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Thursday, September 11, 2014

Hominidae

Hominidae

From Wikipedia, the free encyclopedia

Hominids[1]
Temporal range: Miocene - Holocene, 7–0Ma
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Ham-and-handler.jpg
Two hominids: A human (Homo sapiens) and a chimpanzee (Pan troglodytes)
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Superfamily: Hominoidea
Family: Hominidae
Gray, 1825
Type genus
Homo
Linnaeus, 1758
Genera
Synonyms
  • Pongidae Elliot, 1913
The Hominidae (/hɒˈmɪnɨdiː/; also known as great apes[notes 1]) form a taxonomic family of primates, including four extant genera:
The term "hominid" is also used in the more restricted sense as hominins or "humans and relatives of humans closer than chimpanzees".[2] In this usage, all hominid species other than Homo sapiens are extinct. A number of known extinct genera are grouped with humans in the Homininae subfamily, others with orangutans in the Ponginae subfamily. The most recent common ancestor of the Hominidae lived roughly 14 million years ago,[3] when the ancestors of the orangutans speciated from the ancestors of the other three genera.[4] The ancestors of the Hominidae family had already speciated from those of the Hylobatidae family, perhaps 15 million to 20 million years ago.[4][5]

History

See also: Human evolution
Sumatran orangutan (Pongo abelii)

In the early Miocene, about 22 million years ago, the many kinds of arboreally adapted primitive catarrhines from East Africa suggest a long history of prior diversification. Fossils at 20 million years ago include fragments attributed to Victoriapithecus, the earliest Old World Monkey. Among the genera thought to be in the ape lineage leading up to 13 million years ago are Proconsul, Rangwapithecus, Dendropithecus, Limnopithecus, Nacholapithecus, Equatorius, Nyanzapithecus, Afropithecus, Heliopithecus, and Kenyapithecus, all from East Africa. The presence of other generalized non-cercopithecids of middle Miocene age from sites far distant—Otavipithecus from cave deposits in Namibia, and Pierolapithecus and Dryopithecus from France, Spain and Austria—is evidence of a wide diversity of forms across Africa and the Mediterranean basin during the relatively warm and equable climatic regimes of the early and middle Miocene. The youngest of the Miocene hominoids, Oreopithecus, is from coal beds in Italy that have been dated to 9 million years ago.
Molecular evidence indicates that the lineage of gibbons (family Hylobatidae) diverged from great apes some 18–12 million years ago, and that of orangutans (subfamily Ponginae) diverged from the other great apes at about 12 million years; there are no fossils that clearly document the ancestry of gibbons, which may have originated in a so-far-unknown South East Asian hominoid population, but fossil proto-orangutans may be represented by Sivapithecus from India and Griphopithecus from Turkey, dated to around 10 million years ago.[6]
A reconstruction of a female Australopithecus afarensis (National Museum of Natural History)

Species close to the last common ancestor of gorillas, chimpanzees, bonobos and humans may be represented by Nakalipithecus fossils found in Kenya and Ouranopithecus found in Greece. Molecular evidence suggests that between 8 and 4 million years ago, first the gorillas, and then the chimpanzees and bonobos (genus Pan) split off from the line leading to the humans; human DNA is approximately 98.4% identical to that of chimpanzees when comparing single nucleotide polymorphisms (see human evolutionary genetics). The fossil record of gorillas, chimpanzees and bonobos is limited. Poor preservation in certain conditions (e.g. rain forest soils tend to be acidic and dissolve bone) contributes to this problem and to sampling bias. Other hominins likely adapted to the drier environments outside the equatorial belt, along with antelopes, hyenas, dogs, pigs, elephants, and horses. The wet equatorial belt contracted after about 8 million years ago. There is very little fossil evidence for the split of the hominin lineage from the lineages of gorillas and Pan (chimpanzees and bonobos). The earliest fossils that have been argued to belong to the human lineage are Sahelanthropus tchadensis (7 Ma) and Orrorin tugenensis (6 Ma), followed by Ardipithecus (5.5–4.4 Ma), with species Ar. kadabba and Ar. ramidus.

Taxonomic history

Humans are one of the four extant hominid genera.

The classification of the great apes has been revised several times in the last few decades. These various revisions have led to a varied use of the word "hominid" – the original meaning of Hominidae referred only to the modern meaning of Hominini, i.e. only humans and their closest relatives. The meaning of the taxon changed gradually, leading to the modern meaning of "hominid", which includes all great apes and humans.
A model of a modern human hominid skull
A fossil hominid exhibit at The Museum of Osteology, Oklahoma City, Oklahoma

The primatological term hominid is easily confused with a number of very similar words:
Many scientists, including paleoanthropologists, continue to use the term hominid to mean humans and their direct and near-direct bipedal ancestors.

As mentioned, Hominidae was originally the name given to humans and their extinct relatives, with the other great apes being placed in a separate family, the Pongidae. However, that definition made Pongidae paraphyletic because at least one great ape species appears to be more closely related to humans than to other great apes. Most taxonomists nowadays encourage monophyletic groups – this would require the use of Pongidae to be restricted to one of the great ape groups (containing Pongo, the orangutans) only. Thus, many biologists consider Hominidae to include Pongidae as the subfamily Ponginae, or restrict the latter to the orangutans and their extinct relatives, such as Gigantopithecus. The taxonomy shown here follows the monophyletic groupings according to the modern understanding of human and great ape relationships.

Especially close human relatives form a subfamily, the Homininae. A few researchers go so far as to include chimpanzees and bonobos[7] and gorillas[8][9] in the genus Homo along with humans. Alternatively, those fossil relatives more closely related to humans than the nearest living great ape species represent members of Hominidae without necessarily assigning subfamily or tribal categories.[10]

Many extinct hominids have been studied to help understand the relationship between modern humans and the other extant hominids. Some of the extinct members of this family include Gigantopithecus, Orrorin, Ardipithecus, Kenyanthropus, and the australopithecines Australopithecus and Paranthropus.[11]

The exact criteria for membership in the tribe Hominini under the current understanding of human origins are not clear, but the taxon generally includes those species that share more than 97% of their DNA with the modern human genome, and exhibit a capacity for language or for simple cultures beyond the family or band. The theory of mind including such faculties as mental state attribution, empathy and even empathetic deception is a controversial criterion distinguishing the adult human alone among the hominids. Humans acquire this capacity at about four and a half years of age, whereas it has neither been proven nor disproven that gorillas, chimpanzees and bonobos develop a theory of mind.[12] This is also the case for some New World monkeys outside the family of great apes, as, for example, the capuchin monkeys.

However, without the ability to test whether early members of the Hominini (such as Homo erectus, Homo neanderthalensis, or even the australopithecines) had a theory of mind, it is difficult to ignore similarities seen in their living cousins. Orangutans have also been shown to have culture comparable to that of chimpanzees,[13] and some[who?] say the orangutan may also satisfy these criteria. These scientific debates take on political significance for advocates of great ape personhood.

Classification

 
Evolutionary tree of the Hominoidea : after an initial 
separation from the main line of Hylobatidae (current gibbons), some 18 million years ago, the line of Pongidae broke away, leading to the current orangutan, while the Hominidae split later in Gorillini and Hominini.

Extant

Skulls of an orangutan and a gorilla
Human and chimp skulls and brains (not to scale), as illustrated in Gervais' Histoire naturelle des mammifères

The seven living species of great ape are classified in four genera. The following classification is commonly accepted:[1]

Fossil

A reconstruction of Pierolapithecus catalaunicus
Replica of the skull sometimes known as "Nutcracker Man", found by Mary Leakey.

In addition to the extant species and subspecies above, archaeologists, paleontologists, and anthropologists have discovered numerous extinct great ape species. Below is based on the following taxonomy.[14]

Family Hominidae

Physical description

The great apes are large, tailless primates, with the smallest living species being the bonobo at 30–40 kilograms in weight, and the largest being the gorillas, with males weighing 140–180 kilograms. In all great apes, the males are, on average, larger and stronger than the females, although the degree of sexual dimorphism varies greatly among species. Although most living species are predominantly quadrupedal, they are all able to use their hands for gathering food or nesting materials, and, in some cases, for tool use.[21]

Most species are omnivorous,[citation needed] but fruit is the preferred food among all but some human groups. Chimpanzees and orangutans primarily eat fruit. When gorillas run short of fruit at certain times of the year or in certain regions, they resort to eating shoots and leaves, often of bamboo, a type of grass. Gorillas have extreme adaptations for chewing and digesting such low-quality forage, but they still prefer fruit when it is available, often going miles out of their way to find especially preferred fruits. Humans, since the neolithic revolution, consume mostly cereals and other starchy foods, including increasingly highly processed foods, as well as many other domesticated plants (including fruits) and meat. Hominid teeth are similar to those of the Old World monkeys and gibbons, although they are especially large in gorillas. The dental formula is 2.1.2.32.1.2.3. Human teeth and jaws are markedly smaller for their size than those of other apes, which may be an adaptation to eating cooked food for more than a million years.[22][23]
Gorilla

Gestation in great apes lasts 8–9 months, and results in the birth of a single offspring, or, rarely, twins. The young are born helpless, and they must be cared for long periods of time. Compared with most other mammals, great apes have a remarkably long adolescence, not being weaned for several years, and not becoming fully mature for eight to thirteen years in most species (longer in humans). As a result, females typically give birth only once every few years. There is no distinct breeding season.[21]

Gorillas and chimpanzees live in family groups of around five to ten individuals, although much larger groups are sometimes noted. Chimpanzees live in larger groups that break up into smaller groups when fruit becomes less available. When small groups of female chimpanzees go off in separate directions to forage for fruit, the dominant male(s) can no longer control them and the females often mate with other subordinate males, whether by choice or not. In contrast, groups of gorillas stay together regardless of the availability of fruit. When fruit is hard to find, they resort to eating leaves and shoots. Because gorilla groups stay together, the male is able to monopolize the females in his group. This fact is related to gorillas' greater sexual dimorphism than chimpanzees'. In both chimpanzees and gorillas, the groups include at least one dominant male, and females leave the group at maturity.

Legal status

Due to the close genetic relationship between humans and other great apes, certain animal rights organizations, such as the Great Ape Project, argue that nonhuman great apes are persons and should be given basic human rights. Some countries have instituted a research ban to protect great apes from any kind of scientific testing.

On 25 June 2008, the Spanish parliament supported a new law that would make "keeping apes for circuses, television commercials or filming" illegal.[24]

Conservation

The following table lists the estimated number of great ape individuals living outside zoos.

Species Estimated number
Sumatran orangutan 6,667[25]
Bornean orangutan 61,234[25]
Western gorilla 200,000[26]
Eastern gorilla 6,000[26]
Common chimpanzee 100,000[27]
Bonobo 10,000[27]
Human 7,300,722,300 [28]
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