Determining Divergence Times with Protein Clocks

The study of divergence times of the major groups of organisms as determined by amino acid sequence comparison of 57 sets of enzymes encompassing 531 sequences has been expanded. The data have been reanalyzed with a distance measure that corrects for both constraints on amino acid interchange and variation in substitution rate at different sites. The main finding established a divergence time for prokaryotes and eukaryotes of only slightly more than two billion years ago.