Indian Sikh festival in Ramblas Catalunya | Barcelona, Spain
The first billion people accumulated over a leisurely interval, from the origins of humans hundreds of thousands of years ago to the early 1800s. Adding the second took another 120 or so years. Then, in the last 50 years, humanity more than doubled, surging from three billion in 1959 to four billion in 1974, five billion in 1987 and six billion in 1998. This rate of population increase has no historical precedent.
—Joel E. Cohen, author of “How Many People Can the Earth Support?”Buy This Image