In his long and distinguished career, Jerome Kagan, now emeritus professor of psychology at Harvard, has written numerous books for general audiences on major discoveries and controversies in his field, particularly in his specialty of child development. In works such as "Three Seductive Ideas" (1998), he developed a style of discussing three or four different topics in a series of essays, interweaving each with data and observations across psychology, history and culture, and tying them together with an overarching theme. Or not.

Mr....