Chimpanzee, sometimes colloquially known as a chimp, is the common name for the two extant species of ape in the genus Pan where the Congo River forms the boundary between the native habitat of the two species:

• Common Chimpanzee, Pan troglodytes: the better known chimpanzee lives primarily in West and Central Africa.
• Bonobo, Pan paniscus: also known as the "Pygmy Chimpanzee", this species is found in the forests of the Democratic Republic of the Congo.

Chimpanzees are members of the Hominidae family, along with gorillas, humans, and orangutans. Chimpanzee are thought to have split from human evolution about 6 million years ago and thus the two chimpanzee species are the closest living relatives to humans; all being members of the Hominini tribe (along with extinct species of Hominina subtribe). Chimpanzees are the only known members of the Panina subtribe. The two Pan species split only about one million years ago. Around 94% of human and chimpanzee DNA sequences are the same.

Evolutionary relationships

The genus Pan is now considered to be part of the subfamily Homininae to which humans also belong. These two species are the closest living evolutionary relatives to humans. Humans shared a common ancestor with chimpanzees six million years ago. Groundbreaking research by Mary-Claire King in 1973 found 99% identical DNA between human beings and chimpanzees, although research since has modified that finding to about 94% commonality, with at least some of the difference occurring in non-coding DNA. It has even been proposed that troglodytes and paniscus belong with sapiens in the genus Homo, rather than in Pan. One argument for this is that other species have been reclassified to belong to the same genus on the basis of less genetic similarity than that between humans and chimpanzees.

Fossils

Many human fossils have been found, but chimpanzee fossils were not described until 2005. Existing chimpanzee populations in West and Central Africa do not overlap with the major human fossil sites in East Africa. However, chimpanzee fossils have now been reported from Kenya. This would indicate that both humans and members of the Pan clade were present in the East African Rift Valley during the Middle Pleistocene. This Chimpanzee is bald, allowing his muscles to be easily visible.

Anatomy and physiology

The male common chimp is up to 1.7 m (up to 5.6 ft) high when standing, and weighs as much as 70 kg (154 lb); the female is somewhat smaller. The common chimp's long arms, when extended, have a span half again as long as the body's height and are longer than its legs. The bonobo is a little shorter and thinner than the common chimpanzee but has longer limbs. Both species use their long, powerful arms for climbing in trees. On the ground, chimpanzees usually walk on all fours using their knuckles for support with their hands clenched, a form of locomotion called knuckle-walking. Chimpanzee feet are better suited for walking than are those of the orangutan because the chimp's soles are broader and the toes shorter. Both the common chimpanzee and bonobo can walk upright on two legs when carrying objects with their hands and arms. The coat is dark; the face, fingers, palms of the hands, and soles of the feet are hairless; and the chimp has no tail. A bony shelf over the eyes gives the forehead a receding appearance, and the nose is flat. Although the jaws protrude, the lips are thrust out only when a chimp pouts. The brain of a chimpanzee is about half the size of the human brain.