Krystal D’Acosta:
Everett believes the conditions at higher altitudes may encourage the production of ejective phonemes [a basic unit of sound—a type of phoneme—which when combined with other phonemes create words]. These utterances require that the vocal cords are closed and raised. Everett holds that this is easier to accomplish at higher altitudes where atmospheric pressure is lower, which means that air pressure in the mouth and lungs is lower so it may be easier to force the vocal cords closed. Everett also proposes that the higher incidence of ejective phonemes at higher altitudes may represent a biological adaptation.