Girls selling food at a bus stop.

Throughout tropical Africa, women dominate small-scale commerce, save for butchery and a few other areas. These Yoruba women show how easily Africans balance large loads on their heads, the best way to support heavy weights and ensure good posture.

In the world's poorest countries, country dwellers cook using firewood gathered locally. (Ironically, Nigeria has plenty of wealth from oil production, but practically none of it reaches rural areas.) Solar-power stoves remain expensive - and wood has become extremely hard to find near large villages. These women live close to Nigeria's capital Abuja, situated in the dry central part of the country.