Primate Taxonomy

The Animal Kingdom is divided into 25 to 30 major groups called phyla (singular, phylum): the Arthropoda (insects and spiders), Mollusca,Coelenterata (sea “anemones and jellyfish”), Echinodermata (starfish and sea urchins), and many other phyla that most people would recognize only as “worms.” The phyla are divided into subordinate groups called Classes, [Page 1945]the classes again into subordinate groups called Orders, the orders into Families, the families into Genera (singular, genus), the genera into Species. Within each category, subordinate categories can be inserted: thus, families can be divided into subfamilies where needed (another way of looking at this is to say that the genera of a family can be grouped into subfamilies). Super-families (groups of closely related families) can also be instituted. With finer and finer divisions we may well “run out of ranks,” and unranked groups are perfectly feasible, provided it is widely understood where they belong in the main classification.

The phylum to which Primates belong is called Chordata (crudely speaking, animals with backbones). The phylum Chordata is divided into approximately eight classes, one of them being Mammalia—the mammals, distinguished by having hair and mammary glands. The 20 or so orders of mammals include Carnivora (cats and dogs), Proboscidea (elephants), Chiroptera (bats)—and Primates.

The living groups of Primates are lemurs, lorises, tarsiers, New World (i.e., American) monkeys, Old World (i.e., African and Asian) monkeys, apes, and humans. Linnaeus, the originator of biological taxonomy, in1758, did not adopt the rank of Family, but divided the order Primates directly into four genera: Homo (humans), Simia (apes and monkeys), Lemur, and Vespertilio (the latter being bats—Linnaeus's successors expelled bats from the Primates). Although he thus separated humans from apes, it is very noteworthy that he did classify humans as Primates; unfortunately most of his successors removed humans and, instead of Primates, recognized two different orders—Bimana (humans) and Quadrumana (other Primates). It was not until a century later that the order Primates was definitively re-instituted (by Mivart, in 1863).

For nearly another century there was dispute regarding what should be the major subdivisions of the order Primates. Most authors tended to regard tarsiers as being related to lemurs and lorises, but Pocock, in 1918,showed that they have more in common with monkeys, apes, and humans, and divided the Primates into suborders Strepsirhini (lemurs and lorises)and Haplorhini (tarsiers, monkeys, apes, and humans). A few taxonō mists adopted his classification, but most adopted the one formalized by Simpson in 1945, in which the suborders were Prosimii (lemurs, lorises and tarsiers) and Anthropoidea (monkeys, apes, and humans).

The reason why this matters is because these two competing schemes reflect different philosophies of what the function of taxonomy actually is. The tarsier shares with lemurs and lorises characteristics such as a small brain—a primitive retention from the common ancestor of all Primates. This certainly makes it look superficially more like a lemur than like a monkey—but it has never been clear why it should be important to classify animals together simply because, in certain selected characters, they are “primitive.” Since the1960s, the tendency has been more and more to classify animals together because they share an exclusive common ancestor (phylogenetic systematics: originating with Hennig in 1952, and especially with the translation into English of his book Phylogenetic Systematics in 1966). It is now clear to most primatologists that the tarsier shares a common ancestor with monkeys, apes, and humans that is more recent than the one they all shared with lemurs and lorises—hence Pocock's classification is now overwhelmingly preferred.

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