Domain (biology)

This article is about the "domain" rank in biological classification. For other uses, see Domain (disambiguation).

The hierarchy of biological classification's eight major taxonomic ranks, which is an example of definition by genus and differentia. 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, 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. The arrangement of taxa reflects the fundamental differences in the genomes. 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.
• The six-kingdom system with top-level groupings of Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia.
• The three-empire system (Eubacteria, Archaea, Eukarya) with five supergroups in the Eukarya (Unikonta, Excavata, Chromalveolata, Rhizaria and Archaeplastida)

None of the three systems currently include non-cellular life.^{[citation needed]}

See also

• Phylogenetics
• Systematics