Laqueur argues that in the course of medical history there has been a shift from the one-sex to the two-sex model. Prior to the seventeenth century, scientists of all kinds believed that there was only one kind of human body. Men and women were the same.

In drawings made during dissections, for example, scientists from Aristotle to Galen identified female genitalia as male genitalia which were simply inside the body rather than outside of it. Thus, the vagina was identified as penis and the uterus as testes. Women’s organs were internal, it was believed, because they were colder (and therefore inferior). It was possible for a woman to turn into a man if she over-exerted herself and became hot. After the seventeenth century, this one-sex model slowly transformed into the two-sex model popular today according to which men and women have different bodies and different attributes that follow from those bodies.

Laqueur does not think that earlier scientists were mistaken. They carefully performed dissections and recorded what they saw. Their drawings are correct. However, because their world view did not allow for two sexes, the parts are identified differently. In later centuries it became politically necessary to create a greater, natural distinction between men and women, a distinction that could not be remedied by greater heat. The material evidence of the body was thus interpreted differently.