How would you feel if you found out you had a very high or a very low IQ? Would it change you? The IQ test has an awful allure to it. A single number that ranks your mental ability against everyone else’s, for better or for worse.

Helping Dallas explore the origins of this blasted test is John Carson, historian and author of The Measure of Merit: Talents, Intelligence, and Inequality in the French and American Republics, 1750-1940.

Edited by Joseph Knight, produced by Freddy Chick, senior producer is Charlotte Long.

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