Binomial (Linnaean System)
Despite the overwhelming diversity of life that exists (and once existed) on this planet, it is clear that some organisms are more similar to each other than to others. Thus, organisms can be assigned to groups based on their overall similarity to other organisms. For example, humans belong to the group "mammals" as do all other organisms that possess mammary glands and hair. The grouping of organisms provides a convenient means of classification; that is, an organism can be described by the groups to which it belongs.
The classification system that is used today is called the Linnaean System after its inventor, the Swedish naturalist Carolus Linnaeus (1707-1778). In his 1758 book, Systema Naturae, Linnaeus categorized all organisms into seven hierarchical groupings arranged from most inclusive to least inclusive. They are kingdom, phylum, class, order, family, genus, and species. Humans belong to the kingdom Animalia, the phylum Chordata, the class Mammalia, the order Primates, and the family Hominidae, and have been given the generic name (genus) Homo and the specific name (species) sapiens. The Linnaean System is hierarchical because there may be many species per genus, many genera (plural of genus) per family, and so on.
Because specific names are not unique (i.e., there may exist a plant with the specific name sapiens), the name of a species always includes both the generic name and the specific name, for example, Homo sapiens. This method of giving every species a unique combination of two names is called "binomial nomenclature," and is part of Linnaeus's classification system. By convention, these scientific names for organisms, as opposed to the common names, are always italicized. Furthermore, the generic name is capitalized while the specific name is not. Biologists prefer scientific names to common names because of their uniqueness, stability, and universality. Common names, on the other hand, often refer to more than one species and vary over time and from place to place. Biologists follow a certain Code of Nomenclature when deciding what to name a newly discovered species.
Carolus Linnaeus (1707-1778) is the naturalist responsible for developing the system still used in the twenty-first century for classifying animals.The practice of naming and classifying organisms is termed " taxonomy. " Linnaeus classified organisms mainly by their physical (morphological) characteristics. He believed that his groups held theological significance, that is, that they revealed God's plan in creating life. However, with the recognition that species evolve, which led to Charles Darwin's On the Origin of Species in 1859, it became apparent that Linnaeus's classification system held biological significance as well. Organisms that are morphologically similar and consequently grouped together are usually similar because they share a common ancestry. The Linnaean System thus reflects evolutionary relationships among organisms. For example, humans are grouped with gorillas and chimpanzees in the order Primates because we are more closely related to gorillas and chimpanzees then we are to other mammals. Likewise, Primates are grouped with Rodentia in the class Mammalia because primates and rodents are more closely related to each other than they are to other organisms in the phylum Chordata, such as reptiles and fish.
Linnaeus, Carolus.
Bibliography
Darwin, Charles. On the Origin of Species by Means of Natural Selection. London: John Murray, 1859. Facsimile edition reprinted Cambridge, MA: Harvard University Press, 1975.
Jeffrey, Charles. An Introduction to Plant Taxonomy. Cambridge, U.K.: Cambridge University Press, 1982.
Linnaeus, Carolus. Systema Naturae, 10th ed. Stockholm, Sweden: Laurentius Salvius, 1758. Reproduced New York: Stechert-Hafner Service Agency, 1964.
Schuh, Randall T. Biological Systematics: Principles and Applications. Ithaca, NY: Cornell University Press, 2000.
Simpson, George Gaylord. Principles of Animal Taxonomy. New York: Columbia University Press, 1961.
Internet Resources
Maddison, David R., and Wayne P. Maddison. The Tree of Life. <http://phylogeny.arizona.edu/tr ee/phylogeny.html>.
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