= Two-domain system
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The <two-domain system> recognizes <bacteria> and <archaea> as the two primary lineages, placing the nuclear ancestry of <eukaryotes> within <archaea>. In this model, <archaea> as a complete <clade> includes that <eukaryotic> lineage; restricting the name to <prokaryotic> members describes a different grouping. Williams and colleagues' study, published online in 2019 and in a 2020 journal issue, found support for this model and a close relationship to <Asgard archaea>. See https://doi.org/10.1038/s41559-019-1040-x[Williams et al., 2020: Phylogenomics provides robust support for a two-domains tree of life].
This updates the interpretation of the 1977 and 1990 classifications rather than undoing their discovery of deep differences between <bacteria> and <archaea>. Deep <phylogenetic trees> depend on the sampled <genes>, <organisms> and inference model; the precise closest archaeal relatives and early sequence of events require further evidence. Bacterial ancestry of <mitochondria> through <endosymbiosis> is a separate part of <eukaryotic> history.
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