Kingdom
From EvoWiki
In taxonomy, kingdom is traditionally the highest taxonomic level. The most traditional classifications, starting with Aristotle, have divided living things into:
This classification, however, is a serious shoehorn. Fungi get classified as plants, because of how their overall shape and behavior resembles "true" plants, though their metabolism is animal-like. Many one-celled organisms are ambiguous, having both photosynthesis (a typical plant feature) and mobility (a typical animal feature).
In 1866, Ernst Haeckel proposed an additional kingdom for mostly one-celled organisms, Protista, but he was mostly ignored. Advancing to 1956, Herbert Copeland split the prokaryotes from Protista, and in 1959, Robert Whittaker split the fungi from Plantae. However, this work did not get much notice until the 1970's, when Lynn Margulis publicized a modified version as The Five Kingdoms:
This classification, though widely-used and fairly reasonable, is not without problems. Protista is obviously paraphyletic (having Animalia, Plantae, and Fungi as descendants), and it is not obvious that Animalia, Plantae, and Fungi are monophyletic (have only one ancestor each in them). And the phylogeny emerging from applying molecular techniques is still somewhat ambiguous, but it has supported most of these suspicions. Some of the better-supported groupings are:
- Opisthokonts, containing
- "True" fungi and microsporidians
- Animals and choanoflagellates (collar flagellates)
- Green plants, containing green algae and land plants
- Red algae
- Chromists or Stramenopiles, containing diatoms, golden algae, brown algae, oomycetes (water molds), etc.
- Alveolates, containing dinoflagellates, ciliates, and apicomplexans
- Several others
("Algae" can include one-celled photosynthesizers here)
But all these organisms share the eukaryotic-cell architecture, which is dramatically different from the prokaryotic-cell architecture of Monera. This suggests that an even higher taxonomic level ought to be composed for each kind of cell type, and in 1990, Carl Woese invented the domain, placing the eukaryotes in domain Eukarya, and the prokaryotes into two others: Eubacteria/Bacteria and Archaebacteria/Archaea. This is explained in more detail in the article on domain.
