Its chapters were originally articles published between 1974 and 1979 in various magazines, including The Atlantic Monthly, The New Republic, Physics Today, Playboy, and Scientific American.

He believed that by studying the brains of cadavers and correlating the known experiences of the former owners of the organs, human behavior could eventually be discovered and understood.

When Sagan finds it in the Musée de l'Homme, he poses questions that challenge some core ideas of human existence such as "How much of that man known as Paul Broca can still be found in this jar?

[clarification needed] A major part of the book is devoted to debunking "paradoxers" who either live at the edge of science or are outright charlatans.

In either case the enterprise of knowledge is essential for the welfare of the human species.Kirkus Reviews stated that, as an essayist, Sagan was "no Bronowski", and overall judged the collection to be "a mixed, often surprising bag of treats".