Humanity was up to some pretty dumb stuff in the 20th century. There’s comfort in one fact: Overall, society appears to be slowly getting smarter. Through the decades and across most of the world, people’s scores on IQ tests were slowly improving. Scientists dubbed this the Flynn effect, the phenomenon of the substantial and consistent rise in average IQ scores.

Unfortunately, it appears to be reversing. Not only does the century-long long climb in IQ scores seem to be over, but new evidence also suggests society is actually getting dumber. And many experts suspect phones are to blame. The end of the Flynn effect.

To be clear, worries about the end of the Flynn effect predate the widespread use of smartphones. One huge data set, involving IQ tests given to basically every man in Norway over decades, shows intelligence starting to decline there from the 1970s, so much so that each generation appeared to lose around seven IQ points.

This drop even occured within single families, suggesting it didn’t have anything to do with shifting demographics. Something in the environment appeared to be the culprit, though no one could agree on what. Diet, lack of exercise, pollution, and outsourcing your memory to Google have all been suggested as possible culprits.

Some argued the phenomenon was unique to Norway and reflected the country’s successful project, largely completed by the ’70s, to get everyone a quality education. While demographers and psychologists debated the numbers out of Norway, history and research rolled on. Now, a whole new set of evidence for declining brain power has emerged. This time it’s global and shows an inflection point just about the same time everyone got their hands on a smartphone. There’s evidence your phone is making you dumber.

John Burn-Murdoch, a columnist and the chief data reporter for the Financial Times, gathered the latest batch of evidence that says humanity is getting dumber and phones are to blame. The data was shared in a Twitter (aka X) thread and a fascinating (though paywalled) Financial Times article.

The first worrying data he cites comes from Programme for International Student Assessment, a worldwide study by the Organization for Economic Co-operation and Development. The set of tests studied 15-year-old teenagers around the world to benchmark their performance in reading, mathematics, and science.

You will likely have heard that teenagers’ academic abilities fell sharply after Covid-related school closures. But Burn-Murdoch notes that scores on the test actually peaked in 2012, which is right around when smartphone use became widespread. They’ve been falling steeply since. Say goodbye to long-form reading and your concentration.

How about teens’ concentration and focus? That’s not looking great either. The long-running Monitoring the Future survey of 18-year-olds “finds a steep rise in the percent of people struggling to concentrate or learn new things,” Burn-Murdoch tweets.

Teens’ reading habits reflect their shortened attention spans too. The number of U.S. teens who report reading books for leisure has tanked since the early 2010s.

Today, nearly half of teens say they “hardly ever” read books in their leisure time. Fifteen years ago the number was more like 35 percent. (Here’s a deeper dive into what giving up long-form reason does to your brain.)

Are adults doing much better? Burn-Murdoch points to another survey of mathematical reasoning showing the number of adults in a variety of high-income countries who can’t use basic math skills to assess simple statements has climbed 25 percent over the past several decades.

All in all, it’s a pretty gloomy picture of the ability to retain and synthesize complex information (aka, one crucial form of intelligence). Burn-Murdoch is pretty clear about where he lays the blame. It’s not the phones themselves that are making people dumber, he writes, but the way people use them.

“We have moved from finite web pages to infinite, constantly refreshed feeds and a constant barrage of notifications. We no longer spend as much time actively browsing the web and interacting with people we know. Instead, we are presented with a torrent of content,” he writes in the Financial Times.

This firehose of short, disjointed, context-less information is undermining the ability to focus and think. As a result, people are effectively dumber. It’s possible to build a world that doesn’t make you dumber.

On the one hand, That’s alarming if you’re a phone-owning entrepreneur hoping to keep your brain sharp for the sake of your business and your life. But on the other hand, there is at least a sliver of optimism here.

No one thinks human brains have fundamentally changed in a couple of decades. Evolution doesn’t work that fast. What’s causing these observed declines in intelligence isn’t the machinery in your heads, but the world humanity has built. If humanity has built it this way, it certainly has the capacity to tear down the bad parts and build something better.

Entrepreneurs are in the business of building new, better worlds. So even if the fact that phones are making the world dumber is depressing, it’s important to face it.

Acknowledging just how much scrolling habits affect thinking might encourage society to build tech products and personal lifestyles that get the best out of your brain instead of making you dumber.