Primate - Historical and Modern Terminology

Historical and Modern Terminology

The relationships among the different groups of primates were not clearly understood until relatively recently, so the commonly used terms are somewhat confused. For example, "ape" has been used either as an alternative for "monkey" or for any tailless, relatively humanlike primate.

Sir Wilfrid Le Gros Clark was one of the primatologists who developed the idea of trends in primate evolution, and the living members of the order could be arranged in an ascending series leading to humans. Commonly used names for groups of primates, for example "prosimians", "monkeys", "lesser apes" and "great apes", reflect this arrangement. According to our current understanding of the evolutionary history of the primates, several of these groups are paraphyletic, meaning although all the species in the group descend from a common ancestor, the group does not include all the descendants of that ancestor.

By contrast with approaches such as those of Le Gros Clark, modern classifications typically use groups that are monophyletic, since they include all the descendants of a common ancestor. The diagram below shows one currently accepted classification of the primates, with groups with commonly used names shown on the right.

All the groups that have scientific names are monophyletic (i.e. they are clades), so the scientific classification reflects evolutionary history. Some of the traditional groups shown on the right, which form an "ascending series", are paraphyletic:

• "prosimians" contain two monophyletic groups, the suborder Strepsirrhini (lemurs, lorises and allies), as well as the tarsiers, which are a sister group to the infraorder Simiiformes.
• "monkeys" consist of two monophyletic groups, New World monkeys and Old World monkeys, but exclude hominoids (superfamily Hominoidea).
• "apes" as a whole, and the "great apes" in particular, are not monophyletic because they exclude humans.

Thus, the two sets of groups, and hence names, do not match, which causes problems in relating scientific names to common names. Consider the superfamily Hominoidea. In terms of the common names on the right, this group consists of apes and humans, and there is no single common name for all the members of the group. One possibility is to create a new common name, in this case "hominoids". Another possibility is to expand the use of one of the traditional terms. For example, in a 2005 book, the vertebrate palaeontologist Benton wrote, "The apes, Hominoidea, today include the gibbons and orang-utan ... the gorilla and chimpanzee ... and humans", thereby using "apes" to mean "hominoids". The group traditionally called "apes" must then be called the "nonhuman apes".

As of July 2011, there is no consensus as to which approach to follow, whether to accept traditional paraphyletic common names or whether to use monophyletic names, either new ones or adaptations of old ones. Both approaches will be found in biological sources, often in the same work. Thus, although Benton defines "apes" to include humans, he also repeatedly uses "ape-like" to mean "like an ape rather than a human", and when discussing the reaction of others to a new fossil writes of "claims that Orrorin ... was an ape rather than a human".