Apes are a group of primates that includes gorillas, orangutans, chimpanzees, and gibbons. These are the primate species that are the most closely related to humans. The hands, feet, and face of an ape are hairless, while the rest of its body is covered with coarse black, brown, or red hair. Apes share some characteristics that set them apart from other primates: they have an appendix, lack a tail, and their skeletal structures have certain features not found in the skeletons of other primates.
Gorillas (Gorilla gorilla ) inhabit forests of Central Africa and are the largest and most powerful of all primates. Adult males stand 6 ft (1.8 m) upright (although this is an unnatural position for a gorilla) and weigh up to 450 lb (200 kg), while females are much smaller. Gorillas live about 44 years. Mature males (older than about 13 years), called silverbacks, are marked by a band of silver-gray hair on their backs. Three subspecies of gorillas are usually recognized: the western lowland gorilla (Gorilla gorilla gorilla ), the eastern gorilla (G. g. graueri ), and the mountain gorilla (G. g. beringei ).
Gorillas live in small family groups of several females and their young, led by a dominant silverback male. The females comprise a harem for the silver-back, who holds the sole mating rights among males in the troop. Female gorillas produce one infant after a gestation period of nine months. The large size and great strength of the silverback are advantages in competing with other males for leadership of the group and in defending against outside threats. Despite its ferocious image to some people, the gorilla is not an aggressive animal. Even in a clash between two adult males, most of the conflict consists of aggressive posturing, roaring, and chest-beating, rather than physical contact.
During the day these ground-living, vegetarian apes move slowly through the forest, selecting leaves, fruit, and stems from the vegetation as food. Their home range is about 9–14 sq mi (25–40 sq km). At night the family group sleeps in trees, resting on platform nests that they make each evening from branches; silverbacks usually sleep near the foot of the tree.
The total population of wild gorillas was recently estimated to be about 126,000. Most of these are western lowland gorillas living in Angola, Cameroon, Central African Republic, Congo, Equatorial Guinea, Gabon, and Nigeria, with the largest population in Gabon. The eastern lowland gorilla occurs in the eastern part of the Democratic Republic of Congo (formerly Zaire) and numbers about 5,000-10,000. The mountain gorilla is found in the Virunga volcanoes region of Rwanda, Uganda, and the Democratic Republic of Congo, and in the Bwindi Forest Reserve of Uganda; this group only numbers about 400-650 individuals. Other than humans, gorillas have no real predators, although leopards will occasionally take young individuals. Hunting, poaching (a live mountain gorilla can be worth $150,000), and habitat loss are causing gorilla populations to decline. The trade of gorillas has been banned by the countries where this occurs and by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), but they are nevertheless threatened by the illegal black market. The forest refuge of these great apes is being felled in order to accommodate the needs of the ever-expanding human population in Central Africa, shrinking the territory available for sustaining gorilla populations.
The orangutan (Pongo pygmaeus ) is restricted to the rainforests of the islands of Sumatra and Borneo in Indonesia and Malaysia. The orangutan is the largest living arboreal mammal. It spends most of the daylight hours moving slowly and deliberately through the forest canopy in search of food. Sixty percent of its diet consists of fruit, and the remainder is composed of young leaves and shoots, tree bark, mineral-rich soil, and insects. Orangutans are long-lived, with many individuals reaching 50–60 years of age in the wild. These large, chestnut-colored, long-haired apes are endangered because of habitat destruction and illegal capture for the wild-animal trade.
Even though Indonesia and Malaysia have more than 400,000 sq mi (1,000,000 sq km) of rainforest habitat remaining, the rapid rate of deforestation threatens the continued existence of the wild orangutan population, whose numbers are thought to have declined by 50% since 1990. The Indonesian and Malaysian governments and CITES have banned the local and international trading of orangutans, but they are still threatened by the illegal market. In order to meet the demand for these apes as pets around the world, poachers kill mother orangutans to secure their young. The mortality rate of these captured orphans is extremely high, with fewer than 20% of those smuggled arriving alive at their final destination. Some hope for the species rests in a global effort to manage a captive propagation program in zoos, although this is far less preferable to conserving them in their wild habitat.
The common chimpanzee (Pan troglodytes ) is relatively widespread in the forested parts of West, Central, and East Africa. A closely related species, the pygmy chimpanzee or bonobo (P. paniscus ), is restricted to swampy lowland forests of the Zaire basin. Despite their names, common chimpanzees are no longer common, and pygmy chimpanzees are no smaller than the other species.
Chimpanzees are partly arboreal and partly ground-dwelling. They feed in fruit trees by day, nest in other trees at night, and can move rapidly through treetops. On the ground, chimpanzees usually walk on all fours (this is called knuckle walking), since their arms are longer than their legs. Their hands have fully opposable thumbs and, although lacking a precision grip, they can manipulate objects dexterously. Chimpanzees make and use a variety of simple tools: they shape and strip “fishing sticks” from twigs to poke into termite mounds, and they chew the ends of shoots to fashion fly whisks. They also throw sticks and stones as offensive weapons and when they hunt and kill monkeys.
Chimpanzees live in small nomadic groups of 3–6 animals (common chimpanzee) or 6–15 animals (pygmy chimpanzee), which make up a larger community of 30–80 individuals that occupy a territory. Adult male chimpanzees cooperate in defending their territory against predators. Chimpanzee society consists of promiscuous, mixed-sex groups. Female common chimpanzees are sexually receptive for only a brief period in mid-month (estrous), while female pygmy chimpanzees are sexually receptive for most of the month. Ovulating females capable of being fertilized have swollen pink hindquarters and copulate with most of the males in the group. Female chimpanzees give birth to a single infant after a gestation period of about eight months.
Jane Goodall (1934–) has studied common chimpanzees for more than 40 years (beginning in 1960) in the Gombe Stream National Park of Tanzania. She has found that chimpanzee personalities are as variable as those of humans, and that chimpanzees form alliances, have friendships, have personal dislikes, and carry on feuds. Chimpanzees also have a cultural tradition, that is, they pass learned behavior and skills from generation to generation. Chimpanzees have been taught complex sign language (the chimpanzee larynx will not allow speech), through which abstract ideas have been conveyed to people. These studies show that chimpanzees can develop a large vocabulary and that they can manipulate this vocabulary to frame original thoughts.
Humans share approximately 95-98.5% of their genes with chimpanzees. The close relatedness of chimpanzees (and other apes) with humans is a key element of the ethical argument for a higher standard of care, and even granting of legal rights, for these animals in captivity. Further studies of chimpanzees will undoubtedly help us to better understand the origins of the social behavior and evolution of humans. Despite their status as close relatives of humans, both species of chimpanzees are threatened by the destruction of their forest habitat and by hunting and by capture for research. Both species of chimpanzees are considered endangered, and their international trade is closely regulated by CITES.
Gibbons (genus Hylobates ) are the smallest members of the ape family. Gibbons are found in Southeast Asia, China, and India, and nine species are recognized. They spend most of their lives at the tops of trees in the jungle, eating leaves and fruit. They are extremely agile, swinging with their long arms on branches to move from tree to tree, and they often walk upright on tree branches. Gibbons are known for their loud calls and songs, which are used to announce their territory and warn away others. They are devoted parents, raising one or two offspring at a time and showing extraordinary affection in caring for them. Conservationists and biologists who have worked with gibbons describe them as extremely intelligent, sensitive, and affectionate.
Gibbons have long been hunted as food, for medical research, and for sale as pets and zoo specimens. A common method of collecting them is to shoot the mother and then capture the infant. The mortality rate in collecting and transporting gibbons to places where they can be sold is extremely high, and this coupled with the destruction of their jungle habitat has resulted in severe depletion of their numbers. Despite a ban by CITES on the international trade in gibbons, illegal commerce, particularly of babies, continues in markets throughout Asia.
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Eugene C. Beckham
Lewis G. Regenstein