English: Unrooted trees of life showing two alternative scenarios on the evolutionary relationships between eukaryotes and archaea. a,b, Three-domains tree of life (3D scenario, a) and two-domains tree of life (2D scenario, b). Note that the branches of eukaryotes and Bacteria are much longer than that of Archaea, indicating a higher genetic divergence. Accurately positioning long branches in phylogenetic trees is challenging, as they tend to group together irrespectively of their true relationships, an artefact called "long branch attraction" (Delsuc et. al. 2005, Philippe & Laurent 1998). Accordingly, the emergence of eukaryotes outside the Archaea in phylogenies supporting the 3D scenario may be the product of their artefactual attraction by the long branch of bacteria.

• Delsuc, F., Brinkmann, H. and Philippe, H. (2005) "Phylogenomics and the reconstruction of the tree of life". Nature Reviews: Genetics, 6(5): 361–375. doi:10.1038/nrg1603.
• Philippe, H. and Laurent, J. (1998) "How good are deep phylogenetic trees?". Current opinion in genetics & development, 8(6): 616–623. doi:10.1016/S0959-437X(98)80028-2.

Credit: Gareth Monger