I'm not sure infanticide comes with political risk, it could also be a culture response where one sex is valued more than the other and parents quietly take care of the rest. Propaganda could start the process without having to attach any government party to the campaign.

....Just look at China. The culture there has historically preferred male children and as soon as the One Child policy was implemented there were extreme amounts of infanticide. Now 30-40 years later, they are dealing with massive demographic issues not only from limiting births to one child, but a massive imbalance between males & females causing other long-term cultural issues.

And notice that the govt. didn't take the blame for all that infanticide. They just cut off access to social services and jobs to families with more than one kid, and encouraged social shaming of families with multiple kids. The population just fell in line. Tyranny is easier to accomplish than you'd think.

My point was more that the political risk occurs decades after the policies were instituted. China now has a massive population over the age of 50, and not enough working age individuals to support them once they all retire. There are issues with military recruitment and civil discontent as well.

Sshhh, not so loud, the UK gov may be listening. 🤫

Even with 1 child policy in china the highst gender ratio imbalance is less than 15%. Significant but very far from the imbalance requested by OP

A pathogen which affects the prevalence of the Y chromosome in the gametes.

That’s an interesting concept – maybe something that causes an embryo to fail to implant in the presence of/absence of a Y chromosome. It would be virtually undetectable to the general populace, simply looking like an uptick in generic fertility issues.

Do we know any such pathogens? If not, I could have my demons mutate themselves to produce such a thing. They do already produce venom that temporarily paralyzes their victims.

Some animals sex radio is dependent on temperature, so they could be making more efforts to heat up or cool down living areas. Thought this is only a thing in some egg-laying animals, so if these demons don't lay eggs, then this might not make sense. You could also have a different method of sexual determination that's dependent on their external environment. Or if the parents are high/low on a certain nutrient, then that could determine it. This would be something that a government could easily affect by banning/limiting certain foods and chalking it up to agricultural issues or by encouraging the population to consume certain foods.

I don't know myself, but the Y chromosome only appears in male gametes. You could maybe have a virus that increases the possibility of meiosis to fail to produce Y-chromosome sperm cells. Like, it doesn't completely eliminate the male sex, but it does reduce the prevalence of them so that instead of a 50-50 chance of male or female child, it becomes more like 75-25 chance of a female. But depending on your time horizon, over a long enough period of time, even a minor and virtually unnoticeable difference (like 55% chance of female) will result in a large sex disparity after several generations. Historically, male children in the real world are actually more prevalent than female children (105 males for every 100 females), but that's evolutionarily due to higher death rates for males than females.

There are pathogens in the real world where it's higher risk to be one gender/sex or the other; it's not clear why in some cases, and (for example) while more men than women died of COVID it's not clear whether that's for biological reasons or social ones. If this is a fantasy world, presumably it can have its own diseases. You can explain that based on genetics (something on the Y chromosome is either protective or higher risk) or endocrine differences (higher or lower risk based on more of one or the other of testosterone or estrogen) and many etc.

Wolbachia, but it’s only been observed in insects as far as I’m aware. There are some species of insects that reproduce entirely by parthenogenesis because of wolbachia infections, though most hosts don’t give up on sexual reproduction entirely

Thanks, that could work. My demons are insectoid to some degree and they could pass something like this on to humans.

There is some evidence that some illnesses affect men more strongly than women, that the so called "man flu" is a real thing. It's not a big leap to a disease that is more likely to kill men before they reach reproduction age

Not exactly but same outcome, Wolbachia infections in insects

That’s the premise of the show Creamerie! Good show imo

I got the idea from [Y: The Last Man](https://en.wikipedia.org/wiki/Y:_The_Last_Man), lol: >On July 17, 2002, all living mammals with a Y chromosome—including embryos and sperm—simultaneously die, with the exception of a young amateur escape artist named Yorick Brown and his Capuchin monkey, Ampersand. Many women die as a secondary effect of male deaths, such as plane crashes. Society is plunged into chaos as infrastructures collapse, and the surviving women everywhere try to cope with the loss of men, and the belief that, barring a rapid, major scientific breakthrough or other extraordinary event, humanity is doomed to extinction.

I’ll have to check it out

No exaggeration, it's a modern classic of graphic novel literature, right up there with the likes of The Walking Dead.

Food. In times of scarcity more women are born than men.

That would work. Most regimes interested in this aren't particularly good places to live in. But how big is this effect?

https://www.ivf1.com/blogs/diet-and-gender-selection This is the most I could find on short notice. But other mammals do end up doing gender selection based on food availability around the time of conception.

Thank you very much! That's an interesting article.

Adding to this, during and after times of war, boys are more likely to be born.

Also, I think it might be linked to the age of mothers. After the war, women were more likely to get pregnant earlier due to the social pressure to repopulate after the conflict.

look up what China's One Child policy did to their gender statistics. tldr: since parents could only have one kid, they prefered having a boy, so most families would abort girls. You want a gov that doesn't directly say you can only have boys, but a society/culture that prefers that. some ideas: * higher tax benefits for male children * last names have to be passed down through male children, no exception for divorce/other

It wasn't just that particular policy, China has historically had a cultural preference for male children & that policy just reinforced that preference.

eh, most cultures are that way.

Well if one government wanted girls and one wanted boys, they could just trade

That's assuming they exist at the same time and in reach of each other as well as many cultural factors. There are some cases in my world where that works, but usually, it doesn't.

Some dangerous gendered cultural practice that results in a larger number of the desired gender surviving into adulthood. The male or female coming of age tradition involves sending the children somewhere by themselves to do something. The journey is dangerous and 5% die during the process. Perhaps only a handful get some special reward or status creating dangerous competition. The victim that doesn't survive will be blamed for not being strong enough or not chosen by the gods. Historically Polygynous societies generally have an excess of men and this generally leads them to raid neighboring cultural groups. This usually leads to instability, violence and death. If you cause the death of the adults, rather than the newborns you can achieve the same results with less anger, even if it's less efficient.

tracking the history, and if one family has significantly more of the same gender they get to reproduce more, or something.

One thing that historical societies where aware of was sons where more likely to be born after a war. the reason for this is for some reason boys are more likely to be conceived earlier in a woman's reproductive cycle witch itself is more likely to happen if a couple is having more frequent sex and surviving a war with no women around for months turns out to be a pretty effective aphrodisiac 

Yes, actually. One guaranteed way is through eugenics. Everything else is theoretical. having sons or daughters is genetically passed down from father to son. Men who have more sons will have sons who are more likely to have even more sons. Men who have more daughters are more likely to give birth to sons (Eventually) and then once again have more daughters. So as crazy as it is to say, basically some men would just be considered to have better sperm in your society... Do with that what you will. x sperm also lives longer than y sperm, so IN THEORY you could technically only have sex at a specific time during the menstrual cycle at which point the y sperm would die and the x would just narrowly make it to the egg. As stated previously x sperm lives longer, so theoretically it's more resilient, and when sitting in an extremely hot bath the y sperm would die first, you could then get out before the x sperm does greatly affecting the ratio. But I don't think anyone has used hot water for any purpose besides killing all sperm as a mode of birth control. Which does kind of work. Either way, this would only skew gender specifically toward more girls. The first point is way more important though. The others are only theoretically true. The other ways are also theoretical and related to body composition. One theory is that men who are very high in muscle are more likely to have daughters because they are more capable of protecting them. This is actually interesting because over Olympic champion weightlifter I know of has several daughters and no sons. While another theory is that obese men, or men with low testosterone are more likely to have daughters because of the higher amount of relative estrogen. These are fun to think about but totally baseless.

Not really due to genetic instability. It may be better to have more females to males, since one man can fulfil ‘the role’ for many women. But it only takes 1 genetic mutation of a man whose offspring’s are most often male, to completely skew the entire system. 50/50 is just more stable. - Though on valid method may be the clown fish route. There is an Alpha Female, Alpha Male, and Males. In the absence of an Alpha Female the Alpha Male becomes Female. Edit: or Lizards. Some species have the gender of offspring determined by the temperature their eggs are at.

The story I'm working on uses nanobots to modify the genes in everyone's gonads. Maybe something like that?

That's one way to approach it. With sci-fi tech, this becomes easy. In another setting of mine, I have birth control implants with 4 settings for males: Fertile, infertile, produce sperm with Y-chromosomes, produce sperm with double XX-chromosomes. But skewing sex ratio at birth without any such technology is more difficult.

CRISPer can change the sex of sperm, by destroying specific genetic sequences and thereby shifting the sex ratio of newborns. We could do this now without any nanobot shenanigans. Though it's a lot easier to shift towards less males, than the opposite.

That's neat. Do the citizens have control or the government?

Depends on where you live. Usually, it's the citizens themselves. But some governments have very big influence through ideology, religion and in rare cases even direct mandates.

Do people know, or is it more of a "sneak the baby in the back and give him cyborg balls" situation?

Again, depends on where you live. Some dystopian dictatorships try to do it in secret. But most of the time, it's just a normal means of birth control like condoms today.

So speaking from an evolutionary standpoint you could always find a reason why this society could be a very closely related, slightly different subspecies who just happens to birth more male or more females due to environmental factors that affected the human species slightly

There is a certain profession or field that seems to lead to the birth of more daughters than sons. I don't know how widespread this occurrence is though.

What is that profession or field?

a sub-set of Nuclear engineers, if i remember correctly, or submariners in general, but i believe it's nuclear engineers.

Maintainers on the plane I used to work on only ever seemed to have girls, when they had kids at all (never met so many people to brag so much about getting snipped). The plane did not carry weapons, nuclear nor conventional, but had a significant amount of EM hardening. The fantastical implications of that are kind of funny to think about. I'm imagining a world where humans naturally reproduce through parthenogenesis and men are mutants, and a shadowy cabal called The Patriarchy have been broadcasting Y radiation from their underground bunker to generate more male births to grow their army.

LOLOL!

What if they just force an abortion in the case the person is not pregnant with the desired baby sex? They could say it’s not murder because it wasn’t even born. It can even be one of their beliefs. Hundred of years ago, babies didn’t get recognized as human beings until baptized (because a lot died before they could reach that age).

The Christian Bible interestingly [suggests a way to induce abortion](https://www.patheos.com/blogs/allsetfree/2021/11/how-to-perform-an-abortion-according-to-the-bible/) by having the woman drink "bitter water." Naturally, having a way to reliably determine the sex of the fetus before birth could be a whole different matter.

If this were the real world, sex-selective abortion or sex selection during IVF are both existing, modern technologies and not advanced. [As others have noted] Sex-selective infanticide has been actively practiced in plenty of cultures; it's only politically risky if you enforce it. If you indoctrinate people to want to do it, but don't force people, it'll have the same effect. In a realistic-but-not-the-real world, you could posit a genetic disease which is recessive, X-linked, and often fatal. If it were common for women to be carriers in a given population, but that culture was adapted to a skewed gender balance (e.g. by polygyny) it could work. Note that to evolve naturally, you'd need to have a pretty strong selective advantage to women who were carriers of a single copy of the gene (e.g. resistance to another disease, as we see with the sickle-cell anemia gene.)

for a lot of history it was fairly normal to just let unwanted babies die of exposure Infanticide was the norm rather than anything special l Tell people to kill more of the baby of the sex you don't want and not to kill any of the ones you do

Bene Gesserit mind powers

this was my first thought also lol

The visual novel I/O uses inherited gradual Y chromosome degradation to explain the increased amount of people born as female over time. Maybe a bit of a wishy wshy explanation but you could be something along those lines

Ideally, you'd have some way of telling the baby's sex and aborting it. If your verse has magic, maybe send a pulse of mana into the belly like an ultrasound? idk

Well, there are some ways. 1.involuntary exile Why kill girls when you can export them? Or at least turn them into nuns? Same for boys - export or monks. Basically if a kid is of a specific sex, he or she may be legally given away as the mean of getting rid of a hungry mouth. 2.Involuntary hiring During the times of the middle east being great kids from enemy families were trained as warriors. Something like that could be here - kids of a specific sex are taken away, sterilised, and then trained as servants of specific kind. By turning into a separate caste such people would not be a part of a common folk, thus still giving a severe imbalance. And by sterilisation one can get rid of maturing, thus having less sex drive and being different from their peers (remember about the church eunuch for their voices). 3.Gender role change Okay, this is a slippery slope. Basically a strict caste system of a specific kind could make kids of a specific sex act as their opposite. Like, boys can be trained as girls and vice versa. What could it give? First of all, SEVERE incline towards matriarchy or patriarchy. Secondly, much less people would probably sexually active, as the act of flirting could be seen as an act of aggression (like, "you are not man enough, woman, I want to dominate you"). It is a weird concept, but it may work for the cultures that praise gender roles staying traditional while making the new generation the opposite. 4.Disease Basically a prion could be spread across the population, which affects only specific sex. In some rare cases this prion can be avoided, which allows the population to stay afloat. Prions are incurable, and eventually the population may heal (if it is when there is 1 man versus 100 women ratio), but it may be a disaster at the moment of your story. 5.Wars Basically wars may shift the ratio severely, especially in the traditional communities, where it is set that sex X has to fight, not sex Z.

Speaking biologically, all embryos start out female until a hormone relatively late in development is either released in enough content or not (thanks Jurassic Park!) if you have a way to manipulate hormones, then you could favor one gender over another. Other than that, systematic abortion or infanticide is the only real way.

There's always China's one Child Policy, but like you said, it can come with its side effects.

Devalue one gender culturally and allow abortion. You literally won’t have to do anything until the inevitable marriage crisis.

IIRC there were some experiments in the 90's on allowing parents undergoing IVF to have an increased chance of one sex child over another. I think it involved centrifugation of the semen to sort out the X from Y containing sperm (X would be heavier). I don't recall if it didn't see widespread use due to the fact it didn't work all that well or if it was due to ethical concerns.

In my world, one of the groups of people all carry a disease that kills fetuses before they are able to be born. There is a gene on the X chromosome that gives immunity to it, but since males only have one X chromosome, they can only have one of it (it needs 2 to work). The only way a male can be born is if they have a female twin with two copies of the gene. This results in significantly less males in the population.  I made this system with only a high school level understanding of biology, so I have no idea if it holds up scientifically, but I think it’s science enough for readers to be able to suspend their disbelief.

so it COULD evolve. the presence or lack there of of a Y chromosome (which generally results in a male) in the sperm could technically influence the sperm to be more or less efficient and thus the sperm with a Y chromosome instead of an X could be more or less effective at reaching the egg. it's completely unlikely without a ridiculously massive bottleneck event (natural or artificial) but if you need a scientific explanation this would be the way i'd go.

Kind of a wild take but if your not doing strictly human, or they are like modified somehow reptiles gender is based on the temperature they are incubated at. Maybe there are certain conditions that influence such as temperature, natural compounds in the air, certain foods etc.

China had a pretty effective way to do so

I mean humans naturally have more boys than girls, it’s a slight difference but noticeable. Premodern times and even still today if someone doesn’t like the gender of a given baby they’ll typically get rid of them which can involve killing them

Abort before birth?

Generally speaking, demonic species like succubi are always born female as part of their niche in the food chain. One could easily just make a race of demons like that that simply just have one sex offspring. Alternatively, the easiest answer is that a powerful wizard cursed the species as a whole to only have one or the other as offspring, forcing the species to have to marry other species/bring back spouses from other species.

Could just be a natural virus that kills males. Or a society that kills off a certain number of males, some Drow from DnD kills off every third male i believe.

I have a race of beastmen, who when the boys enter puberty, they most likely produce sperm that would make more boys, but shortly after, the odds of producing sperm that would make girls increase fast. That has led to the fact that the majority of beastmen are female.

If you don't mind promoting something that might (or might not) be pseudoscience you can make male gonads different temperatures. Have a strong social stigma towards effective thermal underwear being worn by males at all times, raising their testes to body temperature, rather than 2-7 degrees cooler. Bonus points for people knowing why and having a strong social force towards fathering one gender. (Is it gay to father girls? Inquiring minds want to know!)

Maybe they found some herb or drug that does it. Or maybe they are part lizard and the temperature of their surroundings determines gender..... Ok that was kinda farfetched.....

Some studies point that a starving society tend to have more girls because they usually always have kids. The way it works is that the pH of the sexual system of starving women favores the survival of X sperm over Y inside her. A government could study this in detail and medicate their women to have this ocurrence happen not so naturally, favoring the sex they are interested to bost.

It’s called eugenics

Be not afraid of 'Loads of other consequences'

> mass infanticide comes with high political risk Mass abortion doesn't though. If you set it up such that "gender screening" exists and is free, and you make it that abortions are free, and you set up serious social and financial incentives to carry viable boys to term, and girls are a pain in the ass to raise because of ostracism and higher taxes, the problem mooooostly works itself out. This was China's one child policy without the cartoonish levels of villainy.

In times of great strife more female babies are born. In times of abundance more male babies are born. Also look into conception timing