- It is the technique of arranging organisms into groups based on their similarities and dissimilarities
- Artificial, Natural and phylogenetic system are the three types of classification.
- Artificial classification uses 1 or 2 morphological characters for grouping organisms. Eg. Aristotle divided animals into Enaima (with RBC) and Anaima (without RBC). Pliny divided animals into Flight and Non-Flight ones.
- An artificial system does not include characters from genetics, biochemistry, cytology etc., and Homology is never studied. So that, the type of classification often results in the placing of unrelated organisms is a group.
- The natural system of classification includes a number of characters into consideration, and so homology is brought out through the study of internal and external characters.
- Natural system for classification of seed plants was proposed by Bentham and Hooker in their three volumes of Genera Plantarum.
- Phylogenetic system of classification is based on the evolutionary concept from “The origin of species”, and was proposed by Engler and Prantl in Die Naturlichen Pflanzen Familien.
- The phylogenetic system is highly dynamic and it is not static, but it is less practicable.
- Before 1969, the two-kingdom classification was proposed by Linnaeus (Father of Taxonomy) which included kingdom Plantae and kingdom Animalia.
- Drawbacks and exceptions from the 2-kingdom classification include Euglena, Fungi, slime moulds, lichens, viruses and unicellular algae.
- In 1866, Ernst Haeckel created the three kingdom classification by including kingdom Protista to the existing 2 kingdoms.
- Four kingdom classification came into the picture only after the invention of the Electron microscope. It was proposed by Copeland during 1956 by creating a special kingdom for bacteria, called as Monera (Mycota).
- But in this type, Fungi remained under Plantae.
- In order to develop phylogenetic classification, in 1969, an American taxonomist R.H. Whittaker developed five kingdom classification, where he had included Monera, Protista, Plantae, Animalia and Fungi, on the basis of cell complexity, organism complexity and mode of nutrition.
- Five kingdom classification also had certain drawbacks such as Euglena can be photosynthetic as well as saprotrophic, Viruses have not been included and other exceptions are archaebacteria and Mycoplasma.
- In 1990, Carl Woese introduced the three domains of life as archae, bacteria and Eukarya, which is also considered as six-kingdom classification.
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