Myths and famous claims
What was Charles Darwin's IQ?
What is documented
Charles Darwin was never given an IQ test: he died in 1882, before the first test appeared in 1905. The figures quoted for him come from Catharine Cox’s 1926 study, which estimated 135 from his childhood records and 140 from his records for ages 17 to 26. These are estimates, not measurements.
Want your own number? The test is 25 visual puzzles, about 12 minutes, no sign-up.
Darwin died before IQ tests existed
Charles Darwin lived from 1809 to 1882 (Cox 1926). Alfred Binet and Theodore Simon developed the first intelligence scales between 1905 and 1911, so Darwin, like anyone who died before 1905, could never have taken one (Britannica, Alfred Binet). Any IQ number for him is a retrospective estimate. The history of IQ tests shows how late those tests arrived.
Where the numbers come from
Darwin is one of 301 people in Catharine Cox's 1926 book, which estimated IQs for eminent historical figures from more than 3,000 biographical sources (Simonton 2020). Cox chose her subjects from a 1903 ranking of the 1,000 most eminent people, limited to those born between 1450 and 1850 whose fame was earned. Three raters gave each person an estimate from childhood records and another from records for ages 17 to 26.
| Cox 1926 estimate for Darwin | Value |
|---|---|
| From childhood records | 135 |
| From records for ages 17 to 26 | 140 |
Cox did not take these raw figures at face value. She wrote that the 135 ratings for Darwin and Leonardo da Vinci were held down by thin records and that their true level was probably above 160 (Cox 1926). Her raters, when evidence was scarce, pulled their estimates toward an average of 100, so a modest number can mean a modest record.
Try one · Logical Reasoning
Which tile completes the second pair?
Tap the option you think is right, or show the answer.
Show the answer
The missing panel shows a large hatched triangle pointing up, with small solid shapes: a square at the bottom-right corner and a square at the top-left corner (option 4).
How to solve it
- Compare the first two panels and name exactly what changed.
- The main shape and the small shapes swap forms: the main shape takes the form of the small ones, and the small ones take the form of the main shape.
- Nothing else changes.
- Apply the same change to the third panel: a large hatched square, with small solid shapes: a triangle at the bottom-right corner and a triangle at the top-left corner.
- So the missing panel shows a large hatched triangle pointing up, with small solid shapes: a square at the bottom-right corner and a square at the top-left corner.
That was 1 puzzle. The full test has 25.
What a retrospective estimate is, and is not
A retrospective estimate is an informed judgment about how far ahead of their age a person seemed, based on what biographers wrote down. It is not a test result. Dean Keith Simonton points out that the Stanford-Binet measures general abilities all children are expected to develop, so a historiometric estimate is a different thing from a test score (Simonton 2020). He also notes that Terman and Cox assumed a study run backward from fame would match a study run forward from childhood, and that this may not always hold.
What the study says about achievement
Darwin's case fits one of Cox's main findings. Her estimates correlated only .25 with eminence, and .16 after adjusting for data reliability (Simonton 2020). She concluded that high but not the highest intelligence, combined with great persistence, achieves more eminence than the highest intelligence with less persistence (Cox 1926). The page on whether IQ predicts success covers what modern studies add.
How the estimates compare on our score pages
Read as points on a modern curve with a mean of 100 and a standard deviation of 15, 135 is higher than about 99% of people and 140 higher than about 99.6%. See IQ 135 and IQ 140. Those are illustrations of the scale, not facts about Darwin.
How to judge a famous IQ claim
- Could the person have been tested in their lifetime? Darwin could not.
- Is the estimator named, and is the method explained?
- Is the number one the source printed, labeled raw or corrected?
- Does the claim repeat the original author's caution?
Read the full method in how historical IQ estimates were made, or compare Isaac Newton.
Sources
- Cox, C. M. (1926). Genetic Studies of Genius, Vol. II: The Early Mental Traits of Three Hundred Geniuses. Stanford University Press (scan of original) gwern.net/doc/iq/high/1926-cox-theearlymentaltraitsof300geniuses.pdf
- Encyclopaedia Britannica. Alfred Binet (read via Wayback Machine, January 2025) www.britannica.com/biography/Alfred-Binet
- Simonton, D. K. (2020). Galton, Terman, Cox: The Distinctive Volume II in Genetic Studies of Genius. Gifted Child Quarterly. doi:10.1177/0016986220921360 doi.org/10.1177/0016986220921360