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The Lesser Apes by Dan Freeman [part 1 of 5]
From tne world of monkeys we now turn io the apes, some of which spend much of their lives on the ground moving around comparatively slowly. One ape can claim to be the most spectacular aerial acrobat of all the primates. This is the gibbon, which is found in South-East Asia. The tailless gibbons are undoubtedly apes, for all the apes by definition have no tails, and their life in the trees means that they probably represent the earliest surviving evolutionary division between the Old World monkeys and the apes. It should not seem too surprising given Nature's devious ways, that the world should be furnished with some largely ground-dwelling monkeys - the macaques and the baboons - and some highly specialized tree-dwelling apes - the gibbons and their close relative the Siamang, also from South-East Asia. Together, the gibbons and the Siamang are known as the 'lesser' apes, into which category they are grouped because they possess certain anatomical features which are shared by all the apes and which are absent from the monkeys and the prosimians. For example, over and above the lack of a tail, the basic arrangement of the apes' teeth is quite different from that of the monkeys, and it would seem feasible to equate this with the change in diet - which led to an emphasis on fruit-eating - that the earliest apes must have undergone. Gibbons are also different from the other apes because they have large horny pads on their buttocks.. These pads serve an important function - that of comfort - and they illustrate the difference of life-styles between the gibbons and other apes.
The term 'lesser apes' by no means implies that the gibbons and the Siamang are at all inferior. It is purely a label of convenience, implying that, while they are certainly apes, they did not pursue the same evolutionary line that eventually gave rise to Man, the 'highest' primate of them all.
The most noticeable feature of the gibbon family is their size compared to that of other apes. A full-grown Gorilla may weigh as much as 159 k-182 kg (350 l-400 lb) and stand a full 2 m (6 ft) at the shoulders, while gibbons never weigh more than 13 kg (29 lb), usually from 5kg (11 lb) to 8kg (17.6 lb). They are, indeed, miniature apes which remained smaller than many of the monkeys because they never came down from the trees to do battle with large predators or to compete with the other emerging apes.
But, ironically, the lesser apes were committed to evolving along many of the same lines as the other apes and this meant that they had to forgo the tail that had proved so indispensable to the monkeys! Without a prehensile tail of the New World monkeys and without the stout balancing tail of the Old World monkeys the gibbons gradually evolved longer and longer limbs, especially their arms. Today, a gibbon standing in an upright position drags its hands on the ground in an ungainly fashion. It seems as though these limbs have been stretched by centuries of use high in the trees as the gibbons became more and more expert in their way of life.
Gibbons travel more quickly than anyone who has not seen them can possibly imagine - looping from branch to branch at breakneck speed or hurling themselves across wide gaps between supports; The speed of their reactions is nicely demonstrated by C. R. Carpenter, an American who spent most of his life working on primates. Carpenter once saw a gibbon launching itself into mid-air but, as it did so, the branch it was leaving snapped and the poor creature had no hope of reaching the other side because all the power of its jump had been lost. But instead of falling, the gibbon, in one continuous movement, was able to twist itself in mid-air, grab hold of the remaining branch stump, haul itself back into an upright position and then launch itself across the 9 m (30 ft) gap to the next tree! Brad and Trouble
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The Lesser Apes by Dan Freeman [part 2 of 5]
Little wonder, then, that the scientific name for the gibbon family is Hylobatidae, which is Greek for 'tree walker'. The name is actually derived from the gibbon's less spectacular and more normal method of moving through the trees - swinging itself from branch to branch in an easy and relaxed fashion. Technically this means of locomotion is known as brachiation and it is ideal for making a hurried retreat from predators or for reaching feeding spots prohibited to less agile creatures. It is a feature shared by all the apes, but the Gorilla, the Chimpanzee and the Orang-utan use it far less than their smaller relatives. Interestingly, the South American spider monkeys also employ this manner of locomotion, which gives them certain affinities with the lesser apes although they evolved quite separately from them.
If we accept gibbons as being the most primitive of the apes, then the simplest interpretation is that they evolved from more primitive, gibbon-like ancestors which eventually gave rise to Man as well. This idea neatly groups the gibbons with Man along the same evolutionary path, although we should always be prepared to adapt our views in the light of fossil evidence.
The earliest gibbons almost certainly lived, as did the earliest Old World monkeys, in Africa, where fossils dating back as much as 22 million years have been found in Uganda and Kenya. The point about these fossils is that while they are extremely gibbon-like in their skulls and in their teeth, the rest of their skeletons are quite different. Their arms and legs are of almost equal length, suggesting that they used all four limbs equally as they clambered around the trees. Further evidence suggests that the gibbons may have evolved from these ancestral quadrupeds after the main ape group had split away from the Old World monkeys.
In all there are about six species of gibbon and they exhibit such individual variation in their colours - depending on which species they belong to, or their age and sex - that unless they present themselves in a threat display it is virtually impossible to identify them reliably from quick forest sightings.
The gibbons' means of locomotion carries them swiftly through the trees and they may cover large distances through the forests. High up in the trees, their buttock pads provide them with an ideal alternative to nests for they simply sleep on a branch, using their well-protected backsides as cushions. By comparison the great apes move relatively slowly by day and when they come to rest each evening they build nests o vegetation in which to spend the night. Such nests may only be simply constructed, but they represent the first primate steps that finally led to Man and his house-building instincts. Brad and Trouble
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The Lesser Apes by Dan Freeman [part 3 of 5]
In all there are about six species of gibbon and they exhibit such individual variation in their colours - depending on which species they belong to, or their age and sex - that unless they present themselves in a threat display it is virtually impossible to identify them reliably from quick forest sightings.
The gibbons' means of locomotion carries them swiftly through the trees and they may cover large distances through the forests. High up in the trees, their buttock pads provide them with an ideal alternative to nests for they simply sleep on a branch, using their well-protected backsides as cushions. By comparison the great apes move relatively slowly by day and when they come to rest each evening they build nests of vegetation in which to spend the night. Such nests may only be simply constructed, but they represent the first primate steps that finally led to Man and his house-building instincts.
Gibbons are found over a wide area of South-East Asia, ranging from sea level to about 2400 m (8000 ft), where they inhabit the thick tropical forests. They must be among the noisiest of mammals, especially in the early morning when neighbouring families remind each other of the borders of their territories. Typically, a family consists of an adult male and female accompanied by their youngsters. As the first light of a tropical dawn filters through the trees, the female stirs her limbs and begins to emit her penetrating hooting calls. She starts off slowly but rises gradually to a crescendo of piercing calls that ring out through the awakening jungle. And then silence before the echo-like reply from the female of a neighbouring family. Verbal contact established, the two families move quickly through the trees until they make visual contact with each other. At this point the males take over. Urged on by the hooting females, they rush at each other through the trees, swinging and leaping to and fro, never crossing the edge of the adjoining territories and always maintaining a respectable distance from each other. After a while this activity dies down, and the families move peacefully away from each other to commence their daily routines of grooming and feeding.
Such potentially aggressive behaviour seems to be specifically concerned with establishing a claim to each other's territory, with no actual harm intended to befall the individuals involved. Gibbons feed extensively on fruit, and as the food-bearing trees ripen at different times of the year the succulently laden trees are indeed prizes worth retaining. Each morning the contact calls ring out and the mock battles take place so that all the gibbons know the exact whereabouts of their nearest rivals.
The family unit of gibbons is strongly preserved because the young take at least six years to mature. The adult female gives birth after a lengthy pregnancy of just over 200 days, and the virtually hairless and helpless infant clings tenaciously to her chest, even while she swings effortlessly through the trees. When she is resting, the mother raises her knees to form a snug and furry cradle in which the youngster sleeps peacefully. Brad and Trouble
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The Lesser Apes by Dan Freeman [part 4 of 5]
By the time the young gibbon is about two years old it is fairly independent, feeding itself and moving freely through the trees on its own. It is, however, still an adolescent and must remain within the family unit for a few more years. Freed from the immediate physical responsibilities of child-care, the mother - who has already been pregnant for several months - gives birth once again and, similarly, when this next baby is finally released from her care, she gives birth once more. Thus, the family unit grows in two-yearly stages until the first-born is fully mature and its presence is gradually resented more and more by its parents who will not tolerate other adults within their territory. The day finally dawns when minor squabbling turns to aggression and the scene is set for the six to ten-year-old to move away into the forest to fend for itself while it searches the trees for a potential mate in a similar predicament.
The Siamang, as we have seen, is closely related to the gibbons. It lives in the same area although it is more restricted in its distribution, occurring only in parts of mainland Malaya and on the island of Sumatra. There is a smaller kind of Siamang which lives on some of the smaller islands close to Sumatra.
The Siamang lives in thick rainforests, but it is found over slightly different altitudes from its relatives - mostly between 600 m (1975 ft) and 2400 m (8000 ft). It is slightly heavier than the gibbons, weighing anything from 8 kg (17'/2 lb) to 13 kg (28 lb), the heaviest weight recorded for any member of the family. Its arms, compared to the length of its legs, are even longer than those of the gibbons.
Up in the trees, where gibbons spend most of their time, these arms are superbly adapted and transform this primate into one of the most graceful, and probably the most agile, of all mammals. Many of the primates propel themselves from branch to branch by using powerfully developed hindlegs but the gibbons rely solely upon their arms to swing their bodies through the trees. These arms are so specialized that they are about two and a half times the length of the gibbon's body and about one and a half times the length of its legs. So far no fossil gibbons with such long arms have been found, suggesting that this unique feature may be of quite recent evolutionary origin.
When they stand erect in the trees and support themselves with their hands, the gibbons look uncannily human. Their faces have a soft, almost weak, expression and their large, warm eyes have an appealing quality matched only by human sympathy. The gibbon's opposable big toe is well demonstrated as it clings powerfully to a smooth and steeply angled branch. Its long arms enable it to swing through the trees and to reach out for otherwise inaccessible food. Gibbons have short trunks but ample chests, and their rigid backs are held straight as they move through the trees, which explain why they have such difficulty in walking on the ground. The short, straight back which is necessary for swinging from branch to branch is fairly inflexible and prevents the gibbon from bending over to walk on all fours.
Occasionally a black adult will challenge even a human intruder into his territory and will present himself on two legs, hooting and arm-waving in an attempt to frighten the trespasser into retreat. Ironically, much of this arm-waving is performed so that the gibbon keeps its balance, but it obviously plays an important secondary role as a threatening gesture and has evolved to look extremely menacing. While it is frantically waving its arms and hooting, the gibbon stamps its feet defiantly and makes small threatening gestures, pretending to rush at its adversary. Its flashing white face and formidable antics are usually enough to put most intruders to flight. The difference in length between its hind and forelimbs is actually not as pronounced as one might suppose from most photographs, for its hindlimbs are invariably kept doubled up to suit its basically tree-top life and it is rarely seen, as here, on the ground. Brad and Trouble
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The Lesser Apes by Dan Freeman [part 5 of 5]
The black male Concolor Gibbons occasionally have white patches on their cheeks but the spectacular females turn a rich golden fawn colour which, combined with a plentiful abundance of shaggy fur, sets them off magnificently against their sombre forest backgrounds. As with all species of gibbon, males and females mate for life, for once the vital relationship so important for protecting the slowly developing young has been formed, it is almost impossible for it to be broken. Some captive gibbons have been known to live for more than 30 years.
Some gibbons, although the same species, may vary in their body colouring. Usually in the animal world, such an extreme, almost pure white, would be singled out by predators which would notice it more easily than its darker and better camouflaged relatives. By attacking these unusual individuals more often, the predators would prevent them from breeding and from producing similarly coloured offspring and eventually the odd colour would disappear. But the case of the gibbons is slightly different because they change colour as they grow older. An aged black male may very well, as a baby, have had a first coat of almost pure white hair, but while it was so vulnerably coloured it was constantly in the protection of its ever-alert parents. The only real threat to the gibbon is the leopard and even such a stealthy animal as this would have the utmost difficulty in approaching too closely, especially as gibbons sleep in such inaccessible places at the tops of trees. In the northernmost part of the gibbons' range, there are two species whose body colouring is related directly to whether they are male or female. In both species all the young are born pale, but as they mature they turn dark so that at about five or six years old they are all dark coloured. From then onwards, the males remain dark, eventually turning almost black, while the females become increasingly brown.
In close up, the face of a Siamang is superficially similar to that of a Chimpanzee. It seems to have a far more protruding bottom half to its face than the rest of the gibbons, but in fact this feature is accentuated by two points. There is no distinctive white border to the face to highlight the whole area, and the lower jaw and the area around the mouth are covered in prominent white hairs which draw attention to this part of the face. The Siamang is just as much at home in the treetops as all the gibbons and, like all the apes, it carries objects with its feet while it swings from branch to branch, although it may be slightly more limited in its carrying capacity because of the strange feature of its second and third toes being united by a web of skin. In many respects the behaviour of the Siamang is typical of the gibbon family, but the female Siamang is pregnant for a few weeks longer than average and Siamangs are predominantly leaf-eating rather than fruit eating. This is just as well in the areas where the Siamang occurs along with other gibbons, because it means that they do not compete for the same food.
Perhaps one of the most striking differences between the Siamang and other gibbons is the bare throat of the Siamang. This adult female, playing in captivity with her youngster, displays this fact superbly. She is actually calling, and in so doing she is distending her throat which is specially designed with loose skin so that it can be swollen with air to form a vocal sac at least the size of her head. If she draws air in through her nose when her mouth is closed, she can produce a deep booming note. When this air is expelled, a higher and more devastating note is produced. These calls are therefore produced alternately and coordinate quite simply with the Siamang's breathing. The speed at which they are produced varies according to the situation for which they are required. The Siamang can quite jusfifiably be regarded as the noisiest of all the noisy gibbon family, its piercing booms and howls echoing over distances of several kilometres shortly after dawn each day. Brad and Trouble
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gibbons change colors
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gibbons change colors
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