There are 7,622,000,000 people in the world today, and not all of them are superheroes in the Marvel Cinematic Universe. But even though rising population figures are good for box-office receipts, it is a real-world trend that has sparked alarm and controversy for decades. And, while it is still a somewhat peripheral concern in contemporary politics – unlike, say, climate change – overpopulation has nevertheless become the crisis du jour in modern blockbuster filmmaking. As a movie-plot issue, population crisis exists between a plausible future and an imagined dystopia, offering Hollywood a force of moral nuance that exceeds the brute power of pure evil’s wrecking balls.

The makers of Avengers: Infinity War (2018) actually grappled with a double-pronged population crisis in the latest instalment in the Marvel’s Avengers series. First, they had to ram dozens of standalone superheroes, from Doctor Strange to Black Panther, into a tolerable length of film, and second, only anxiety over population growth could provide sufficient moral complexity for the franchise’s big boss, Thanos.

“It’s a simple calculus,” Thanos declares with near Shakespearean panache, “This universe has finite resources … if life is left unchecked, life will cease to exist. It needs correcting.” Thanos is using the same reasoning as Bertrand Zobrist from Inferno (2016), adapted from the Dan Brown novel. “The darkest places in hell are reserved for those who refuse to act in times of crisis. We have created our own hell on Earth,” he says from beyond the grave, having released a virus to deplete global populations, before taking his own life. “Expect the current population to be culled by half. The survivors will witness horrors unknown to this planet but I want them to know why, that this was our doing and this is our salvation. Now is the time.” Zobrist, like Thanos, is almost an anti-hero who accepts the necessity of doing bad in order to do good.

The trend is not just present in comic-book movies, nor simply as an explanation of untrammelled evil. Helga Luthersdottir, an academic specialising in superhero studies, says that the focus for plotlines is now “competition for limited resources”, with some movies depicting the aftermath of unchecked population growth.

In Steven Spielberg’s 2018 film Ready Player One, the inhabitants of a metropolis of slum housing escape into a VR landscape called the OASIS, where they can live with a freedom denied them in their cramped reality. Alexander Payne’s Downsizing, meanwhile, released last year takes overpopulation and climate change as jumping-off points for a social parable in which Matt Damon is shrunk to the size of a Ken doll to cut the size of his carbon footprint. With Okja (2017), a sinister multinational food corporation struggles to breed genetically engineered superpigs to feed an ever-growing population. Films such as these display specific contemporary anxieties about population growth but build, cinematically, on a foundation laid when the underground proletariat toiled to provide for the high-rise aristocracy in Fritz Lang’s 1927 film Metropolis.

Hollywood’s interest in population crises reflects a publishing trend. Back in 2013, in the space of a month, two books were published with near identical titles and subjects: Stephen Emmott’s bite-sized, apocalyptic, vision, Ten Billion, and Danny Dorling’s longer, more optimistic, Population 10 Billion. Both posed the question: when the global population count hits 10 billion, as projections suggest it will around 2050, can we sustain life on Earth at current levels of consumption?

Emmott takes rather the same view as Thanos and Zobrist (though without encouraging genocide), considering waste reduction and technological solutions as equally unlikely. When I ask him whether he feels his concerns about population growth have resonated in pop culture, he is unconvinced. “While these science-fiction films view the consequences of population growth in different, but uniformly dystopian, ways they all share a common thread that is anything but science fiction, it is science fact,” he says. “Since [Ten Billion] was published in 2013, it is absolutely clear that this is a message that no one wants to hear. So instead we are happy to continue to treat it as science fiction.”

For Dorling, a more optimistic attitude about the future is reflected in a more political diagnosis of moviemaking trends. “It is probably not a coincidence that immigration has risen as a political issue in the United States, and in the UK before the Brexit result deflated that bubble of fear,” he says. “This especially applies to Hollywood. I would be amazed if Bollywood uses this trope much, but I don’t get out enough to watch enough films!”

Indeed, you can read immigration anxiety into older films with population disasters, such as Soylent Green (1973) where, in a Swiftian twist, the excess population is euthanised and turned into nutritious wafers, and Children of Men (2006), which inverts these visions by showing a future where resource scarcity is caused by sterility, rather than reproduction. As Dorling observes, “At some point we should begin to get low fertility apocalyptic films, when a director realises that average human fertility is falling rapidly and not set to stop at two babies per couple but below that after 2100 (if not before 2100).” As Luthersdottir says: “Popular culture reflects that which is popular – and as such it will always reflect that which is the perceived reality … rather than attempting to enlighten us about actual reality.”

Regardless of its salience, the issue of rising population is likely to reappear in the fourth Avengers movie. When you have enacted a plan that murders half the population of the universe, the industrial sabotage and family revenge plotlines of earlier Marvel movies start to feel rather small fry. Thanos’s personal mystique and the logic of his position have been maintained into the next stage of the film. When Doctor Strange asks him what he would do after killing half of all living things, he responds: “I finally rest, and watch the sun rise on a grateful universe.”