Abstract
Mammalian auditory system has the variety of the hearing ranges and thresholds, so that the system is of great interest especially from the viewpoint of mammalian evolution. To reveal the reason why these diverse functions evolved in the mammalian auditory systems, we conducted the molecular evolutionary study based on the genes responsible for the human nonsyndromic-deafness. From OMIM database and literatures, we selected 54 genes directly-related nonsyndromic-deafness. First, to estimate the sequence variability of these genes among the mammalian orders, we performed phylogenetic analysis. Consequently, we identified CCDC50 and SLC26A5 as the top two genes which have higher evolutionary ratio on the linage toward placentals. Those genes were described in the database to express in outer hair cells but not in inner hair cells. Therefore, our results suggest that outer hair cells may have a key role in an evolution of the auditory system in placentals.