Five descriptive parameters of hearing—high‐frequency and low‐frequency sensitivity, lowest threshold. best frequency, and area of the audible field—are compared statistically, first, among mammals in general, and then, among seven animals selected to approximate a phylogenetic sequence of man's ancestors. Three potentially explanatory parameters body size, maximum binaural time disparity, and recency of common ancestry with man—are also explicitly included in the analysis. The results show that: high‐frequency hearing (above 32 kHz) is a characteristic unique to mammals, and, among members of this class, one which is commonplace and primitive. Being highly correlated with functionally close‐set ears, it is probably the result of selective pressure for accurate sound localization. Low‐frequency hearing improved markedly in mankind's line of descent, but the kind and degree of improvement are not unique among mammalian lineages. High sensitivity developed in the earliest stages of man's lineage and has remained relatively unchanged since the simian level. The frequency of the lowest threshold has declined in Man's lineage—the greatest drop probably occurring during the Eocene. The total area of the audible field increased until the Eocene and has decreased since then.