Tree of life (biology)
The model of a tree is still considered valid for eukaryotic life forms. Research into the earliest branches of the eukaryote tree suggests a tree with either four supergroups, or two supergroups. There does not yet appear to be a consensus; in a review article, Roger and Simpson conclude that "with the current pace of change in our understanding of the eukaryote tree of life, we should proceed with caution".