Thomas Sowell has written about the male/female wage gap several times. On 4/15/14 and again on 3/15/2015. And I know he has addressed this several other times. Other economists have written about it Here and here.
As a comment I ran across says. Women want the ability to choose when and how they work (staying home with babies, etc.) without any consequences.
The latest wrinkle is the female soccer players don't get paid what male soccer players do. Well, that is a market-driven decision. Some baseball players don't make what prime basketball players make, either.
58 minutes ago