Bonobo

It is commonly considered to be more gracile than the common chimpanzee, and females are somewhat smaller than males. Body mass in males ranges from 34 to 45 kg (75 to 99 lb), against an average of 30 kg (66 lb) in females. The total length of bonobos (from the nose to the rump) is 70 to 83 cm (28 to 33 in). Its head is also smaller than that of the common chimpanzee with less prominent brow ridges above the eyes. It has a black face with pink lips, small ears, wide nostrils, and long hair on its head that forms a part. Females have slightly more prominent breasts, in contrast to the flat breasts of other female apes, although not so prominent as those of humans. The bonobo also has a slim upper body, narrow shoulders, thin neck, and long legs when compared to the common chimpanzee.

Bonobos are both terrestrial and arboreal. Most ground locomotion is characterized by quadrupedal knuckle walking. Bipedal walking has been recorded as less than 1% of terrestrial locomotion in the wild, a figure that decreased with habituation, while in captivity there is a wide variation. Bipedal walking in captivity, as a percentage of bipedal plus quadrupedal locomotion bouts, has been observed from 3.9% for spontaneous bouts to nearly 19% when abundant food is provided. These physical characteristics and its posture give the bonobo an appearance more closely resembling that of humans than that of the common chimpanzee. The bonobo also has highly individuated facial features, as humans do, so that one individual may look significantly different from another, a characteristic adapted for visual facial recognition in social interaction.

Multivariate analysis has shown bonobos are more neotenized than the common chimpanzee, taking into account such features as the proportionately long torso length of the bonobo. Other researchers challenged this conclusion.

Bonobo

The bonobo ( /bəˈnoʊboʊ/ or /ˈbɒnəboʊ/), Pan paniscus, previously called the pygmy chimpanzee and less often, the dwarf or gracile chimpanzee, is a great ape and one of the two species making up the genus Pan. The other species in genus Pan is Pan troglodytes, or the common chimpanzee. Although the name "chimpanzee" is sometimes used to refer to both species together, it is usually understood as referring to the common chimpanzee, while Pan paniscus is usually referred to as the bonobo. It is distinguished by relatively long legs, pink lips, dark face and tail-tuft through adulthood, and parted long hair on its head. The bonobo is found in a 500,000 km2 (190,000 sq mi) area of the Congo Basin in the Democratic Republic of the Congo, Central Africa. The species is omnivorous and inhabits primary and secondary forests including seasonally inundated swamp forests.

The bonobo is popularly known for its high levels of sexual behavior. Sex functions in conflict appeasement, affection, social status, excitement, and stress reduction. It occurs in virtually all partner combinations and in a variety of positions. This is a factor in the lower levels of aggression seen in the bonobo when compared to the common chimpanzee and other apes. Bonobos are perceived to be matriarchal: females tend to collectively dominate males by forming alliances and use sexuality to control males. A male's rank in the social hierarchy is often determined by his mother's rank.

Along with the common chimpanzee, the bonobo is the closest extant relative to humans. Because the two species are not proficient swimmers, it is possible that the formation of the Congo River 1.5–2 million years ago led to the speciation of the bonobo. They live south of the river, and thereby were separated from the ancestors of the common chimpanzee, which live north of the river. There is no concrete data on population numbers but it is estimated to be between 29,500 and 50,000 individuals. The species is listed as Endangered on the IUCN Red List and is threatened by habitat destruction and human population growth and movement, though commercial poaching is the most prominent threat. It typically lives 40 years in captivity, though its lifespan in the wild is unknown.