In his novel The Sun Also Rises, Ernest Hemingway uses Brett's short hair, among other things, as a symbol of the reversal of gender roles. Brett (she's a woman; it's even in her name) has short hair, no tits (like any other "flapper"), a massive sex drive, and no emotional attachment to her sexual partners.
Jake, on the other hand, possesses the attributes we associate with women, namely the lack of a penis, almost no sex drive, and strong emotional attachments. He was definitely the "woman" in the relationship, and therefore in the weaker position, because if you are in love you will aquiesce to having sex, but if you want to have sex with someone you will not let them make you love them.
Throughout the novel, we see the way Jake is emasculated and abused by Brett, but this is actually an indictment of the largely male attitude that love is meaningless. Brett really represents the men of the world, and Jake the women, a fact that makes the book all the more poignant. Clearly, women can easily become more "male" and physical in their attitudes toward sex, but men can only be changed into romantics by the severe physical and psychological scarring of war.