10.5: How do we name species?

Keeping track of a large group of anything requires an organizational system. Many libraries, for example, catalogue their books by using the Dewey decimal system, which organizes books into 10 different classes, further subdivides each class into 10 divisions, and each division into 10 sections.

With the huge number of species on earth, a classification system is particularly important. Biologists use the system developed by the Swedish biologist Carolus Linnaeus in the mid-1700s. Here’s how it works (FIGURE 10-9). Every species is given a scientific name that consists of two parts, a genus (pl. genera) and a specific epithet. Linnaeus named humans Homo sapiens, meaning “wise man.” Homo is the genus and sapiens is the specific epithet, and Homo sapiens is the species name. (The genus is capitalized, and both genus and specific epithet are italicized.) The redwood tree has the name Sequoia sempervirens. The strength of Linnaeus’s system is that it is hierarchical—that is, each element of the system falls under a single element in the level just above it.

In the Linnaean system, the species is the narrowest classification for an organism. The name for every species within a genus is unique, but many different species may be in the same genus. Similarly, many genera are grouped within a family. And many families are grouped within an order. Orders are grouped within a class. Classes are grouped within a phylum. And, as Linnaeus originally set it up, all phyla were classified under one of three kingdoms: the animal kingdom, the plant kingdom, or the “mineral kingdom.”

Today, many of the species classifications that Linnaeus described have been revised, and some of his designations, such as the “mineral kingdom,” have been left out, while two other kingdoms (fungi and protists) have been added. Also, all of the kingdoms are now classified under an even higher order of classification, the domain. But Linnaeus’s basic hierarchical structure remains, and all life on earth is still named using this system, with all organisms belonging to one of the three domains: the bacteria, the archaea, and the eukarya.

When new species are discovered, they are given names based on the Linnaean system. The higher-level groups into which a new species should be classified are generally clear—that is, it’s usually obvious whether something is in the animal or plant kingdom, or whether it is in the mammalian or amphibian class. But when scientists are assigning a specific epithet, they frequently have a little fun. In recent years, for example, an amphibian fossil was named Eucritta melanolimnetes, which translates roughly into “creature from the black lagoon.” And in honor of Elvis Presley, a wasp species was named Preseucoila imallshookupis. A variety of other celebrities also have had species named after them, including the Beatles, Mick Jagger, Kate Winslet, and Steven Spielberg.

Plants and animals often are referred to by common names, which are different from their “official” names in the Linnaean system and are based on similarities in appearance. These common names, however, can cause confusion. “Fish” for example is used as part of the names of jellyfish, crayfish, and silverfish, none of which is closely related to the vertebrate group of fishes that includes salmon and tuna. Later in this chapter we’ll see how an important goal of modern classification and the naming of organisms is to link an organism’s classification more closely with its evolutionary history than with its physical characteristics.