For the first time in modern ballet history, a male dancer is performing as part of the female ensemble at an international ballet company, signaling an important moment in an art form that often celebrates a particular ideal of femininity. Or, as the great choreographer George Balanchine said, “ballet is woman.” But in a world with a heightened awareness of gender fluidity, and with transgender people increasingly accepted in a variety of professions, including acting and modeling, ballet is taking its own brave leap.