"The IQ test has a dark history" if you only have time for one read and want the overall history of what/how of IQ testing, this is it. Succinct and well referenced should you decide to jump down some rabbit holes.
"The Origins and History of IQ Tests" gives a solid cursory explanation of the justifications for the measurements and how those have evolved.
"The birth of American intelligence testing" is a bit darker.
Discourse is a critical look at one topic influencing our lives each month. If you're not already a subscriber and found this newsletter worth your while then please sign up.