Kingdoms of organisms

Copeland, Herbert F. The Kingdoms of Organisms. Quart. Rev. Biol. 13 383-420. 1938. 

As the tree shows, the true relatives of the archaea are not the bacteria but the eukaryotes. However, because the archaea branch-off closest to the root of the tree, the suggestion is that they are the most primitive of the three kingdoms of organisms whereas the eukaryotes are the least primitive (or the most derived). Placement of the archaea closest to the universal ancestor is supported by the fact that many archaea inhabit extreme environments involving high temperature, low pH, high salinity, and so on. Thus, archaea may well be evolutionary relics of the Earth s earliest forms of life. 

Barr DJS Evolution and kingdoms of organisms from the perspective of a mycologist. Mycologia 1992 84 1-11. 

Figure 20. A diagram illu.< trating phylogenetic relationships between the three kingdoms of organisms. The data used to determine these come from the base sequences of nucleic acids. The tree presently has no root because u f have no unambiguous kmtwledge of the ancestral forms (from Engel and Macko, 1993).

Animalia The kingdom of organisms to which all animals belong. 

Protista The kingdom of organisms that are unicellular but contain internal organelles typical of the eukaryotes. 

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