Image: Three Kingdoms of Life

Based on sequence analyses of the 16 S ribosomal RNA gene, which is contained in all Earthly organisms, it is possible to construct a molecular phylogeny that can quantitatively compare all organisms, even those that can not be cultivated in the laboratory.  Such an approach has yielded quite a different view of life, as shown here, in which the major kingdoms of life (animals, plants, fungi, and protists) shown in Figure 3, are grouped into one kingdom, and the prokaryotes are expanded into two kingdoms, called the Archaea and the Bacteria.