This volume argues that the difference between men and women lies in the basic biological differences between the male and female brain, which the authors contend make it impossible for the sexes to share equal emotional or intellectual qualities. They explain how the embryonic brain is shaped as either male or female at about six weeks, when the male fetus begins producing hormones that organize its brain's neural networks into a male pattern; in their absence, the brain will be female. According to the authors, there are endless variations in degree of maleness, and mishaps can lead to a male brain in a female body and vice versa. This book includes a brain sex test that lets the reader discover just how masculine or feminine his an individual's brain is.