CHIMPANZEE

West African, or masked, chimpanzee (Pan troglodytes verus). (Pan troglodytes), byname chimp species of great ape (family Pongidae) that inhabits the tropical rainforests and woodland savannas of equatorial Africa from The Gambia in the west to Lake Albert, Lake Victoria, and northwestern Tanzania in the east. Chimpanzees are classified taxonomically into one species and three subspecies within the genus Pan. Generally recognized forms include the tschego (Pan troglodytes troglodytes), known as the common chimpanzee in continental Europe; the masked chimpanzee (P. troglodytes verus; see photograph), known as the common chimpanzee in Great Britain; and the eastern, or long-haired, chimpanzee (P. troglodytes schweinfurthii). The so-called pygmy chimpanzee, or bonobo , is a separate species (P. paniscus). Genetic analysis indicates that the chimpanzee is humanity's closest living relative. Individuals vary considerably in size and appearance, but chimpanzees usually stand approximately 1-1.7 m (3-5.5 feet) tall when erect and weigh about 35-60 kg (55-130 pounds). Males tend to be larger and more robust than females. Chimpanzees are covered by a coat of brown or black hair, but their faces are bare. The body and facial skin of mature chimpanzees is dark in colour, but the faces of younger animals may be pinkish or whitish. Chimpanzees spend time both in the trees and on the ground. In the trees, where most feeding takes place, they use both hands and feet in moving about or they swing by their arms (brachiate) from branch to branch. Movement over any significant distance usually takes place on the ground, where, though they may walk erect, chimpanzees more often walk on all fours, leaning on the knuckles of their hands. They are active during the day, and at night they usually sleep in the trees in nests they build of branches and leaves. The chimpanzee diet is primarily vegetarian and consists mostly of fruits, berries, leaves, and seeds. Termites and ants are eaten, and chimpanzees occasionally stalk and kill young baboons and bush pigs. Wild chimpanzees have been observed poking twigs, grass, or other objects into ant and termite nests, withdrawing the tool, and eating the insects that cling to it. They can also use sticks as tools in other ways, and they have been observed using leaves to soak up drinking water or to clean themselves. Younger animals apparently acquire these tool-using behaviours from older animals. Chimpanzees are lively animals with more extroverted dispositions than either gorillas or orangutans. They are gregarious and live in loose and flexible groups known as "communities" that are based on associations between adult males in a home range, or territory. A community has 15-80 members and consists of several subgroups of varying size and unstable composition. The dominance hierarchy that exists among male chimpanzees is unusually fluid, and individuals associate with each other and join and leave different subgroups with complete freedom. Female chimpanzees spend most of their time with their young or with other females. The relations between different communities tend to be hostile; intruders on a group's home range may be attacked, and members of one community have been known to destroy a smaller neighbouring community by driving away or killing its members. Adult chimpanzees regularly groom each other's fur to remove external parasites, a behaviour that reinforces the social bonds between them. Chimpanzees communicate by facial expressions, gestures, and a large array of vocalizations, including screams, hoots, grunts, and roars. Males display excitement by standing erect, stamping or swaying, and letting out a chorus of screams. The female chimpanzee bears a single young at any time of year after a gestation period of about 230 days. The newborn weighs about 1.8 kg (4 pounds), is almost helpless, and clings to the fur of the mother's belly when she is in motion. From about 6 months to 2 years, the youngster rides on the mother's back. Weaning takes place at about 5 years, and females begin to reproduce at 13-15 years of age. The life expectancy is about 50 years under favourable conditions. Chimpanzees' numbers in the wild have been gradually reduced by hunting, by the destruction of their habitat from logging or farming, and by commercial exportation for use in zoos and research laboratories. They are now listed as endangered in the Red Data Book. Chimpanzees are highly intelligent and are able to solve many kinds of problems posed to them by human trainers and experimenters. Chimpanzees' intelligence, responsiveness, and exuberance make them ideal nonhuman subjects for psychological, medical, and biological experiments. Young chimpanzees can become very attached to their human trainers, and their expressions of feeling resemble those of humans more closely than any other animal. A number of researchers have taught chimpanzees to use sign language or languages based on the display of tokens or pictorial symbols. The implications of these language studies have been contested, however. Critics charge that the apes have not acquired true language in the sense of understanding "words" as abstract symbols that can be combined in meaningful new ways. Other investigators maintain that more recent language training has resulted in the chimpanzees' acquiring a true recognition of "words" as abstractions that can be applied in novel contexts.