IQ Scores Began Falling in The 1990s as The Flynn Effect Reversed, Latest Study Confirms

The long rise in IQ scores that shaped much of the 20th century began to break in the 1990s, with research from Norway, Denmark, and later U.S. datasets showing that younger cohorts stopped gaining ground on the reasoning tests used for decades.

The latest analysis by Space Daily pulled together findings from Norway, Denmark, Finland, France, Britain, and Australia, reporting that average IQ scores in several developed countries have fallen by an estimated five to seven points per generation since the mid-1990s. The pattern follows what researchers call the reverse Flynn Effect.

The finding adds weight to a question we previously examined in our previous report on Gen Z IQ decline. Younger people are not simply scoring lower in isolated internet claims.

Long-running national test records and peer-reviewed studies show a broader shift that began before smartphones, social media, and AI tools became part of daily life.

What Changed In The 1990s

For most of the last century, average IQ scores rose in industrialized countries. James Flynn documented that increase, later called the Flynn Effect, after historical test data showed gains of about three IQ points per decade in many countries.

The rise did not mean human biology had changed within a few generations. Researchers generally tied the gains to schooling, nutrition, smaller families, public health, urbanization, and daily exposure to abstract reasoning.

By the 1990s, the same upward line had flattened in parts of Europe. In Denmark, Thomas Teasdale and David Owen found in a 2005 paper that scores from military conscription testing rose for decades, then showed a later decline in young men tested for service, according to their study, A Long-Term Rise And Recent Decline In Intelligence Test Performance.

Norway later gave researchers a larger dataset. Bernt Bratsberg and Ole Rogeberg analyzed cognitive test results from Norwegian male conscripts and found that scores rose for cohorts born from 1962 to 1975, then fell among cohorts born after 1975, according to their 2018 paper in the Proceedings of the National Academy of Sciences.

Why Gen X Is Central To The Timeline

The Norwegian turning point matters because people born after 1975 fall inside Generation X by most U.S. definitions. That does not mean every Gen X adult scored lower than every Boomer or that one generation is biologically less capable than another.

It means the oldest clear reversal appears among cohorts born late enough to be tested as young adults during and after the 1990s.

For that reason, Gen X sits at the hinge of the IQ trend. Earlier cohorts benefited from the long rise in schooling, nutrition and public-health conditions. Later cohorts entered adulthood after those gains had started to level off in several countries.

As we already covered in our U.S. average IQ analysis, an IQ score is normed around 100 and mainly measures specific reasoning skills, pattern recognition and problem-solving. It does not measure the full range of human ability.

The Decline Looks Environmental, Not Genetic

The strongest evidence against a genetic explanation comes from Norway. Bratsberg and Rogeberg compared brothers within the same families and still found the rise, peak and decline in test scores. Their conclusion was that the Flynn Effect and its reversal were driven by environmental factors.

That point narrows the debate. A genetic shift over one or two generations would be too fast, and the within-family pattern weakens claims that immigration, family size or inherited ability caused the drop.

The harder question remains open: which environmental factors changed enough to affect test scores? Researchers have discussed schooling, reading habits, nutrition, family structure, media exposure, test motivation and the kinds of reasoning modern life rewards.

The US Pattern Shows Declines In Several Skills

The American evidence is more complicated because the United States does not have a single military-conscription testing system comparable to Norway or Denmark. Still, a large U.S. sample found movement in the same direction.

In March 2023, Northwestern University reported that researchers found evidence of a reverse Flynn Effect in a large online U.S. adult sample between 2006 and 2018. The team analyzed 394,378 responses from the Synthetic Aperture Personality Assessment project, according to Northwestern University.

Three cognitive domains fell: verbal reasoning, matrix reasoning and letter-number series. One domain rose: three-dimensional spatial rotation. That split matters because it suggests a shift in cognitive practice rather than a simple across-the-board collapse.

Elizabeth Dworak, the lead author, warned against reading the study as proof that Americans are becoming less intelligent. The data showed lower scores in several test areas, but the reason could include changes in test motivation, test familiarity or the kinds of tasks people practise in daily life.

IQ Tests May Be Capturing A Change In Mental Training

The old Flynn Effect rewarded skills that expanded during the 20th century: formal schooling, classification, abstract reasoning, written instructions, and symbolic problem-solving. If those habits become less central in daily life, IQ scores can fall without proving that people have lost every form of intelligence.

Digital environments may train different abilities. Navigation apps, gaming, visual interfaces, and 3D environments can support spatial reasoning, which may help explain why the Northwestern study found gains in three-dimensional rotation while other domains declined.

At the same time, lower scores in verbal reasoning and pattern-based tasks raise a harder issue for education and work. Those skills feed reading comprehension, structured argument, math reasoning, legal analysis, scientific thinking and technical problem-solving.

What The Research Does And Does Not Prove

The evidence does not prove that every younger person is less intelligent than every older person. It also does not prove that digital life alone caused the reversal. The decline began before smartphones reached mass adoption, which means any serious explanation has to start earlier than the 2010s.

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Bottom Line

The 1990s marked the period when the old upward trend became harder to sustain in multiple developed countries. Better nutrition, wider schooling, and basic public-health gains had already delivered much of their measurable benefit.

Later cohorts grew up in a different learning environment, with new media habits, changing school systems, and different forms of cognitive practice.

We also looked at how IQ is measured today, and that context is necessary here. Modern IQ scores compare people with others in the same age group, which means a falling national or generational trend comes from how groups perform against test norms over time, not from one person losing a fixed number of points.

The decline, therefore, points less to sudden individual loss and more to a broad shift in what societies train. The question for researchers is whether schools, families, and work environments still build the kinds of reasoning those tests measure.