one sex?

Weirdest thing I learned from grad school today:

Prior to the eighteenth century, people thought that there was only one sex, and men and women were both within that sex. They thought that women's bodies were "essentially male bodies" without the necessary "heat" for internal structures to become seen outside the body.

Basically, they thought the vag was an inverted, interior penis, so women were categorized as deformed men.

And that's my "wtf?" of the day.