Science Fair Project Encyclopedia
- the family Hylobatidae consists of 12 species of gibbons, including the Lar and the Siamang, collectively known as the "lesser apes"
- the family Hominidae consisting of gorillas, chimpanzees, orangutans, and Humans, collectively known as the "great 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 small quantities of meat (either hunted or scavenged), along with anything else available and easily digested. They are native to Africa and Asia.
The great ape family was previously referred to as Pongidae, and humans (and fossil hominids) were omitted from it, but on grounds of relatedness there is no argument for doing this. Chimpanzees, gorillas, humans and orangutans are all more closely related to one another than any of these four genera are to the gibbons and siamangs. Awkwardly, 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). It is now usual to use the subfamily Homininae to separate the hominids, in this narrow sense, from the extant non-human members of the family Hominidae.
Current evidence implies that humans share a common, extinct, ancestor with the chimpanzee/bonobo line, from which we separated more recently than the gorilla line. 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.
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, ribcages that are flatter front-to-back, and a shorter, less mobile spine compared to Old World monkeys. These are all anatomical adaptations to vertical hanging and swinging locomotion (brachiation) in the apes.
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 apes occurred between 5 and 10 million years ago, and probably in the lower end of that range. Ramapithecus therefore is no longer considered a hominin.
The term "ape" 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 may 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 Sulawesi Crested Macaque , M. niger.
The intelligence and humanoid appearance of apes are responsible for legends which attribute human qualities; for example, apes are sometimes said to be able to speak but refuse to do so in order to avoid work. They are also 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 Elath became apes as punishment for fishing on the Sabbath. Christian folklore claims that 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 is specifically to apes, since all date from a period when the distinction between apes and monkeys was not widely understood, or not understood at all.
Also in 2002, a new giant ape troop was discovered in the Democratic Republic of Congo. These apes share many features of both chimpanzees and gorillas. According to a report from the BBC News Online, the apes have large black faces, are two meters tall and make nests on the ground, all like gorillas. However, they live hundreds of kilometers from any other gorilla troops, and their diet is high in fruits, similar to the chimpanzee diet.
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, anatomy comparisons 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.
In 1758, Carolus Linnaeus, relying on second- or third-hand accounts, placed two species in Homo along with H. sapiens: Homo troglodytes ("cave-dwelling man") and the Homo caudatus ("tail-bearing man"). It is not clear to which animals these names refer, 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.
Until about 1980 the hominoids were divided into three familes: humans and their extinct relatives in Hominidae, the 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 great apes in 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.
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.
Classification and evolution
As discussed above, hominoid taxonomy has unergone several changes. Current understanding has the apes diverge from the Old World monkeys about 25 million years ago. The lesser and greater apes split about 18 mya, and the hominid splits happen 14 mya (Pongo), 7 mya (Gorilla), and 6 mya (Homo & Pan)
- Superfamily Hominoidea
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