While many sources cite the origins of this custom in Ireland or Scotland, this tradition holds today and continues, what one author calls, the masculine & sexist tradition of marriage proposal:
"Parkin, however, argues that leap day proposals were far from a feminist occasion–she believes the tradition perpetuated the idea that initiating matrimony was an exclusively male right, and harmed female agency. "Leap year, by virtue of its exceptionalism, reinforced traditional gender roles."
This interesting story could help introduce the idea of marriage traditions in history to present day.
