Scientific classification, also known as Linnaeus classification, is a hierarchical system used by biologists to classify all life on Earth. It has eight levels of categorization, with the current top-level system being three domains: Bacteria, Archaea, and Eukarya. The higher levels of scientific classification have changed several times over the years, with the most recent update occurring in 1990.
Scientific classification is the system used by biologists to classify all life on Earth. It is also known as scientific classification in biology or Linnaeus classification, named after Carolus Linnaeus (1707-1778), who first attempted this huge project. The pioneering work was Systema Naturae, first published in 1735, which went through twelve editions during Linnaeus’ lifetime. The first version had a few thousand entries, grouped into taxa based on shared physical characteristics. Today, over two million species are recognized by science, although the total number of plant, animal and single-celled species on Earth is estimated at between 10 and 100 million.
The scientific classification system used in biology is hierarchical, with eight levels of categorization. Going from smallest to largest, they are: species, genus, family, order, class, phylum, kingdom, and domain. Often even more divisions are added between these levels, as life itself has no special obligation to be naturally classified into just eight hierarchical levels. To give an example of each, consider the position of humans in scientific classification. Humans are species Homo sapiens, genus Homo, family Hominidae (great apes), order Primates, class Mammalia (mammals), phylum Chordata (vertebrates and some close relatives), kingdom Animalia (animals), domain Eukarya (eukaryotes, organisms with complex cells).
The higher levels of scientific classification have changed several times over the years. In 1735 Linnaeus introduced two kingdoms: Vegetabilia (plants and fungi) and Animalia. In 1866, the German biologist Ernst Haeckel introduced another kingdom, Protista, for all single-celled organisms. In 1937, the French biologist Edouard Chatton divided life into two “empires” – Prokaryota and Eukaryota, based on more detailed observations of plant, animal and bacterial cells. Plants and animals were found to have fundamental similarities in the complexity of their cells and the presence of cell nuclei, while bacteria lack both nuclei and organelles (intracellular structures).
Several other major updates followed in the 1950s, 60s, and 70s, which were a time of rapid advances in biology. Herbert Copeland updated the four kingdom system in 1956, when he renamed Prokaryota to Monera and divided Eukaryota into three kingdoms: Protista, Plantae and Animalia. Another change occurred in 1969, when Robert Whittaker split Protista into Fungi and Protista, giving fungi their top-level classification for the first time.
In 1977, Carl Woese and his collaborators introduced the most crowded top-level system ever, with six kingdoms: Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia. Then, in 1990, the system was thankfully simplified by Woese, reduced to three domains: Bacteria, Archaea and Eukarya. The latter is the current top-level classification system used.
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