The secret behind the smile of Leonardo da Vinci's most famous work of art has plagued art historians for centuries.  But according to U.S. historian and author William Varvel, her subtle smile may actually be a statement about women's rights. And he's sharing his theory in his new book titled "The Lady Speaks: Uncovering the Secrets of the Mona Lisa".

Varvel spent 12 years working on his theory, which claims that La Gioconda (which is Mona Lisa in Italian) represents an early feminist who lived during the 16th century, and was a proponent of gender equality in the church:
Varvel is referring to the biblical prophecy of a new city that some have interpreted as the establishment of an ideal society, and argues that this "New Jerusalem" hinges on how people perceive the real meaning behind Mona Lisa's smile. What do you think?