Orangutan's spontaneous whistling opens new chapter in study of evolution of speech

Throughout history, human beings have used the whistle for everything from hailing a cab to carrying a tune. Now, an orangutan's spontaneous whistling is providing scientists at Great Ape Trust of Iowa new insights into the evolution of speech and learning.

In a paper published this month in Primates, an international journal of primatology that provides a forum on all aspects of primates in relation to humans and other animals, Great Ape Trust scientist Dr. Serge Wich and his colleagues provide the first-ever documentation of a primate mimicking a sound from another species without being specifically trained to do so. Bonnie, a 30-year-old female orangutan living at the Smithsonian National Zoological Park in Washington, D.C., began whistling – a sound that is in a human's, but not an orangutan's, repertoire – after hearing an animal caretaker make the sound.

"This is important because it provides a mechanism to explain documented between-population variation in sounds for wild orangutans," Wich said. "In addition, it counters a long-held assumption that non-human primates have fairly fixed sound repertoires that are not under voluntary control. Being able to learn new sounds and use these voluntarily are also two important aspects of human speech and these findings open up new avenues to study certain aspects of human speech evolution in our closest relatives."

Previous studies have indicated that orangutans and chimpanzees are capable of species-atypical sounds and vocalizations, but only under the strong influence of human training. Bonnie, however, was not explicitly trained to whistle, according to Wich and his co-authors – Great Ape Trust scientists Dr. Karyl Swartz and Dr. Rob Shumaker; Madeleine E. Hardus and Adriano R. Lameira, doctoral candidates at the Utrecht University in The Netherlands assigned to the Ketambe Research Center in Sumatra, where Wich is research co-manager; and Erin Stromberg, an animal caretaker at the National Zoo.

Scientists have long known that orangutans copy physical movements of humans, but Bonnie's whistling indicates that the learning capacities of orangutans and other great apes in the auditory domain might be more flexible than previously believed, Wich said. The behavior goes against the argument that orangutans have no control over their vocalizations and the sounds are purely emotional – that is, an involuntary response to stimuli such as predators.

Bonnie appears to whistle for the sake of making a sound rather than to receive a food reward or some other incentive. If asked to whistle, she is likely to oblige, another indication to scientists that she makes the sound voluntarily. ... - physorg

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