I learned today from the NYT today that "American girls ages 10 to 17 spend two more hours than boys on chores each week, and boys are 15 percent more likely to be paid for doing chores." http://www.nytimes.com/2016/02/23/upshot/how-society-pays-when-womens-work-is-unpaid.html?_r=0
I can see how this happens. Once I was old enough not to burn the house down, I cooked dinner every day so we could eat as soon as my mom got home from work: typical girl chore. In contrast, my brother did the typical boy chore of mowing our small lawn once per week. It had to be significantly less time... Of course, I'm old, and this is apparently still happening...
As for paying your son but not your daughter to do chores, seriously???
Another random tidbit learned from this article - Bill Gates did preschool drop off while working as Microsoft's CEO - "Moms started going home and saying to their husbands, ‘If Bill Gates can drive his daughter, you better darn well drive our daughter or son,’ ” Ms. Gates said." Love it.