Auditory hyperostosis and the environment: an update

Abstract

Auditory exostoses have been included in craniological investigations since the last century and recently comprised among epigenetic traits. There is general agreement on the importance of environmental and behavioural factors on the expression of these bony formations, in particular habitual diving and swimming in cold water. The present study contributes new data to our knowledge of the world frequency of this character. Cranial series from New Guinea and Melanesia (139 skulls), Australia (36) and, for the first time, South Africa (123, from Bushmen, Hottentots and other ethnic groups) were analysed. While the character is absent in the African series — possibly due to environmental factors — the frequency of exostoses varies from 4.0 to 4.7% in the other skull collections, mainly belonging to coastal populations. When the frequency distribution of this pathology is considered in a world context and subdivided according to frequency classes, a direct relation between occurrence and environmental factors is confirmed. Nevertheless, the widespread distribution of low frequencies (0.1–3.0%) cannot be solely attributed to the action of cold water, but appears to be the result of different kinds of stresses or ear pathologies.