Could we be struck by species-wide infertility? The science behind 'Children of Men'

Set in 2027, Alfonso Cuarón's movie Children of Men presented a vision of humanity which was entirely infertile, as a result of some unspoken or unknown event. The youngest person was 18 years old, having been born in 2009, and in the wake of nearly two decades of biological uncertainty, things had gotten rough.

The movie, which turns 15 years old this year, paints a stark picture, not just of the potential slow death of our species, but of the way society crumbles beneath the weight of that loss. The precise mechanism which led to global, species-wide infertility may be unknown within the context of the film, but it raises the question of whether such a calamity could befall us in real life.

DISEASE

There are a number of infectious pathogens that, if left untreated, can cause infertility in both males and females. Many of these are STIs, by virtue of the fact that the site of infection is generally anatomically convergent with reproductive organs.

Both Chlamydia and Gonorrhea create symptoms which, if allowed to get out of control, can cause permanent damage to the reproductive structures in males. Untreated chlamydia causes scarring which is capable of lower production of sperm and even blocking their exit from the body. Mycoplasma, another STI, directly attacks the sperm cells, lowering their motility. In fact, this infection often has no other symptoms in males and isn't diagnosed until infertility is noticed.

Even illnesses as common as urinary tract infections can lead to infertility. In males, UTIs can spread to the testicles and glands reducing sperm count and motility until you have fewer swimmers and they're all bad at doing their one job. In females, UTIs cause inflammation and can scar the fallopian tubes. In short, any infection which impacts your reproductive organs has the potential to reduce their ability to function properly, leading to infertility.

This is a reality for a significant portion of the population, already. In the United States, approximately 10 percent of couples attempting to procreate have persistent challenges with fertility, even after two years of trying to conceive, according to the National Institute of Child Health and Human Development.

All of these diseases, however, are already common in the population and haven't resulted in species-wide infertility. Unless they made some serious moves to up their game, we probably don't need to worry about them, at least not at a global level.

Less common diseases, like the mumps, can also cause infertility. Males infected with mumps, particularly pubescent males or older, may experience a complication known as orchitis. It occurs in 20 percent to 30 percent of cases and causes atrophy of the testicles. As the virus attacks the glands the internal pressure increases, and the body may develop antibodies which begin to attack the sperm cells. In patients who experience bilateral mumps, infertility is observed in 30 percent to 87 percent of people.

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The good news is mumps has been very nearly eliminated since the introduction of childhood vaccine programs. In 2021, only 122 cases have been reported in the United States, as of the time of this writing. In order for mumps, or something like it, to reach a species-level threat, it would have to change the way it operates to become significantly more infectious and have a higher incidence of complications leading to infertility.

Of course, there's always the possibility of a novel, as yet undiscovered viral contagion.

RADIATION

We're exposed to radiation all the time. There's a whole bunch just hanging out in the background all the time. Every time the Sun strikes your face, radiation. The electronics in your house, radiation. The banana you had for breakfast, radiation. Even you are emitting radiation, dear reader. It's just that most common forms and doses of radiation aren't harmful. Even higher levels of radiation, like the kind you get from an x-ray—the kind that has your doctor or dentist hiding behind a lead wall—aren't dangerous at the frequency you're likely to be exposed to them.

Then there's the type of radiation you think of when you hear that word, the kind that melts down reactors, creates Godzilla, and ends worlds. This is called ionizing radiation, and it's actually the same kind present in an x-ray. It's called ionizing because it has the ability to strip electrons off of atoms as it passes. Ionizing radiation is also present in nuclear reactors and atomic bombs, though to a much higher degree.

Radiation is capable of causing infertility in high enough doses and especially when directed at particular parts of the body. Individuals who receive radiation to treat cancers can receive the unwanted side effect of damage either to the reproductive organs or to other glands which regulate reproductive processes. Sufficient radiation can result in irreparable damage and infertility.

A review of people living around Chernobyl at the time of the meltdown shows some evidence of longstanding reproductive changes as a result of exposure to ionizing radiation. Per capita, those populations have higher incidence rates of fertility treatments and have fewer children overall. The exposure was relatively low-dose and among individuals who relocated away from the radiation zone.

One can imagine a nightmare scenario in which the world falls to all out nuclear war, spreading radiation over the globe. There would be nowhere to relocate to. The exposure would be ongoing and the consequences potentially more severe.

Still, the likelihood of some disease or calamity stripping our species of its reproductive ability is quite low. After all, life wants to beget more life. There's plenty to concern ourselves with as it pertains to the future of humanity, but the lack of children likely isn't one of those things.