Abstract
This composite theory is based on the concept of ‘Gestalt Function’ i.e. the acoustic needs of the 'whole animal' as the vertebrates evolved out of the primordial fish. During the first two hundred million years of terrestrial life, hearing was directed solely to substrate sound. When belatedly the mammals achieved air sensitive hearing they were tiny omnivorous creatures with functional needs comparable with those of the modern rat i.e. (i) A frequency analysing system for communication, and (ii) a low threshold ‘startle mechanism’ for the detection and localisation of nearby enemy or prey. It is herein suggested that
(i) The two functions are subserved respectively, the IHC and OHC
(ii) That the two systems evolved independently
(iii) That they have always acted independently
(iv) That they continue to do so.
This theory conflicts sharply with the widely held ‘Siamese twin’ theory that the two populations act in tandem to provide for the controversial ‘second filter'. It is shown herein that that theory conflicts with basic principles and is devoid of physiological validation.