LAGOS, Nigeria (AP) — The world's population will likely hit an estimated 8 billion people on Tuesday, according to a United Nations projection, with much of the growth coming from developing nations in Africa.

Among them is Nigeria, where resources are already stretched to the limit. More than 15 million people in Lagos compete for everything from electricity to light their homes to spots on crowded buses, often for two-hour commutes each way in this sprawling megacity. Some Nigerian children set off for school as early as 5 a.m.

And over the next three decades, the West African nation's popu...