In the WSJ, Carrie Lukas notes that once the ceteris is paribus, there is no male-female wage gap; indeed, for single, childless urban workers between 22 and 30, women earn 8% more than men. Women and men make different career choices and choose different career paths, which accounts for any difference in results below a certain age.
I see this in two-lawyer households frequently: more often than not, the wife stays home with the kids or drops out of the BigLaw rat-race for a less stressful job. And the most of the BigLaw husbands billing 2500/hours a year I talk to think their wives are getting the better end of the bargain (though their wives may not always agree). In the legal profession, women leave the BigLaw partnership track because it's socially acceptable for them to do so, but law firms continually express surprise that their attrition rates are higher for women than for men and that, decades after women started making up half of law graduates, women are still a minority of new partners.