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The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative the bonobo was more commonly known as the pygmy chimpanzee, this species was often called the common chimpanzee or the robust chimpanzee. The chimpanzee and the bonobo are the only species in the genus ''Pan''. Evidence from fossils and DNA sequencing shows that ''Pan'' is a sister taxon to the human lineage and is humans' closest living relative. The chimpanzee is covered in coarse black hair, but has a bare face, fingers, toes, palms of the hands, and soles of the feet. It is larger and more robust than the bonobo, weighing for males and for females and standing .

The chimpanzee lives in groups that range in size from 15 to 150 members, although individuals travel and forage in much smaller groups during the day. The species lives in a strict male-dominated hierarchy, where disputes are generally settled without the need for violence. Nearly all chimpanzee populations have been recorded using tools, modifying sticks, rocks, grass and leaves and using them for hunting and acquiring honey, termites, ants, nuts and water. The species has also been found creating sharpened sticks to spear small mammals. Its gestation period is eight months. The infant is weaned at about three years old but usually maintains a close relationship with its mother for several years more.

The chimpanzee is listed on the IUCN Red List as an endangered species. Between 170,000 and 300,000 individuals are estimated across its range. The biggest threats to the chimpanzee are habitat loss, poaching, and disease. Chimpanzees appear in Western popular culture as stereotyped clown-figures and have featured in entertainments such as chimpanzees' tea parties, circus acts and stage shows. They are sometimes kept as pets, though their strength, aggressiveness, and unpredictability makes them dangerous in this role. Some hundreds have been kept in laboratories for research, especially in America. Many attempts have been made to teach languages such as American Sign Language to chimpanzees, with limited success.

Etymology

The English word ''chimpanzee'' is first recorded in 1738. It is derived from Vili ''ci-mpenze'' or Tshiluba language ''chimpenze'', with a meaning of "ape". The colloquialism "chimp" was most likely coined some time in the late 1870s. The genus name ''Pan'' derives from the Greek god, while the specific name ''troglodytes'' was taken from the Troglodytae, a mythical race of cave-dwellers.

Taxonomy and genetics

The first great ape known to Western science in the 17th century was the " orang-outang" (genus ''Pongo''), the local Malay name being recorded in Java by the Dutch physician Jacobus Bontius. In 1641, the Dutch anatomist Nicolaes Tulp applied the name to a chimpanzee or bonobo brought to the Netherlands from Angola. Another Dutch anatomist, Peter Camper, dissected specimens from Central Africa and Southeast Asia in the 1770s, noting the differences between the African and Asian apes. The German naturalist Johann Friedrich Blumenbach classified the chimpanzee as ''Simia troglodytes'' by 1775. Another German naturalist, Lorenz Oken, coined the genus ''Pan'' in 1816. The bonobo was recognised as distinct from the chimpanzee by 1933.

Evolution

Despite a large number of ''Homo'' fossil finds, ''Pan'' 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, but chimpanzee fossils have now been reported from Kenya. This indicates that both humans and members of the ''Pan'' clade were present in the East African Rift Valley during the Middle Pleistocene.

DNA evidence suggests the bonobo and chimpanzee species separated from each other less than one million years ago (similar in relation between ''Homo sapiens'' and Neanderthals). A 2017 genetic study suggests ancient gene flow ( introgression) between 200 and 550 thousand years ago from the bonobo into the ancestors of central and eastern chimpanzees. The chimpanzee line split from the last common ancestor of the human line around six million years ago. Because no species other than ''Homo sapiens'' has survived from the human line of that branching, both chimpanzee species are the closest living relatives of humans; the lineage of humans and chimpanzees diverged from gorillas (genus ''Gorilla'') about seven million years ago. A 2003 study argues the chimpanzee should be included in the human branch as ''Homo troglodytes'' and notes "experts say many scientists are likely to resist the reclassification, especially in the emotionally-charged and often disputed field of anthropology".

Subspecies and population status

Four subspecies of the chimpanzee have been recognised, with the possibility of a fifth:
* Central chimpanzee or the tschego (''Pan troglodytes troglodytes''), found in Cameroon, the Central African Republic, Equatorial Guinea, Gabon, the Republic of the Congo, and the Democratic Republic of the Congo, with about 140,000 individuals existing in the wild.
* Western chimpanzee (''P. troglodytes verus''), found in Ivory Coast, Guinea, Liberia, Mali, Sierra Leone, Guinea-Bissau, Senegal, and Ghana with about 52,800 individuals still in existence.
* Nigeria-Cameroon chimpanzee (''P. troglodytes ellioti'' (also known as ''P. t. vellerosus'')), that live within forested areas across Nigeria and Cameroon, with 6000–9000 individuals still in existence.
* Eastern chimpanzee (''P. troglodytes schweinfurthii''), found in the Central African Republic, South Sudan, the Democratic Republic of the Congo, Uganda, Rwanda, Burundi, Tanzania, and Zambia, with approximately 180,000–256,000 individuals still existing in the wild.
* Southeastern chimpanzee, ''P. troglodytes marungensis'', in Burundi, Rwanda, Tanzania, and Uganda. Colin Groves argues that this is a subspecies, created by enough variation between the northern and southern populations of ''P. t. schweinfurthii'', but it is not recognised by the IUCN.

Genome

A draft version of the chimpanzee genome was published in 2005 and encodes 18,759 proteins, (compared to 20,383 in the human proteome). The DNA sequences of humans and chimpanzees are very similar and the difference in protein number mostly arises from incomplete sequences in the chimp genome. Both species differ by about 35 million single-nucleotide changes, five million insertion/deletion events and various chromosomal rearrangements. Typical human and chimpanzee protein homologs differ in an average of only two amino acids. About 30% of all human proteins are identical in sequence to the corresponding chimpanzee protein. Duplications of small parts of chromosomes have been the major source of differences between human and chimpanzee genetic material; about 2.7% of the corresponding modern genomes represent differences, produced by gene duplications or deletions, since humans and chimpanzees diverged from their common evolutionary ancestor.

Characteristics

Adult chimpanzees have an average standing height of . Wild adult males weigh between with females weighing between . In exceptional cases, certain individuals may considerably exceed these measurements, standing over on two legs and weighing up to in captivity.

The chimpanzee is more robustly built than the bonobo but less than the gorilla. The arms of a chimpanzee are longer than its legs and can reach below the knees. The hands have long fingers with short thumbs and flat fingernails. The feet are adapted for grasping, and the big toe is opposable. The pelvis is long with an extended ilium. A chimpanzee's head is rounded with a prominent and prognathous face and a pronounced brow ridge. It has forward-facing eyes, a small nose, rounded non-lobed ears, a long mobile upper lip. Additionally, adult males have sharp canine teeth. Chimpanzees lack the prominent sagittal crest and associated head and neck musculature of gorillas.

Chimpanzee bodies are covered by coarse hair, except for the face, fingers, toes, palms of the hands, and soles of the feet. Chimpanzees lose more hair as they age and develop bald spots. The hair of a chimpanzee is typically black but can be brown or ginger. As they get older, white or grey patches may appear, particularly on the chin and lower region. The skin may range from pale to dark, though females develop swelling pink skin when in oestrus.

Chimpanzees are adapted for both arboreal and terrestrial locomotion. Arboreal locomotion consists of vertical climbing and brachiation. On the ground, chimpanzees move both quadrupedally and bipedally. These movements appear to have similar energy costs. As with bonobos and gorillas, chimpanzees move quadrupedally by knuckle-walking, which probably evolved independently in ''Pan'' and ''Gorilla''. The physical strength of chimps is around 1.5 times greater than humans due to higher content of fast twitch muscle fibres, one of the chimpanzee's adaptations for climbing and swinging. According to Japan's Asahiyama Zoo, the grip strength of an adult chimpanzee is estimated to be 200 kg (441 lb), while other sources claim figures of up to 330 kg (727 lb).

Ecology

The chimpanzee is a highly adaptable species. It lives in a variety of habitats, including dry savanna, evergreen rainforest, montane forest, swamp forest, and dry woodland-savanna mosaic. In Gombe, the chimpanzee mostly uses semideciduous and evergreen forest as well as open woodland. At Bossou, the chimpanzee inhabits multistage secondary deciduous forest, which has grown after shifting cultivation, as well as primary forest and grassland. At Taï, it is found in the last remaining tropical rain forest in Ivory Coast. The chimpanzee has an advanced cognitive map of its home range and can repeatedly find food. The chimpanzee builds a sleeping nest in a tree in a different location each night, never using the same nest more than once. Chimpanzees sleep alone in separate nests except for infants or juvenile chimpanzees, which sleep with their mothers.

Diet

The chimpanzee is an omnivorous frugivore. It prefers fruit above all other food items but also eats leaves, leaf buds, seeds, blossoms, stems, pith, bark, and resin. A study in Budongo Forest, Uganda found that 64.5% of their feeding time concentrated on fruits (84.6% of which being ripe), particularly those from two species of ''Ficus'', ''Maesopsis eminii'', and ''Celtis gomphophylla''. In addition, 19% of feeding time was spent on arboreal leaves, mostly ''Broussonetia papyrifera

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