The Anatomy of Chimpanzees
The male common chimp stands up to 1.7 m (5.6 ft) high and weighs as much as 70 kg (150 lb); the female is somewhat smaller. The common chimp’s long arms, when extended, span one and a half times the body’s height. A chimpanzee's arms are longer than its legs.[9]The bonobo is slightly shorter and thinner than the common chimpanzee but has longer limbs. In trees, both species climb with their long, powerful arms; on the ground, chimpanzees usually knuckle-walk, or walk on all fours, clenching their fists and supporting themselves on the knuckles thereof. Chimpanzee feet are better suited for walking than are those of the orangutan because the chimp has broader soles and shorter toes.
Both the common chimpanzee and bonobo can walk upright on two legs when carrying objects with their hands and arms. The bonobo has proportionately longer upper limbs and more often walks upright than does the common chimpanzee. The coat is dark; the face, fingers, palms of the hands, and soles of the feet, hairless; the chimp, tailless. The exposed skin of the face, hands and feet varies from pink to very dark in both species but is generally lighter in younger individuals, darkening as maturity is reached. A University of Chicago Medical Centre study has found significant genetic differences between chimpanzee populations.[10] 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 has been measured at ~337cc,[11][12] ~393 cc,[13] with a general range of 282–500 cc.[14] Human brains, in contrast, have been measured as being three times larger, variously reported volumes include ~1,299 cc,[11][12] ~1,158 cc,[13] and averages of ~1330 cc.[15][16][17][18][19][20][21][22]
Chimpanzee testicles are unusually large for their body size, with a combined weight of about 4 oz (110 g) compared to a gorilla's 1 oz (28 g) or a human's 1.5 ounces (43 g). This relatively great size is generally attributed to sperm competition due to the polyandrous nature of chimpanzee mating behavior.[23] Chimpanzees reach puberty at an age of between eight and 10 years and rarely live past age 40 in the wild, but some have lived longer than 60 years in captivity.