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Declining global IQ: reality or moral panic?

Frank Ramus
Franck Ramus
Director of research at CNRS and head of the "Cognitive Development and Pathology" team at Cognitive Sciences and Psycholinguistics Laboratory at Ecole Normale Supérieure in Paris
Key takeaways
  • IQ is a measure of an individual’s general intelligence within the population.
  • It is a controversial measure, suspected of being used as a basis for discrimination in some countries, for example through selective migration or forced sterilisation.
  • Since the middle of the 20th century, IQ has been rising worldwide, mainly in the BRIC countries.
  • Since the 1990s, IQ has been rising more slowly, perhaps reaching a plateau due to the limits of the human brain.
  • Studies warning of a decline in global IQ are being debated in the scientific community as being biased.

The first met­ric of intel­li­gence came from the Binet-Simon test1 (named after a French psy­chol­o­gist and psy­chi­a­trist), used specif­i­cal­ly to iden­ti­fy cog­ni­tive delay in chil­dren. A few years lat­er, William Stern coined the term “intel­li­gence quo­tient”: the index con­sists of divid­ing the “men­tal” age obtained by the child in the test by his or her phys­i­cal age, then mul­ti­ply­ing the ratio by 100. A 10-year-old child obtain­ing results equiv­a­lent to those of a 12-year-old would thus have an IQ of (12/10) x 100, or 120 points.

The IQ, now mea­sured in both teenagers and adults, sit­u­ates an individual’s gen­er­al intel­li­gence with­in his or her pop­u­la­tion (accord­ing to age, nation­al­i­ty, etc.), with all the val­ues fol­low­ing a Gauss­ian curve. The so-called “stan­dard” IQ (recal­i­brat­ed approx­i­mate­ly every decade) sets the mean val­ue at 100 points and the stan­dard devi­a­tion at 15. In today’s bench­mark Wech­sler tests2, 95% of the pop­u­la­tion has an IQ between two stan­dard devi­a­tions, i.e. between 70 and 130 points.

The first half of the 20th cen­tu­ry was marked by the con­tro­ver­sial use of this index as a means of dis­crim­i­na­tion. Eugeni­cist the­o­ries, epit­o­mised in par­tic­u­lar by the nascent sta­tis­tics of Fran­cis Gal­ton3, aimed to prove sci­en­tif­i­cal­ly that the lev­el of intel­li­gence was innate­ly low­er in peo­ple of a cer­tain char­ac­ter­is­tic (alco­holism, men­tal ill­ness, etc.) or eth­nic­i­ty. This frame­work of thought has prompt­ed coun­tries such as the Unit­ed States to use IQ as the main cri­te­ri­on for select­ing immi­grants4, and even for forced ster­il­i­sa­tion5.

But despite the vari­ety of uses and mod­els for IQ, recent meta-analy­ses6 make it pos­si­ble to trace its evo­lu­tion over the decades.

We are more intelligent than we used to be

The IQ scores of 300,000 peo­ple in 72 coun­tries between 1948 and 2020 were com­piled in the 2023 meta-analy­sis by Wongup­pa­raj et al7. In the space of a cen­tu­ry, they increased by around 30 points, or twice the stan­dard devi­a­tion of the dis­tri­b­u­tion of scores. But how can these val­ues be com­pared when the index is recal­i­brat­ed every ten years or so?

“It is the raw scores of the tests, before cal­i­bra­tion, that are com­pared from one peri­od to the next”, explains Franck Ramus. And not just any test, since the meta-analy­sis only con­sid­ers the Raven Matri­ces to reassess IQ. This geo­met­ric test, which has remained unchanged since its cre­ation in 1936, mea­sures so-called “flu­id” intel­li­gence, enabling prob­lem solv­ing with­out the need for pri­or knowl­edge. It is there­fore not sub­ject to cul­tur­al obso­les­cence, as ver­bal tests typ­i­cal­ly are.

The Flynn effect is flattening out, but is not going away

The Fly­nn effect8 describes the grad­ual rise in the lev­el of intel­li­gence observed through­out the 20th cen­tu­ry: improved nutri­tion9, access to or qual­i­ty of med­ical care10 and tech­nol­o­gy11 are all favourable socio-eco­nom­ic con­di­tions for the devel­op­ment of edu­ca­tion and intel­li­gence. Accord­ing to the meta-analy­sis, it is in the BRICs (Brazil, Rus­sia, India and Chi­na) that we are cur­rent­ly see­ing the great­est increas­es (2.9 points per decade on aver­age) com­pared with the rich­est and poor­est coun­tries (2 and 0.4 points respectively).

In short, IQ is ris­ing and con­tin­u­ing to rise, but less marked­ly now: 2.4 points per decade between 1948 and 1985, com­pared with 1.8 between 1986 and 2020. “But trees can’t reach the sky, there are inevitably lim­its to what the human brain can do,” says Ramus. This stag­na­tion, or reduc­tion in the Fly­nn effect, can there­fore be inter­pret­ed as an inevitable plateau in cere­bral and cog­ni­tive devel­op­ment: just as an athlete’s per­for­mance is lim­it­ed by the pow­er of their mus­cles, so too is that of the brain (which is not a mus­cle!) from both a phys­i­o­log­i­cal and socio-eco­nom­ic point of view.

IQ decline: a moral panic

Edward Dut­ton and Richard Lynn (British anthro­pol­o­gist and psy­chol­o­gist) have put for­ward a the­o­ry in the media sug­gest­ing a recent decline in intel­li­gence in sev­er­al coun­tries.  How­ev­er, the arti­cles that sup­port this hypoth­e­sis are rid­dled with method­olog­i­cal bias­es and dubi­ous extrap­o­la­tions. Whether because of the lim­it­ed sam­ple size (79 peo­ple) in Dut­ton and Lynn’s study of France12, or the fact that only cer­tain types of test (numer­i­cal or ver­bal) were con­sid­ered to be declin­ing, despite an increase in oth­ers (abstract rea­son­ing) in Nor­way13, such results remain on the fringes and do not meet with con­sen­sus in the sci­en­tif­ic community.

“What­ev­er beliefs peo­ple may have about what’s going wrong, or what’s worse than before, the argu­ment that IQ is falling seems to con­firm them. So it’s under­stand­able that it would be pop­u­lar,” explains Ramus. The moral pan­ic sur­round­ing the decline in intel­li­gence is not new: numer­ous envi­ron­men­tal fac­tors such as expo­sure to screens, endocrine dis­rup­tors or the dete­ri­o­ra­tion of edu­ca­tion are reg­u­lar­ly sin­gled out as poten­tial cul­prits. Although these fac­tors can have a neg­a­tive impact on some peo­ple, both chil­dren and adults, none of them seems to cause a decline in IQ on a more glob­al scale. 

Lancelot du Lag
1Binet A., Simon T. (1905) “Méth­odes nou­velles pour le diag­nos­tic du niveau intel­lectuel des anor­maux”, L’Année psy­chologique, 11, p. 191–244.
2« Each test bat­tery is adapt­ed to a spe­cif­ic age group: the WPPSI-IV test for chil­dren before pri­ma­ry schools, the WISC‑V for chil­dren and ado­les­cents, and WAIS-IV for adults. »
3Jay Gould, S. (1997). La Mal-Mesure de l’homme.
4Ohay­on, A. (2012). La querelle du QI aux États-Unis. Dans : Jean-François Marmion éd., His­toire de la psy­cholo­gie (pp. 78–80). Aux­erre: Édi­tions Sci­ences Humaines. https://​doi​.org/​1​0​.​3​9​1​7​/​s​h​.​m​a​r​m​i​.​2​0​1​2​.​0​1​.0078
6Pietschnig, J., & Voracek, M. (2015). One Cen­tu­ry of Glob­al IQ Gains : A For­mal Meta-Analy­sis of the Fly­nn Effect (1909–2013). Per­spec­tives on Psy­cho­log­i­cal Sci­ence, 10(3), 282‑306. https://​doi​.org/​1​0​.​1​1​7​7​/​1​7​4​5​6​9​1​6​1​5​5​77701
7Wongup­pa­raj, P., Wongup­pa­raj, R., Mor­ris, R. G., & Kumari, V. (2023). Sev­en­ty years, 1000 sam­ples, and 300,000 SPM scores : A new meta-analy­sis of Fly­nn effect pat­terns. Intel­li­gence, 98, 101750. https://​doi​.org/​1​0​.​1​0​1​6​/​j​.​i​n​t​e​l​l​.​2​0​2​3​.​1​01750
8Fly­nn J.R. (1984) “The mean IQ of Amer­i­cans: Mas­sive gains 1932 to 1978”, Psy­cho­log­i­cal Bul­letin, 95‎, p. 29–51.
9Lynn (2009). What has caused the Fly­nn effect? Sec­u­lar increas­es in the Devel­op­ment Quo­tients of infants. Intel­li­gence, 35(1), p. 16–24. https://​doi​.org/​1​0​.​1​0​1​6​/​j​.​i​n​t​e​l​l​.​2​0​0​8​.​0​7.008
10Pietschnig J. (2016). The Fly­nn Effect: Tech­nol­o­gy May Be Part of It, But Is Most Cer­tain­ly Not All of It. Mea­sure­ment : Inter­dis­ci­pli­nary Research and Per­spec­tives, 14(2), p.70–73. https://​doi​.org/​1​0​.​1​0​8​0​/​1​5​3​6​6​3​6​7​.​2​0​1​6​.​1​1​71612
11Brats­berg B. & Roge­berg O. (2018). Fly­nn effect and its rever­sal are both envi­ron­men­tal­ly caused. Psy­cho­log­i­cal and cog­ni­tive sci­ences, 115(26), p. 6674–6678.
12L. G. Weiss et al., Flaws in Fly­nn Effect Research With the Wech­sler Scales, J. Psy­choe­duc. Assess. vol. 34, pp. 411–420, 2016.
13E. Dut­ton et R. Lynn, A neg­a­tive Fly­nn effect in France, 1999 to 2008–9, Intel­li­gence, vol. 51, pp. 67–70, 2015.

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