Great Apes

The closest living relatives to humans, great apes belong to the Family Pongidae and include four species in three genera: common chimpanzees (Pan troglodytes) and bonobos (Panpaniscus), orang-utans (Pongopygmaeus), and gorillas (Gorilla gorilla). Like all apes, the great apes lack tails and have broad, shortened trunks (in contrast to the flattened trunks seen in monkeys). Their forelimbs are as long as or longer than their hind limbs and are equipped with mobile wrist and shoulder joints that make them good climbers. All of these characteristics reflect adaptations for suspensory locomotion, although the great apes are less acrobatic in the trees than are their smaller ape relatives, gibbons and siamangs. Great apes are very similar to humans in their reproductive biology. Females give birth to one offspring at a time and will have relatively few offspring over a lifetime. In all apes the period of infancy and maternal care is prolonged, but in great apes it can last up to four years. The average life span of great apes is exceptionally long. In the wild gorillas may live to age thirty-five, while chimpanzees can live to about fifty. In captivity, this life span is even longer.

Members of the genus Pan, common chimpanzees and bonobos, are found in West and Central Africa. Common chimpanzees are found north of the River Zaire, from Senegal to Tanzania, while bonobos are confined to Zaire between the rivers Zaire and Kasai. Common chimpanzees inhabit humid forests, deciduous woodland, or mixed savanna habitats. Bonobos are found in humid forests only. Both species exhibit only moderate sexual dimorphism, with females weighing in at approximately 68 lbs (31 kg) and males at approximately 88 lbs (40 kg). Captive chimpanzees are known to weigh much more than their wild counterparts. Chimpanzees (espe cially the young) spend a considerable amount of time in the trees but frequently come to the ground to feed. When on the ground they normally walk on all fours, supporting their weight on the knuckles of their clenched fists. Chimpanzees will sometimes move about bipedally, especially while carrying food or during male displays. Bipedal locomotion is more common to bonobos than to common chimpanzees.

Both bonobos and common chimpanzees feed primarily on fruits, but leaves make up a substantial proportion of their diet as well. As much as 5 percent of their diet consists of animal prey. This primarily includes insects (for example, ants, termites, caterpillars) but may also include small mammals. Insect prey may be taken by hand or with tools, as seen in termite fishing by the common chimpanzee. The chimpanzee is known to hunt in groups, and it will take monkeys, pigs, and antelope when the opportunity presents itself. Chimpanzee social groups range between forty and eighty individuals that include adult males, females, and their offspring.

Common chimpanzees and bonobos present an interesting contrast in social behavior for two species so closely related (they are thought to have split only 2 million years ago). Common chimpanzees are known to be quite aggressive, with incidents recorded (in Gombe) in which one group systematically hunted down and killed every member of another nearby group. Unlike common chimpanzees, which resolve issues through violence, pygmy chimpanzees (bonobos) resolve issues through sex. Another contrast to common chimpanzees is that bonobo females are occasionally dominant to males. Members of this genus are the closest living relatives to humans. Chimpanzees and humans differ significantly in only 2 percent of their genes. This evidence suggests that they share a very

Male pygmy chimpanzee (Gallo Images/Corbis)

recent common ancestor and perhaps diverged into separate species only 5 to 7 million years ago.

Members of the genus Pongo, orang-utans are the only great apes to live outside of Africa. Their reddish-brown fur probably helps them maintain visual contact with one another in the lowland and hilly tropical rain forests in Northern Sumatra and in Borneo. Of the three great ape genera, orang-utans spend the most time in the trees. They move slowly and deliberately, using all four limbs (quadramanus)

to support their great body weight. Females and young spend much more time in the trees than do males, which is probably a consequence of the much greater size of males. When on the ground orang-utans walk resting the weight of their body on the sides of their clenched fists, a different form of locomotion from the knuckle walking seen in chimpanzees and gorillas. Orang-utans exhibit marked sexual dimorphism both in body size and in secondary sex characteristics. Male orang-utans can reach up to 200 lbs (90 kg), while females are about half their size, reaching 110 lbs (50 kg). In addition, males develop pronounced cheek flanges and throat pouches upon sexual maturity. Orang-utans are primarily frugivorous (fruit-eating) and males and females forage separately. Male and female orang-utans come together only for a brief courtship and return to their solitary lifestyle immediately after mating. Females and their single offspring form feeding groups, and the territories of males may include that of several females and their offspring.

Members of the genus Gorilla are the largest of all the primates: males can reach up to 5-feet-9-inches and weigh as much as 400 lbs (180 kg). The two subspecies of lowland gorilla live in hot lowland forests of west and central Africa. The other subspecies, the mountain gorilla, lives high in the cool mountains of central Africa (elev. 5,450 to 12,500 ft). Gorillas are predominantly folivorous, subsisting primarily on leaves and stems rather than fruit. Although the young spend quite a bit of time in trees, adult gorillas are primarily terrestrial, spending more time on the ground than other great apes. Consequently, they have lost much of the grasping capability of their foot. Gorillas normally walk on all fours, clenching their hands so that their knuckles take their weight. The gorilla's social group can range between two and thirty-five individuals but usually numbers five to ten. Their close-knit groups consist of one dominant male (called a sil-verback because the fur on their back turns silvery gray), several females, and their immature offspring. The same dominant male may lead a group for several years.

—Ken Mowbray and Shara Bailey

See also: Monkeys; Physical Anthropology; Primates Bibliography

Conroy, Glen. 1990. Primate Evolution. New York: W. W. Norton; Falk, Dean. 2000. Primate Diversity. New York: W. W. Norton; Goodall, Jane. 1986. The Chimpanzees of Gombe: Patterns of Behavior. Cambridge: Harvard University Press; Sussman, Robert. 1997. The Biological Basis for Human Behavior. New York: Simon and Schuster Custom Publishing; Tattersall, Ian. 1982. The Primates of Madagascar. New York: Columbia University Press.

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