Contrary to popular belief, apes and humans did not have a common ancestor who habitually relied on their arms to swing between branches. Although all apes have long arms and flexible shoulders, and are able to stand upright, only the upper limbs of gibbons have strong propulsion capabilities. They rely on strong arms to climb and eat in an upright position (sitting or hanging), a behavioral posture from their ancestors that may be common to all apes.
The most obvious features of gibbons are the way they swing their arms (hanging climbing) and their usual upright postures, all of which are designed to accommodate their unique suspension behavior. They make a loud and complex rather pure call in a fixed way, showing the vibrant yet melancholy qualities of these Far Eastern jungle animals. These beautiful calls are mainly "duets" that can be used to promote and maintain "conjugal" ties and to expel neighboring groups from the family territory of "one male and one female". Taken together, the key features of gibbons form a personality that is unique among primates.
Although great apes have sex dimorphism in body size, gibbons have similar adult male and female sizes. Gibbons are graceful apes that are relatively small, slender, have very long arms, longer legs than expected, and have thick hairs. Compared to large apes, they are better at bipedal walking as long as there is enough support. For example, they will walk on branches that are too big to swing, rather than just walking on the ground as people assume. Their species can be clearly distinguished by their coat color and markings, and in some cases, their age and sex can be distinguished based on these characteristics. Some species of gibbons also have a laryngeal sac, which enhances the ability of sound to travel. These calls, especially those of adult females, provide us with the easiest way to identify species.
In terms of diversity and number, gibbons are the most successful of the apes. Starting with ancestors who were able to climb and eat fruit skillfully, gibbons have become more and more diverse in the last 1 million years and are now spread throughout the forests of Southeast Asia. They maintained the same size as their ancestors (with the main exception being gibbons), were able to feed on the ends of branches, and hung from the forest canopy for climbing. During the period of sea level change in the Pliocene (5 million to 1.8 million years ago), the frequent isolation of Sunda land sheds led to the differentiation of gibbons into the current species.
Gibbons, which spread throughout Southeast Asia, are the continents and islands that make up the Sunda shed, and they are almost entirely arboreal and dependent on tropical evergreen rainforests. About 1 million years ago, the ancestors of gibbons appear to have come to Southeast Asia, whereby they were divided into southwest, northeast, and east (the Asian continent was not suitable for habitat in the early ice age). These three families form the Great Gibbon, the Crowned Gibbon, and other gibbons, respectively. The biggest change then occurred in the eastern group, which returned to the Asian continent during the Interglacial Period, leaving first the white-browed gibbon and the western Kerry gibbon, then the black-crowned gibbon, and after the last ice age, leaving behind the descendants of the black-handed gibbon and the white-handed gibbon, while the gray gibbon and the silver gibbon evolved in Borneo and Java, respectively. Some pundits now place the white-browed gibbon in a single subgenus because of its large size and fewer chromosomes. Gibbons' range has been squeezed farther south over time— and according to Chinese literature, gibbons stretched north to the Yellow River 1,000 years ago. Curiously, among species north of the gibbon range, females and males have different colors (males are predominantly black, while females are pale yellow or gray); black gibbons live in the southwest, with gibbons in the middle having a variety of colors, while eastern gibbons are gray. Hermaphroditic species live in seasonal forests where visual signal visibility is relatively high.