We know what the birth of a revolution looks like: A student stands before a tank. A fruit seller sets himself on fire. A line of monks link arms in a human chain. Crowds surge, soldiers fire, gusts of rage pull down the monuments of tyrants, and maybe, sometimes, justice rises from the flames. (..) This is the tantalizing idea for activists concerned with poverty, with disease, with the rise of violent extremism: if you want to change the world, invest in girls. (..) And the World Food Programme has found that when girls and women earn income, they reinvest 90% of it in their families.