Women hold up half the sky. — Chinese proverb Less than a month ago, 15-year-old Malala Yousafzai was shot in the head by the Taliban, merely for advocating for the rights of girls and women in Pakistan. On that same day, and on every day of every year, millions of girls were, and are, traded as sex slaves. Millions of other girls are deprived of education, medication, and basic nutrition, and many die from neglect, all because women are not valued. In “Half the Sky,” Pulitzer Prize-winners Nicholas D. Kristof and Sheryl WuDunn argue that the oppression of women and …