This phylogenetic tree is based on comparisons of the nucleotide sequences of the RNAs in the small ribosomal subunits from various prokaryotes and eukaryotes. The vertical length of each branch corresponds quantitatively to the number of base sequence changes that have occured in that lineage since its divergence from its nearest neighbor. Most of the tree is made up of microorganisms. The animal, plant, and fungal kingdoms are but 3 of the 23 lineages. All living organisms fall into three groups: Bacteria, Archaea, and Eukaryotes. The eukaryotes are more closely related to the archaeons than to the bacteria. The common ancestor at the base of the tree lies between the Archaea and the Bacteria. This prokaryote was probably a hyperthermophile (q.v.). See Classification, Prokaryotes, Eukaryotes; Chronology, 1977, Woese and Fox; 1980, Woese et al.; ribosome, 16S rRNA.
Universal tree of life. From André Brack, ed., The Molecular Origins of Life, 1998, Fig. 16, page 338, Cambridge University Press, NY.
Subjects: Genetics and Genomics.