7 Billion Humans | National Geographic Magazine: Water Fight at China Folk Culture Villages | Shenzhen, China

Huge Crowds at Water Fight at China Folk Culture Villages | Shenzhen, China

But there is plenty of bad news, too. Nearly half the world lives on $2 a day, or less. In China, the figure is 36 percent; in India, 76 percent. More than 800 million people live in slums. A similar number, mostly women, are illiterate.

—Joel E. Cohen, author of “How Many People Can the Earth Support?”