Phylogenetic and symbiogenetic tree of living organisms, showing the origins of eukaryotes and prokaryotes
Thetwo-empire system (two-superkingdom system) was the top-level biological classification system in general use from the early 20th century until the establishment of thethree-domain system (which itself is currently being challenged by thetwo-domain system). It classified cellular life intoProkaryota andEukaryota 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 betweenArchaea andBacteria. 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.
Some prominent scientists, such as the lateThomas Cavalier-Smith, still hold and held to the two-empire system.[1] The lateErnst 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 scientistRadhey 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]
^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.PMID9733652.
^Linnaeus, C. (1735).Systemae Naturae, sive regna tria naturae, systematics proposita per classes, ordines, genera & species.
^Haeckel, E. (1866).Generelle Morphologie der Organismen. Reimer, Berlin.
