A mathematical analysis of stereocilia height and cochlear tonotopic organization along the length of the receptor epithelium in six species provided the basis for a resonant model of hair cell stereocilia. The analysis demonstrated an inverse power function between the distribution of frequency (f) and stereocilia height (h). The average empirical relation was: f∝h−2.67. These results are consistent with a resonant “clamped bar” model which has the relation: f∝h−2.00. The model provides conceptual insight into the mechanical properties of stereocilia by showing that Young's Modulus remains constant for all stereocilia in a given cochlea. The mechanical properties of stereocilia can be understood further in terms of their macromolecular structure and the bending of crossbridge molecules. The uniform bending of every crossbridge molecule, coupled with the constant number of crossbridges per unit volume within the stereocilia, leads to a constant value for Young's Modulus. Finally, the model raises the intriguing possibility that nature may have evolved two frequency selective mechanisms in the cochlea. [Work supported in part by The Deafness Research Foundation and NINCDS.]