Life Gets Simpler

In a new article, published in Nature on December 12, 2013, Williams et al. present evidence supporting the "Eocyte hypothesis" that the Tree of Life has only two branches (Bacteria and Archaea), not three (Bacteria, Archaea, and Eukaryota).  Their article, entitled "An archaeal origin of eukaryotes supports only two primary domains of life," situates the Eukaryota (organisms with cellular nuclei), for the most part, within the Archaea.  Here is the article's abstract:

The discovery of the Archaea and the proposal of the three-domains ‘universal’ tree, based on ribosomal RNA and core genes mainly involved in protein translation, catalysed new ideas for cellular evolution and eukaryotic origins. However, accumulating evidence suggests that the three-domains tree may be incorrect: evolutionary trees made using newer methods place eukaryotic core genes within the Archaea, supporting hypotheses in which an archaeon participated in eukaryotic origins by founding the host lineage for the mitochondrial endosymbiont. These results provide support for only two primary domains of life—Archaea and Bacteria—because eukaryotes arose through partnership between them.

Apparently, even evolutionary phylogenetics follows the ancient, familiar, and inviolable principle that two's company, but three's a crowd.