The Three
Domains of the
Tree of Life

From the first dawn of life, all organic beings are found to resemble each other in descending degrees, so they can be classed in groups under groups.

Charles Darwin, Origin of Species, Chapter 13

The tree in the figure below follows the contributions of Woese from the University of Illinois, who observed in the 1970s that the molecular differences between organisms that has preveously been called bacteria were profound. Woese divided bacteria into distinct groups and he adopted a new ranking: domain. In this system, all living things are divided into three domains:

1 - Archae (once called Archaebacteria)
2 - Eubacteria
3 - Eucarya

Eucarya comprise ALL the eukaryotic creatures (i.e., protists; fungi; plants; and animals), that is, creatures composed of cells with nuclei and that perform oxidative energy production.

Tree of Life - The Three Domains of Life