The increasing involvement of fathers in childbirth has been mirrored by a decreasing involvement of fathers in fatherhood. Between 1940 and 1980, the American divorce rate more than doubled. In 1940, 2% of babies were born out of wedlock. Today that number is closer to 40%. There is something unwell about a society that requires fathers to pretend to find beauty in effaced cervixes, episiotomies and the bloody show — but then allows them to skip out on the rearing of the child.

Explaining how the dinosaurs once rationalized keeping men in the Stork Club, Ms. Leavitt quotes one doctor’s argument from the mid-1960s: “As the charm of woman is in her mystery, it is inconceivable that a wife will maintain her sexual prestige after her husband witnessed the expulsion of a baby — a negligee will never hide this apparition.” Another doctor concluded: “On the whole, it is not a show to watch.”