Humans, or human beings, are bipedal primates belonging to the mammalian species Homo sapiens (Latin: "wise human" or "knowing human"2) in the family Hominidae (the great apes).34 DNA evidence indicates that modern humans originated in Africa about 200,000 years ago.5 Compared to other species, humans have a highly developed brain, capable of abstract reasoning, language, introspection, and emotional suffering. This mental capability, combined with an erect body carriage that frees the forelimbs (arms) for manipulating objects, has allowed humans to make far greater use of tools than any other species. Humans now inhabit every continent on Earth, except Antarctica (although several governments maintain permanent research stations there, inhabited for short periods by scientists and other researchers). Humans also now have a continuous presence in low Earth orbit, occupying the International Space Station. The human population on Earth now amounts to over 6.6 billion, as of May 2008.6
