After Decades Of Rising IQ Scores, A Puzzling Decline Is Emerging

For much of the 20th century, each new generation seemed to score a little better on IQ tests than the one before it. Then, in parts of the developed world, that long-running upward climb began to bend the other way.

The reversal does not mean people are suddenly becoming less intelligent. But it has created a scientific mystery about the environmental forces that once appeared to lift test performance generation after generation, and may now be pulling it back.

Between 1962 and 1991, more than 700,000 Norwegian men took the same IQ test before military service. Scores climbed until the men born around 1975, then reversed. Economists Bernt Bratsberg and Ole Rogeberg showed in the Proceedings of the National Academy of Sciences in 2018 that the rise, turning point and decline could all be recovered from variation within families.

The pattern behind that data has a name: the Flynn effect. Its reversal in a handful of wealthy countries is contested, not because anyone doubts the numbers, but because nobody has settled on why they are moving.

What Did The Flynn Effect Actually Measure?

Named for political scientist James Flynn of the University of Otago, who died in 2020, the effect describes the substantial rise in test scores across the 20th century. A 2015 meta-analysis by Jakob Pietschnig and Martin Voracek of the University of Vienna in Perspectives on Psychological Science covered 271 samples and nearly 4 million participants from 31 countries,.

Flynn himself never argued people had become innately smarter: his 1987 paper held that IQ tests measure something with only a weak causal link to intelligence. Nearly every researcher agrees a shift this large in a generation or two could not be genetic, which makes the reversal a puzzle: if environment built the gains, environment is presumably taking them back.

Where Have The IQ Scores Actually Turned Downward?

Norway first. Because it compared brothers within the same family, it ruled out immigration or shifting parental composition as explanations for the roughly 0.2-point annual drop after the 1975 peak.

Denmark shows a similar arc. Thomas Teasdale and David Owen, writing in the journal Intelligence, examined over 500,000 Danish men tested between 1959 and 2004 and found performance peaked in the late 1990s before declining, ruling out nutrition and pointing to how schooling emphasized abstract reasoning.

Finland follows the same shape on a different timeline. Edward Dutton and Richard Lynn, analyzing roughly 25,000 conscripts in a study also published in Intelligence, reported IQ scores rising about 4.0 points a decade from 1988 to 1997, then falling about 2.0 points a decade to 2009, with strong reversal evidence limited mainly to Finland.

The United States is messier. Elizabeth Dworak, William Revelle and David Condon, led a study in 2023, examined 394,378 Americans surveyed between 2006 and 2018, finding verbal and matrix reasoning scores dropping while spatial reasoning rose. Dworak, a research assistant professor at Northwestern University’s Feinberg School of Medicine, said in a statement: “It doesn’t mean their mental ability is lower or higher; it’s just a difference in scores.”

Did Ruling Out Genetics Narrow The Search?

Not toward biology, since that door was already closed.

Because brothers born a few years apart showed the same downward drift, the authors concluded the changes reflect environmental factors. That leaves education and diminishing returns as live candidates: the same meta-analysis found gains decreasing in recent decades overall.

What Does The Evidence Actually Support?

It’s much narrower than the headlines suggest. Declining reading has real backing: psychologist Jean Twenge of San Diego State University found the share of 12th graders reporting no pleasure reading nearly tripled between 1976 and 2016 to one in three.

But collapsing attention does not hold up: a 2024 meta-analysis in Personality and Individual Differences by Andrzejewski, Zeilinger and Pietschnig found moderate gains in adult concentration performance.

What remains true is that the rise happened, the reversal happened in specific countries, and the explanation is still being argued over.