Men are more likely to work a 40 hour week, men are more likely to take on higher paying jobs in the work force, and men typically have more experience than women because women may have to take time off for a child or other reasons.
Can you, please, tell me what "other reasons" are those you were refering to? I'd really like to know.
One final note, men commonly major in higher payer fields than women.
Did you know that women are allowed to go to university nowadays? Some of them even go after giving birth.
There are women in every profession, with the same qualifications and experience and yet, they are earning less than their male co-workers. This is not something invented, it's a fact, and it can be proven at any time if you ask people without the need of reading any field study.
I was one rank above my partner, I was getting less money, I was working more than he was (and forget the 40hours/week talk, that is "load of bs"), and yet we had the same employer, the Government, who was supposed to be above all suspicious when it comes to gender equality.
And this happens everywhere. Why is my sister in law earning less than my brother when they both work in a insurance company, for the same boss, in the same field, in the same team, doing the exactly same work 65 hours a week? They both have the same qualification. The child she has is the same that he has. When the kid needs to go to the doctor, they both go. Where's the reasonable explanation for that?