Monkey

Lore & Background

In 1812, Étienne Geoffroy grouped the apes and the Cercopithecidae group of monkeys together and established the name Catarrhini, 'Old World monkeys'. The extant sister of the Catarrhini in the monkey 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. 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.

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.

Reader's Guide

Monkeys, including apes, can be distinguished from other primates by having only two pectoral nipples, a pendulous penis, and a lack of sensory whiskers. 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. A group of monkeys may be commonly referred to as a tribe or a troop. Tailless monkeys may be called 'apes', incorrectly according to modern usage; thus the tailless Barbary macaque is historically called the 'Barbary ape'.

Did You Know?

• Lemurs, lorises, and galagos are not monkeys, but strepsirrhine primates.
• The simians' sister group, the tarsiers, are also haplorhine primates; however, they are also not monkeys.
• Monkeys range in size from the pygmy marmoset, as small as 117 mm with a 172 mm tail and just over 100 g in weight, to the male mandrill, almost 1 m long and weighing up to 36 kg.
• New World monkeys have long tails, with those in the Atelidae family being prehensile, while Old World monkeys have non-prehensile tails or no visible tail at all.