Life on our planet can be divided into three domains: the Archaea, Eukarya and Bacteria. In all three domains of life, the speed required for DNA synthesis is only possible because of the evolution of a donut shaped protein that interacts with a replicative DNA polymerase to duplicate the genome in a processive manner. The donut-shaped proteins are loaded by a heteropentameric protein complex that harnesses energy through hydrolysis of ATP bound at its interfaces. In this presentation, I will discuss the evolution of the clamp loader in the archaeal/eukaryotic sister lineages, and provide evidence for an alternative mechanism for loading the Methanosarcina acetivorans clamp loader, an intermediate between the commonest clamp loader in the archaea and the very complex forms found in eukaryotic organisms. I will further discuss our attempt to use these processive factors to test Woese’s hypothesis of the existence of a Darwinian threshold.