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Experts were sure that the 20th century would make us stupid. Never before had culture and technology reshaped daily life so quickly, and every new invention brought with it a panic over the damage it was surely causing to our fragile, defenseless brains. Lightbulbs, radio, comic books, movies, TV, rock and roll, video games, calculators, pornography on demand, dial-up internet, the Joel Schumacher Batmans — all of these things, we were plausibly warned, would turn us into drooling idiots.

The test results told a different story. In the 1930s, in the U.S. and across much of the developed world, IQ scores started creeping upward — and they kept on going, rising on average by roughly three points per decade. These gains accumulated such that even an unexceptional bozo from the turn of the millennium would, on paper, look like a genius compared to his Depression-era ancestors. This phenomenon came to be known as the Flynn effect, after the late James Flynn, the social scientist who noticed it in the 1980s.

Because these leaps appeared over just a few generations, Flynn ruled out genetics as their cause. Evolutionary change takes hundreds of thousands of years, and the humans of 1900 and 2000 were running on the same basic mental hardware. Instead, he posited that there had been a kind of software update, uploaded to the collective mind by modern life itself. Better education trained students to reason with hypotheticals instead of just memorizing facts. Office and industrial jobs required workers to grapple with ideas rather than physical objects. Mass media exposed audiences to unfamiliar places and perspectives. People got better at classifying, generalizing, and thinking beyond their own daily experience, which are some of the basic skills IQ tests are designed to measure. Flynn liked to illustrate this shift from literalism toward abstraction with the example that, a century ago, if you asked someone what dogs and rabbits have in common, they might answer “Dogs hunt rabbits,” not “They’re both mammals.”

Maybe, then, all the noise and novelty wasn’t rotting our minds but upgrading them. (Studies suggest that better nutrition and reduced exposure to lead may have also helped.) In any case, the Flynn effect held steady for so long and through so many apparent threats that there was no reason to believe it wouldn’t last forever, even if, someday, somebody invented a chatbot that could do homework or Theo Von started podcasting.

Or so thought Elizabeth Dworak, now an assistant professor at Northwestern University’s medical school, when she chose the topic of her 2023 master’s thesis. She decided to analyze the results of 394,378 IQ tests taken in the U.S. between 2006 and 2018 to see if they exhibited the same climb. “I had all this cognitive data and thought, Hey, there’s probably a Flynn effect in there,” she says. But when she ran the numbers, “I felt like I was in Don’t Look Up,” the movie in which an astronomy grad student played by Jennifer Lawrence discovers a comet speeding toward Earth. “I spent weeks going back through all the code. I thought I’d messed something up and would have to delay submitting. But then I showed my adviser, and he said, ‘Nope, your math is right.’”

The math showed declines in three important testing categories, including matrix reasoning (abstract visual puzzles), letter and number series (pattern recognition), and verbal reasoning (language-based problem-solving). The first two, in which losses were deepest, measure what psychologists call fluid intelligence, or the power to adapt to new situations and think on the fly. The drops showed up across age, gender, and education level but were most dramatic among 18-to-22-year-olds and those with the least amount of schooling.

Dworak knows what her findings suggest, but as a scientist, she’s required to add a few caveats. First, scores weren’t down in every category. They rose in spatial reasoning, or the ability to mentally rotate 3-D objects, which is crucial for playing Fortnite. Second, her data came from voluntary unproctored online tests. “This wasn’t like an SAT. Somebody could have been taking it on a bus,” she says. “But I did have almost 400,000 data points.” Third and most important, “we can’t exactly say that people are getting dumber, just that scores in these categories are going down.” IQ has always been a rough proxy for intelligence, less a direct gauge than a reflection of certain mental habits that society rewards. Its scales are renormalized every decade or so and its meaning constantly debated among statisticians, some of whom still wonder if both the original Flynn effect and its reversal might owe more to inconsistent methodology than to real cognitive change.

“So I spoke with reviewers who were really well established in the field, and I got great feedback, and I was able to add some wonderful nuance so I wasn’t just publishing clickbait,” says Dworak. “And then after the paper came out, it was funny. Most of the reaction among both academics and laymen was like, ‘Oh, IQ scores are down? I could have told you that.’”

The world is dumber, and we all know it. Lately, it feels like that culturewide upgrade to our mental operating systems has been rolled back to an older and buggier version.

Stupidity, like intelligence, is a nebulous thing, hard to define but easy to spot in the wild. It’s not just that children have been bombing their standardized tests (ACT scores are at their lowest in more than 30 years, and high-school seniors’ average math scores in a national exam were the lowest since 2005) or that more than a quarter of U.S. adults now read at the lowest proficiency level. It’s also that in nearly all aspects of life, we’re opting for routines, entertainment, and entire belief systems that ask less and less of our brains. The stigma that was once attached to ignorance has disappeared, and the loudest and least informed voices now shape the conversation, forcing everyone else to learn to speak their language.

For example, polls suggest as much as a quarter of the electorate is now composed of so-called low-information voters — the type who can’t name their representatives and get most of their news from memes but tend to be more persuadable than their better-informed neighbors. That makes them all-powerful in........

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