The New World monkeys (superfamily Ceboidea) are classified within the parvorder of Platyrrhini, whereas the Old World monkeys (superfamily Cercopithecoidea) form part of the parvorder Catarrhini, which also includes the hominoids (apes, including humans). Thus, as Old World monkeys are more closely related to hominoids than they are to New World monkeys, the monkeys are not a unitary (monophyletic) group.
Monkey child treating its parent
According to the Online Etymology Dictionary, the word "monkey" may originate in a German version of the Reynard the Fox fable, published circa 1580. In this version of the fable, a character named Moneke is the son of Martin the Ape.[1] In English, no very clear distinction was originally made between "ape" and "monkey"; thus the 1910 Encyclopædia Britannica entry for "ape" notes that it is either a synonym for "monkey" or is used to mean a tailless humanlike primate.[2] Such ambiguities persist. Colloquially, the terms "monkeys" and "apes" may still be used interchangeably.[3] 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.[4] Monkeys thus constituted a "grade" on the path to humans and were distinguished from "apes".