The study by Hebert et al. (2003) explores the potential of using cytochrome c oxidase subunit 1 (COI) sequences as a DNA-based identification system for animal life. The authors analyze COI divergences among closely related species across 11 animal phyla, finding that sequence differences at COI regularly enable the discrimination of species in all phyla except Cnidaria. The results indicate high rates of sequence change at COI in most animal groups and constraints on intraspecific mitochondrial DNA divergence, partly due to selective sweeps mediated by interactions with the nuclear genome. The study supports the feasibility of a COI-based identification system, which could resolve the vast diversity of animal species, potentially reducing the number of species to a generic assemblage with an average of less than 10 species per genus.The study by Hebert et al. (2003) explores the potential of using cytochrome c oxidase subunit 1 (COI) sequences as a DNA-based identification system for animal life. The authors analyze COI divergences among closely related species across 11 animal phyla, finding that sequence differences at COI regularly enable the discrimination of species in all phyla except Cnidaria. The results indicate high rates of sequence change at COI in most animal groups and constraints on intraspecific mitochondrial DNA divergence, partly due to selective sweeps mediated by interactions with the nuclear genome. The study supports the feasibility of a COI-based identification system, which could resolve the vast diversity of animal species, potentially reducing the number of species to a generic assemblage with an average of less than 10 species per genus.