Urbanisation

Aside from the growth of the population itself, urbanisation was the dominant demographic trend of the 20th century, and will likely continue to be. In 1900, some 16 cities had a million people or more, and roughly 10 percent of humanity lived in cities. Today, 326 cities have at least that many people, and there are 14 "mega-cities" with 10 million or more residents.

If cities continue to grow as projected they will contain more than half the population by 2010, making the world more urban than rural for the first time in history. In effect, we will become an urban species, far removed from our hunter-gatherer origins and more separated from our natural underpinnings than ever before.