EARLY EVOLUTION OF THE EUKARYOTA

The evolution of eukaryotes represents one of the most fundamental transitions in the history of life on Earth; however, there is little consensus as to when or over what timescale it occurred. Review of recent hypotheses and data in a phylogenetic context yields a broadly coherent account. Critical re-assessment of the palaeontological record provides convincing evidence for the presence of crown-group eukaryotes in the late Palaeoproterozic, and stem-group eukaryotes extending back to the early Archaean. Despite their relatively early establishment, crown-eukaryotes appear not to have become ecologically significant until the middle Neoproterozoic. I argue that this billion-year delay was due to the singular, contingent evolution of crown-group animals and their unique capacity to drive co-evolutionary change.