Fig. 5

A comparison of autogenous and prokaryotic endosymbiotic models of eukaryogenesis with third-space model. In the autogenesis model, Proto-eukaryotes, Archaea and Bacteria all emerge from a last universal common ancestor. The Proto-eukaryotes then acquire a bacterial mitochondrial precursor by phagocytosis. In prokaryotic endosymbiosis, only Archaea and Bacteria connect directly to a last universal ancestor. Eukaryotes emerge as the result of endosymbiosis of an archaeon (the host) with a eubacterium (the passenger) that subsequently evolves into the eukaryotic mitochondrion. Massive horizontal gene transfer (H.G.T) then transfers the majority of prokaryote-derived genes to the emerging eukaryote. In the strong third-space model only Archaea and Bacteria link directly to a last universal ancestor. By co-existing in a closed and stable third-space, mitochondria and nuclei emerge by division of labour, gene transfer and cell fusion