Note this is postulating that this starts from Stone Age.

'Mate' is defined as penile-vaginal sex with ejaculation.

Requirement starts at puberty. People know when it starts, how long they've got, the general info that this death-clock resets by sex, and they are also killed, via magic. Cannot be circumvented by science. Inter-sexuality does not exist, as I can't figure out how to rework the mating condition to prevent that from being an automatic death sentence.

Each mating gets each partner 30 days of life. Unless it's a woman, whose pregnancy keeps her alive for the whole pregnancy, and 30 days after birth.

Mating with condoms or any other kind of physical contraceptive, grants 1/2 the time to live of the previous mating. Like a 30-day girl and 30-day guy mate, and then they both have 15 days to live, keep doing it, and they could get to a point where they can't mate fast enough to prevent death.

However, non-physical, non-immediate contraceptives, like the Pill, or the rhythm method, or douching, don't shrink the 30-day death clock.

But, Inter-Uterine Implants or any kind of Surgery, do shrink the death clock.

Note that if a male gets a girl pregnant from mating, and they still get 30 days from that mating, but if they mate with her again, on their 16th day, then they just get one extra day of life. So, it's best to space it out farther apart... And there's some math like... 30+15+7.5+~4 +~2 + ~1 = ~59 ... If you time it so they cut it really close, they get a little bit less than ~2 months before they have to switch to a non-pregnant girl.

That's also how it works with normal sex. If you have non-pregnant sex on consecutive days, you keep adding only 1 day to your death clocks. as 30 days from day of last sex is 1 day before the last time. The death clock counts from day of last mating, and resets at each mating.

Also, women don't run out of eggs.

Effects of males mating with pregnant females is the same as contraception-mating.

People can die by injury and illness, but not of old age. Immortality begins at 20, but the 'immortals' are still subject to Mate Or Die.

Infertile people function basically as normal in the universe, as long as males can still ejaculate, and women still have a vagina, so certain injuries will kill by proxy.

Lastly, for now, if you're on life support, you still need sex, or you'll die.

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Tim B Dec 10 '15 at 23:38
  • $\begingroup$ Is it permitted to be monogamous, or must every mating be with a new partner? $\endgroup$ – Mawg says reinstate Monica Dec 11 '15 at 8:42
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    $\begingroup$ Practical note: You should possibly adjust the "30 days after birth" thing. One month after birth the infant is still heavily reliant on the mother, and she may not have fully recovered form childbirth yet. One year sounds way more practical child-rearing wise. $\endgroup$ – Layna Dec 11 '15 at 11:46
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    $\begingroup$ Living through crisis for such humans would be near-impossible. Immortality becomes increasingly less sustainable as partners dwindle. Perhaps the uninteresting, but logical prediction is that beings with such harsh survival requirements would just die out and there would be no "society" to speak of. $\endgroup$ – Epigene Dec 11 '15 at 12:28
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    $\begingroup$ I suggest you read The Left Hand of Darkness by Ursula Le Guin which deals with a similar theme where humans go into oestrus during which not mating is extremely unpleasant. Abstinence is not actually deadly, just unpleasant, but you might get some ideas from it and it's a great book anyway. $\endgroup$ – terdon Dec 12 '15 at 12:50

15 Answers 15


As Samuel stated, society would develop in such a radically different way that it would probably be unrecognizable to us.

I think there would be several major consequences to consider:

Hey there, good lookin'!

People who are poor AND ugly/unhealthy/unattractive will die off rather quickly. A number of ugly women would die, although in fewer numbers. Eventually the human species would become a lot ... prettier.

No longer a taboo

Talking about sex, or negotiating a session strictly as a means for survival would probably become commonplace. Prostitution would become not just a legitimate profession, but probably an incredibly important, respected, and lucrative one.

Family structure

It's been argued that we are not genetically wired to spend our lives with a single mate. This situation would more than likely mean that monogamy would never even arise as a concept, let alone be enshrined in society.

If you examine how deeply monogamy affects our societal structure, and many of our morals, laws (laws to property, for example), etc. you'll understand why this is such a big deal.


The way wars are fought will have changed to a great degree. You need to take carefully plan your supply chain, etc when planning a campaign, but now, in addition to having to pack enough food and supplies, you must also bring an adequate balance of women and men to keep your troops alive for any campaign lasting more than 30 days.


Sexually transmitted diseases would run rampant through the population. Seriously. Rampant.


This situation will more than likely lead to the enslavement of women everywhere, and to their being treated as prized commodities more so than actual human beings.

Additionally, a woman who becomes pregnant instantly loses her value, so forced abortions would also probably become commonplace (with the associated loss of life involved). Being pregnant may very well become something like a faux pas - especially if a woman can't depend on the support of a husband.

Just to add to their misery, sex crimes would likely become completely acceptable. Imagine a man in front of a judge saying:

"Your honor, if I didn't have sex right then and there I would have died, and she wasn't going to accommodate me. I had to rape her!"

Of course, I don't think it would even get to the point where this would become a serious offence. Most likely rape will just become a completely acceptable practice, as long as you're "keep your hands off of other people's property". More of an issue would be made if you got some other man's property pregnant than over the fact that you forced yourself on her.

Furthermore, having no effective contraceptives will lead to a lot of women getting pregnant all the time. This will take a horrible toll on their health, and I can guarantee you that they will die in droves.

Baby girls would be valued above baby boys, with most boys probably being left to die in the woods, or sacrificed, etc. Who would want their sons to grow up only to become their "competition"?

This is just off the top of my head ... I'll think about it a little more and maybe come back to edit my answer, but basically, it would be pretty grim.

  • $\begingroup$ What is considered attractive or unattractive varies around the world, so I doubt the human species would evolve in any particular direction. $\endgroup$ – Mohair Dec 10 '15 at 19:20
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    $\begingroup$ @Mohair - I don't think you realize what the first part of your sentence implies. Yes, societies may have different standards for beauty (as do all individuals), however, it makes perfect sense that looks would improve within any given population based on the situation which the OP describes. Would an outsider consider them attractive? Who knows. But someone who had been around 300 years ago would probably look around and think to themselves: "wow, people we're uglier when i was young!". You make the mistake of thinking of "beauty" in terms of our own modern, internationalized standards. $\endgroup$ – AndreiROM Dec 10 '15 at 19:26
  • $\begingroup$ I am supportive of this answer. However it would become more grim. Everyone has the potential to live forever. You already need to start forcing abortions. For those in power killing others would become common place. If you where allowed to live past infancy you would be judged every year weather you where worth the resources to be kept alive. Check out the movie "In Time" for a similar thought experiment. Oh, and homosexuality would still be around, they'd just have to close their eyes and imagine it was a boy once a month. Wars would be common as rulers throw away life for personal gain. $\endgroup$ – PCSgtL Dec 10 '15 at 20:34
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    $\begingroup$ Note that certain contraception methods don't shrink the death-clock. $\endgroup$ – Malady Dec 10 '15 at 21:24
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    $\begingroup$ "People who are poor AND ugly/unhealthy/unattractive will die off rather quickly. A number of ugly women would die, although in fewer numbers." Um, what? How are women not people? $\endgroup$ – terdon Dec 12 '15 at 12:58

Your world becomes "Abortion-world", "Baby-killing-world" or "Bloody-sex-world".

The core of the problem is that getting all women pregnant means death for the men because of the diminishing returns. This needs to be solved one way or another.

The somewhat gross but non-nightmare way would be for the men to only have sex with the women during their menstruation, assuming they still have one. If this has the same diminishing returns as sex-while-pregnant, it will not work.

The next way is to abort 90% or more of all pregnancies as soon as they are detected. That way things can be back to normal before the men reach 30+15+7.5 etc. days.

The final way is to start killing men, boys and male babies, until the ratio men-women (of age 15+) is about 1:10. Then each man can have sex with one of his 10 wives every 30 days and the last one should have given birth by the time it's her turn again. You can bet that the strongest and most violent men will pass on their genes in this scenario, completely changing their world from how ours developed.

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    $\begingroup$ Note that certain contraception methods don't shrink the death-clock. $\endgroup$ – Malady Dec 10 '15 at 21:24
  • $\begingroup$ You know that women only have a few fertile days per month? You can even calculate them (which is what people did before condoms and the pill were introduced), or determine them by measuring the hormones (which is far more reliable than calculating). $\endgroup$ – Bounce Dec 11 '15 at 10:09
  • $\begingroup$ Modern Age Variant, 'cause I'm bored?: worldbuilding.stackexchange.com/questions/31285/… $\endgroup$ – Malady Dec 11 '15 at 15:01

There's not a lot of mystery here; people would have a lot of sex.

Sex would lose its taboo in society (if it ever gained one). When it becomes as essential as eating, except with even greater benefit, people aren't going to be all squeamish about it.

We'd see a lot more mixing of genders in places like the military, expeditions, and remote postings. We'd have no celibate priests (not for long) and religions in general would look quite different. We'd also probably see a lot more terminations of pregnancies. Since this started in the stone age, human societies wouldn't have anything near the same views as we do on these subjects.

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    $\begingroup$ How come I can't see your edits? Is that a thing mods have? The ability to hide edits so only the final version is visible? $\endgroup$ – Malady Dec 10 '15 at 18:25
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    $\begingroup$ @Malandy I'm not a mod. You can't see my edits, but saw my answer was edited because I changed it within the first five minutes and no one commented. Any edits from here on out will show in history. $\endgroup$ – Samuel Dec 10 '15 at 18:26
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    $\begingroup$ Note that certain contraception methods don't shrink the death-clock. $\endgroup$ – Malady Dec 10 '15 at 21:24
  • $\begingroup$ Modern Age Variant, 'cause I'm bored?: worldbuilding.stackexchange.com/questions/31285/… $\endgroup$ – Malady Dec 11 '15 at 15:01

If this begins in a stone-age society, odds are that everyone would die long before they figured out that having sex would keep them alive.
The first most likely scenario is the extinction of the human race. Congratulations.

But let's assume some shaman or whatever explains it to the tribe and they all start procreating en masse. Within 3 months every female capable of having children is pregnant. Within the next 60 days all of the men die because having sex with a pregnant woman doesn't count. With no more men to impregnate them when they give birth, all of the women die 30 days after giving birth.
Second most likely scenario: The extinction of the human race.

But let's assume there's at least one infertile woman per tribe. (And let's assume the holy so-and-so told them about pregnant math, too, because otherwise we face human extinction.) The infertile woman would quickly become the most popular in town! And the most sore...

So now that we've established a deus ex machina for the human race to survive the "die" part of "mate or die", we can actually talk about the interesting part. FREAKING IMMORTALITY.

Even accounting for disease and war, a society of neanderthals with the reflexes and immune systems of 20 year olds would have a dramatically lower death rate1. Factor in the insanely high birth rate caused by non-stop mating, and you have a population boom the likes of which this world has never seen.

But how much of a boom? Let's play with some numbers. The average population growth rate from 10,000BCE to 1000CE is about .03%, so let's use that number as our control. In 1000 years at .03% population growth, a tribe of 30 would grow to 40.

With an increased birth rate and decreased death rate, we can easily double the population growth rate. In 1000 years at .06% population growth, a tribe of 30 would grow to 54. That's not so bad...

But slightly more optimistic numbers could give us 4x the control growth rate. In 1000 years, at .12% population growth, a tribe of 30 would grow to 100.

But to get more accurate math... The average woman in a 3rd world country today has about 4 children in her lifetime. In your world, since everyone would constantly be having sex and neanderthals were not known for their knowledge of contraceptives, it's likely that women would spend the majority of their lives pregnant, potentially having a baby once every year2. So we would go from 4 children per average adult mating life to as many as 50.... Which would give us 15x the growth rate.

In 1000 years, at .46% population growth, a tribe of 30 would grow to 29843.
It would take a tribe of 30 neanderthals 4,188 years to reach a population of 7 billion. Since agriculture won't be invented for another 30,000 years, I'm sure you can figure out what happens to 7 billion neanderthals competing for very scarce resources.
Third most likely scenario: Extinction of the human race4.

  • 1For the purposes of my math, I'm using a death rate modifier of 1/2. Most of the reason old age kills us is because our bodies grow weaker and more susceptible to disease and injury as we age.
  • 2 In this scenario where everyone's having sex and condoms won't exist for another 50,000 years, the men can easily outnumber the non-pregnant women 10:1. Therefore, we can assume that non-pregnant women would be having sex with multiple partners potentially multiple times per day. With typical human fertility rates, yes, they would be getting pregnant.
  • 3 None of these numbers are really accurate. My math is woefully inadequate (as are my math skills). I suspect that I am vastly underestimating the impact of immortality on a vivaciously procreating race.
  • 4 Of course, as population increases, famine, disease, and war will increase as well. They'd never reach 7 billion. It's even possible they might reach a balancing point between baby booming and famine, where death by attrition keeps the population growth to 0. But that's highly unlikely when you're talking about migrant hunter-gather tribes. Your society is doomed.

Basically, to summarize, you can not introduce immortality without dramatically cutting the birthrate or increasing the death rate in other ways. Overpopulation is a big deal even today with all of our agriculture and techno-wizardry and myriad contraceptive methods. A stone age society with a mating mandate could not survive the explosive population growth.

However, since this whole idea is hypothetical and fictional, maybe we can figure out a way such a society could survive. Here are some things we can focus on:

  • The death rate would have to increase substantially to compensate for the immortality.
  • The birth rate would have to drop substantially to compensate for the immortality.
  • The ratio of men to non-pregnant women would have to remain close to 1.
  • The rules surrounding your mating mandate may need some changes. You have a lot of problematic conditions and non-sequitur stipulations.

And here are a few thoughts to kick around:

  • You must have war. Lots of it. And only men go to war. It may even become a ritualized aspect of society. Send all the old men a-viking so we don't have to feed them. Or send all the pubescent young men to war as a "coming of age" test, and only the survivors can come home to mate (I personally like this one - it puts an interesting selective pressure on the species).
  • Women and men are significantly less fertile than normal humans, reducing pregnancy rates to once every few years.
  • Infertility may be more common than it is in humans. This guarantees that you have enough non-pregnant women to keep all your men from dying, and it slows your birth rate.
  • I don't like explanations like "because magic". I'd recommend a biological reason for your mating mandate and then let biology determine the rules that govern the mandate. That will also help you sort out how the society would evolve and survive. It gives you ways to mess with fertility rates and gender ratios and death rates that wouldn't be "normal" for us. It also solves your intersex problem and simplifies a number of your conditions that are simply unrealistic. It also removes the requirement for a deus ex machina shaman to tell everyone the news.
  • As others have mentioned, yes, STDs would be a big big thing. But so would immunity. STDs would put a tremendous selective pressure on your society, causing immunity to evolve rapidly. AIDS might be no more dangerous to your neanderthals than HPV is to us. Similarly, immunity to other diseases would develop rapidly, as disease becomes the biggest selective pressure and those with greater immunity live longer and reproduce much much more.
  • When in doubt, remember Star Trek.
  • $\begingroup$ Modern Age Variant, 'cause I'm bored?: worldbuilding.stackexchange.com/questions/31285/… $\endgroup$ – Malady Dec 11 '15 at 15:01
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    $\begingroup$ @Malandy I should add that the accelerated evolution of immunity would lead to a substantially lower death rate. Within a few generations, the death rate due to "natural causes" would begin to approach 0. This means even faster population growth. $\endgroup$ – Thomas Dec 11 '15 at 18:54
  • $\begingroup$ " But let's assume there's at least one infertile woman per tribe." somewhere between 20 and 40 percent of pregnancies end in miscarriage, most of those within the first four weeks after conceptions,so they don't need to be incredibly lucky for one woman to not be pregnant three months into that. $\endgroup$ – YviDe Dec 13 '15 at 0:25
  • $\begingroup$ @YviDe - Yeah had I been more motivated when I wrote this I probably would've included research on current hunter-gatherer tribe birth & death rates and more statistically accurate math. A quick search suggests between 50 and 75% of pregnancies end before showing up on a pregnancy test (Not sure how much I trust those numbers but). Risk of miscarriage after 6 weeks drops to 10%. Soo miscarriage rates decline rapidly after that first month (well, with modern medicine). Accounting for miscarriage rates, you might get an extra month or two between pregnancies. Available women would still be rare. $\endgroup$ – Thomas Dec 4 '20 at 21:43

Everybody would die and the human race would be extinct before getting to the bronze age.


If this starts somehow in the middle of the Stone Age, people won't be able to make sex on the speed needed to survive.

Your rules regarding pregnancy would kill everyone in a few generations. Women aren't really comfortable to engage in those types of act soon after a pregnancy, and even with modern medicine the recovery time for comfortable intercourse can take up a few months. But, that's not your only problem.

Those rules are really hard for someone on the stone age to understand. Most males would simply die out during puberty - for young males, getting a mate is really hard when you have to compete against stronger, older, and more experienced males. Since successful males don't die out, they will keep reproducing with available females - including their own offspring, since females are a really limited resource. That would make inbreeding defects skyrocket, and soon everybody would have serious genetic defects to cope.

But, that's not all.

Unless you somehow had 9-to-1 female-to-male ratio, your people won't survive two generations.

Let's suppose you have about half of your population of each sex, at the start of our experiment. That's the normal ratio for humans, so let's use that. Let's consider only people at reproductive age, at first.

Consider that there are around 15 people on a settlement. That's a good number for a stone-age family.

From those 15 people, let's suppose that you have 10 adults, 5 of each sex.

Once the females get pregnant, and they WILL get pregnant, their death-delaying abilities would be useless and all the males would die in a month. The females would last a few more months, but would die soon after, followed by the children.

That's it.

  • $\begingroup$ Okay... I'll give them the rules via magic too. $\endgroup$ – Malady Dec 11 '15 at 12:32
  • $\begingroup$ @Malandy You would have to decrease the fertility of women drastically... So a women having sex every day will on average only get pregnant after some years.... So only ever 20% of your women will be pregnant at the same time and the rest can have sex with the males... $\endgroup$ – Falco Dec 11 '15 at 12:37
  • $\begingroup$ @Falco - The question is what it is... For now. If they all die, then they all die. I might not like it, but it would be, apparently, the most probable scenario, and if I wanted a different one, I'd make another question. $\endgroup$ – Malady Dec 11 '15 at 12:42
  • $\begingroup$ @Malandy with a little bit of luck they could survive - see my answer $\endgroup$ – Falco Dec 11 '15 at 12:50
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    $\begingroup$ @Malandy if you're asking those questions because you're bored, please stop. WB.SE is for helping people with actual problems, not for random idea generation. $\endgroup$ – T. Sar Dec 11 '15 at 15:58

Sex, and many of its currently taboo components, will be a culturally accepted concept that children are familiarized with from a young age. This will make some of what follows sound disturbing to many of us.

Youth will grow up in a society where advertising, pop culture, and parenting all handle sex in an open and relaxed way. Given the life-or-death situation, parents and society will be very involved in ensuring that their children begin mating as soon as their clock starts ticking at puberty. Science will take great efforts to pinpoint this moment as precisely as possible. There will likely be school services in place to help children pair up at an appropriate time to get an age-appropriate mate.

More generally, familial and age-related taboos about sex are going to be very different. It’s possible that age-related taboos may not exist at all — what we currently consider to be pedophilia may not be a societal concern as long as the child is on the onset of or at least near puberty. Incest or close familial mating will maintain its genetic risk, but may very well be a go-to option when you get into the last week of your thirty day period.

Sex will also take on a very different emotional role and may be divided into two (or three) categories — sex for survival, sex for fun, and romantic sex. It’s very likely that an entire industry will evolve around this with prostitution being legal and both men and women being involved in it.

Disease will be a tricky one. It’s possible that the sudden appearance of a disease like AIDS could actually wipe out a massive portion of the human population. It would also be treated as an epidemic on the level of ebola or other mass-casualty bugs. For other less deadly STDs, there may be some societal classification systems that require frequent testing and give you an ID card that certifies your status.

Pregnancy also has an interesting aspect. Prior to a society in which a major “prostitution” industry has developed, the pregnant woman would have significant control over the man given that she can survive without him for 10 months. Considering that this change is expected to begin in stone-age humans, it’s not inconceivable that society would develop with a matriarchal focus controlled by women rather than one dominated by men.

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    $\begingroup$ I think your mistake is imagining our own society suddenly becoming like this overnight. The OP states, however, that this phenomenon would begin in the middle ages. It's highly unlikely that a society as open and advanced as ours may never even come to be. $\endgroup$ – AndreiROM Dec 10 '15 at 18:40
  • $\begingroup$ @AndreiROM If this happened overnight society would probably collapse. The OP states that it starts in the stone age, not the middle ages, suggesting that it's part of "human nature". While I do agree that my answer is optimistic (and yours appropriately explores the more pessimistic route), I think this change, particularly immortality, would change our societal structure so much that it’s difficult to even imagine what a modern-day version of this world would look like. $\endgroup$ – Avernium Dec 10 '15 at 18:45
  • $\begingroup$ @AndreiROM - Yeah, human nature was the idea. ... Would it help if I changed it to modern-day world shift? Or would that be changing the question too much? $\endgroup$ – Malady Dec 10 '15 at 18:50
  • $\begingroup$ @Malandy I think the question is fine as-is. A modern-day shift is interesting to consider, but most likely results in either the end of the world or a drastic reduction in the human population. $\endgroup$ – Avernium Dec 10 '15 at 19:10
  • $\begingroup$ @Malandy - changing it to modern day would completely change the way you have to answer the question. Maybe ask it in a different thread if you're curious about it $\endgroup$ – AndreiROM Dec 10 '15 at 19:19

Expansion to new lands would be limited. Wars over resources would be common and abortion would happen regularly.

It's likely that small communities, lone rangers, family pioneers, etc. would be non-existent. Essentially, individuals can't be separated from a breeding population. As soon as a woman became pregnant, she would lose her usefulness to men wanting to have sex to stay alive. Since as you say "Effects of males mating with pregnant females is the same as contraception-mating."

  • $\begingroup$ @Samuel - Yes, that's right. You get a girl pregnant from mating, and you still get 30 days from that mating, but if you mate with her again, on your 16th day, then you just get one extra day of life. So, it's best to space it out farther apart... And there's some math like... 30+15+7.5+~4 +~2 + ~1 = ~59 ... If you time it so you cut it really close, you get a little bit less than ~2 months before you have to switch to a non-pregnant girl. $\endgroup$ – Malady Dec 10 '15 at 18:45
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    $\begingroup$ When does the pregnancy rule start? A woman may not realize she is pregnant for days or weeks. Time of conception? That would come as an unwelcome surprise to males who mated on the 16th day. They thought they were getting 30 days, but they only got one! $\endgroup$ – Mohair Dec 10 '15 at 19:27
  • $\begingroup$ @Mohair - Pregnancy Rules start at uterine implantation, Note that certain contraception methods don't shrink the death-clock. ... I didn't say that they can feel their death clock by magic? $\endgroup$ – Malady Dec 10 '15 at 21:26
  • $\begingroup$ @Mohair - Modern Age Variant, 'cause I'm bored?: worldbuilding.stackexchange.com/questions/31285/… $\endgroup$ – Malady Dec 11 '15 at 15:02

People will also become quite miserable in their earlier years(before puberty).

In the real world, boyfriends/girlfriends might have sex more often than husbands/wives do or parents of young children do, simply due to it being not much of a medium of "relaxation" after marriage.

What will happen to a baby when the mother is constantly forced to abort/have sex with someone as a job/anything else? Who will take care of the baby? The 30-day requirement is too short. The woman lives till she has a baby, but what about the father of that baby? He'll still need sex every 30 days, at least, if he ever wants to live long enough to see the baby grow up. Heck, the concept of a baby having a father might have to be abolished.

Raising a kid will become immensely difficult.


[ I accidentally skipped a paragraph in my first read of the question, I didn't notice that sex with a pregnant women doesn't keep the man alive. So unfortunately my answer below assumes that people with partners are basically OK, and that's not true.

Therefore, either this problem can be solved (because there are enough post-menopausal or otherwise infertile women alive to make things work), and things proceed as below, or else very quickly men become rare in the population and the social order is rather different. Possibly the species doesn't survive that: it's theoretically possible, but we aren't really set up for it.]

This starts in the Stone Age, so human society already exists in some form. Everyone understands the death clock, so they know what they have to do. There is probably a rather traumatic time during which everyone's understanding of the social role of sex has to change, or else the species dies out. Basically, dominant men can't monopolise women (or vice-versa) or else the numbers don't add up and too many people drop dead at puberty.

Men without partners seek prostitutes (once commerce exists: before that they seek any women available). As was the case historically, prostitution is an even worse deal without effective contraception than with it. We know what prostitution is and how it works, all you've changed is that those without partners now need it to live.

Without wishing to dwell on it, rape might be much more common since it's "justified" by the need to live. Elevating the urge for sex into a legitimate survival requirement is potentially an extremely disturbing notion. Then again, people need food to live and societies still managed to somewhat police theft. Perhaps there would exist charitable infertile men and women willing to take one for the team to keep others alive.

I'd like to say that women without partners seek male prostitutes, but I think we all know that's not how human history really happened.

A couple that didn't want children could in theory get by reasonably well by having sex once a month at the right time of month. OK, that's not 100% effective at preventing pregnancy, but it's not bad and if you're only having sex once a month then it's a lot more effective than the "headline" figure for the rhythm method in real-world practical use. But history tells us that's not what people will choose to do. Fertile women are going to spend most of their time pregnant, with all the medical danger that entails, but that's nothing really different from 99% of human history and it's not because of "mate or die".

I think society could develop just about as normal (it might not: but it could). There will be a different attitude to the sexual act itself, but not necessarily to gender roles. Obviously there are no celibate religious roles. Maybe the Catholic church is still opposed to contraception, but since it cannot preach abstinence I suspect that the notion of the sexual urge being sinful is much less entrenched in society the first place, and so the Church never considers it a big deal either way.

The "sexual revolution" came about from the contraceptive pill, not merely from barrier contraception (sausage skin with a knot in it or whatever). So, the pill is basically a complete escape from the "mate or die" scenario, since it's permitted by the magical powers that be who enforce the rules. So it has a similar or even stronger effect on social gender roles. In modern technological societies, the "mate or die" requirement is a mundane historical inconvenience that has been dealt with, just like cholera or short-sightedness.

Then the question devolves to "how do societies with immortals function?", which (if it hasn't been already) could be asked as a separate question since the reason for the immortality is almost insignificant.


I find myself disagreeing with many of the answers here.

I see no reason to think ugly people would die. There are ugly people of both genders and they'll end up desperate--ugly will have sex with ugly.

What I would expect to see are sex houses--places people whose clock is running out can go with the expectation of sex when you're desperate. There are two parts, the first akin to a swinger's club (although it's all individuals rather than couples) and the second part where you're matched by lottery and expected to have sex with whoever you are matched with, perhaps even with more than one person (if the genders don't come out even.)

You'll also see sex workers of both genders providing such services.

I don't think you'll see the huge abortion rates many are picturing but you certainly will have to abort most pregnancies as the death rate from accidental death will be well below the oops rate of any permitted contraception.

Another thought: I think you would see more emphasis on a male version of the pill. The likely candidate we have would actually be tested.


Since all this starts in the Stone Age, all social norms will develop differently, but at first, back then, things wouldn’t be all that different.

I do not know what the life expectancy was 10’000 years (or more) ago, but I think it’s a safe guess that people often started reproduction earlier, i.e. before puberty ended, so they could raise their children, although the group/family/clan would be there as a backup. Since many infants died early (and more than pregnant or delivering women) there should be enough wet nurses available if a girl had not enough milk because her breasts hadn’t developed yet.

Overall, however, there would be more successful child births than in OTL. Populations would grow more and feel the pressure to supply more food. Farming would be invented much earlier. That, or infanticide would be common (before abortions became safely possible), especially of male babies. Even a society that can support all children may accept to deny sex to some of its pubescent (male) members.

It might also become normal to have “gang-bangs” to compensate for the pregnancy advantage of women. Fatherhood then wouldn’t mean much. Monogamy wouldn’t evolve in any case, except maybe if enough infertile prostitutes were available and extramarital sex with them was accepted during a wife’s pregnancy. Naturally infertile people would be very popular, probably they would become the clergy. They would also become the hubs of STIs, but maybe these diseases wouldn’t be as bad as in our world, because people became immune to them over time.

With almost every girl in their teens delivering about one baby per year, children are plenty and with better health care there’s a constant explosion of population (further fueled by the immortality of adults), although it will see setbacks in waves due to famines and epidemics. A single life doesn’t count much, losses are coped with. Overall, this keeps the pressure on innovation and expansion constantly high. Humanity will cover the planet even quicker and may not have time to diversify as much, because there’ll be lots of contact between ethnic groups which either results in wars or intermingling. Evolution will probably prefer the fittest women who have wide hips early on. The sexual dimorphism would be stronger than we know it.

Then, some day, abortions are invented – apart from beating a pregnant girl up until she has a miscarriage – and quickly perfected, although some women die or become infertile (since dozens of abortions before your twentieth birthday won’t be a fun ride). Even if pregnancy control isn’t possible, birth control is. Some traditionalists will say it’s against the will of the gods, but soon many girls will bear less or no children before they reach adulthood (and immortality). From then on, humanity will develop similar to how we know it except that teenage sexuality is nowhere close to being a taboo. It’s the most normal thing in the world – and always has been – that puberty means experiencing sexuality. Adults will glorify the memory of their Wild Days.

Big projects that are mostly executed by men due to their physique (e.g. the pyramids, wars etc.) require extra logistics for the supply of non-pregnant women and are therefore less likely, though still possible.

PS: I also can see the “women as commodity” variant happen.

  • $\begingroup$ +1-ed and... Modern Age Variant, 'cause I'm bored?: worldbuilding.stackexchange.com/questions/31285/… $\endgroup$ – Malady Dec 11 '15 at 15:03
  • $\begingroup$ "I do not know what the life expectancy was 10’000 years (or more) ago" -- probably around 30, but life expectancy is a bit of a misleading comparison. Probably what happened is that more than 50% of people didn't make it out of childhood (keeping the average low), and infant mortality was high. But those who reach puberty had a pretty good chance of reaching 50, albeit that to do so they have to dodge death in childbirth, disease, and mammoth-tramplings. $\endgroup$ – Steve Jessop Dec 11 '15 at 16:11

As well as the other points raised in answers, society would be very much more religious, since there would be daily proof in everyone's lives of some kind of God or other supernatural entity, causing miraculous deaths with no reasonable biological or evolutionary explanation.


A dark and grim future ahead...

With usual female fertility most tribes would die out in less than a year, because all women would be pregnant in no time, then the men die after 2 months and the women will die 30 days after giving birth, leaving the newborns to starve and die.

Except the lucky chosen tribe with an infertile women, who can't get pregnant but can give live eternally! She would be the center of religion for generations to come and be regularly used by the whole town for survival. other tribes would fight for their own "eternal maiden" or "live spending infertile slave" however the worldview. And the rest of society would process normally. Except women being pregnant almost all the time, producing children without end. Children would be raised and used for war and everything before puberty. Because there are more newborns then society can sustain, many of them would be slaughtered after birth. Women would most likely also less favored in society, since they are pregnant 90% of the time and so need a lot more food, care and cannot work 2 months every year.

So society would be mostly immortal males, using the eternal maiden to survive, there would probably a lot of experminets with young girls after puberty to make them eternal maidens.

If the twisted society survives till the modern day and finds a usable contraceptive which still grants the 30 days, women would for the first time gain equals rights to men and live an eternal live with them (if the church and powers in charge would let it come to this)

  • $\begingroup$ +1-ed and... Modern Age Variant, 'cause I'm bored?: worldbuilding.stackexchange.com/questions/31285/… $\endgroup$ – Malady Dec 11 '15 at 15:03
  • $\begingroup$ At least in our modern age, with people tracking ovulation and everything, only around 90 percent of women are pregnant after one year. About 60 percent after 4 months. And that's not considering the miscarriage rate of 20 to 40 percent within the first three months. I don't think the human race would be extinct that fast :-) $\endgroup$ – YviDe Dec 13 '15 at 0:41

You don't need a nine-to-one ratio. Even a one-to-one ratio would be workable. First realize that the fertilization rate for one intercourse session is going to be less than one-in-six, assuming standard human fertility rates. So if you only have sex when you have to, never just for fun, you have a one-in-six chance of fertilization per month.

Or to put it another way, take fifty men and fifty women, thirty-six of whom are pregnant and four just delivered. Each man's time comes up and half grab one of the pregnant women. The other half have sex with the ten non-pregnant women. So that's four pregnancies (twenty-five acts of intercourse divided by six). Next month the half that had sex with non-pregnant women switch to pregnant women. The other half have sex with the ten non-pregnant women, producing four pregnancies. That's steady state. There will always be thirty-six pregnant women, four recently delivered women, and ten available fertile women.

Now you might point out that there may be more than four pregnancies in a month. That's an average. And some women will die in pregnancy. But twenty-four children will reach adulthood each year (half die between birth and adulthood). Two a month, a boy and a girl (average). So if women die once in a hundred pregnancies and half of births grow to adulthood, that's twenty-five new women for every death.

Also, men will die off in battles with other tribes or while hunting. If there's a real shortage of women, the men will get together and raid another tribe for women. That both reduces the number of men (some die in battle) and increases the number of women.

They'll have tremendous excess population, as the population doubles every two years. Cannibalism maybe? Human sacrifice? Constant war? Presumably they'll use whatever mechanism to increase the ratio of women to men. Even if a one-to-one ratio is workable, it puts more pressure on women than men. If fertile women have sex once a month, that would give them an average of six months not pregnant for every ten months either pregnant or newly delivered. So that's an eight to three ratio of women to men is optimal.

At eight to three, each man and available fertile woman has sex once a month. Each woman averages three kids in four years. Ignoring deaths, population doubles every thirty-two months. With deaths, that may decrease to every six years.


Other people have written about how women would be pregnant a lot. This is going to be incredibly hard on the women, with many losses of life:

  • because of vaginal tearing from the birth, most doctors recommend waiting at least six to eight weeks after birth to have sex. Being forced to have sex after 30 days at most after every pregnancy is going to result in pain, possible infection and possible scarring making subsequent sex even more painful
  • subsequent pregnancies within a year are hard on the body and nowadays usually classed as "high risk pregnancies". That's one year after birth, not after the last conception
  • since 20 to 40 percent of pregnancies end in miscarriage, which can be dangerous, and pregnancy and birth is dangerous, especially in a society without modern medicine, you'd lose a lot of women to these causes. Many women won't see menopause.

However, at least some of that can be at least lessened if your society recognizes that longer breastfeeding can delay the next pregnancy. Usually, breastfeeding women don't get their normal menstrual cycle back - it's not even close to accurate, but in a world where the pill and condoms aren't used, the six to eighteen months this gives a woman might just save the tribe. So, lots of sex with breastfeeding mothers might ensue.

And one the bright side for the women (God knows there aren't many for them in this scenario), even today with well-nourished people tracking their ovulation and having sex precisely on the most fertile days, only about 20 to 30 percent of women get pregnant each month if they are trying to. So you won't have them pregnant all the time, having 15 kids over their lifetime. Maybe closer to 7 or so - which is still hard on the body and will result in high maternal death rates. And possibly infanticide, because who's going to feed all those heads?

  • $\begingroup$ There were other people that brought up the "Sex nearly right after birth is very, very bad." So, now I'm thinking of a second variant, where the death clock restarts 2 years after conception. As I said to @Lanya in the question comments. What do you think that change would do? $\endgroup$ – Malady Dec 13 '15 at 1:20
  • $\begingroup$ @Malandy jealously towards women from the men, at the least ;-) might end in violence if the women refuse to have sex because they are "safe" for so long, while the men still need to have sex, maybe? $\endgroup$ – YviDe Dec 13 '15 at 1:22

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