The Flynn Effect: Why Average IQ Has Risen 30 Points in 100 Years

The Finding That Upended How We Think About IQ

In the 1980s, political scientist James Flynn noticed something troubling in the IQ data. Across multiple countries, going back decades, raw test scores had been rising generation after generation — by roughly 3 IQ points per decade. The finding was so unexpected that it became known simply as the Flynn Effect.

The implication is striking: if you took an IQ test standardised in 1930 and applied it today without renorming, the average person would now score approximately 130 — a number that would classify them as "Very Superior" by historical standards. Conversely, if someone from 1930 took a modern test, the average score would land around 70.

This is not because people were unintelligent in 1930. It tells us something profound about what IQ tests actually measure — and what intelligence really is.

What Is Causing It?

The Flynn Effect is too large and too fast to be explained by genetics — natural selection simply does not operate on a timescale of decades. The causes are environmental, and researchers have identified several credible contributors:

• Better nutrition — Particularly in early childhood. Iodine deficiency alone is estimated to reduce IQ by 10–15 points; its elimination through iodised salt accounts for a measurable portion of the 20th-century gains. Reduced lead exposure following the removal of leaded petrol is another significant factor.
• Expanded education — Modern education systems specifically train the kind of abstract, hypothetical thinking that IQ tests measure. Flynn himself argued that the 20th century saw a shift from concrete, practical thinking toward abstract classification — exactly the skill measured by most test items.
• Smaller family sizes — The birth-order effect (earlier-born children tend to score slightly higher) combined with declining average family sizes may contribute a modest effect.
• Reduced infectious disease burden — Childhood illness diverts metabolic resources away from brain development. Lower disease rates, particularly in early childhood, free those resources.
• Greater cognitive stimulation — More visually complex environments, greater exposure to abstract problem-solving in daily life, and increased familiarity with test-taking formats.

The Reversal: The Anti-Flynn Effect

More recently, researchers in Scandinavia noticed something unexpected: the Flynn Effect appears to have stalled or reversed in several high-income countries. A 2018 study of Norwegian military conscripts by Bratsberg and Rogeberg found declining raw scores from cohorts born after 1975.

This reversal is not well understood. Proposed explanations include changes in educational approach (less emphasis on abstract reasoning), the cognitive effects of modern media consumption patterns, and the possibility that the low-hanging fruit of environmental improvement has already been harvested in wealthy nations.

What the Flynn Effect Tells Us About IQ

The most important lesson from Flynn's work is that IQ scores are not measuring some fixed biological property of the brain. They measure developed cognitive skills — skills that respond to environmental conditions, educational opportunities, and cultural norms around abstract thinking.

This is both reassuring and sobering. Reassuring, because it means the cognitive tools measured by IQ tests are genuinely malleable. Sobering, because it means test scores are always relative to a time, place, and norming sample — not an absolute measure of some platonic "intelligence."

All modern IQ tests are periodically renormed precisely to account for this drift. When you take a properly standardised test today, you are being compared to a contemporary sample — not to people tested fifty years ago.

Further Reading

Flynn Effect — Wikipedia provides a solid overview of the research history and ongoing debates. For a deeper treatment, James Flynn's book Are We Getting Smarter? is the definitive account from the researcher who documented the effect.