<Li> The chronocyte hypothesis postulates that a primitive eukaryotic cell was formed by the endosymbiosis of both archaea and bacteria by a third type of cell, termed a chronocyte . </Li> <Li> The universal common ancestor (UCA) of the current tree of life was a complex organism that survived a mass extinction event rather than an early stage in the evolution of life . Eukaryotes and in particular akaryotes (Bacteria and Archaea) evolved through reductive loss, so that similarities result from differential retention of original features . </Li> <P> Assuming no other group is involved, there are three possible phylogenies for the Bacteria, Archaea and Eukaryota in which each is monophyletic . These are labelled 1 to 3 in the table below . The eocyte hypothesis is a modification of hypothesis 2 in which the Archaea are paraphyletic . (The table and the names for the hypotheses are based on Harish and Kurland, 2017 .) </P> <Table> Alternative hypotheses for the base of the tree of life <Tr> <Th> 1--Two empires </Th> <Th> 2--Three domains </Th> <Th> 3--Gupta </Th> <Th> 4--Eocyte </Th> </Tr> <Tr> <Td> <Table> <Tr> <Td> UCA </Td> <Td> <Table> <Tr> <Td> </Td> <Td> <P> Eukaryota </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> <Table> <Tr> <Td> </Td> <Td> <P> Archaea </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> <P> Bacteria </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> <Td> <Table> <Tr> <Td> UCA </Td> <Td> <Table> <Tr> <Td> </Td> <Td> <Table> <Tr> <Td> </Td> <Td> <P> Eukaryota </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> <P> Archaea </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> <P> Bacteria </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> <Td> <Table> <Tr> <Td> UCA </Td> <Td> <Table> <Tr> <Td> </Td> <Td> <Table> <Tr> <Td> </Td> <Td> <P> Eukaryota </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> <P> Bacteria </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> <P> Archaea </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> <Td> <Table> <Tr> <Td> UCA </Td> <Td> <Table> <Tr> <Td> </Td> <Td> <Table> <Tr> <Td> </Td> <Td> <Table> <Tr> <Td> </Td> <Td> <P> Eukaryota </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> <P> Archaea - Crenarchaeota </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> <P> Archaea - Euryarchaeota </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> <P> Bacteria </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> </Tr> </Table>

He structure that divides the bacterial cell in two is termed the