I. but even fully grown adult males
Apes have 13 species of large, highly intelligent primates, including Chimpanzees, Gorillas, Gibbons, and Orangutans. Apes are sometimes confused with Monkeys, but unlike their smaller primate counterparts, apes do not have tails and their arms are usually longer than their legs. Apes live in tropical woodlands and forests of Africa and Asia. Despite sharing similar habitats, different ape species show striking differences in behaviors and ways of life.
At one time, apes were classified as a single group of primates, but today most zoologists divide them into two distinct families: the lesser apes, or gibbons, and the great apes. Gibbons are similar to monkeys, with lithe, slender bodies and extremely agile movements. Gibbons spend all of their lives in trees, using their hands like hooks to swing arm-over-arm between branches. Known as brachiation, this method of locomotion is so fast that gibbons can easily overtake a person running on the forest floor.
The great apes include the gorilla, the orangutan, and two species of chimpanzee: the common chimp and the bonobo (sometimes called the pygmy chimpanzee). Great apes are bigger than gibbons and also much less acrobatic. However, they are still good climbers. While orangutans spend most of their life in trees, where they use their long arms and dexterous hands and feet to grasp branches and vines, chimpanzees frequently come to the ground to feed. Gorillas are primarily terrestrial, but even fully grown adult males have been observed clambering among tree branches more than 15 m (49 ft) high. Chimpanzees and gorillas—the apes that spend the most time on the ground—normally walk on all fours, clenching their hands so that their knuckles take their weight.
From physical and fossil evidence, biologists know that apes and humans share a common ancestry. In recent years, biochemical analysis has shown just how close this link is—chimpanzees and humans differ significantly in only 2 percent of their genes. This evidence suggests that they diverged from a common ancestor around five to seven million years ago.
II. Range and Habitat
The gorilla, the common chimpanzee, and the bonobo live in dense tropical forests on the African continent. Chimpanzees also inhabit wooded savanna, where there are more opportunities for foraging out in the open. Most gorillas live in the hot, lowland forests of west and central Africa, but a subspecies called the mountain gorilla lives in a very different habitat. Its range extends as high as 3400 m (11,200 ft) on the cool, mist-covered slopes of the Virunga Mountains.
The gibbons and orangutans inhabit Southeast Asia. Gibbons live in rain forests and seasonal forests of India, Indochina, and the Malay Archipelago. The orangutan is purely a rain forest animal. Today its range is restricted to two large islands—Sumatra and Borneo—but fossils show that it once had a far greater range, reaching as far north as China.
III. Physical Characteristics
With their long limbs and opposable thumbs, apes are well adapted to a tree-climbing life. The smallest gibbons stand just 44 cm (17 in) tall and weigh just 4.5 kg (10 lb)—light enough to swing from the highest, smallest branches. Great apes are considerably larger, particularly male gorillas, which can be as tall as 1.8 m (about 6 ft) and weigh up to a quarter ton, making them by far the largest apes alive today. Male and female gibbons are usually similar in size, but in great apes, the sexes can differ greatly. Male orangutans, for example, often weigh more than twice as much as females.
Most apes are covered with thick fur. Gibbons have long fur of one color on the body and short fur of a contrasting color surrounding the face. A diverse range of colors distinguishes the different species and subspecies of gibbons, and there is frequently a difference in coloring between the sexes. The coloring of the great apes is drab by comparison. Orangutans have reddish brown fur, while the fur of chimpanzees and gorillas is black. Mature male gorillas are called silverbacks because the fur on their backs turns silvery gray.
Ape skulls and skeletons share the same underlying structure as those of humans, allowing for large brains and forward-pointing eyes. Like humans, apes also have bare skin on their faces, which enables them to communicate by making different facial expressions.
Great apes are exceptionally long-lived. Wild gorillas may survive to age 35, and wild chimps live about 50 years. Great apes in captivity have been known to survive into their late fifties. The life span of gibbons is considerably shorter, probably lasting about 25 years.
Great apes have well-developed brains and are among the most intelligent of all animals. In the wild, chimpanzees and orangutans are known to make simple tools, such as sharpened sticks used to extract insects from holes in tree trunks. Toolmaking involves a preconceived image of what the tool will look like, a visualization ability that is only possible with an advanced brain. Orangutans have even been observed untying knots, working out for themselves the steps necessary to achieve this complex task. Some scientists believe that apes have the capability to learn and use language, and considerable success has been achieved in training chimps and gorillas to communicate with humans using symbols or sign languageWith the exception of orangutans, which spend most of their lives alone, apes live in social groups. These groups range from 3 or 4 animals in the case of some gibbons, an average of about 10 in gorillas, and often more than 50 in chimpanzees. In general, the larger the group size, the looser the social structure is. Gorilla groups are generally close-knit, and may be led by the same dominant male for many years. By contrast, chimpanzee social life is marked by constantly shifting alliances and sometimes by violent confrontations between neighboring groups. Gibbons are also strongly territorial, but they are not as aggressive. They lay claim to patches of forest with extraordinarily loud hooting calls that can be heard up to 3 km (2 mi) away.
Some of these behavioral differences are related to the way apes feed. Chimpanzees eat a wide variety of foods, including fruit, leaves, honey, and insects, and they sometimes hunt and eat other mammals. During the course of a day’s foraging, they may travel nearly 18 km (11 mi). By banding together they improve their chances of finding food and also of spotting danger. Gorillas, on the other hand, are vegetarians, eating leaves, plant stems, and roots. This kind of food is comparatively easy to find, and although gorillas also move about, they rarely travel more than 2 km (1 mi) a day. Their great size also means that they are less vulnerable to attack. Consequently, gorillas would gain few advantages from living in larger groups.
Most apes breed throughout the year. Male and female orangutans come together only for a brief courtship and return to their solitary lifestyle immediately after mating. Other apes follow very different patterns: gibbons, for example, pair up for life. In these social species, long-term bonds develop between the adults, as well as between the adults and their young.
Female apes usually give birth to just a single young after a gestation period ranging from seven to nine months. Succeeding births normally occur only after the previous infant has been weaned. This process—like all aspects of ape development—takes a remarkable length of time. A gibbon is weaned by the age of about 2 years, while chimps take more than 4 years. Like young monkeys, young apes are carried by their mothers. They either cling to the mother’s belly or, in the case of older chimps, ride on her back. In great apes, infant care is largely the job of the females, while in some gibbons the mother hands over responsibility to the father when the infant gibbon’s first year is complete.
V. Endangered Apes
Like nearly all rain forest animals, ape populations have been harmed by deforestation. Some also face additional threats. Most vulnerable of all is the mountain gorilla, which has recently been extensively hunted by starving people ravaged by war. Today just a few hundred of these animals are left, and their future looks uncertain.
In Asia, five of the nine species of gibbons are listed as endangered, as is the orangutan. Despite a ban on their export, young orangutans are sometimes captured and sold as pets after their mothers have been killed. The massive forest fires on Sumatra and Borneo in 1997 and 1998 killed thousands of orangutans and destroyed the habitat of thousands more, further endangering the survival of the species.
Scientific Classification: The gibbons make up the family Hylobatidae and the great apes make up the family Hominidae. The gorilla is classified as Gorilla gorilla, the common chimpanzee as Pan troglodytes, the bonobo as Pan paniscus, and the orangutan as Pongo pygmaeus.