Simplification or complexity

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Most of the theories explaining the origin of eukaryotes by fusion/endosymbiosis start as the basic material of already highly evolved prokaryotic cells. Recently, several researchers have questioned the validity of such starting precepts. Indeed, these authors criticize the methods of establishing phylogenies which suggest that bacteria and/or archaebacteria are the most primitive organisms. On the contrary, they suggest that bacteria are very evolved cells and that eukaryotic and prokaryotic cells derive from a complex common ancestor, LUCA, which in fact has many more properties of a eukaryotic cell than a prokaryotic. With this theory, prokaryotes would be derived from a proto-eukaryotic cell by simplification via the selection of efficient and rapid mechanisms and eukaryotic cells by complexification. This type of hypothesis unfortunately does not explain in a convincing way how LUCA appeared, and especially the stages of its evolution towards eukaryotes.

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