Gibbons effortlessly use the same techniques as professional opera singers when calling out to other animals, scientists found by listening to the squeaky songs of one of the apes on helium.
The Japanese study provides evidence for an unusual physiological similarity between gibbons and humans.
"The complexity of human speech is unique among primates as it requires varied soft sounds made by the rapid movements of vocal tracts," lead researcher Takeshi Nishimura, from the Primate Research Institute at Kyoto University, said in a statement. "Our speech was thought to have evolved through specific modifications in our vocal anatomy. However, we've shown how the gibbons' distinctive song uses the same vocal mechanics as soprano singers, revealing a fundamental similarity with humans."
Nishimura's team analyzed 20 melodious and loud calls of a captive white-handed gibbon (Hylobates lar) in a normal atmosphere, followed by 37 calls in an environment infused with helium.
Sucking in helium from a balloon gives humans a squeaky, high-pitch-sounding voice, because the gas, which is less dense than air, pushes the resonance frequencies of the vocal tract upwards, but doesn't change the sound at its source. An analysis of the gibbon's squeaky songs suggested that the same is true for these apes. Like humans, the origin of the sound of a gibbon's call, which occurs in the larynx, is separate from the vocal tools used to modify it, the research showed. [Listen to Gibbon Calls]
What's more, the analysis demonstrated gibbons have expert control over the tuning of their vocal cords and tract when singing — an ability that is important to the subtleties of human speech and is mastered by soprano singers.
"This is the first evidence that gibbons always sing using soprano techniques, a difficult [vocalization] ability for humans which is only mastered by professional opera singers," Nishimura said. "This gives us a new appreciation of the evolution of speech in gibbons while revealing that the physiological foundation in human speech is not so unique."
The study was published this week in the American Journal of Physical Anthropology.