Have you ever heard an opera singing ape? Researchers in Japan have
discovered that singing gibbons use the same vocal techniques as
professional soprano singers. The study, published in the American
Journal of Physical Anthropology, explains how recording gibbons
singing under the influence of helium gas reveals a physiological
similarity to human voices.
The research was led by Dr Takeshi Nishimura from the Primate Research
Institute at Kyoto University, Japan. His team studied the singing of a
white-handed gibbon (Hylobates lar) at Fukuchiyama City Zoo, in
northern Kyoto.
A gibbon’s song is acoustically unique among primates, with a loud
melody which can be heard over two miles away. In the wild gibbons use
their songs to communicate with neighboring pairs, strangers and
potential mates through impenetrable jungle where visibility is poor.
“The complexity of human speech is unique among primates as it requires
varied soft sounds made by the rapid movements of vocal tracts,” said Dr
Nishimura. “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.”
To explore these similarities the team conducted the first acoustic
investigation on non-human primates using helium gas. The gas is famous
for making human voices appear high pitched by shifting the resonance
frequencies of the vocal tract upwards. The gas is useful for studying
animal vocal mechanisms as it increases sound velocity and resonance
frequencies.
The team recorded 20 gibbon calls in normal air atmosphere, before
recording 37 calls in a helium-enriched atmosphere. The resulting
sounds, which are available as audio files, reveal how gibbons can
consciously manipulate their vocal cords and tract to make their
distinctive sound.
“The lowest frequency of harmonics is amplified in a gibbon’s song when
performed in normal air,” said Nishimura. “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.”
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 always, and with minimal effort, adopt the complex vocal
techniques which are only mastered in humans by professional soprano
singers. This discovery suggests the development of complex vocal
abilities in humans was not due to unique evolutionary modifications.
Instead it shows that humans share the biological fundamentals of
vocalisation with other primates, but in speech have simply acquired
another of its most sophisticated forms.
“This is the first evidence that gibbons always sing using soprano
techniques, a difficult vocalisation ability for humans which is only
mastered by professional opera singers,” concluded Nishimura. “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.”
