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History
First used in the 1500s by a family of Swiss-French doctors, the Bauhins, binomial nomenclature was developed as a formal way to provide every species with a unique, two-part name. For instance, humans were given the designation "Homo sapiens." Two hundred years later, Swedish scientist Carl Linnaeus would become the father of modern taxonomy by refining this system into a full-blown methodology for classifying living things. In the mid-1700s, Linnaeus divided the elements of the natural world into three kingdoms: Plantae, Animalia, and Mineralia (although the group for minerals was later discarded).
Types
In Linnean taxonomy, all species have a place in a hierarchy of living things. Scientific advancement, such as microscopes and the theory of evolution, refined this taxonomy into a widely recognized seven-rank system. Kingdoms were broken down into phylums, phylums into class, class into order, order into family, family into genus, and genus into species. In 1969, ecologist Robert Whittaker proposed a popular taxonomic system that included five kingdoms: Animalia, Plantae, Fungi, Protista and Monera.
Features
In the five-kingdom system, each kingdom is classified largely according to its system of nutrition. Plantae are multi-cellular organisms that produce energy from inorganic light, chemicals or minerals. Animalia obtain their energy from organic matter. Fungi obtain nutrients through decomposing organic matter. Protista, meanwhile, are organisms with a defined nucleus (which contained the genetic material) while Monera consist of bacteria and single-celled organisms that mostly lack a nucleus.
Expert Insight
In 1977, the five-kingdom system was challenged. Two microbiologists, Carl Woese and George E. Fox, demonstrated that an unusual group of bacteria called archaebacteria (previously classified under Monera) had actually evolved independently from other forms of life. The Monera was then divided into two separate kingdoms, called Eubacteria and Archaebacteria. And by 1990, Woese had also proposed a three-domain system, in which domains actually ranked above kingdoms in the taxonomic hierarchy. These domains included Archaea, Eubacteria and Eukaryota.
Potential
Woese's proposed changes to biological taxonomy relied primary on the relatively new science of phylogenetics, the study of evolutionary relatedness between living things. By sequencing an organism's genes, that organism can be very precisely classified. Over time, the classification system itself can be significantly redrawn, as it has been since its creation.