We have lots of words to identify organisms: blue jay, oak tree, monarch butterfly, dandelion. But these common names aren't always precise, and they can't possibly cover all the species of organisms in the world. There are hundreds of thousands of species of plants and over a million species of animals known today. And it's likely that far more remain undiscovered. There are about 400,000 known species of beetles alone!

Worldwide, biologists have adopted a single system of naming organisms, a system first devised by the Swedish biologist Carolus Linnaeus in the 18th century. This is a binomial system of nomenclature. Each species is identified by two Latin names. The first name designates the genus; it's the generic name. The second name designates the particular species; it's the specific name.

When several species are believed to be closely related evolutionarily, they may be given the same generic name. For example, the lion, the tiger, and the leopard all have the same generic name, Panthera. They're said to belong to the same genus. The three species of cats are distinguished by their specific names. The lion is Panthera leo. The tiger is Panthera tigris. The leopard is Panthera pardus.

Although the cheetah may look similar to these cats, there are some important differences in its anatomy and in other characteristics. Therefore, the cheetah has a different generic name. The cheetah's scientific name is Acinonyx jubatus. Many smaller cats are placed in the genus Felis, including the central American ocelot, Felis pardalis; the African serval, Felis serval, and the house cat, Felis catus.

The identification and naming of species of organisms is the main goal of the scientific field of taxonomy. Taxonomists classify organisms into a hierarchy of increasingly broader categories. Related species are contained within a single genus. Related genera are contained within a family. Related families are contained within an order. Then orders within a class, classes within a phylum, and phyla within a kingdom.

For example, the house cat belongs to the genus Felis, one of several genera within the cat family Felidae. Felidae is a family in the order Carnivora, which encompasses cats, dogs, weasels,and bears. Carnivora is one of several orders in the class Mammalia, which includes such familiar furry warm-blooded creatures as bats, rabbits, horses, and humans.

Mammalia is a class in the phylum Chordata, which includes all organisms with a backbone—for example, fish, amphibians, and reptiles. Chordata is a phylum in the kingdom Animalia, encompassing all animals, including earthworms, jellyfish, and snails.

In the next section we'll continue to explore the task of classifying organisms into larger taxonomic groups.

Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education