<P> In 1977, Carl Woese proposed dividing prokaryotes into the Bacteria and Archaea (originally Eubacteria and Archaebacteria) because of the major differences in the structure and genetics between the two groups of organisms . Archaea were originally thought to be extremophiles, living only in inhospitable conditions such as extremes of temperature, pH, and radiation but have since been found in all types of habitats . The resulting arrangement of Eukaryota (also called "Eukarya"), Bacteria, and Archaea is called the three - domain system, replacing the traditional two - empire system . </P> <P> One criticism of the dichotomous prokaryote - eukaryote distinction points out that the word "prokaryote" is based on what these organisms are not (they are not eukaryotic), rather than what they are (either archaea or bacteria). </P> <P> The current model of the evolution of the first living organisms is that these were some form of prokaryotes, which may have evolved out of protocells . In general, the eukaryotes are thought to have evolved later in the history of life . </P> <P> However, some authors have questioned this conclusion, arguing that the current set of prokaryotic species may have evolved from more complex eukaryotic ancestors through a process of simplification . </P>

What cellular structures do prokaryotic and eukaryotic cells have in common