in increased levels of violent sexual behavior, as one party (or both) cannot stop being a willing victim.

If you mean aggression in the sense of aggressively seeking other partners, that can happen even in relationships where both partners are very strongly bound. It is typically destructive. What would happen is your scenario would be that the aggression is focused within the single relationship, leading potentially to more extreme behavior by one or both parties.

how this biological pair bonding would apply to LGBTQ attraction.

No differently from heterosexual couples. It's the same process.

what biologically could cause complete sexual monogamy within a pair-bond ? I'm not looking for cultural norms, but rather a biological reason for why a bonded pair would only be able to mate with one another after having sex.


The problem is that you would no sooner create such a mechanism that someone would figure out how to bypass it. It's what humans are good at.

what scientifically could break or reverse such a biological pair bond?

The mind.

What the mind giveth the mind taketh away.

You can use psyschology (and maybe a bit of chemistry to help) to bond people, but the problem is once you stop manipulating them they tend to revert to type. Even if that doesn't happen someone else can break the bond using similar techniques.

In a long recorded history no cult, politician, military leader or religious leader has succeeded in stomping out adultery. The Great Augustus tried (on penalty of death, IIRC) and failed. Religions tried (penalty of all sorts including death and eternal damnation - a thing people at one time feared more than death) and failed. Cults ranging in size, sophistication and scope tried and failed.

Call in Marketing, forget R&D

To actually do this would require completely robbing people of their free will. You mention not relying on cultural norms, but in practical terms cultural norms are much better at enforcing monogamy than anything else. No system is 100% perfect, but I think cultural norms are more successful than average. With cultural norms you can get people to do things that you would consider unthinkable. It was at one time culturally normal to put people in an arena and let wild animals rip them apart - and that's the tip of the unpleasant iceberg for the dark side of cultural norms. Today we have so-called "honor killings" for the sake of what some people consider cultural norms or pressures. Don't ever underestimate the power of cultural norms to make people do and endure extreme things.

It is basically trivial to create a society where cultural norms make staying in a loveless or sexless marriage common and where transgressions are treated are crimes. It is, by comparison, beyond our current science to even guess how you would impose such behavior on people using chemistry - we don't even know what buttons you need to press.

I can't imagine a mechanism you could come up with that didn't amount to basically discarding the entire personality and replacing it with something else. Any chemical mechanism could fail, become tolerated (and ineffective) over time, or have long term side effects that were worse than the disease, as it were.

So if you want to manipulate people on a grand scale, don't call R&D, call Marketing.

Every Doctor Evil needs a marketing department.


She keeps his balls in a jar

The first time a male and female mate, the male transfers his testicles into the female's body instead of ejaculating just the sperm. This would be a completely separate event from a normal orgasm as it would be a once in a lifetime thing that seals thier bond. From then on, the female's body sustains the testicles inside of a specialized organ (which we will call her jar from here out) for the rest of her life. To ensure monogamy, once the woman has the man's testicles it provides her body a pheromone that is exactly keyed to the man's physiology. This pheromone makes the woman repulsive to any man who it does not match, and attractive to the man who the pheromone belongs too.

Furthermore, once a woman has his testicles in her jar, she would likewise lose all sexual attraction to any man who does not match the hormones they now pump into her body.

From this point on, when they have sex, the man does not ejaculate any sperm, but he does ejaculate an activator hormone that signals the testicles to release sperm into her body. Even in extreme cases where the female does find some other guy to copulate with despite natures attempts to make them chemically repulsive to each other, the woman could only ever have the 1st man's children because the jar seals up once it has some testicles in them.

How to break or reverse such a biological pair bond?

The only way to break the bond would be to surgically remove the testicles from the female's body. This would make breaking the bond far more difficult than just choosing to, but rather it would REQUIRE significant scientific intervention.

How does it affect sexual aggression?

The prominent theory about why humans experience sexual aggression is because of the role cuckolding holds in selective fitness. A man can only produce enough resources to support so many children. Being cuckolded means you will limit your number of offspring because you are wasting resources on someone else's offspring and cuckolding another man allows you to save resources on reproduction and have more children than you can support. Because of this, letting another man have sex with your partner is much the same as letting him murder your children (evolutionarily speaking); so, we have evolved to be aggressively protective of our mating rights.

But, if your mate could only ever have your children, this would mean that no matter what she does, she can never cuckold you. With this out of the way as a concern men would no longer have a reason to fear or be angry about his mate having relations with other men; so, sexual aggression would be virtually non-existent.

How does this affect LGBTQ relationships?

In a since, LGBTQ can be described as various kinds of failures for nature to create selectively fit bonds based on pheromonal/hormonal paring. But in this world, we get a whole new dimension to the sexual orientation spectrum resulting in things like men who are only attracted to women who are paired to other men, men who are repulsed by the woman they are paired to, paired men who are only attracted to unpaired women. Paired woman who are only attracted to unpaired men. So on and so forth... so this system would allow for all of the normal atypical relationships we have in our world, but also opens up a ton of new ones as well.


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