The Flynn Effect: Are Humans Getting Smarter?

In 1984, political scientist James Flynn published a finding that would reshape how we think about intelligence: IQ scores had been rising steadily across the developed world for as long as records existed. The gains averaged roughly 3 points per decade — meaning the average person today would score in the gifted range on a test normed 70 years ago. Flynn extended his original analysis to 14 nations in his landmark 1987 paper in Psychological Bulletin, and the phenomenon has been replicated in dozens of countries since. But the story doesn’t end there. Recent evidence suggests the trend has plateaued or reversed in several developed countries. Are humans getting smarter, getting dumber, or is the question itself misleading?

What Exactly Is the Flynn Effect?

The Flynn effect refers to the sustained increase in IQ test scores observed across successive generations throughout the 20th century. The phenomenon was named by Richard Herrnstein and Charles Murray in The Bell Curve (1994) after Flynn’s work documenting it.

The most comprehensive modern estimate comes from two large meta-analyses. Trahan, Stuebing, Hiscock, and Fletcher (2014) pooled 285 studies (N = 14,031) and reported an overall gain of 2.31 IQ points per decade (95% CI [1.99, 2.64]); for modern Wechsler and Stanford-Binet tests post-1972 the gain was 2.93 points per decade. Pietschnig and Voracek (2015), using 271 independent samples and almost 4 million participants from 31 countries spanning 1909–2013, found rates that varied by cognitive domain: fluid intelligence rose by 0.41 IQ points per year, spatial ability by 0.30, full-scale IQ by 0.28, and crystallized intelligence by 0.21.

The asymmetry — bigger gains on fluid and spatial subtests than on crystallized vocabulary and knowledge — is one of the most theoretically informative features of the Flynn effect. It is also exactly the pattern that makes the effect difficult to interpret as a simple rise in “intelligence.”

What Caused the IQ Gains?

The Flynn effect cannot be genetic — 70 years is far too short for significant evolutionary change in a species with a 25–30 year generation time. The causes are overwhelmingly environmental:

• Improved nutrition. Better prenatal and childhood nutrition, including the fortification of staple foods with iodine, folic acid, and iron, has supported healthier brain development across populations. Research on early nutrition and cognitive outcomes provides the evidence base for this mechanism.
• Reduced environmental toxins. The phase-out of leaded gasoline, reduced mercury exposure, and lower air pollution have eliminated cognitive harm that was once ubiquitous. The reduction in childhood blood lead levels alone is estimated to have contributed several IQ points to the cohort effect.
• More and better education. Average years of schooling increased substantially throughout the 20th century. Since education causally raises IQ by approximately 1–5 points per year, the expansion of education is a major contributor.
• Smaller families. The demographic transition from large to small families increased per-child parental investment — more one-on-one interaction, more resources, and more cognitively stimulating home environments.
• Greater cognitive complexity of daily life. Modern life demands more abstract thinking than it did a century ago. Navigating technology, interpreting visual media, understanding bureaucratic systems, and processing information-dense environments all exercise the fluid reasoning abilities that showed the largest gains. Flynn himself argued that the rise of “scientific spectacles” — the habit of treating concrete problems as instances of abstract categories — best explained why the largest gains appeared on Raven’s-type matrix tests.
• Improved healthcare. Better prenatal care, reduced childhood infectious disease, and improved management of conditions affecting brain development have all contributed to healthier cognitive development at the population level.

One important nuance comes from te Nijenhuis and van der Flier’s (2013) meta-analysis of 31 datasets: Flynn-effect gains correlate negatively with the g-loadings of the subtests showing them. In other words, the rising scores on matrix-type tests may reflect improvements in narrower abilities (abstraction, hypothesis testing, fluency with two-dimensional stimuli) rather than a real increase in general intelligence. The Flynn effect is robust; whether it reflects gains in g specifically is more contested.

Has the Flynn Effect Reversed?

This is the question generating the most attention — and controversy — in current intelligence research. Sundet, Barlaug, and Torjussen (2004), in a paper titled The end of the Flynn effect?, were the first to document a clear reversal: Norwegian conscript scores peaked for cohorts born around the mid-1970s and declined thereafter. Teasdale and Owen (2008) documented similar declines in Danish conscript data of roughly 1.5 IQ points between cohorts tested in 1998 and 2003/2004.

The most rigorous test of whether the reversal is real came from Bratsberg and Rogeberg’s (2018) PNAS analysis of Norwegian administrative register data. They demonstrated that the decline occurs within families — younger siblings born to the same parents score lower than older siblings. This finding rules out compositional explanations (immigration, dysgenic fertility) and points firmly to environmental factors that have changed between cohorts. The same environmental responsiveness that produced the rise produced the reversal.

Several countries have shown the reversal pattern with varying timing:

• Norway: Decline of approximately 0.3 points per year for cohorts born after 1975 (Bratsberg & Rogeberg, 2018).
• Denmark: Plateau or slight decline beginning in the late 1990s (Teasdale & Owen, 2008).
• Finland and France: Comparable declines reported in conscript data since the late 1990s.

However, the pattern is not universal. Some developing countries continue to show IQ gains, likely because they are still capturing the same environmental improvements (better nutrition, more education, less pollution) that drove gains in the West during the mid-20th century.

Why Might IQ Scores Be Declining?

Several hypotheses have been proposed, and they are not mutually exclusive:

The Bratsberg–Rogeberg within-family finding is the strongest single piece of evidence: whatever is causing the decline operates inside families, between siblings born a few years apart, in genetically similar environments that have nonetheless changed. That points clearly at environmental and cultural factors — schooling content, media use, lifestyle, exposures — rather than population composition or evolutionary forces.

Are People Actually Getting Dumber?

Not necessarily — and this is where the question becomes philosophically interesting. The Flynn effect forced researchers to confront a paradox: if people in 1930 had measured IQs of 80 by modern norms, were they intellectually disabled? Obviously not — they built cities, wrote literature, fought wars, and conducted science.

The resolution is that IQ scores measure a specific set of cognitive skills that are responsive to environmental demands — not some fixed, context-independent “intelligence.” The 20th-century gains likely reflected genuine improvements in abstract reasoning ability driven by a world that increasingly demanded abstract reasoning. If the environment is now changing in ways that emphasize different cognitive skills (rapid information filtering rather than deep analytical reasoning, for example), scores on traditional IQ tests might decline even as other cognitive capabilities improve. The te Nijenhuis–van der Flier finding that Flynn gains are not concentrated on g supports this reading: what changed between 1930 and 1990 was not raw cognitive horsepower but the cognitive style the test rewards.

What Does This Mean for Individuals?

The Flynn effect is a population-level phenomenon — it describes average shifts across millions of people, not changes within any individual’s lifetime. Your personal IQ is far more influenced by your genetics, education, health, and life experiences than by which generation you happen to belong to.

However, the Flynn effect has practical implications for anyone who takes an IQ test, because it affects the norms against which you are scored. Tests are periodically re-normed (the WAIS, for example, is updated roughly every 15–20 years). A test normed during a period of rising scores will produce slightly lower IQ values than an older edition for the same true ability — a clinically important effect at the diagnostic boundaries (intellectual disability at IQ 70, giftedness at IQ 130). The continuous norming approach represents one solution, producing more current and accurate norms that reduce the influence of generational score drift on individual assessment.

Frequently Asked Questions

Who discovered the Flynn effect?

James Flynn first documented the rise in American IQ scores in 1984. He extended the analysis to 14 nations in his 1987 Psychological Bulletin paper. The term “Flynn effect” was coined by Richard Herrnstein and Charles Murray in The Bell Curve (1994).

How much have IQ scores risen?

About 2–3 IQ points per decade through most of the 20th century. Trahan and colleagues (2014) reported 2.31 points per decade overall and 2.93 for modern Wechsler/Stanford-Binet tests. Pietschnig and Voracek (2015) found higher rates for fluid (4.1 points/decade) and spatial (3.0/decade) than for full-scale (2.8/decade) or crystallized intelligence (2.1/decade).

Has the Flynn effect ended?

It has plateaued or reversed in several developed countries — Norway, Denmark, Finland, France — for cohorts born after roughly 1975. Bratsberg and Rogeberg’s (2018) Norwegian within-family analysis confirmed the reversal is real and environmentally driven, not a measurement artifact or population-composition effect.

Why did the Flynn effect reverse?

The most likely explanation is a combination of an environmental ceiling (low-hanging improvements in nutrition, schooling, and toxin reduction have largely been captured) and changes in education, media, and lifestyle that shift the cognitive skills children develop. The decline appears within families, ruling out genetic and compositional explanations.

Does the Flynn effect mean people in 1900 were stupid?

No. IQ tests measure performance on specific abstract-reasoning tasks under specific test conditions. Earlier generations excelled at cognitive tasks that mattered in their environment — practical problem-solving, large-scale memory, agricultural and craft expertise — that modern IQ tests don’t capture. The Flynn effect reflects shifts in the cognitive style modern testing rewards, not a uniform rise in raw mental capacity.

Are Flynn-effect gains “real” intelligence gains?

Contested. te Nijenhuis and van der Flier’s (2013) meta-analysis found that Flynn-effect gains correlate negatively with the g-loadings of the tests showing them — meaning the rising scores may reflect narrower abilities (abstraction with abstract symbols, two-dimensional pattern recognition) rather than a real increase in general intelligence. The score gains are robust; the interpretation is not.

Conclusion

The Flynn effect demonstrates that intelligence — as measured by IQ tests — is substantially responsive to environmental conditions. Population-level scores rose by roughly 20 points over the 20th century, driven by better nutrition, less pollution, more education, smaller families, and greater cognitive complexity in daily life. The recent plateau or reversal in several developed countries suggests that these environmental gains may have reached a ceiling, and new pressures — educational, media-related, lifestyle — may be counteracting them. Bratsberg and Rogeberg’s within-family finding has settled one important debate: the reversal is environmental, not genetic. Whether the rise and fall track changes in g itself or merely in the narrower abilities IQ tests sample is a separate question that remains open. Either way, the Flynn effect is a powerful reminder that intelligence is not a fixed endowment but a capacity that depends, in part, on the world we build around developing minds.