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Monkey

Animal of the "higher primates", excluding apes

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Mom, dad & two young monkeys in Ubud Monkey Forest
Deerpeter · CC BY-SA 4.0

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In 1812, Étienne Geoffroy grouped the apes and the Cercopithecidae group of monkeys together and established the name Catarrhini, "Old World monkeys" ("singes de l'Ancien Monde" in French). The extant sister of the Catarrhini in the monkey ("singes") group is the Platyrrhini (New World monkeys). Some nine million years before the divergence between the Cercopithecidae and the apes, the Platyrrhini emerged within "monkeys" by migration to South America likely by ocean. Apes are thus deep in the tree of extant and extinct monkeys, and any of the apes is distinctly closer related to the Cercopithecidae than the Platyrrhini are.

Many monkey species are tree-dwelling (arboreal), although there are species that live primarily on the ground, such as baboons. Most species are mainly active during the day (diurnal). Monkeys are generally considered to be intelligent, especially the Old World monkeys.

Within suborder Haplorhini, the simians are a sister group to the tarsiers – the two members diverged some 70 million years ago. New World monkeys and catarrhine monkeys emerged within the simians roughly 35 million years ago. Old World monkeys and apes emerged within the catarrhine monkeys about 25 million years ago. Extinct basal simians such as Aegyptopithecus or Parapithecus (35–32 million years ago) are also considered monkeys by primatologists.

Lemurs, lorises, and galagos are not monkeys, but strepsirrhine primates (suborder Strepsirrhini). The simians' sister group, the tarsiers, are also haplorhine primates; however, they are also not monkeys.

Apes emerged within monkeys as sister of the Cercopithecidae in the Catarrhini, so cladistically they are monkeys as well. However, there has been resistance to directly designate apes (and thus humans) as monkeys, so "Old World monkey" may be taken to mean either the Cercopithecoidea (not including apes) or the Catarrhini (including apes). The classification of apes as monkeys was realized by Georges-Louis Leclerc, Comte de Buffon in the 18th century. Linnaeus placed this group in 1758 together with the tarsiers, in a single genus "Simia" (sans Homo), an ensemble now recognised as the Haplorhini.

Monkeys, including apes, can be distinguished from other primates by having only two pectoral nipples, a pendulous penis, and a lack of sensory whiskers.

Historical and modern terminology

According to the Online Etymology Dictionary, the word "monkey" may originate in a German version of the Reynard the Fox fable, published c. 1580. In this version of the fable, a character named Moneke is the son of Martin the Ape. In English, no clear distinction was originally made between "ape" and "monkey"; thus the 1911 Encyclopædia Britannica entry for "ape" notes that it is either a synonym for "monkey" or is used to mean a tailless human-like primate. Colloquially, the terms "monkey" and "ape" are widely used interchangeably. Also, a few monkey species have the word "ape" in their common name, such as the Barbary ape.

Later in the first half of the 20th century, the idea developed that there were trends in primate evolution and that the living members of the order could be arranged in a series, leading through "monkeys" and "apes" to humans. Monkeys thus constituted a "grade" on the path to humans and were distinguished from "apes".

Scientific classifications are now more often based on monophyletic groups, that is groups consisting of all the descendants of a common ancestor. The New World monkeys and the Old World monkeys (Cercopithecidae, excluding apes) are each monophyletic groups, but their combination was not, since it excluded hominoids (apes and humans). Thus, the term "monkey" no longer referred to a recognized scientific taxon. The smallest accepted taxon which contains all the monkeys is the infraorder Simiiformes, or simians. However this also contains the hominoids, so that monkeys are, in terms of currently recognized taxa, non-hominoid simians. Colloquially and pop-culturally, the term is ambiguous and sometimes monkey includes non-human hominoids. In addition, arguments have been made for a monophyletic usage of the word "monkey" from the perspective that usage should reflect cladistics.

Several science-fiction and fantasy stories have depicted non-human (fantastical or alien) antagonistic characters referring to humans as monkeys, usually in a derogatory manner, as a form of metacommentary.

A group of monkeys may be commonly referred to as a tribe or a troop.

Two separate groups of primates are referred to as "monkeys": New World monkeys (platyrrhines) from South and Central America and Old World monkeys (catarrhines in the superfamily Cercopithecoidea) from Africa and Asia. Apes (hominoids)—consisting of gibbons, orangutans, gorillas, chimpanzees and bonobos, and humans—are also catarrhines but were classically distinguished from monkeys. Tailless monkeys may be called "apes", incorrectly according to modern usage; thus the tailless Barbary macaque is historically called the "Barbary ape".

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