Title Loss of Air Sacs Improved Hominin Speech Abilities Corresponding Author

In this paper, the acoustic-perceptual effects of air sacs are investigated. Using an adaptive hearing experiment it is shown that air sacs reduce the perceptual effect of vowel-like articulations. Air sacs are a feature of the vocal tract of all great apes, except humans. Because presence or absence of air sacs is correlated with the anatomy of the hyoid bone, a probable minimal and maximal date of the loss of air sacs can be estimated from fossil hyoid bones: Australopithecus afarensis did still have air sacs about 3.3 Myr ago, while Homo heidelbergensis, some 600 kyr ago and Homo neandethalensis some 60 kyr ago, did no longer. The reduced distinctiveness of articulations produced with an air sac is in line with the hypothesis that air sacs were selected against because of the evolution of complex vocal communication. This relation between complex vocal communication and fossil evidence may help to get a firmer estimate of when speech first evolved.