Has the typical female role in film evolved since the 50's?

I am doing an project for media studies based on women in film, particularly dealing with whether or not female roles has changed since the 50's. I am also comparing Audrey hepburn to Keira knightley. So do you think the roles of women in film has changed since the 50's? And in what ways would you say that Keira knightley and audrey hepburn are similar or different?

Thanx