Sir Morell Mackenzie's 1889 treatise examines speech as the physiological power to modify vocal sound into distinct elements, distinguishing it from language as the particular manifestation of this universal faculty. He traces the voice's origin to sexual attraction and emotional expression, arguing that vocal organs developed through practice and association with emotional states. Mackenzie establishes that vocal sound is produced solely in the larynx, a complex musical instrument, and clarifies misconceptions about voice production.
Silbo Gomero is a whistled form of Spanish used by inhabitants of La Gomera in the Canary Islands to communicate across distances up to five kilometers. Originally used by the Guanche people and adapted to Spanish in the 16th century, the language declined due to modernization and social attitudes but was revitalized through education policies starting in 1999, earning UNESCO recognition as intangible cultural heritage in 2009.