Taxonomy (biology)

Taxonomy (biology)

Introduction :

The term is derived from the Greek taxis (“arrangement”) and nomos (“law”). Taxonomy is, therefore, the methodology and principles of systematic botany and zoology and sets up arrangements of the kinds of plants and animals in hierarchies of superior and subordinate groups. There are several branches of Zoology. For example Taxonomy (taxis – arrangement; nomos – law) science of identification, nomenclature and classification of organisms. Today is the 290th anniversary of the birth of Carolus Linnaeus, the Swedish botanical taxonomist who was the first person to formulate and adhere to a uniform system for defining and naming the world's plants and animals. Linnaeus' hierarchical system of classification includes seven levels. They are, from largest to smallest, kingdom, phylum, class, order, family, genus, and species. 2. In taxonomic nomenclature, each level is called a taxon (plural: taxa) or taxonomic category. The three domains are the Archaea, the Bacteria, and the Eukarya. Prokaryotic organisms belong either to the domain Archaea or the domain Bacteria; organisms with eukaryotic cells belong to the domain Eukarya. The six kingdoms are Eubacteria, Archae, Protista, Fungi, Plantae, and Animalia. Why is taxonomy so important? Well, it helps us categorize organisms so we can more easily communicate biological information. Taxonomy uses hierarchical classification as a way to help scientists understand and organize the diversity of life on our planet. 

Definition

The exact definition of taxonomy varies from source to source, but the core of the discipline remains: the conception, naming, and classification of groups of organisms. As points of reference, recent definitions of taxonomy are presented below:

Theory and practice of grouping individuals into species, arranging species into larger groups, and giving those groups names, thus producing a classification.

1. A field of science (and major component of systematics) that encompasses description, identification, nomenclature, and classification

2. The science of classification, in biology the arrangement of organisms into a classification

3. "The science of classification as applied to living organisms, including the study of means of formation of species, etc."

4. "The analysis of an organism's characteristics for the purpose of classification"

5. "Systematics studies phylogeny to provide a pattern that can be translated into the classification and names of the more inclusive field of taxonomy" (listed as a desirable but unusual definition).

The varied definitions either place taxonomy as a sub-area of systematics (definition 2), invert that relationship (definition 6), or appear to consider the two terms synonymous. There is some disagreement as to whether biological nomenclature is considered a part of taxonomy (definitions 1 and 2), or a part of systematics outside taxonomy. For example, definition 6 is paired with the following definition of systematics that places nomenclature outside taxonomy:

Systematics: "The study of the identification, taxonomy, and nomenclature of organisms, including the classification of living things with regard to their natural relationships and the study of variation and the evolution of taxa".

In 1970 Michener et al. defined "systematic biology" and "taxonomy" (terms that are often confused and used interchangeably) in relationship to one another as follows:

Systematic biology (hereafter called simply systematics) is the field that (a) provides scientific names for organisms, (b) describes them, (c) preserves collections of them, (d) provides classifications for the organisms, keys for their identification, and data on their distributions, (e) investigates their evolutionary histories, and (f) considers their environmental adaptations. This is a field with a long history that in recent years has experienced a notable renaissance, principally with respect to theoretical content. Part of the theoretical material has to do with evolutionary areas (topics e and f above), the rest relates especially to the problem of classification. Taxonomy is that part of Systematics concerned with topics (a) to (d) above.

Modern system of classification

A pattern of groups nested within groups was specified by Linnaeus' classifications of plants and animals, and these patterns began to be represented as dendrograms of the animal and plant kingdoms toward the end of the 18th century, well before Charles Darwin's On the Origin of Species was published. The pattern of the "Natural System" did not entail a generating process, such as evolution, but may have implied it, inspiring early transmutationist thinkers. Among early works exploring the idea of a transmutation of species were Erasmus Darwin's (Charles Darwin's grandfather's) 1796 Zoönomia and Jean-Baptiste Lamarck's Philosophie Zoologique of 1809. The idea was popularized in the Anglophone world by the speculative but widely read Vestiges of the Natural History of Creation, published anonymously by Robert Chambers in 1844.

With Darwin's theory, a general acceptance quickly appeared that a classification should reflect the Darwinian principle of common descent. Tree of life representations became popular in scientific works, with known fossil groups incorporated. One of the first modern groups tied to fossil ancestors was birds.[citation needed] Using the then newly discovered fossils of Archaeopteryx and Hesperornis, Thomas Henry Huxley pronounced that they had evolved from dinosaurs, a group formally named by Richard Owen in 1842. The resulting description, that of dinosaurs "giving rise to" or being "the ancestors of" birds, is the essential hallmark of evolutionary taxonomic thinking. As more and more fossil groups were found and recognized in the late 19th and early 20th centuries, palaeontologists worked to understand the history of animals through the ages by linking together known groups. With the modern evolutionary synthesis of the early 1940s, an essentially modern understanding of the evolution of the major groups was in place. As evolutionary taxonomy is based on Linnaean taxonomic ranks, the two terms are largely interchangeable in modern use. 

History

While some descriptions of taxonomic history attempt to date taxonomy to ancient civilizations, a truly scientific attempt to classify organisms did not occur until the 18th century. Earlier works were primarily descriptive and focused on plants that were useful in agriculture or medicine. There are a number of stages in this scientific thinking. Early taxonomy was based on arbitrary criteria, the so-called "artificial systems", including Linnaeus's system of sexual classification for plants (Linnaeus's 1735 classification of animals was entitled "Systema Naturae" ("the System of Nature"), implying that he, at least, believed that it was more than an "artificial system"). Later came systems based on a more complete consideration of the characteristics of taxa, referred to as "natural systems", such as those of de Jussieu (1789), de Candolle (1813) and Bentham and Hooker (1862–1863). These classifications described empirical patterns and were pre-evolutionary in thinking. The publication of Charles Darwin's On the Origin of Species (1859) led to a new explanation for classifications, based on evolutionary relationships. This was the concept of phyletic systems, from 1883 onwards. This approach was typified by those of Eichler (1883) and Engler (1886–1892). The advent of cladistic methodology in the 1970s led to classifications based on the sole criterion of monophyly, supported by the presence of synapomorphies. Since then, the evidentiary basis has been expanded with data from molecular genetics that for the most part complements traditional morphology.

Pre-Linnaean

Early taxonomists

Naming and classifying human surroundings likely begun with the onset of language. Distinguishing poisonous plants from edible plants is integral to the survival of human communities. Medicinal plant illustrations show up in Egyptian wall paintings from c. 1500 BC, indicating that the uses of different species were understood and that a basic taxonomy was in place

Ancient times

Organisms were first classified by Aristotle (Greece, 384–322 BC) during his stay on the Island of Lesbos. He classified beings by their parts, or in modern terms attributes, such as having live birth, having four legs, laying eggs, having blood, or being warm-bodied. He divided all living things into two groups: plants and animals. Some of his groups of animals, such as Anhaima (animals without blood, translated as invertebrates) and Enhaima (animals with blood, roughly the vertebrates), as well as groups like the sharks and cetaceans, are still commonly used today. His student Theophrastus (Greece, 370–285 BC) carried on this tradition, mentioning some 500 plants and their uses in his Historia Plantarum. Again, several plant groups currently still recognized can be traced back to Theophrastus, such as Cornus, Crocus, and Narcissus

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