Their report this month in the American Journal of Physical Anthropology finds that gibbons, the southeast Asian primate, vocalize in a very similar way to classically-trained human sopranos, when exposed to helium gas.
You can hear what that sounds like here.
(Compare it to a gibbon's normal call here.)
The researchers first recorded those normal gibbon calls, then recorded their singing in a helium-infused room. The scientists noted that the apes make their distinctive sound by consciously manipulating their vocal cords and vocal tract.
"The lowest frequency of harmonics is amplified in a gibbon's song when performed in normal air," said the lead author in a press statement. "However, in a helium-enriched atmosphere the tuning of the vocal cord vibration and the resonance of the vocal tract are altered as the gas causes an upward shift of the resonance frequencies."
The press statement continues:
This supports the theory that, as with humans, there is independence between the origin of the sound and the vocal tools used to manipulate it.
This shows that gibbons use the same process for producing speech as humans, whereby acoustic sound originates from the larynx and is controlled by a filter, determined by the shape of the supralaryngeal vocal tract. This manipulation forms speech and is known as the 'source-filter' process of speech production.
Singing gibbons use the same complicated vocal techniques usually only heard in humans in professional soprano singers.
So what's the point?
These findings suggest that our complex vocal abilities are not unique to human evolution. We share the physical capacity for speech with other primates -- which isolates our intellect, and not our vocal cords, as the primary bestower of our gift of gab.
Photo: Thomas Tolkien/Flickr