The deep roots of eukaryotes.

Most cultivated and characterized eukaryotes can be confidently assigned to one of eight major groups. After a few false starts, we are beginning to resolve relationships among these major groups as well. However, recent developments are radically revising this picture again, particularly (i) the discovery of the likely antiquity and taxonomic diversity of ultrasmall eukaryotes, and (ii) a fundamental rethinking of the position of the root. Together these data suggest major gaps in our understanding simply of what eukaryotes are or, when it comes to the tree, even which end is up.