I'm looking for a way to render a large percentage (30 to 50%) of Earth's human population infertile in about 10 years. Medicine and tech levels are approximately where they are now, maybe slightly more advanced.

  • Sterility is permanent. No medical advances in the next 30 years will be able to undo the damage done.
  • Absolutely non-lethal. Whatever makes people sterile can't kill them.
  • People don't know that they have been rendered sterile till they attempt to have children.
  • Common infertility tests will detect the infertility.
  • Men and women are equally affected.
  • The effect is global by the end of the 10 years.
  • Wild life is unaffected by this event. They continue to reproduce, same as they always have.

This is a question so a minimum of hand waving, please. Journal articles, equations or other authoritative sources are nice to have but not required in your answer.

  • $\begingroup$ Reminds me of en.wikipedia.org/wiki/Inferno_%28Brown_novel%29 (read the end of the plot if you're wondering why) $\endgroup$
    – Varrick
    Commented Aug 18, 2015 at 14:44
  • $\begingroup$ Is alien intervention or nanotech a bit too advanced or hand-wavey, even if we can show exactly how it might work? $\endgroup$
    – Monty Wild
    Commented Aug 18, 2015 at 23:45
  • 1
    $\begingroup$ There is a Star Gate episode that is basically this. Aliens disguise their infertility drug as a miracle drug that makes people live longer and makes them resistant to disease and simply play "the long game" to conquer Earth. $\endgroup$
    – Theik
    Commented Sep 3, 2015 at 11:29
  • 3
    $\begingroup$ Solution: get everyone addicted to worldbuilding so that they are so busy trying to write answers that they forget to come home to their wife at night. Did you know that women get angry when you let their homemade Chicken Pot Pie go cold before you arrive at home, and forget to give her a warning call? Funny story about that... $\endgroup$
    – Cort Ammon
    Commented Sep 3, 2015 at 20:24

5 Answers 5


Gasoline Additive Gone Wrong

Rendering 30 to 50% of humanity infertile is a challenging prospect. That's a lot of people spread over a very large area that the OP requires become infertile in a short period of time. We already have an example of where a man-made environment toxin can have significant health effects in the form of Tetraethyllead (TEL). It has been widely linked to increased crime and brain damage in children. When tetraethyllead was removed from fuels, crime rates began to drop.

There are approximately 70,000 chemicals in use in industrial and commercial environments. Few of them have any kind of testing for toxicity or biological impairments. Surely we can use one of them that causes infertility but no other noticeable side-effects. Let's assume we've found one and it also has a highly desirable effect on gasoline efficiency. The additive adds 15% efficiency to gasoline.

A huge industry for this additive will have a sales force dedicated to spreading it as far across the world as possible, in much the same way the TEL industry spread TEL across the world. Since there are no known side effects, any opposition to the additive won't appear for 10 or 20 years after it's introduction when birth rates among 20 to 40 year-olds drops for no good reason. The additives industry will be able to persist for several years or decades on the backs of misinformation campaigns and expensive lawyers who win lawsuits.

Since 53% of the world lives in cities, we have ensured that at least 50% of the world population have been exposed. Some in the cities will evade infertility because of quirks in their biology. Similarly, out in the country where exposure is lower, some will also become infertile because of enhanced weakness to the additive.

  • $\begingroup$ One objection here: TEL was let into public use because at the time it was introduced - the 1920's - almost none of the environmental safeguards that we have today existed. For example: this was nearly half a centrury before the EPA even existed as an agency. Today a harmful fuel additive, or any other such chemical, would have little chance to come into use before it is noticed and stopped. However(!)... it can be made plausible if 1) it comes from something that is sorely needed and 2) it is innocuous at first glance. Hydrogen fuel cells that leave somthing in the water vapor for instance. $\endgroup$
    – MichaelK
    Commented Sep 4, 2015 at 8:57
  • $\begingroup$ @MichaelKarnerfors Please post a citation of where all chemicals are tested? gizmodo.com/… $\endgroup$
    – user3082
    Commented Sep 23, 2015 at 6:34

I agree with Max Williams: a virus is a plausible candidate. Especially considering it is already suspected that viruses causing infertility do exist in real life.

A virus that spreads and mutates like flu and that targets the special cells that are sperm and ova, that only have one of each chromosome instead of two.

To look at your requirements:

Sterility is permanent. No medical advances in the next 30 years will be able to undo the damage done.

Virus infections cannot be cured. The best you can hope for is to halt the symptoms until the body deals with the infection. As is shown with HIV/AIDS, some virus infections will not be dealt with by the body. And for instance the Varicella Zoster virus that gives chickenpox can live in your body for decades and then break out in shingles.

Absolutely non-lethal. Whatever makes people sterile can't kill them.

Virus-infections are mostly non-lethal.

People don't know that they have been rendered sterile till they attempt to have children.

There are many examples of asymptomatic virus infections. These are called subclinical infections.

Common infertility tests will detect the infertility.

If the virus infection creates bad quality sperm or non-viable ova, that will be detected upon examination.

Men and women are equally affected.

With the premise I stated above: check.

The effect is global by the end of the 10 years.

Virus infections can easily go global. Flu - again - is a prime example. The common cold as well.

Wild life is unaffected by this event. They continue to reproduce, same as they always have.

Virus infections are often species specific.

  • $\begingroup$ Chlamydia for women. $\endgroup$
    – user3082
    Commented Sep 23, 2015 at 6:31

Chemical castration

Cyproterone acetate

Cyproterone acetate is one choice for chemical castration. Hormonal Therapy for Male Sexual Dysfunction describes it as a "potent, dose-dependent antiandrogenic and progestational agent" which can block "T and estrogen synthesis in the gonads" - meaning that it can work for women as well as men. To replicate the (potentially potent) effects shown in studies, cyproterone acetate must be taken orally daily, generally in doses of 50-200 mg. However, it can also be taken as an injection every week in doses of 300-600 mg. Transsexual and Other Disorders of Gender Identity notes that there may be side effects, notably liver problems and depression. However, these would not be attributed right away to a drug like this. While oral treatment is generally supposed to be undergone every day, Jeffcoate et al. (1980) were able to produce effects lasting for up to 28 days in special cases of tests.

Depot medroxyprogesterone acetate

I'm also currently investigating the usage of depot medroxyprogesterone acetate, which is often better known as Depo-Provera. It should be similarly effective.


For advice on this, I went to the question that drew me to Worldbuilding, How do I drug a population in the most efficient way?. For the oral option, there is the old fallback of conspiracy theorists: Putting it in the water supply. granted, dilution would have to be accounted for, but it's a possibility. The other, better solution is TimB's suggestion for that question: periodic vaccination.

The downside is that this isn't a once-and-done procedure. However, it satisfies all of the other requirements, as far as I can tell. That said, I am not aware of any extremely long-term studies, so it is possible that Jeffcoate et al.'s lasting effects cold be replicated and extended far beyond 28 days if dosage is upped and extended for longer periods of time.

  • $\begingroup$ Potential example: ethinyl estradiol $\endgroup$
    – user3082
    Commented Sep 23, 2015 at 6:41

I'd think that a virus would be the way forward. It would need to have the following characteristics:

  • extremely infectious
  • very long dormancy period, eg at least 5 years, before having any effect
  • targeting a specific element/function of the female reproductive system (if we target male fertility, women can fall back on the large amounts of frozen sperm in sperm banks)
  • no other symptoms besides the infertility.
  • mutating, so hard to vaccinate against.

You have a requirement that men and women are equally affected - this will be difficult to achieve with a single virus so maybe you'd need one virus per sex and let them spread independently.

It's likely that some people would be naturally immune to the virus due to various unique characteristics or mutations.

  • 1
    $\begingroup$ How would the virus spread? $\endgroup$
    – Green
    Commented Aug 18, 2015 at 14:28
  • $\begingroup$ airborne, contact, water, any of the usual vectors. $\endgroup$ Commented Aug 18, 2015 at 14:29
  • 1
    $\begingroup$ This was the premise of the book Galapagos, by Kurt Vonnegut. In that case, a virus killed all eggs, so it just affected females. It had no other symptoms. One group only managed to avoid the disease, as it was marooned on an island. $\endgroup$
    – user11599
    Commented Sep 2, 2015 at 21:39
  • $\begingroup$ The "flaw" with targeting eggs is that there are frozen eggs too, so humanity could keep these safe until the disease had been eradicated, and then defrost them. Better* to attack a function of the female reproductive system, for example some specific thing which makes fertilised eggs attach to the uterus wall or something like that. (I mean better in terms of the effectiveness of the virus, obviously it would be a terrible thing to happen) $\endgroup$ Commented Sep 3, 2015 at 9:06

First, you need people around a world to hook up on some very popular habit. It has to make them feel a little better for short time, or even just give them an illusion of feeling better. It also should make them look cool among their peers, especially at young age.

Surely, as the common saying goes, everything good in life is illegal, immoral or causes obesity, and your habit should also have some known bad side effects. But those effects should be delayed in time. Essentially people at the age of 15 will be given a choice: look cool now and risk 10% higher chance of cancer at the age of 75, or have no friends for being a dorky nerd.

In the meantime you can spread unproven rumours that your habit have some good side effects, for example it helps to lose weight. No doctor ever confirmed it, nobody knows anyone who actually lost any weight thanks to it, but someone read about it somewhere, doesn't even remember where, so it must be true, right?

Now you wait. After some time people will get used to the fact, that they keep hearing exaggerated stories how bad that habit is, and they will learn to ignore them and dismiss them, for the sake of short time gains. You have to die of something sooner or later, right? Might as well be cancer.

So even when half of medical world will be screaming bloody murder that everyone hooked up on that habit is slowly but steady losing fertility, that voice will be listened to, acknowledged, and then everyone will leave the room for a smoke break, including half of those, who were just preaching how bad cigarettes are bad for your health.



You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .