"I leave the 20th century with no regrets," intones the brave male astronaut embarking on an intense and inexplicable mission across space and time, in a science-fiction film celebrating its 50th anniversary today.

1968 was a flashpoint in American culture: it was the year that Lyndon B. Johnson decided not to run again for President, allowing Richard Nixon to be elected in the middle of several crises, from the Vietnam War to the year of race riots that kicked off after the assassination of civil-rights leader Martin Luther King, Jr. The film world looked to the future, with the release of two of the most seminal science-fiction films of all time: 2001: A Space Odyssey and Planet of the Apes.

But while 2001: A Space Odyssey comes from the cold, calculating mind of Stanley Kubrick, the quote in the first paragraph isn't said by one of the astronauts in his film, who embark on a mission to Jupiter on the spaceship Discovery One. No, the astronaut who is almost gleefully happy to be free of the vagaries of modern humanity is George Taylor, Charlton Heston's lead in Planet of the Apes, heard in the opening moments of the film giving his final sign-off before a long period of hibernation. 2001 is one of the many masterpieces from a more typically bleak filmmaker, but even amidst his frosty storytelling, 50 years later, the future painted in Kubrick's space odyssey is weirdly more encouraging than the one depicted in Franklin Schaffner's Planet of the Apes.

The latter film is perhaps best known now — aside from being the creative foundation for the recent Apes revival trilogy — for its grim finale as much as for Heston hissing out a warning to some damn dirty walking, talking apes. 2001 is, in its own way, vastly more ambitious, but there's something pretty daring about ending a film with the reveal that Heston's character has only traveled hundreds of years in time, not in space. For the majority of the film, George Taylor thinks he's stuck on an alien planet, not his own, which will eventually be torn apart by nuclear war and overrun by talking, walking, fighting apes, gorillas, and chimpanzees.

Apes's ending is more direct than that of 2001, which famously inspired disdain from some famous attendees of its Hollywood premiere. (Roger Ebert's Great Movies entry on the film documents his experience watching that premiere, including seeing Rock Hudson and others walk out, Hudson loudly asking, "Will someone tell me what the hell this is about?") While 2001: A Space Odyssey is the better film, it's the more fantastical and took a longer time to sink in for many audiences. Planet of the Apes quickly inspired a franchise and grossed roughly double what 2001 did in its initial release.

Video of Planet of the Apes (1968) trailer

Hollywood likes to presume that audiences like escapism, but the general success of these films — 2001 is now one of the highest-grossing films of all time adjusted for inflation, thanks to re-releases— goes against that theory. The timing of the release of these films was coincidental to King's assassination, which occurred a day after they opened and kicked off a series of hundreds of riots around the United States. Planet of the Apes has a lead character who's thrilled to realize that he and his fellow astronauts are stranded with no hope of returning to Earth.

2001's most humane character capable of expressing emotions is HAL 9000, a computer that's shut off after it sabotages the Discovery One mission because it's unable to handle the stress of not telling the astronauts about the true purpose of their mission. These films, even Planet of the Apes, with its goofy ape costuming and makeup, are as far as you can get from escapist.

Yet 2001, released just over a year before man first walked on the Moon, is slightly more hopeful about the state of mankind. Planet of the Apes may have resonated more in the spring and summer of 1968 not just because it was less impenetrable to general audiences, but because it only confirmed what was going on in the streets of the country. Its twist ending is as much a twist of the knife to Taylor, whose disdain for his fellow man makes his realization that he never left Earth all the more pained, as it allows co-writer Rod Serling to further his grim (yet reasonable) belief that man is simply unable to stop attacking his own kind.

2001, on the other hand, is meant as an oblique but fervent depiction that evolution is built into the human condition. Just as the apes in the opening section of 2001 evolve to use tools and weapons to survive, so too does human curiosity enable one of us to evolve to the higher consciousness depicted in the film's phenomenal finale.

Credit: Metro-Goldwyn-Mayer (MGM)

50 years later, it's all but impossible to imagine any major studio releasing or even greenlighting genre fare like 2001: A Space Odyssey or Planet of the Apes. (Sure, the latter inspired a new trilogy, but would any of those films have been greenlit if 20th Century Fox wasn't interested in remaking a presumably viable bit of intellectual property?) Even the more positive 2001 doesn't have much use for the human race in terms of developing them as three-dimensional characters; Dave Bowman may turn into the Star Child at the film's conclusion, but it's hard to say we know him as anything other than the next step for mankind.

In 1968, audiences may have wanted to run away from the harsh realities of the world outside, but these two films offered few easy answers in terms of what our collective desires to explore and destroy would lead to. That they existed at all is something of a miracle.