Excellent question! We examined three cities: Paris, London and New York. While evidence suggests some mixed dining happened as early as the 18th century, this practice was not fashionable until the late 19th/early 20th century. The primary drivers were rise of the middle class (economic), growth of the hotel industry (restaurants catered to traveling couples), and demise of restrictive Victorian culture (social). Did you know? Long before it was fashionable for men and women to be seen dining in public together, they dined "out" in private rooms. Fine restaurants and hotels established separate dining rooms for ladies. Tea rooms, ice cream parlors and department store restaurants catered exclusively to female clientele. Sooo, there you are!!