Taxonomy

Taxonomy is the science of classifying living things. It follows rules and procedures for classifying organisms according to their differences and similarities. Classifying living things enables scientists to see how an organism is related to others and to trace its evolution (the process by which gradual genetic change occurs over time to a group of living things).

Until modern taxonomy was invented by the Swedish naturalist, Carolus Linnaeus (1707–1778), a name for any given organism was usually a long, detailed description rather than an actual name. Since there were no rules, or standards, to follow when naming a newly discovered form of life, most people went about it in an unscientific and rather individual way. Linnaeus realized that some system of order had to be imposed on the great diversity of life if people were to understand one another. As a result, Linnaeus not only devised a system that identified and named each living thing, but was able to place each living thing in one of several related categories.

HIERARCHICAL CLASSIFICATION

Most people do this type of organizing in their daily lives without thinking about it. For example, a music store groups all CDs together and keeps them separate from music on tape. Within the CD section, the store makes more detailed categories of music, like rock, jazz, hip-hop, and others. Within one of these categories, it may further break it down into groups or solo artists, and alphabetize within one of those categories. This type of systematic arranging that goes from general groups to more specific groups is called hierarchical classification.

It was hierarchical thinking that Linnaeus used when he first built his classification system. He divided all forms of life into the first and largest group called kingdoms. In the mid-eighteenth century, science recognized only two kingdoms, plant and animal. With more knowledge, scientists have added three more: fungi, protists, and bacteria.

Taxonomy is an always-growing and adaptable science that allows room for additions, changes, and even corrections. As a result, each kingdom was divided into smaller and smaller categories, with each level more general than the one below it. These seven categories are kingdom, phylum, class, order, family, genus, and species. A useful trick to remember this order is the sentence, "King Philip Came Over From Great Spain." These categories, or taxonomic groupings, are also called taxa (singular, taxon). For example, the taxon Carnivora is an order that includes many different families. Amazingly, the seven taxa, or hierarchical levels, that were finalized by Linnaeus in 1758 are still the ones used today.

BINOMIAL SYSTEM OF NOMENCLATURE

Linnaeus made another major contribution to organizing the natural world. He gave a two-part scientific name to every living thing. Since this method was based on certain standards, or rules, and was made up from Greek or Latin words, it gave everyone an agreed-upon name to use for a particular organism. This system avoided the confusion that could arise when different languages or countries used different names for the same animal. It also allowed all scientists to speak the same language. As a result, a Russian researcher knows exactly what organism is discussed in a paper published by a French biologist.

The Linnean system came to be called the "binomial system of nomenclature," and there are several strictly followed rules that govern its use. The system uses two Latin names—the genus and species to which an organism belongs—for its scientific name. Binomial names are always underlined or italicized. The first letter of the genus is always capitalized, while the species is always written in lowercase letters. For instance, Homo sapiens is the scientific name for humans. The genus name may be used alone, but the particular species name is never used without the genus name. There are now taxonomic rules that govern the worldwide classification of organisms. No changes can be made without the approval of the appropriate international body.

NEW METHODS OF CLASSIFICATION

Since taxonomy is an evolving science, it is not surprising that it includes more sophisticated ways of grouping and classifying organisms. One new method is to take into account new molecular and biochemical information. Another looks only at the chromosomes (coiled structures in the nucleus of a cell that carries the cell's genetic information) of an organism to see how it the organism is related to others. In many ways, the aim of modern taxonomy is to arrive at an evolutionary-based classification system that will let scientists see more clearly the real relationships between all living organisms.

[See alsoClass; Classification; Family; Genus; Kingdom; Order; Phylum; Species ]