Two-empire system

The two-empire system (two-superkingdom system) was the top-level biological classification system in general use before the establishment of the three-domain system. It classified cellular life into Prokaryota and Eukaryota as either "empires" or "superkingdoms". When the three-domain system was introduced, some biologists preferred the two-superkingdom system, claiming that the three-domain system overemphasized the division between Archaea and Bacteria. However, given the current state of knowledge and the rapid progress in biological scientific advancement, especially due to genetic analyses, that view has all but vanished.

Phylogenetic and symbiogenetic tree of living organisms, showing the origins of eukaryotes and prokaryotes

Some prominent scientists, such as Thomas Cavalier-Smith, still hold to the two-empire system.[1] The late Ernst Mayr, one of the 20th century's leading evolutionary biologists, wrote dismissively of the three-domain system, "I cannot see any merit at all in a three empire cladification."[2] Additionally, the scientist Radhey Gupta argues for a return to the two-empire system, claiming that the primary division within prokaryotes should be among those surrounded by a single membrane (monoderm), including gram-positive bacteria and archaebacteria, and those with an inner and outer cell membrane (diderm), including gram-negative bacteria.[3]

Taxonomical root node Two superdomains (controversial) Two empires Three domains Six kingdoms
Biota / Vitae
life		 Acytota / Aphanobionta (Viruses, Viroids, Prions?, ...)
Cytota
cellular life		 Prokaryota / Procarya
(Monera)		 Bacteria Eubacteria
Archaea Archaebacteria
Eukaryota / Eukarya Protista
Fungi
Plantae
Animalia

This system was preceded by Haeckel's three-kingdom system: Animalia, Plantae and Protista.

Linnaeus
1735[4]		 Haeckel
1866[5]		 Chatton
1925[6][7]		 Copeland
1938[8][9]		 Whittaker
1969[10]		 Woese et al.
1977[11][12]		 Woese et al.
1990[13]		 Cavalier-Smith
1993[14][15][16]		 Cavalier-Smith
1998[17][18][19]		 Ruggiero et al.
2015[20]
(not treated) (not treated) 2 empires 2 empires 2 empires 2 empires 3 domains 3 superkingdoms 2 empires 2 superkingdoms
2 kingdoms 3 kingdoms (not treated) 4 kingdoms 5 kingdoms 6 kingdoms (not treated) 8 kingdoms 6 kingdoms 7 kingdoms
(not treated) Protista Prokaryota Monera Monera Eubacteria Bacteria Eubacteria Bacteria Bacteria
Archaebacteria Archaea Archaebacteria Archaea
Eukaryota Protista Protista Protista Eucarya Archezoa Protozoa Protozoa
Protozoa
Chromista Chromista Chromista
Vegetabilia Plantae Plantae Plantae Plantae Plantae Plantae Plantae
Fungi Fungi Fungi Fungi Fungi
Animalia Animalia Animalia Animalia Animalia Animalia Animalia Animalia

See also

References
  1. Cavalier-Smith, T (2002). "The neomuran origin of archaebacteria, the negibacterial root of the universal tree and bacterial megaclassification". International Journal of Systematic and Evolutionary Microbiology. 52 (1): 7–76. doi:10.1099/00207713-52-1-7. PMID 11837318.
  2. Mayr, E. (1998). "Two empires or three?". Proceedings of the National Academy of Sciences. 95 (17): 9720–9723. Bibcode:1998PNAS...95.9720M. doi:10.1073/pnas.95.17.9720. PMC 33883. PMID 9707542.
  3. Gupta, Radhey S (1998). "Life's Third Domain (Archaea): An Established Fact or an Endangered Paradigm?". Theoretical Population Biology. 54 (2): 91–104. doi:10.1006/tpbi.1998.1376. PMID 9733652.
  4. Linnaeus, C. (1735). Systemae Naturae, sive regna tria naturae, systematics proposita per classes, ordines, genera & species.
  5. Haeckel, E. (1866). Generelle Morphologie der Organismen. Reimer, Berlin.
  6. Chatton, É. (1925). "Pansporella perplexa. Réflexions sur la biologie et la phylogénie des protozoaires". Annales des Sciences Naturelles - Zoologie et Biologie Animale. 10-VII: 1–84.
  7. Chatton, É. (1937). Titres et Travaux Scientifiques (1906–1937). Sette, Sottano, Italy.
  8. Copeland, H. (1938). "The kingdoms of organisms". Quarterly Review of Biology. 13: 383–420. doi:10.1086/394568.
  9. Copeland, H. F. (1956). The Classification of Lower Organisms. Palo Alto: Pacific Books. p. 6. doi:10.5962/bhl.title.4474.
  10. Whittaker, R. H. (January 1969). "New concepts of kingdoms of organisms". Science. 163 (3863): 150–60. Bibcode:1969Sci...163..150W. doi:10.1126/science.163.3863.150. PMID 5762760.
  11. Woese, C. R.; Balch, W. E.; Magrum, L. J.; Fox, G. E.; Wolfe, R. S. (August 1977). "An ancient divergence among the bacteria". Journal of Molecular Evolution. 9 (4): 305–311. Bibcode:1977JMolE...9..305B. doi:10.1007/BF01796092. PMID 408502.
  12. Woese, C. R.; Fox, G. E. (November 1977). "Phylogenetic structure of the prokaryotic domain: the primary kingdoms". Proceedings of the National Academy of Sciences of the United States of America. 74 (11): 5088–90. Bibcode:1977PNAS...74.5088W. doi:10.1073/pnas.74.11.5088. PMC 432104. PMID 270744.
  13. Woese, C.; Kandler, O.; Wheelis, M. (1990). "Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya". Proceedings of the National Academy of Sciences of the United States of America. 87 (12): 4576–9. Bibcode:1990PNAS...87.4576W. doi:10.1073/pnas.87.12.4576. PMC 54159. PMID 2112744.
  14. Cavalier-Smith, T. (1981). "Eukaryote kingdoms: seven or nine?". Bio Systems. 14 (3–4): 461–481. doi:10.1016/0303-2647(81)90050-2. PMID 7337818.
  15. Cavalier-Smith, T. (1992). "Origins of secondary metabolism". Ciba Foundation symposium. 171: 64–80, discussion 80–7. PMID 1302186.
  16. Cavalier-Smith, T. (1993). "Kingdom protozoa and its 18 phyla". Microbiological reviews. 57 (4): 953–994. doi:10.1128/mmbr.57.4.953-994.1993. PMC 372943. PMID 8302218.
  17. Cavalier-Smith, T. (1998), "A revised six-kingdom system of life", Biological Reviews, 73 (03): 203–66, doi:10.1111/j.1469-185X.1998.tb00030.x, PMID 9809012
  18. Cavalier-Smith, T. (2004), "Only six kingdoms of life" (PDF), Proceedings of the Royal Society B: Biological Sciences, 271: 1251–62, doi:10.1098/rspb.2004.2705, PMC 1691724, PMID 15306349, retrieved 2010-04-29
  19. Cavalier-Smith T (June 2010). "Kingdoms Protozoa and Chromista and the eozoan root of the eukaryotic tree". Biol. Lett. 6 (3): 342–5. doi:10.1098/rsbl.2009.0948. PMC 2880060. PMID 20031978.
  20. Ruggiero, Michael A.; Gordon, Dennis P.; Orrell, Thomas M.; Bailly, Nicolas; Bourgoin, Thierry; Brusca, Richard C.; Cavalier-Smith, Thomas; Guiry, Michael D.; Kirk, Paul M.; Thuesen, Erik V. (2015). "A higher level classification of all living organisms". PLOS ONE. 10 (4): e0119248. Bibcode:2015PLoSO..1019248R. doi:10.1371/journal.pone.0119248. PMC 4418965. PMID 25923521.
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