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The IQ Flynn Effect

May 8, 2023

I recently watched the 2006 movie, Idiocracy (Mike Judge, Director),[1] on one of the many streaming services. The plot of the movie involves an experiment in which a man and a woman are placed into a suspended animation state and forgotten for 500 years. After reanimation, they find themselves in a world in which overall human intelligence has significantly declined and they are the smartest people in the world. There's an entertaining clip of this evolutionary dumbing-down process on YouTube.[2]

Greater intelligence appears to have had an evolutionary advantage for humans, since we have achieved mastery of our planet, for better, or for worse. Scientists and mathematicians of high intelligence have been esteemed by their lesser human peers. More than a decade ago, I compiled a list of the estimated Intelligence Quotients (IQs) of some famous scientists. Alas, my references to these estimates have been lost as a consequence of link rot, but most of these derive from an historiometric study by American psychologist, Catharine Morris Cox (1890-1984).[3] The list appears below.

Estimated Intelligence Quotients (IQs) of Some Famous Scientists and Mathematicians
Person Estimated IQ
Leonardo da Vinci220
Gottfried Wilhelm von Leibniz205
Francis Galton200
Blaise Pascal195
Isaac Newton190
Pierre Simon de Laplace190
Galileo Galilei185
Joseph Louis Lagrange185
René Descartes180
Johannes Kepler175
Sofia Kovalevskaya170
Linus Pauling170
Charles Darwin165
Nicolaus Copernicus160
Albert Einstein160
Stephen Hawking160
William Shockley129
Richard Feynman126
James Watson124

It's apparent to all that the degree of intelligence among people is not uniform; and, when something is variable, scientists want to affix a number to it, and that's how the idea of an IQ score arose. The psychologist, Lewis Terman, invented the Stanford-Binet IQ test to assign a number to intelligence, the Intelligence Quotient. The quotient label comes from the original definition of intelligence as the ratio of "mental age" to "physical age," the idea being that people learn throughout their lives, and a ten year old who knows as much as a twelve year old is obviously intelligent. The IQ number is now used statistically, and it no longer follows the quotient rule (see figure).[3]

Distribution of IQ scores

Idealized distribution of IQ scores.

The mean is 100, and the standard deviation is 15.

It can be seen from the curve that IQ scores above 140 and below 60 are very rare.

(Graph by Alessio Damato, via Wikimedia Commons))

The foremost question about intelligence is whether it's primarily determined by nature or nurture; that is, are genetics more important than childhood development. It's estimated that the heritability of IQ is about 0.75, which is quite significant. As my wife often states, it's important for children to choose their parents wisely. As for nurture, Richard Feynman had the modestly high IQ of 126, but he was a notable child prodigy, and his scientific achievements were in the same class as Albert Einstein (estimated IQ of 160).

Does IQ above a certain point really matter? One idea is that middling high IQ, such as Feynman's, is good, but extreme IQ comes with some emotional baggage that counteracts its beneficial affects. As David Brooks wrote in his book, "The Social Animal,"[4]
"A person with a 150 IQ is in theory much smarter than a person with a 120 IQ, but those additional 30 points produce little measurable benefit when it comes to lifetime success."

There are many anecdotal examples of emotionally disturbed people with high IQ, Nobel Physics Laureate, William Shockley (IQ = 129), being one example.[5] However, a 2011 study by psychologists at Southern Illinois University, published in the journal, Current Directions in Psychological Science, concludes that "A high level of intellectual ability puts a person at a measurable advantage – and the higher the better."[6] They present evidence that working memory, which is closely related to general intelligence of the type measured by IQ tests, may distinguish between the "good," and the "great." A series of studies by the authors showed that people who were tested to have greater working memory outperformed others at tasks such as piano sight reading, outperforming even people with extensive experience and knowledge of the task.

One criticism of IQ tests is that they are culturally biased and that they assess not intelligence, but a preconceived perception of what's intelligent. One non-verbal intelligence test that's supposedly free of cultural bias was devised by John C. Raven as his Master's thesis project in 1936. The graphical multiple choice questions of this test are now known as Raven's Progressive Matrices, and an example of one such question appears below. One interesting fact is that Asperger and autistic individuals achieve high scores on the Raven test.[7]

Example question, Raven Intelligence Test

An example question from an intelligence test known as Raven's Progressive Matrices.

The images show a clockwise migration of the shaded area, and the blank box is where the next identified image is sketched.

(Colorized version of a Wikimedia Commons image.)

As I wrote in an earlier article (Rising IQ, April 6, 2015), the scores on IQ tests have been increasing over the years. The non-culturally biased Raven scores have been rising most rapidly. This effect of increasing IQ from generation to generation is named the Flynn effect after its discoverer, James Flynn (1934-2020). The effect is quite pronounced, as the graph shows. When today's test subjects take the intelligence tests of yesteryear, they score higher than the original test takers.[8]

Trend in IQ test scores

Increase in intelligence test scores over the years. The non-verbal Raven's Progressive Matrices test, presumed to be non-culturally biased, shows higher scores. (Graph rendered using Inkscape from data in James R. Flynn, "What Is Intelligence: Beyond the Flynn Effect")

Whenever intelligence tests were revised, the test developers would administer both the older and revised tests to a panel of subjects as a calibration. As Flynn discovered in 1982, the test subjects always achieved a strikingly higher IQ score on the older test than the newer one, about three percentage points per decade. The average person today has an IQ of 130 when scored by a hundred year old intelligence test; and, conversely, an average person of yesteryear would appear to have an IQ of just 70 if scored by today's tests, thereby ranking him as mentally deficient.[2]

There are several hypotheses to explain the Flynn effect.[8-9]
• Modern people are just better test takers.

• People now think more logically and hypothetically. In the past, education emphasized amassing facts; thus, the idea that memorizing the capitals of the US states was an important task. Today, people who can function abstractly do better in life than those who can recite a poem by memory.

• Parents are pushing their children to excel at an early age.

• The elderly are less burdened by disease.

• Our lives are enhanced by artificial lighting and better nutrition.

• We live in a more visual world, and television, the Internet, and video games prepare us to excel on visual tests such as Raven's Progressive Matrices.

James R. Flynn, June 8, 2007

James R. (Jim) Flynn (1934-2020).

Flynn was an emeritus professor of political studies at the University of Otago, Dunedin, New Zealand.

He was born American, and he was an ardent socialist.

Humans strive to adapt to their environment; and, as Flynn remarked in a 2013 TED talk, just 3% of Americans held "cognitively demanding" jobs in 1900, while the percentage is now 35%.[9]

(Wikimedia Commons image by Bryce Edwards.)

A research team of psychologists from the Northwestern University Feinberg School of Medicine (Chicago, Illinois), Northwestern University (Evanston, Illinois) and the University of Oregon (Eugene, Oregon) have recently published a study in the journal, Intelligence, of American IQ scores from 2011 to 2018.[10-11] They found a reverse Flynn effect for a large sample of American adults regardless of age, education, or gender.[10] The steepest declines occurred for ages 18–22 and lower levels of education in the intelligence domains of matrix reasoning, letter and number series, and verbal reasoning.[10] However, the scores for tasks involving three-dimensional rotation generally increased.[10]

Psychologists differentiate two types of intelligence; namely, fluid intelligence and crystallized intelligence.[10] Fluid intelligence is an individual's ability to reason abstractly and solve problems, and it peaks at age 25 and then steadily declines.[10] Crystallized intelligence is knowledge that's accumulated and learned over the course of time. Crystallized intelligence seems to increase until age 60 and then it declines.[10] Fluid intelligence is often categorized as having three components, verbal, perceptual, and image rotation.[10] Image rotation intelligence is the ability to mentally rotate an object in order to solve a puzzle.[10]

In this study showing the reverse Flynn effect, the researchers used data from a subset of 394,378 adult Americans between 2006 to 2018 from the Synthetic Aperture Personality Assessment Project (SAPA).[10-11] The SAPA is a free, survey-based, online personality test that provides data on 27 temperament traits, such as adaptability, impulsivity, anxiety, and humor, and their cognitive ability scores.[11]

It's encouraging to think that your children and grandchildren will always be smarter that you, but Flynn supposed that this trend would not go on forever. The Flynn effect of IQ scores was expected to plateau as early as 2004.[10] This is what the present research seems to indicate. Recent evidence also suggests that visual-spatial intelligence could be declining across certain regions of Europe.[10]

Trends of 35-item composite International Cognitive Ability Resource (ICA) scores from 2006-2018, stratified by education, showing the reverse Flynn effect.

Trends of 35-item composite International Cognitive Ability Resource (ICAR) scores from 2006-2018, stratified by education, showing the reverse Flynn effect. (A portion of Fig. 1 of Ref. 10.[10] Released under a Creative Commons license. Click for larger image.)

Despite the evidence for declining intelligence, study author Elizabeth Dworak of the Northwestern University Feinberg School of Medicine says that she doesn't want people to think that Americans are getting less intelligent.[11]
"It doesn't mean their mental ability is lower or higher; it's just a difference in scores that are favoring older or newer samples... It could just be that they're getting worse at taking tests or specifically worse at taking these kinds of tests."[11]

The study didn't examine the reason for this decline in IQ scores, but some potential reasons might be poor nutrition, worsening health, media exposures and changes to education.[11] A shift in societal values might have affected scores; that is, if society is emphasizing and reinforcing certain behaviors, this would affect performance on an IQ test.[11] As an example, the present emphasis on STEM education might mean that abstract reasoning skills are receiving less attention in schools.[11] This study was partially supported by the National Science Foundation.[11]


  1. Idiocracy, 2006, Mike Judge, Director, from the Internet Movie Database.
  2. Idiocracy (2006), Opening Scene, Mike Judge, Director, YouTube video.
  3. Catherine Morris Cox, "The Early Mental Traits Of Three Hundred Geniuses," Stanford University Press, 1926, 842 pages, ISBN: 9780804700108 (via Google Books).
  4. David Brooks, "The Social Animal: The Hidden Sources of Love, Character, and Achievement," Random House, March 8, 2011, 448 pp, ISBN: 978-1400067602 (via Amazon).
  5. As I've written in an earlier article (The Multifaceted William Shockley, July 20, 2020), Shockley's personality may have been affected by an automobile accident in July, 1961, in which he was seriously injured.
  6. David Z. Hambrick and Elizabeth J. Meinz, "Limits on the Predictive Power of Domain-Specific Experience and Knowledge in Skilled Performance," Current Directions in Psychological Science, vol. 20, no. 5 (October 2011), pp. 275-279. PDF file is available, here.
  7. Michelle Dawson, Isabelle Soulières, Morton Ann Gernsbacher, and Laurent Mottron, , "The Level and Nature of Autistic Intelligence," Psychological Science August, vol. 18 no. 8 (August, 2007), doi:10.1111/j.1467-9280.2007.01954.x, pp.657-662.
  8. William Kremer, "Are humans getting cleverer?" BBC World Service, March 1, 2015.
  9. James Flynn: Why our IQ levels are higher than our grandparents, TED talk, March, 2013.
  10. Elizabeth M. Dworak, William Revelle, and David M. Condon, "Looking for Flynn effects in a recent online U.S. adult sample: Examining shifts within the SAPA Project," Intelligence, vol. 98, (May-June, 2023), Article no. 101734, https://doi.org/10.1016/j.intell.2023.101734. This is an open access paper with a PDF file available at the same URL.
  11. Kristin Samuelson, "Americans' IQ scores are lower in some areas, higher in one," Northwestern University News, March 20, 2023.

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