In biological taxonomy, a domain (also superregnum, superkingdom, or empire) 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 the following three domains: Archaea, Eubacteria and Eukaryota. The arrangement of taxa reflects the fundamental evolutionary differences in the genomes. There are some alternative classifications of life:

• The two-empire system or Superdomain system, with top-level groupings of Prokaryota (or Monera) and Eukaryota empires.
• The six-kingdom system with top-level groupings of Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia.

As these groupings depend primarily on the analysis of genetic sequence data and cladistics, additional proposed arrangements are to be expected.

See also

• Phylogenetics
• Systematics

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