Temporal range: Late Oligocene - Recent
|Lar Gibbon (Hylobates lar)|
Apes are the members of the Hominoidea superfamily of primates, which includes humans. Under the current classification system there are two families of hominoids:
- the family Hylobatidae consists of 4 genera and 13 species of gibbons, including the Lar Gibbon and the Siamang, collectively known as the lesser apes.
- the family Hominidae consisting of orangutans, gorillas, chimpanzees, and humans, collectively known as the great apes.
A few other primates, such as the Barbary Ape, have the word "ape" in their common names (usually to indicate lack of a tail), but they are not regarded as true apes.
Except for gorillas and most humans, all true apes are agile climbers of trees. They are best described as omnivorous, their diet consisting of fruit, grass seeds, and in most cases some quantities of meat and invertebrates—either hunted or scavenged—along with anything else available and easily digested. They are native to Africa and Asia, although humans have spread to all parts of the world.
Most ape species are rare or endangered. The chief threat to most of the endangered species is loss of tropical rainforest habitat, though some populations are further imperiled by hunting for bushmeat.
Historical and modern terminology
"Ape" (Old Eng. apa; Dutch aap; Old Ger. affo; Ger. Affe; Welsh epa; Old Czech op) is a word of uncertain origin and is possibly an onomatopoetic imitation of animal chatter. The term has a history of rather imprecise usage. Its earliest meaning was a tailless (and therefore exceptionally human-like) non-human primate, but as zoological knowledge developed it became clear that taillessness occurred in a number of different and otherwise unrelated species.
The original usage of "ape" in English might have referred to the baboon, an African monkey. Two tailless species of macaque are commonly named as apes, the Barbary Ape of North Africa (introduced into Gibraltar), Macaca sylvanus, and the Sulawesi Black Ape or Celebes Crested Macaque, M. nigra.
Until a few decades ago, humans were thought to be distinctly set apart from the other apes (even from the other great apes), so much so that many people still don't think of the term "apes" to include humans at all. However, it is not considered accurate by many biologists to think of apes in a biological sense without considering humans to be included. The terms "non-human apes" or "non-human great apes" is used with increasing frequency to show the monophyletic relationship of humans to the other apes while yet talking only about the non-human species.
A group of apes may be referred to as a troop or a shrewdness.
The gibbon family, Hylobatidae, is composed of thirteen medium-sized species. Their major distinction is their long arms, which they use to brachiate through the trees. As an evolutionary adaptation to this arboreal lifestyle, their wrists are ball and socket joints. The largest of the gibbons, the Siamang, weighs up to 23 kg (50 lb). In comparison, the smallest great ape is the Common Chimpanzee at a modest 40 to 65 kg (88 to 143 lb).
The great ape family was previously referred to as Pongidae, and humans (and fossil hominids) were omitted from it, but there is no biological case for doing this. However, this definition is still used by many anthropologists and by lay people. However, that definition makes Pongidae paraphyletic, whereas most taxonomists nowadays encourage monophyletic groups. Chimpanzees, gorillas, humans and orangutans are all more closely related to one another than any of these four genera are to the gibbons. However, the term " hominid" is still used with the specific meaning of extinct animals more closely related to humans than the other great apes (for example, australopithecines), even though " hominin" is now correct in that usage. It is now usual to use even finer divisions, such as subfamilies and tribes to distinguish which hominoids are being discussed. Current evidence implies that humans share a common, extinct, ancestor with the chimpanzee line, from which we separated more recently than the gorilla line.
Both great apes and lesser apes fall within Catarrhini, which also includes the Old World monkeys of Africa and Eurasia. Within this group, both families of apes can be distinguished from these monkeys by the number of cusps on their molars (apes have five—the "Y-5" molar pattern, Old World monkeys have only four in a bilophodont pattern). Apes have more mobile shoulder joints and arms due to the dorsal position of the scapula, broad ribcages that are flatter front-to-back, and a shorter, less mobile spine compared to Old World monkeys (with caudal vertebrae greatly reduced, resulting in tail loss in some species). These are all anatomical adaptations to vertical hanging and swinging locomotion (brachiation) in the apes, as well as better balance in a bipedal pose. All living members of the Hylobatidae and Hominidae are tailless, and humans can therefore accurately be referred to as bipedal apes. However, there are also primates in other families that lack tails, and at least one (the Pig-Tailed Langur) that has been known to walk significant distances bipedally. The front skull is characterised by its sinuses, fusion of the frontal bone and Post-Orbital Constriction.
Although the hominoid fossil record is far from complete, and the evidence is often fragmentary, there is enough to give a good outline of the evolutionary history of humans. The time of the split between humans and living apes used to be thought to have occurred 15 to 20 million years ago, or even up to 30 or 40 million years ago. Some apes occurring within that time period, such as Ramapithecus, used to be considered as hominins, and possible ancestors of humans. Later fossil finds indicated that Ramapithecus was more closely related to the orangutan, and new biochemical evidence indicated that the last common ancestor of humans and other hominins occurred between 5 and 10 million years ago, and probably in the lower end of that range.
Cultural aspects of non-human apes
The name "Hominoidea" can be loosely translated as 'ape'. However, although the superfamily of Hominoidea has always included great apes such as humans, as well as the Hylobatidae, a different connotation of the word 'ape' exists in the vernacular. The historical, common usage of the word often excludes humans when referring to apes. Humans are also often excluded from the larger classifications of "animal" and " primate" in common usage, despite belonging to both of these groups as well. The reason for this is that scientific nomenclature and everyday language abide by different rules. Other examples of this are " butterfly" (not a member of Diptera), "ladybird" (not a member of Aves) and " jellyfish" (not a fish). Taxonomic labels can be redefined according to the latest scientific findings; as such, they may or may not overlap with their vernacular counterparts.
Often, non-human apes are said to be the result of a curse—a Jewish folktale claims that one of the races who built the Tower of Babel became apes as punishment, while Muslim lore says that the Jews of Eilat became non-human apes as punishment for fishing on the Sabbath. Some sects of Christianity have folklore that claims that these apes are a symbol of lust and were created by Satan in response to God's creation of humans. It is uncertain whether any of these references are to any specific apes. All of these concepts date from a period when neither the distinction between apes and monkeys, nor the fact that humans are apes, was not widely understood, or understood at all.
History of hominoid taxonomy
The history of hominoid taxonomy is somewhat confusing and complex. The names of subgroups have changed their meaning over time as new evidence, from fossil discoveries and comparisons of anatomy and DNA sequences, has changed understanding of the relationships between hominoids. The story of the hominoid taxonomy is one of gradual demotion of humans from a special position in the taxonomy to being one branch among many. It also illustrates the growing influence of cladistics (the science of classifying living things by strict descent) on taxonomy.
As of 2006, there are eight extant genera of hominoids. They are the four great ape genera ( Homo (humans), Pan (chimpanzees), Gorilla, and Pongo (orangutans)), and the four genera of gibbons ( Hylobates, Hoolock, Nomascus, and Symphalangus). (The genus for the hoolock gibbons was recently changed from Bunopithecus to Hoolock.)
In 1758, Carolus Linnaeus, relying on second- or third-hand accounts, placed a second species in Homo along with H. sapiens: Homo troglodytes ("cave-dwelling man"). It is not clear to which animal this name refers, as Linnaeus had no specimen to refer to, hence no precise description. Linnaeus named the orangutan Simia satyrus ("satyr monkey"). He placed the three genera Homo, Simia and Lemur in the family of Primates.
The troglodytes name was used for the chimpanzee by Blumenbach in 1775 but moved to the genus Simia. The orangutan was moved to the genus Pongo in 1799 by Lacépède.
Linnaeus's inclusion of humans in the primates with monkeys and apes was troubling for people who denied a close relationship between humans and the rest of the animal kingdom. Linnaeus's Lutheran Archbishop had accused him of "impiety." In a letter to Johann Georg Gmelin dated February 25, 1747, Linnaeus wrote:
- It is not pleasing to me that I must place humans among the primates, but man is intimately familiar with himself. Let's not quibble over words. It will be the same to me whatever name is applied. But I desperately seek from you and from the whole world a general difference between men and simians from the principles of Natural History. I certainly know of none. If only someone might tell me one! If I called man a simian or vice versa I would bring together all the theologians against me. Perhaps I ought to, in accordance with the law of Natural History.
Accordingly, Johann Friedrich Blumenbach in the first edition of his Manual of Natural History (1779), proposed that the primates be divided into the Quadrumana (four-handed, i.e. apes and monkeys) and Bimana (two-handed, i.e. humans). This distinction was taken up by other naturalists, most notably Georges Cuvier. Some elevated the distinction to the level of order.
However, the many affinities between humans and other primates — and especially the great apes — made it clear that the distinction made no scientific sense. Charles Darwin wrote, in The Descent of Man:
- The greater number of naturalists who have taken into consideration the whole structure of man, including his mental faculties, have followed Blumenbach and Cuvier, and have placed man in a separate Order, under the title of the Bimana, and therefore on an equality with the orders of the Quadrumana, Carnivora, etc. Recently many of our best naturalists have recurred to the view first propounded by Linnaeus, so remarkable for his sagacity, and have placed man in the same Order with the Quadrumana, under the title of the Primates. The justice of this conclusion will be admitted: for in the first place, we must bear in mind the comparative insignificance for classification of the great development of the brain in man, and that the strongly-marked differences between the skulls of man and the Quadrumana (lately insisted upon by Bischoff, Aeby, and others) apparently follow from their differently developed brains. In the second place, we must remember that nearly all the other and more important differences between man and the Quadrumana are manifestly adaptive in their nature, and relate chiefly to the erect position of man; such as the structure of his hand, foot, and pelvis, the curvature of his spine, and the position of his head.
Changes in taxonomy over time
|Until about 1960, the hominoids were usually divided into two families: humans and their extinct relatives in Hominidae, the other apes in Pongidae.|
|The 1960s saw the application of techniques from molecular biology to primate taxonomy. Goodman used his 1964 immunological study of serum proteins to propose a division of the hominoids into three families, with the non-human great apes in Pongidae and the lesser apes (gibbons) in Hylobatidae. The trichotomy of hominoid families, however, prompted scientists to ask which family speciated first from the common hominoid ancestor.|
|Within the superfamily Hominoidea, gibbons are the outgroup: this means that the rest of the hominoids are more closely related to each other than any of them are to gibbons. This led to the placing of the other great apes into the family Hominidae along with humans, by demoting the Pongidae to a subfamily; the Hominidae family now contained the subfamilies Homininae and Ponginae. Again, the three-way split in Ponginae led scientists to ask which of the three genera is least related to the others.|
|Investigation showed orangutans to be the outgroup, but comparing humans to all three other hominid genera showed that African apes (chimpanzees and gorillas) and humans are more closely related to each other than any of them are to orangutans. This led to the placing of the African apes in the subfamily Homininae, forming another three-way split. This classification was first proposed by M. Goodman in 1974.|
|To try to resolve the hominine trichotomy, some authors proposed the division of the subfamily Homininae into the tribes Gorillini (African apes) and Hominini (humans).|
|However, DNA comparisons provide convincing evidence that within the subfamily Homininae, gorillas are the outgroup. This suggests that chimpanzees should be in Hominini along with humans. This classification was first proposed (though one rank lower) by M. Goodman et al. in 1990. See Human evolutionary genetics for more information on the speciation of humans and great apes.|
|Later DNA comparisons split the gibbon genus Hylobates into four genera: Hylobates, Hoolock, Nomascus, and Symphalangus.|
Classification and evolution
As discussed above, hominoid taxonomy has undergone several changes. Current understanding is that the apes diverged from the Old World monkeys about 25 million years ago. The lesser and greater apes split about 18 mya, and the hominid splits happened 14 mya (Pongo), 7 mya (Gorilla), and 3-5 mya (Homo & Pan).
Listed are the families and genera of apes; also listed are the extant species.
- Superfamily Hominoidea
- Family Hylobatidae: gibbons
- Genus Hylobates
- Lar Gibbon or White-handed Gibbon, H. lar
- Agile Gibbon or Black-handed Gibbon, H. agilis
- Müller's Bornean Gibbon, H. muelleri
- Silvery Gibbon, H. moloch
- Pileated Gibbon or Capped Gibbon, H. pileatus
- Kloss's Gibbon or Mentawai Gibbon or Bilou, H. klossii
- Genus Hoolock
- Western Hoolock Gibbon, H. hoolock
- Eastern Hoolock Gibbon, H. leuconedys
- Genus Symphalangus
- Siamang, S. syndactylus
- Genus Nomascus
- Black Crested Gibbon, N. concolor
- Eastern Black Crested Gibbon, N. nasutus
- White-cheeked Crested Gibbon, N. leucogenys
- Yellow-cheeked Gibbon, N. gabriellae
- Genus Hylobates
- Family Hominidae: great apes
- Family Hylobatidae: gibbons
Behaviour and cognition
Although there had been earlier studies, the scientific investigation of behaviour and cognition in non-human apes expanded enormously during the latter half of the twentieth century. Major studies of behaviour in the field were completed on the three better-known great apes, for example by Jane Goodall, Dian Fossey and Birute Galdikas (field work on gibbons and the Bonobo is still relatively underdeveloped). These studies have shown that in their natural environments, the different apes show sharply varying social structure: gibbons are monogamous, territorial pair-bonders, orangutans are solitary, gorillas live in small troops dominated by a single adult male, while chimpanzees live in larger troops with Bonobos exhibiting promiscuous sexual behaviour. Their diets also vary; gorillas are foliovores while the others are all primarily frugivores, although the Common Chimpanzee does some hunting for meat. Foraging behaviour is correspondingly variable.
All the apes are generally thought of as highly intelligent, and scientific study has broadly confirmed that they perform outstandingly well on a wide range of cognitive tests - though again there is relatively little data on gibbon cognition. The early studies by Wolfgang Köhler demonstrated exceptional problem-solving abilities in chimpanzees, which Köhler attributed to insight. The use of tools has been repeatedly demonstrated; more recently, the manufacture of tools has been documented, both in the wild and in laboratory tests. Imitation is much more easily demonstrated in great apes than in other primate species. Almost all the studies in animal language acquisition have been completed with great apes, and though there is continuing dispute as to whether they demonstrate real language abilities, there is no doubt that they involve significant feats of learning. Chimpanzees in different parts of Africa have developed tools that are used in food acquisition, demonstrating a form of animal culture.