Their environment is extreme and unchanging - so little need to evolve. Eukaryotes are more related to archaebacteria than are eubacteria are to archaebacteria. Therefore eubacteria represent the most evolved at least with respect to core cellular components. Eukaryotes have evolved genome complexity. Gene families that can rapidly evolve .
Gives rise to the diversity of cell types in multi-cellular organisms.
Allows them to deal more effectively with changing environment . Probably responsible in large part for changing the earth's atmosphere. With the production of oxygen, organism evolved to use this highly reactive molecule to further oxidize glucose to gain more energy. This is respiration. As molecular oxygen built up, those bacteria that developed respiratory systems had an advantage.