Value of species
Humans have the widest distribution of any terrestrial mammal species, inhabiting every continent on earth (although there are no permanent settlements on Antarctica). A small group of humans has been introduced to space, where they inhabit the International Space Station.
In mid-2007, the total population of human beings was estimated at 6.6 billion, an increase from 6.1 billion in 2001. Two countries, China and India, hold approximately one-third of the entire human population alone, with 1,318 million and 1,312 million people, respectively. The United States of America is third with 302 million. The annual rate of increase is about 1.2%; the total population is expected to reach 7,965 million by mid-2025, and 9,294 by mid-2050 (Population Reference Bureau 2007).
Humans are found in a wide variety of habitats, largely thanks to their ability to use technology to adapt to and modify their habitats. Major concentrations are found in urban centers: over the past 30 years, the urban population has increased so that more than half of the world population will be living in cities by 2008 (Population Reference Bureau 2007).