1. Women earn less because they enter low-paying fields and become moms.

While it’s true that men tend to enter higher-paying fields than women, that difference alone does not explain the gender wage gap. Even when they work in the same occupations, men earn more. For instance, the median weekly salary for full-time male pharmacists was $1,954 in 2009, compared to $1,475 for female pharmacists, according to the Institute for Women’s Policy Research . And men even earn more than women in traditionally female-dominated occupations. For example, full-time female registered nurses earned an average of $1,035 per week, whereas men earned $1,090 — or an extra $2,860 per year.