People are getting dumber, but don't expect the real world to take a sharper turn towards Idiocracy than it already has, researchers say.
Since World War II, IQ scores had been increasing by about three IQ points a decade, a phenomenon dubbed the 'Flynn effect' after the Kiwi researcher who discovered it, James Flynn.
But a new study has found intelligence, as measured by IQ, has been decreasing since 1975 - without an obvious cause
"It's something to do with the environment, because we're seeing the same differences within families," Ole Rogeberg of the Ragnar Frisch Center for Economic Research in Norway, who led the study, told CNN.
The cause could be education systems, media, nutrition or time spent online, the study suggests.
While his research looked at Norwegians, he says other data has shown the same thing happening in Denmark, the Netherlands, Finland, France, the UK and Estonia.
The study, published in journal Proceedings of the National Academy of Sciences, says people born in 1991 averaged five IQ points worse than those born in 1975.
In the 2006 film Idiocracy, made by Beavis and Butthead creator Mike Judge, over the next 500 years dumb people continue to have more and more children, while intelligent people only have one, or don't get around to procreating at all. This results in a society that feeds plants sports drinks, watches TV shows called Ow! My Balls and elects a President who used to be a pro-wrestling champ and porn star.
"It's not that dumb people are having more kids than smart people, to put it crudely," said Dr Rogeberg.
In fact, the study found higher-IQ people tend to have more children, ruling out the Idiocracy hypothesis of societal decline.
The researchers said more work needed to be done to understand whether people really are getting dumber however, suggesting that perhaps the tests used to measure IQ are becoming outdated with the rapid pace of technological change.