As
zoological knowledge developed, it became clear that taillessness occurred in a number of different and otherwise distantly related
species. The term "ape" was then used in two different senses, as shown in the 1910
Encyclopædia Britannica entry. Either "ape" was still used for a tailless humanlike primate or it became a synonym for "monkey".
[7]
Sir
Wilfrid Le Gros Clark was one of the
primatologists who developed the idea 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. Within this tradition, "ape" refers to all the members of the superfamily Hominoidea, except humans.
[3] Thus "apes" are a
paraphyletic group, meaning that although all the species of apes descend from a common ancestor, the group does not include all the descendants of that ancestor, because humans are excluded.
[13]
Greater and lesser[edit]
The diagram below shows the commonly accepted evolutionary relationships of the Hominoidea,
[2] with the group traditionally called "apes" marked by a bracket.
Hominoidea
Hominidae
Homininae
Hominini
humans (genus
Homo)
chimpanzees (genus
Pan)
gorillas (genus
Gorilla)
orangutans (genus
Pongo)
gibbons (family Hylobatidae)
apes
The "apes" are traditionally divided further into the "lesser apes" and the "great apes":
[14]
Hominoidea
Hominidae
Homininae
Hominini
humans (genus
Homo)
chimpanzees (genus
Pan)
gorillas (genus
Gorilla)
orangutans (genus
Pongo)
gibbons (family Hylobatidae)
great apes
lesser apes
In summary, there are three common uses of the term "ape": English-speaking non-biologists may not distinguish between "monkeys" and "apes", or may use "ape" for any tailless monkey or non-human hominoid, whereas English-speaking biologists commonly use the term "ape" for all non-human hominoids as shown above.
In recent years biologists have generally preferred to use only
monophyletic groups in classifications;
[15] that is, only groups which include
all the descendants of a common ancestor.
[16] The superfamily Hominoidea is one such group (or "
clade"). Some then use the term "ape" to mean all the members of the superfamily Hominoidea. For example, in a 2005 book,
Benton wrote "The apes, Hominoidea, today include the gibbons and orang-utan ... the gorilla and chimpanzee ... and humans".[6] The group traditionally called "apes" by biologists is then called the "non-human apes".