Common ancestry of eukaryotes and Asgardarchaeota: Three, two or more cellular domains of life?

There is much evidence that eukaryotes have many traits in common with archaea and in phylogenetic analyses they are closely linked. In particular, it has been suggested that Asgardarchaeota would be part of the same Glade of eukaryotes. If so - and being the difference between Asgardarchaeota and eukaryotes very large - then all this would imply that their common ancestor was a progenote, i.e. a protocell in which the relationship between genotype and phenotype was still evolving. This, in turn, would imply that true cells would appear on the tree of life only later, that is to say, only when the ancestor of Asgardarchaeota and the one of eukaryotes appeared. However, this way of seeing would define these ancestors as primary fundamental cells, namely, as cellular domains of life because it would be in this evolutionary stage that true cells would appear for the first time. Finally, the Asgardarchaeota-eukaryote transition is discussed, that is, some aspects of eukaryogenesis and the taxonomic rank of eukaryotes are analyzed. (C) 2019 Elsevier Ltd. All rights reserved.