Actor Charlton Heston and director Richard Fleischer didn’t agree on everything. In the early ‘70s, however, they found common ground with the idea that overpopulation was a serious threat to the future of humanity.

The resulting film, Soylent Green, was one of the first ecological dystopian horror movies. It still packs something of a punch too, since key elements of the argument remain in our current debate.

Set in an environment so trashed that it’s more or less impossible to be a decent human, Heston plays a corrupt NYPD cop who’s fortunate enough to share a tiny apartment with his senior friend, police analyst Sol Roth, played by Edward G. Robinson in his final role. Heston's Robert Thorn clambers over hordes of people living in the stairwell to go about his business while Roth boards a converted pedal bike to run a generator when the electricity supply cuts out.

Real food is a treat – normally people rely on the products of the Soylent Corporation, which produces nutrition bars they describe as “a miracle food of high-energy plankton gathered from the oceans of the world.” Even then, it’s difficult to get enough of Soylent Red or Solyent Yellow. The new flavor, Soylent Green, is the most sought-after, fueling regular riots.

When a senior executive of the Soylent Corporation is murdered, Thorn gains experience of how the 1% live in the movie’s imagined version of 2022: real food is plentiful, fresh water is available, comfortable space and clean air abound, and even concubines (known as “furniture”) are part of everyday life. “If I had the money I’d smoke two, three of these every day,” Thorn beams as he enjoys a cigarette.

After he takes advantage of everything offered, he gets on with the murder investigation and then finds his life in danger on several occasions. As they struggle to survive, Roth continues to try to educate Thorn about what’s gone wrong with the planet. “I know, I know – when you were young people were better,” he says dismissively. “Aw, nuts,” Roth replies. “People were always rotten. But the world was beautiful.”

Thorn's inquiry leads to a revelation so horrifying that Roth takes himself to a clinic for assisted suicide once he’s worked out the truth. Roth's dying moments find him surrounded by projections of the lost beauty of past Earth (“How could I know?” Thorn wails as he watches), and the cop pushes even harder until he discovers the big secret: The oceans are no longer able to provide food, meaning “Soylent Green is people!” It was one of the most famous spoilers of all time.

Stanley Greenberg's screenplay was inspired by sci-fi icon Harry Harrison’s 1966 novel Make Room! Make Room! which explored a scenario that differed significantly from the movie version. Crucially, the Soylent Corporation made steaks from soya and lentils (hence the contracted name) and didn’t produce a green line. Elements like the action sequences and the “furniture” drama were also not an important part of Harrison’s account. He had no input, despite being allowed to visit the set and hand out copies of the novel, and later declared himself 50% happy with what appeared on the silver screen.

Watch the Trailer for 'Soylent Green'

The dystopian setting was a dilapidated New York with a population of over 40 million, which is less than a fourth of its size today. They realized the look of a back lot that was about to be demolished. Fleischer’s legacy was planted firmly in Hollywood’s Golden Age, so the production largely ignored the ideas being advanced by other science fiction movies such as 2001: A Space Odyssey and Silent Running. Instead, the action takes place in a scruffy world akin to a Kojak TV movie.

An attempt was made to shock with the “scoops,” armored bulldozers that lift rioters in giant shovels and cast them into a trough. But the visuals, while loaded with character, are not awe-inducing. That could be said to contribute to the movie’s sense of crushing claustrophobia: Scenes of a bountiful Earth as Roth dies are thrown into starker contrast.

Released on April 19, 1973, Soylent Green would go on to claim the Saturn Award for best science-fiction film of the year, the Nebula Award for the best film script of the year and the Grand Prize at the Avoriaz International Film Festival. The movie drew a range of opposing reviews, but most critics agreed that the darkness of the story transmitted well and the acting was strong.

Robinson died two months after the shooting was completed, having kept his terminal cancer diagnosis quiet as he worked. “I’m still haunted, though, by the knowledge that the very last scene he played in the picture, which he knew was the last day’s acting he would ever do, was his death scene,” Heston said in his memoir The Actor’s Life. “I know why I was so overwhelmingly moved playing it with him.”

Heston was commended for delivering a performance that differed from his usual concrete-jawed stoicism. Still, what gives Soylent Green relevance today is the wider implication of a seemingly powerless population. No one seems to be fighting the powers that be; they appear to accept that there’s nothing to live for.

By the early ‘70s, the concept of sexual equality was being discussed louder and clearer all the time, so the reduction of women to “furniture” still bites – although no one in the script challenges it. At the same time, it’s not often that big business is presented as relatively innocent in a sci-fi movie. The Soylent Corporation’s desperate attempts to hide a panic-inducing truth while trying to limit its effects are just about as noble as anyone gets in this film.

Perhaps the most powerful element of Soylent Green is that we remain in danger for other ecological reasons, even if overpopulation isn’t the problem some people expected it to be. Yet in the middle of seemingly boundless corruption, Thorn and Roth are still able to express genuine love for each other – and that perhaps wasn’t the easiest thing for an actor of Heston’s stature to perform.

Maybe, just maybe, decades after warnings began on the big screen, love can still save us.

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