I think it depends on the environment we're in, particularly at work. I work with a company which - by accident, not by design - has a majority of women in senior positions, including the CEO, and it's an unusually supportive (and highly successful) business. Perhaps when there's nothing to prove, women support each other. But when we have to fight to be heard, or work in an environment where we're considered insignificant, we get pitted against each other, and respond accordingly. I'd bet men would do the same, in the same circumstances. Sadly, young girls still often judge themselves, and therefore their peers, in superficial terms (am I attractive, thin enough, wearing the right brands etc). Maybe some of this stays with us as we grow up.