The evolutionary history of the DAOA gene was constructed. No paralogs of DAOA had been reported in biological databases. ENSEMBL Blastp/Blat was also performed for paralogs of DAOA but with the same result. Only orthologs of DAOA were used to construct the phylogenetic tree. Complete-deletion, p-distance and Uncorrected options were used. Bootstrap values are given as numbers of branches (based on 1000 replications) supporting that branch; values of ≥80% are presented. Amino acid substitution rate per site is shown by the scale bar. Eight orthologs were used and Ciona was the outgroup. Two main clusters were generated. Human, Gorilla and Chimpanzee lie in the same cluster and show sequence similarity. Tetrapods are also closely related to each other in the analysis. Organisms in the same clusters show the highest similarity with point mutations.