Apes and humans differ from all of the other primates in that they lack external tails. They also are more intelligent and more dependent for survival on learned behavior patterns. There are several internal body differences as well, such as the absence of an appendix in monkeys.
The apes and humans are members of the same superfamily, the Hominoidea . Until the last few years, humans were separated into their own family within this superfamily because it was believed that we are significantly different from the apes. However, recent genetic studies and discoveries from the fossil record have made it clear that some of the apes are more similar to humans than previously believed. Subsequently, the living hominoids are now commonly classified into only two families with humans grouped with the great apes: 1. Hylobatidae (gibbons )
2. Hominidae (orangutans , gorillas , chimpanzees , and bonobos , and humans)
Gibbons and orangutans live in Southeast Asia, while gorillas, chimpanzees, and bonobos are exclusively African apes. Humans originated in Africa as well.
The smallest and the most arboreal apes are the 12-13 species of gibbons. Because of their diminutive size, these members of the family Hylobatidae are also referred to as the "lesser apes." Most adult gibbons are only about 3 feet (90 cm.) tall standing upright and 12-20 pounds (5.5-9 kg.) in weight. Males in the biggest gibbon species, known as siamangs , are up to 30 pounds (13.5 kg.) and have longer arms. Siamangs are different enough from other gibbons to be in their own genus. All gibbons are very slender. Long bushy hair on their bodies makes them look stockier than they actually are. Unlike all of the larger ape species, gibbons have little sexual dimorphism in body size.
The long arms, permanently curved fingers, and light bodies of gibbons make them excellent brachiators . That is, they move around in trees by swinging under branches with a hand over hand motion. This is also referred to as suspensory climbing. At times, gibbons also walk bipedally, or two footed, on top of branches. However, they are more efficient at brachiation, and 90% of their locomotion is by this means. Each swing can transport a gibbon 20 feet (6 m.) at speeds approaching 35 miles (56 km.) an hour.
Gibbons are monogamous in their mating patterns and form nuclear family groups. That is to say, their communities consist of a single mating pair of adults with their juvenile offspring. They live in well defined territories in the tree tops and rarely go down to the forest floor. Adults regularly defend their territory against others of their species with piercingly loud whooping and hooting vocalizations, much like the indris of Madagascar and the howler monkeys of the New World. However, the calls of the latter two primates sound very different. The calls of different gibbon species are easily distinguished from each other as well. When they are vocalizing, the front of the necks of gibbons and siamangs expand with air, much like the flexible bag on a bagpipe.
Orangutans are the largest and the rarest of the Asian apes. Males often grow to 175-200 pounds (80-90 kg.) and 4� feet (1.4 m.) tall. At this size, they are usually too large to cross from one tree to another by the branches and must go down to the ground and walk quadrupedally between them. There is marked sexual dimorphism among the orangutans. Males have huge fleshy pads framing the upper part of their faces.