The hierarchy of biological classification's eight major taxonomic ranks. Life is divided into domains, which are subdivided into further groups. Intermediate minor rankings are not shown.

In biological taxonomy, a domain (also superregnum, superkingdom, empire, or regio) is the highest taxonomic rank of organisms in the Woese taxonomic system (there is sometimes a superkingdom Neomura), higher than a kingdom. According to the three-domain system of Carl Woese, introduced in 1990, the Tree of Life consists of three domains: Archaea, Bacteria and Eukarya.^[1] The arrangement of taxa reflects the fundamental differences in the genomes.

Alternative classifications []

Alternative classifications of life so far proposed include:

• The two-empire system or superdomain system, with top-level groupings of Prokaryota (or Monera) and Eukaryota.^[2][3]
• The Three-domain system (Bacteria, Archaea, Eukarya) with five supergroups in the Eukarya (Unikonta, Excavata, Chromalveolata, Rhizaria and Archaeplastida)^[2][4][5]

None of the three systems currently include non-cellular life. As of 2011 there is talk about Nucleocytoplasmic large DNA viruses possibly being a fourth branch domain of life, a view supported by researchers in 2012 who explain in their abstract, "The discovery of giant viruses with genome and physical size comparable to cellular organisms, remnants of protein translation machinery and virus-specific parasites (virophages) have raised intriguing questions about their origin. Evidence advocates for their inclusion into global phylogenomic studies and their consideration as a distinct and ancient form of life." They continue, "Results call for a change in the way viruses are perceived. They likely represent a distinct form of life that either predated or coexisted with the last universal common ancestor (LUCA) and constitute a very crucial part of our planet’s biosphere."^[6]

See also []

• Phylogenetics
• Systematics

References []