What’s currently in your pockets? If the answer is, “I don’t have any,” then you’re probably wearing a garment designed for women; the fist-sized pouch of hidden fabric holds a surprisingly gendered history.

Imagine a world turned inside out—storage-wise, at least. In 1250 A.D. in medieval England, both men and women strapped bags to the outside of their tunics. As fashions changed, fitchets—slits in outerwear that allowed access to bags worn hidden beneath—became au courant.

A few hundred years later in the 17th century, men’s fashion took a giant leap forward in functionality: Slimmer, flatter versions of purses were sewn into the seams of breeches to deter thieves. In the 1800s, tailors standardized a suit design still used today, featuring 17 pockets that could h...