Domain (biology)

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.