The Evolution and Adaptations of the Tropical Rainforest Primates, the Gibbons

The very first primates were very similar to squirrels and tree shrews in both size and appearance. Therefore gibbons had a lot of adapting to do to become the animals we see today. Gibbons are classified as kingdom Animalia, phylum Chordata, class Mammalia, order primate, suborder haplorhine, superfamily Hominoidea, and family Hylobatidae. They live in the tropical rainforests of Southeast Asia including China, Laos, Vietnam, Cambodia, Thailand, Myanmar, Malaysia, eastern Bangladesh, northeast India southern China, and Indonesia. Gibbons live in “both the tropical and subtropical regions.

They tend to enjoy the warmer climates where they can find plenty of food and shelter. They are arboreal which means that they only live in the trees.” (Monkey Worlds.) They are adapted to eat mainly flowers, fruits, insects, and leaves. Because they cannot swim, and rarely go on the ground many of these primates are limited in their movements by large rivers.

Gibbons are drastically anatomically different from other primates, they have strong, hook-shaped hands for grabbing branches, and very long arms, often longer than their bodies and legs put together, for swinging across the canopy of their treetop habitats.

Like all apes, gibbons have no tail and also possess small ischial callosities which are “generally related to the sitting positions of cercopithecoid monkeys, gibbons, and siamangs, but the selective advantage of ischial callosities to the sitting postures of these animals is uncertain. It is suggested that ischial callosities are adaptations that evolved for comfortable and stable sitting on thin branches during feeding in the peripheral branch zone.

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” (Vilensky.) Gibbons move about with a very dramatic form of locomotion called brachiation. They can move through the jungle at up to 35 miles our and can leap across gaps as wide as 50 feet with a single swing, making them very efficient, and rarely preyed upon. Brachiating also gives the gibbons access to vast amounts of food and limits competition. Although they prefer to be in the trees, “whether along branches or in the rare instances when they descend to the ground, [gibbons] often do so on two feet, throwing their arms above their head for balance.

They are the most bipedal of all non-human primates and are often studied for clues to what evolutionary pressures may have led to human walking.” (Society National Geographic.)

Bipedalism is not the only thing that these primates have in common with humans. Perhaps the most impressive adaptation gibbons have would be the development of their ball and socket joint at the shoulder or upper arm like humans have. The gibbon’s ball and socket wrist and shoulder joints greatly reduce both the stress on the shoulders, and the amount of energy expelled when moving long distances. Their shoulder joints are specially adapted to allow a greater hour range of motion. This joint is so far advanced that even after hours of hanging, their arms do not tire or strain. Giving them a big advantage over predators.

Gibbons are very social animals, they are active during the day and sleep at night like most other primates. They live in small close-knit families, of a male and female, who mate for life and their offspring or juveniles that are less than 7 years old. Gibbons live in groups, known as troops which consist of the alpha male and female, or mom and dad. Gibbons are monogamous, meaning they mate for life. The female ape will be pregnant for about seven months, before giving birth to a single baby, twins are incredibly rare. The new family will stay together to look after the baby gibbon until it is about a year old. The baby gibbon usually stays close to its mother until it is older, and is between the ages of six and seven when it will find a mate of its own, and start its family. Gibbons are very territorial, “they are very aggressive when it comes to defending their territory and their groups. They can be very vocal and heard for long distances. Fights can occur between pairs but usually, it is between the males. Groups often sing songs and that can be a problem that leads poachers to find them.” (Monkey Worlds.) The calls, o vocal displays are almost always started by the female apes, they can turn into a duet between the couple who have distinct male and female calls.

The calls are also used for mating. The howls can be heard over miles, which comes in handy because of their environment. With the vastness of the forests, and the high speed that the gibbons move at the calls have to be very loud and distinct to travel, and be audible.

Natural Selection is the cause for most of these adaptations. Early primates that did not have the long arms and fingers for swinging and grasping branches, would not be able to quickly escape predators, or perhaps even fall out of the trees to their deaths if their grips were not strong enough. In line with their climatic way of moving, their shoulder joints had to adapt to be strong enough to hold up their body weight for an extended period. The ball and socket joint allowing for the swinging motion that is a staple for the gibbon. The tail disappeared very early on in the ape adaptations. Because apes have bigger bodies, they do not need tails to balance. In the case of gibbons they rarely walk on two legs, although when they do they are the best at it, they walk with their arms over their head for balance, taking the place of a tail.

Gibbons are among the smaller of the non-human primates, but they have made big strides in their adaptations since the first primates. Although they are spread out widely in southeast Asia, Gibbons are severely endangered due to deforestation. Gibbons have adapted to their environments with their long arms and fingers, their unique locomotion, their troops, and family styles, and finally their loud vocalization, or howling. All of which have made gibbons one of the more advanced non-human primates.

Works Cited

1. Monkey Worlds. “Gibbon.” Monkey Facts and Information. Word Press, n.d. Web. 28 Nov. 2016.
2. Society, National Geographic. “Gibbons, Gibbon Pictures, Gibbon Facts — National Geographic.” National Geographic. National Geographic, n.d. Web. 28 Nov. 2016.
3. Vilensky, Joel A. “The Function of Ischial Callosities.” SpringerLink. Short Communications, 27 Dec. 1976. Web. 27 Nov. 2016.