In the three-domain model, eukaryotes belong to a separate branch that shares a common ancestor with archaea. But phylogenetic analyses suggest that complex cells emerged from within the archaea. This ...

There are two major types of hypothesis about how eukaryotes and their nuclei may have originated (Poole & Penny 2007). One of these involves fusion between cells from domains Archaea and Bacteria ...

and different from eukaryotes. However, until scientists determined the position of the LUCA (what evolutionary biologists call the root position) in the tree, all three domains appeared equal.