Move over, Renée Fleming. There’s a new diva on the block—a white-handed gibbon from the Fukuchiyama City Zoo in Kyoto, Japan. And though this small-bodied ape may never star in a Verdi opera, researchers have found that she belts out her song using the same vocal techniques that human sopranos use to sing to the rafters.
Received wisdom holds that human speech, which is unique among primate vocalizations, originated as a result of evolutionary modifications to our vocal anatomy. Recent studies have shown that key aspects of our anatomy and physiology related to speech are not specific to humans, however. The new research on gibbon song, published in the American Journal of Physical Anthropology, adds to that body of evidence.
Gibbons live in the dense tropical forests of Southeast Asia. The animals routinely sing to each other, presumably as a means of defending their turf and attracting mates in an environment where visibility is poor. Their calls are melodic and loud--audible more than two kilometers away.
To figure out how gibbons produce their distinctive songs, Takeshi Nishimura of Kyoto University and his colleagues studied the calls of a captive gibbon exposed to normal air and to helium-rich air, which increases sound velocity and shifts the resonance frequencies of the vocal tract upward, they explain. This effect helped the researchers test two hypotheses about the mechanism of gibbon song production.
The study results imply that the vocal source (the larynx) is not coupled to the vocal tract in gibbons, as envisioned in one of the hypotheses. Instead the two components are independent, as they are in humans. The sound originates in the larynx and then the gibbon actively manipulates the sound by changing the shape of the vocal tract, using the same techniques sopranos use to create their intense, high-pitched sounds. And just as sopranos change their mouth opening while singing, so too do gibbons open their mouths wider with rising pitch.
The researchers note that many primates have special anatomical modifications to their vocal apparatus that help them to produce their distinctive calls. Humans and gibbons, in contrast, rely primarily on enhanced neural control over their vocal anatomy.