The Evolution of Mammalian Sound Localization

Introduction The ability to localize sound is useful for survival because it allows an animal to determine the location of sound sources, which, in nature, are usually other animals. Indeed, the need to localize sound explains why terrestrial vertebrates have two ears, as differences in the time of arrival and the intensity of a sound at the two ears gives information about the direction of its source. However, unlike other terrestrial vertebrates (amphibians, reptiles, and birds), mammals have evolved the ability to hear high-frequency sounds. Specifically, amphibians and reptiles rarely hear above 5 kHz, and birds do not hear much above 10 kHz; however, almost all mammals hear far higher, with over half of mammals tested so far able to hear above 50 kHz. As we show, the primary source of selective pressure for the evolution of mammalian high-frequency hearing has come from the need to localize sound.