In the upcoming Netflix movie What Happened to Monday, a future dystopian government faces an overpopulation crisis. A disturbing twist on China’s old “one child” policy, families in this world are legally limited to only one child each; subsequent, and therefore illegal, siblings are put into a “long sleep.” That’s a problem for seven sisters named after the days of the week. They’ve managed to evade capture until one day, when Monday goes missing.

Overpopulation is not a new trope in science fiction. It started in 1798, with the publication of philosopher Thomas Malthus’s An Essay on the Principle of Population, who theorized that human population was similar to animals in swinging through periods of skyrocketing birth rates and deadly eras of famine and war.

The idea took root in the imagination of people, with American biologist Paul Ehrlich’s revisiting of the subject in his bestselling, controversial book The Population Bomb. The crux of the book is the same point of conflict that movies like What Happened to Monday jump off of — we live on a finite planet with finite resources, and infinite population growth isn’t possible without terrifying repercussions.

While Ehrlich was correct in foreseeing a massive population surge, the carrying capacity that Earth has for these populations has proven to be much greater than predicted. This doesn’t mean that the mass consumption of our resources hasn’t screwed us (hello, climate change), but it does mean that the relationship between population numbers, consumption, and sustainable development is much more complicated than previously realized.

It took thousands of years for our planet’s population to reach 1 billion in 1804, but it only took 33 years for the population to jump from 2 billion in 1927 to 3 billion in 1960. This huge growth, says the United Nations Population Fund, brings challenges but also “represents humanity’s success” — lower mortality represents achievements in health, education, and human rights.

Today, the global population stands at about 7.5 billion — but to what extent that number will grow is anybody’s guess.

The Child Allocation Bureau in 'What Happened to Monday.'

The UN has three population projections: one high, one low, and one in the middle. The medium variant suggests that the world population will reach 10 billion by the middle of this century before “leveling off” at 11 billion by 2100. If fertility rates don’t decline as much as anticipated, we could be inhabiting this planet with 16.5 billion other humans by 2100. If fertility rates decline at a faster rate that expected, however, the world population could still hover at 7 billion by the century’s end.

Fertility rates are key here; in particular, replacement levels, or when a pair of parents replace themselves in the next generation with at least two children, with each subsequent child adding to growth.

And that concept is why What Happened to Monday’s premise is questionable. Fertility levels have not declined at the same rates as mortality levels — for example, while mortality levels in Africa have declined, more than half of the population growth anticipated to happen between now and 2050 is expected to happen there. Meanwhile, the population of 48 countries around the world, including Japan, Bosnia, and Croatia, are expected to decline by more than 15 percent by 2050. The fertility rate of each European country is below the level required for full replacement of the population, once the eldest generations die. The United States saw it’s own population grow by the smallest amount in 2016 than it had in the past 80 years.

The problem isn’t that there are too many children so much as there aren’t enough children. Plunging populations mean that there’s not enough people to take care of the elderly and drive the economy, and these “local extinctions” have policy makers concerned that successful economies that drove down fertility rates will in turn crash with declining populations.

This makes for an entirely different dystopian future. Researchers have found sustainable development is possible and happening — but that doesn’t make for a very good movie.

What Happened to Monday will be released by Netflix on August 18.

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