Science Fair Project Encyclopedia
- Taxonomy in general refers either to a hierarchical classification of things, or the principles underlying that classification.
Linnaean taxonomy is a system of classification widely used in the biological sciences. It was first developed by Carolus Linnaeus in the 18th century during the great expansion of natural history knowledge. Linnaean taxonomy classifies living things into a hierarchy, starting with domains or kingdoms. Kingdoms are divided into phyla (singular: phylum)—for animals; the term divisions is used for plants. Phyla are divided into classes, and they, in turn, into orders, families, genera (singular: genus), and species (singular: species). Groups of organisms at any of these ranks are called taxa (singular: taxon), or phyla, or taxonomic groups.
A summary of this scheme, from most general to most specific, would be:
- Phylum (or division)
Mnemonics for remembering the major divisions of this list in order via common initials, include:
- Kids Playing with Cars On Freeways Get Squashed. (popular with HS Biology students)
- Kids Playing Chicken On Freeways Get Smashed.
- King Phillip called out for good soup.
- King Philip came over from Germany swimming.
- King Philip came over for good spaghetti.
- King Philip came over for good sex.
- Kings play chess on fat green stools.
- Kings play cards on fairly good soft velvet. (with "v" standing for "variety")
- Kings possess crowns of fine gem stones.
- Kenneth, please close our front gate soon.
- Keep plates clean or family gets sick.
- Killing people causes outbursts from general society.
- Klingon phasers charge on fast gray ships.
- Keep putting condoms on for good sex.
- King pine cones often form great saplings
Example classification: humans
As an example, consider the Linnaean classification for modern humans:
- Kingdom: Animalia (all animals, which are heterotrophs)
- Phylum: Chordata (all animals with a notochord)
- Subphylum: Vertebrata (all vertebrates, i.e., with a spinal column)
- Class: Mammalia (all vertebrates whose females secrete milk to nourish young)
- Subclass: Placentalia (Eutheria) (mammals who are nourished in utero through a placenta)
- Order: Primates (mammals with five opposable digits, binocular vision, and large brains)
- Family: Hominidae (all hominids, current and ancestral)
- Genus: Homo (upright primates; 'man')
- Species: Homo sapiens (humanity; 'wise man')
- Subspecies: Homo sapiens sapiens
A strength of Linnaean taxonomy is that it can be used to develop a simple and practical system for organizing the different kinds of living organisms. The most important aspect of this is the general use of binomial nomenclature, the combination of a genus name and a specific epithet ('sapiens', in the example above), to uniquely identify each species of organism. In the example, humankind is uniquely identified by the binomial Homo sapiens. No other species of animal can have this binomial. In this way, every species is given a unique and stable name (compared with common names that are often neither unique nor consistent from place to place and language to language). This uniqueness and stability are, of course, a result of the acceptance by working systematists (biologists specializing in taxonomy), not merely of the binomial nomenclature in itself, but of much more complex codes of rules and procedures governing the use of these names.
These rules—or at least those governing the nomenclature and classification of plants and fungi—are contained in the International Code of Botanical Nomenclature, maintained by the International Association for Plant Taxonomy. The current code, the 'Saint Louis Code' was adopted in 1999 and supersedes the 'Tokyo code'. Similar codes exist for animals and bacteria. Scientists follow these codes so that the names of organisms can be as clear and stable as possible.
Over time, our understanding of the relationships between living things has changed. The greatest change was the widespread acceptance of evolution as the mechanism of biological diversity and species formation. After this, it became generally understood that classifications ought to reflect the phylogeny of organisms, where each taxon should originate from a single ancestral form. In some systems it is generally encouraged that taxa should be strictly monophyletic, but this idea is controversial.
Originally, Linnaeus established three kingdoms in his scheme, namely Plantae, Animalia and an additional group for minerals, which has since been abandoned. Since then, various life forms have been moved into three new kingdoms: Monera, for prokaryotes (i.e., bacteria); Protista, for protozoans and most algae; and Fungi. This five kingdom scheme is still far from the phylogenetic ideal and has largely been supplanted in modern taxonomic work by a division into three domains: Bacteria and Archaea, which contain the prokaryotes, and Eukaryota, comprising the remaining forms. This change was precipitated by the discovery of the Archaea.
See also: Evolutionary tree, which has further subdivisions and presents the most current taxonomic viewpoint.
- "Taxonomy (the science of classification) is often undervalued as a glorified form of filing—with each species in its prescribed place in an album; but taxonomy is a fundamental and dynamic science, dedicated to exploring the causes of relationships and similarities among organisms. Classifications are theories about the basis of natural order, not dull catalogues compiled only to avoid chaos." Stephen Jay Gould (1990, p.98)
- Gould, S.J. (1990), Wonderful Life: The Burgess Shale and the Nature of History. Hutchinson Radius.
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