Danica May Camacho weighed 5.5 pounds when she was born in the Philippines on Monday. She was one of several babies chosen by the United Nations to celebrate the arrival of the 7 billionth person on earth.
The world's population has expanded exponentially in the past fifty years, and it is expected to continue growing in the coming decades at an equally astonishing rate. The U.N. calculates 8 billion people will live on earth by 2025 and 10 billion by 2083.
Yet the growth of the world population hasn't always been so drastic. It took the world until 1804 to reach its first billionth inhabitant, the United Nations Population Fund (UNFPA) writes in its latest report, "State of the World Population Report 2011." A century later, the planet already counted two billion inhabitants. In 1959 there were 3 billion people; in 1974, 4 billion; 5 billion in 1987; and 6 billion in 1998.
In the report, the UNFPA describes some remarkable trends in the world's population increase. About one in two people lives in a city, the report finds, and in about 35 years that number will rise to two out of three. People under the age of 25 make up nearly half of the world's population, and in some countries that percentage is as high as 60.
While the U.N. considers the world's 7 billionth inhabitant a major milestone, global population growth also brings unprecedented challenges. "Clearly we are living through an extraordinary period in human history, an era of unprecedented growth in our species," explains Steven Sinding, director of the office of population at the United States Agency for International Development, in the Population Fund's report. "The pace of growth poses enormous challenges for many of the poorest countries, which lack the resources not only to keep up with demand for infrastructure, basic health and education services and job opportunities for the rising number of young people, but also to adapt to climate change."
Take a look at the slideshow below to see where the world is headed. You can find more details in UNFPA's "State of the World Population Report 2011."