The new phylogeny of eukaryotes.

Molecular phylogeny has been regarded as the ultimate tool for the reconstruction of relationships among eukaryotes-especially the different protist groups-given the difficulty in interpreting morphological data from an evolutionary point of view. In fact, the use of ribosomal RNA as a marker has provided the first well resolved eukaryotic phylogenies, leading to several important evolutionary hypotheses. The most significant is that several early-emerging, amitochondriate lineages, are living relics from the early times of eukaryotic evolution. The use of alternative protein markers and the recognition of several molecular phylogeny reconstruction artefacts, however, have strongly challenged these ideas. The putative early emerging lineages have been demonstrated as late-emerging ones, artefactually misplaced to the base of the tree. The present state of eukaryotic evolution is best described by a multifurcation, in agreement with the 'big bang' hypothesis that assumes a rapid diversification of the major eukaryotic phyla. For further resolution, the analysis of genomic data through improved phylogenetic methods will be required.