We're not the only singing simians. Not only do gibbons sing, but a new study of one singing, helium-breathing gibbon shows they use the same vocal technique as human sopranos.
"This is the first study to show a non-human primate using a mechanism similar to humans to make the very distinct vocalization of songs," said primatologist Takeshi Nishimura of Japan's Kyoto University.
In the wild, gibbons produce loud, melodious vocalizations, ideal for communicating in the dense Southeast Asian jungles where they live. The tones are difficult to analyze, though, and are actually more amenable to study in helium-rich air, in which sounds travel faster and certain frequencies shift to a higher pitch.
To study the songs' acoustic properties, Nishimura and colleagues placed a female white-handed gibbon named Fuku-chan in a chamber with helium-enriched air, then analyzed her crooning (sidebar). The results were reported August 23 in the American Journal of Physical Anthropology.
Two hypotheses exist for how gibbons produce sound. According to one, their oral and nasal pathways could resonate in tandem with the folds of their larynx, where sounds are produced, so that their vocal system behaves like a musical wind instrument. Alternatively, the vocal system could be more human-like, in which vocal tract and larynx resonate independently.
This allows humans to amplify the lowest-pitched sounds differently from the highest-pitched. Nishimura's team found just such a division in Fuku-chan's song. According to Nishimura, human speech was long believed to arise from unique anatomy and physiology. These results suggest that our anatomy isn't so unique.
The study "illustrates the broad applicability of source-filter theory" – the fancy name for how how humans vocalize – "to nonhuman animals," said evolutionary biologist and cognitive scientist Tecumseh Fitch in an email.
Fitch, who was not involved in the study, has demonstrated in his own research that human speech relies on neural control of the vocal system, rather than a unique anatomy. The new study indicates that gibbon vocalization works similarly.
What's more, Fuku-chan's singing technique resembled a human soprano's: she modulated it in a way that amplified her voice.
Gibbon song is quite literally a far cry from the musical stylings of sopranos like Maria Callas. But whereas human sopranos spend years perfecting their technique, according to Nishimura, "it's easy for gibbons."
Citation: "Soprano singing in gibbons." By Hiroki Koda, Takeshi Nishimura, Isao T. Tokuda, Chisako Oyakawa, Toshikuni Nihonmatsu, Nobuo Masataka. American Journal of Physical Anthropology, August 2012.
