Significance Lipoxygenases are lipid-peroxidizing enzymes that have been classified according to their reaction specificity. ALOX15 (12/15-lipoxygenase) has been implicated in inflammatory resolution via biosynthesis of antiinflammatory and proresolving lipoxins. We found that lower mammals including lower primates express arachidonic acid 12-lipoxygenating ALOX15 orthologs, whereas higher primates express 15-lipoxygenating enzymes. Gibbons constitute the missing link interconnecting 12- and 15-lipoxygenating ALOX15 orthologs. To explore the evolutionary driving force for this specificity alteration, we quantified the lipoxin synthase activity of 12- and 15-lipoxygenating ALOX15 orthologs and observed that the lipoxin synthase activities of 15-lipoxygenating enzymes were significantly higher. These results suggest an evolution of ALOX15 specificity, which optimizes the biosynthetic capacity for antiinflammatory and proresolving lipoxins.