do women get paid less because they're nicer?

That's what Nancy Folbre wonders in a recent NY Times blog post about supersized executive compensation. She says:

Some personality traits — like conscientiousness — are likely to increase productivity. But other traits, including Machiavellianism and aggressiveness, can increase earnings via a more direct route. They can increase both efforts to demand higher pay and propensity to lie, cheat and steal.

Men score significantly higher than women on Machiavellianism and aggressiveness, which may help explain why 15 times as many men as women were in prison in 2008.

I've wondered if women tend to get paid less because, on average, they're less self-centered, egotistical, and more realistic, than men. If you look at your salary and always think you're underpaid, you'll constantly engage in behaviors that seek to raise your pay, and some of those will be successful, whether or not you "deserve" it. I think men tend to do that more than women. I emphasize that I'm talking about averages. If only a small fraction of men behave this way more than women do, it could skew salaries in favor of men quite a lot. To be fair, I've known men who, to my knowledge, took no active steps to increase their salary, since they felt like they were paid plenty as is.

I suspect a lot of this has to do with the way that men in our society are still expected to be the main breadwinners in a family. A man with a family to support is probably more driven to get higher pay than a women who brings in secondary income. Also, I suspect that bosses are more likely to give male heads of households higher salaries because, in the back of their minds, they think that he "needs" it more. I wish I had some statistics to compare the salaries of single men with married men.