The Evolutionary history of Cide family proteins based on a phylogenetic tree of animals. The evolutionary history of Cide family proteins is divided into several stages based on the phylogenetic tree of animals [63–66]. '*' indicate three key model organisms whose whole genomes have not been fully sequenced thus far. Absence of Cide or Dff family proteins from each species is indicated by a cross next to the respective branch of the evolutionary tree. Model organisms used are S. cerevisae, hydra (Hydra vulgaris), sea anemone (Nematostella vectensis), nematode (Caenorhabditis elegans), fruit fly (Drosophila melanogaster), sea squirt (Diazona violacea), amphioxus (Branchiostoma floridae), sea lamprey (Petromyzon marinus), little skate (Leucoraja erinacea), zebrafish (Danio rerio), medaka (Oryzias latipes), stickleback (Gasterosteus aculeatus), tetraodon (Tetraodon nigroviridis), fugu (Takifugu rubripes), X. tropicalis, chicken (Gallus gallus), opossum (Monodelphis domestica), mouse (Mus musculus), human (Homo sapiens).