5) Willingness to bargain hard for pay, a trait that is significantly greater in men, or so the psychologists tell us.
This I think is the over riding factor in all of this.
I'm willing to bet beer tokens that the moment a study is done to relate the level of 'risk taking' behaviour in regards to negotiating for a higher salary against not getting a job there will be a direct correlation.
I joined a new company where they took on three of us each covering a different sector, two guys and a girl. Talking together a few months later, I was the only one to ask to discuss starting salary. I started almost 10% higher than both the others, even though being honest we were all at about the same level of experience and knowledge.