This paper examines the phonetic typology of pharyngeal sounds and presents external articulatory evidence for the phonological shift from uvular ejectives to pharyngeals in the Nootka dialects of Nuuchahnulth, based on the theory of the function of the aryepiglottic laryngeal sphincter mechanism. The phonetic structure of postvelar sounds is evaluated laryngoscopically in Wakashan and in Salish (cross-linguistically) to explain the historical phonological change through articulatory data. The physiological evidence suggests that uvulars may acquire phonetic characteristics of pharyngeals by adding an extra gesture to an existing sound. We conclude that postvelars can increase in complexity incrementally and that the complex pharyngeals of Wakashan and Salish can be explained through an articulatory phonetic hierarchy. The evolution of epiglottal components in each of the two phonologies is accounted for by the adaptation of existing glottal and pharyngeal elements. Implications for phonology are that features such as [RTR] and nodes such as pharyngeal can be attributed to the action of the laryngeal sphincter mechanism.