True apes vary in size from the 3-ft (90-cm), 15-lb (6.8-kg) gibbon to the 6-ft (1.8-m), 450-lb (200-kg) gorilla. All apes are forest dwellers and most spend at least some of the time in trees. Except for adult gorillas, they can run along branches on all fours; they are also able to move about by brachiation, or arm-over-arm swinging. Gibbons (including siamangs) are particularly adept at this type of locomotion; the heavier orangutan prefers to grasp a neighboring tree and pull itself across to it. Gorillas and chimpanzees are the most terrestrial of the apes, normally traveling on all fours by leaning on the knuckles of their forelimbs with the fingers of their hands curled under (knuckle-walking); orangutans ball their fingers into fists during the short periods they walk. Most apes are able to walk on two feet for short distances.
The skeleton of an ape is quite similar to that of a human in the structure of the chest and shoulders. Apes have broad, flat chests and arms capable of reaching up and backward from the shoulder; this construction is associated with brachiation. The pelvis, on the other hand, is more like that of a monkey, designed for walking on all fours, hence the use of knuckle-walking for ground locomotion. The arms of an ape are longer than the legs. The hands are similar to human hands, but with fingers and thumb of more equal length; the feet are handlike, grasping structures. Apes have neither tails nor the cheek pouches found in Old World monkeys; gibbons are the only apes that have the buttock callosities found in Old World monkeys. Like other anthropoid primates, the eyes are highly developed, with stereoscopic color vision. The brains of great apes are different from old world monkeys and some structures are reminiscent of the uniquely elaborate features of the human cortex, rendering these primates capable of fairly advanced reasoning. Chimpanzees, bonobos, orangutans, and gorillas have been observed using objects as tools in the wild.
Estimates of the amount of identical genetic material (DNA) in chimpanzees and humans range from 94.6% to 99.4%. This marked similarity, and additional evidence, have led primatologists to suggest that the taxonomy of the apes should include three groups: hylobatidae (gibbons and siamangs); pongidae (orangutangs); and hominidae (gorillas, chimpanzees, and humans). Apes are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Primates.
See S. Montgomery, Walking with the Great Apes (1991).
Under the current classification system there are two families of hominoids:
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 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.
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 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.
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.
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 25 February 1747, Linnaeus wrote:
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:
|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.|
Listed are the families and genera of apes; also listed are the extant species.
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.