Many Sci-Fi futures portray humanity as getting smarter. This is the inverse of that, a future where instead of becoming more intelligent, the average person is much, much stupider than they are today. Sometimes, this is portrayed as the result of a Dystopia deliberately repressing intellectuals, while other times it is a result of corporatism run amok, over-reliance on technology, evolutionary pressures that cause the stupid to outbreed/outcompete the intelligent, or any combination of these.
Expect there to be one or two exceptions, possibly from a different time or place, or just rebelling against the Crapsack World (which this trope invariably overlaps with) in which they live. If there are exceptions, they will invariably be the heroes of the story.
Sub-Trope of Humans Are Morons, and a Sister Trope to Medieval Morons. May overlap with Big, Fat Future (via Fat Idiot), Advert-Overloaded Future, and, in extreme cases, Formerly Sapient Species. If the future people are generally intelligent but ignorant about their past/our present, see Future Imperfect and All Hail the Great God Mickey!.
- Judge Dredd: Most citizens of Mega-City One are right morons. For example, when there was a vote on whether to return the city to democracy or continue the rule of the Judges, many couldn't even figure out what the issue was or how to vote. Although for appearances' sake the Judges can't officially ban advocating democracy, a secret "dirty tricks" division works to undermine and discredit any nascent democracy movement, up to and including mindwiping and exiling the movement's leaders.
- Dilbert: Series creator Scott Adams speculated the future would involve people doing less and less - as machines do more of the physical labour - and eating more and more readily accessible junk food, and not seeing a correlation between the two things. A series of cartoons shows the Dilbert characters rolling around on the floor of a futuristic house, huge fat blobs with vestigial arms and legs, perfectly happy with this state and not caring about it so long as the Internet provides entertainment and the food supply is uninterrupted.
- Idiocracy: The whole premise - evolutionary and corporatism variety, the less intelligent have outcompeted and outbred the more intelligent and as a result, we have devolved into a pop-culture obsessed Big, Fat Future where no one has a desire to learn.
- Ripley mockingly suggests this in Aliens to explain why no one is listening to her story about the alien after she woke from a 57 year hypersleep.
"Did IQs just drop sharply while I was away?"
- Feed (2002): A dystopia variety in which all information is available in implanted chips inside the head, but all of it is laced with advertisements, so almost no one bothers to actually figure out the significance of the information.
- Fahrenheit 451 - dystopia variety reading is deliberately suppressed in favor of TV watching.
- Cyril M. Kornbluth's The Marching Morons. A combination of smart people not having children and enthusiastic breeding by low intelligence people leads to a world population of idiots, except for a minority of intelligent people who work hard to keep things running. The solution of the man the intelligent people release from cryogenics (a former con artist) is simple: lots of murder, via tossing the idiots into the sea and say they are in an off-world colony. It works, and the intelligent people grant the man his recompense and summarily execute him because the man, who explicitly based his plan on the Holocaust, horrifies them.
- Paolo Bacigalupi's Pump Six is revision of The Marching Morons, but without eugenics involved. The handful of people with anything even resembling intelligence, each on their own and separated from others, are doing their very best to maintain the world populated by lethally stupid, nearly feral humanity, only to get more and more tired and less and less caring in the process. And unlike The Marching Morons, we are talking about not-too-bright repairmen and maintenance techs, not some titans of intellect.
- The Time Machine: Because of Extreme Speculative Stratification and over-reliance on technology, the lower class have evolved into brutal savages, while the upper class have evolved into flimsy dimwits with the physical and mental capabilities of small children.
- Harrison Bergeron is another deliberate dystopia example. Intellectuals are repressed for the simple reason that having some people smarter makes everyone else feel inferior.
- Downplayed in Brave New World- while the masses (Gammas, Deltas, and Epsilons) are deliberately made stupid, Alphas and Betas are quite intelligent. However, the intelligent elite are just as shallow and superficial in their philosophical worldview as the stupid people.
- In Nineteen Eighty-Four, the government removes Proles who get too smart. However, this trope is not in place with regards to Party members, who are left alive to do tasks of intermediate difficulty, but experience even more surveillance because they're much more of a threat. They create Newspeak, intended to dumb down the population by eliminating words.
- Incompetence shows that Europe is going this way thanks to political correctness dictating laws. People can't be fired for being bad at their jobs, so there's no incentive to be any good. One character suffers from a condition called "Non-Specific Stupidity", which is just general idiocy recognised as a medical condition. The protagonist finds that dealing with many of the idiots in society tends to hamper his job a bit.
- Also by Rob Grant is Colony which is set on a Generation Ship full of these. The protagonist is unfrozen for his ability to read with nobody realising that everybody in the past could do it. Also a breeding program with jobs being selected centuries in advance has led to some unqualified people such as a child captain and a womanising, atheist priest.
- Isaac Asimov's Foundation Trilogy attributes the fall of the Galactic Empire to a variant of this trope that was more to do with complacency than evolutionary pressure per se. Everyone believes that the system is perfect and needs no further innovation or adjustment so nobody does much in the way of scientific research anymore, particularly in the "soft" sciences like economics or sociology... or Hari Seldon's newly invented discipline of "psychohistory". note Nobody bothers listening to the few people who can see that this isn't sustainable in the long-term until it's too late.
- In the original 1963 French novel on which the Planet of the Apes was based (La Planète des singes by Pierre Boulle), the apes got smarter after being trained by the humans to be their servants, while a 'cerebral laziness' took over the humans until a change in the balance of power occurred. The Hollywood adaptations replaced this with a different kind of stupidity.
- The Humanist movement in the stories by Poul Anderson is a social version. Automation lead to widescale unemployment, an anti-intellectual backlash against the geniuses who still have jobs, and a call for a return to Ye Goode Olde Days. The movement inevitably collapsed because even their supporters had become reliant on technology.
The new situation was ugly. Anti-robot riots, the lynching of technies and scientists; the election of intellectually corrupt representatives—lunacy was building up as rapidly and unnecessarily as—to quote a classic example!—it did in the old United States between World Wars II and III.
- In Star Trek: The Original Series, a society of Brainless Beauties steal Spock's brain because they need a replacement Brain in a Jar to run their automated Underground City. Because all their needs are catered for in the city, over thousands of years their intelligence has atrophied until they have the mental age of children. They have a device called the Teacher that implants them with the Knowledge of the Ancients on the rare occasions that intelligence is required.
- Warhammer 40,000:
- The Vast Bureaucracy combined with the Ecclesiarchy of the Imperium relies on keeping its people as ignorant as possible of the existence of Chaos. How easy this is depends on the world, there are some that haven't seen change in millenia, others where Chaos is a daily occurrence (here they're not as strict about it), and still others where they're prevented from executing countless amounts of Guardsmen who'd been exposed to Chaos by the Space Wolves who'd fought alongside them. This results in Witch Hunts and mass frenzies that tend to kill more innocents than guilty.
- The Tau use mass mind-control to keep their population happy and unwilling to change their caste system. Whether or not they're kept deliberately ignorant is unknown, though they have been known to purge their kroot allies to make sure Chaos corruption (to which the Tau are immune) wouldn't spread (though to be fair, this is also practiced by the Imperium and for very good reason, they just tend to go overboard with it).
- The Jetsons tried to show this by having the worst problems in society being getting tired of pushing buttons all the time, portraying it as being joint-breaking labor that the characters did nothing but complain about. Ha ha, ignorant future people don't know what work is.
- The 31st century setting of Futurama is filled with many less-than-smart peoplenote , although it is mostly for comedy's sake, and the 20th century's folks were not the brightest either. At worst, they stagnated, which could explain why Fry feels so at ease in the future.