Rocky, an eleven-year-old male orangutan living at Indianapolis Zoo, offers clues to how human speech evolved, according to new research led by Durham University’s Adriano Lameira.
Orangutans (Pongo pygmaeus).
In an imitation ‘do-as-I-do’ game, Rocky, who was eight at the time of the research, was able to copy the pitch and tone of sounds made by the scientists to make vowel-like calls.
“We provide the first evidence for real-time, dynamic and interactive vocal fold control in a great ape during an imitation ‘do-as-I-do’ game with a human demonstrator,” Dr. Lameira and co-authors said.
During the study, a human demonstrator made random sounds with variations in the tone or pitch of her voice which Rocky then mimicked.
The researchers compared these sounds against the largest available database of orangutan calls collected from over 12,000 hours of observations of more than 120 orangutans from 15 wild and captive populations.
They were able to conclude that the sounds made by Rocky were different compared to the sounds on the database, showing that he was able to learn new sounds and control the action of his voice in a ‘conversational’ context.
“It’s not clear how spoken language evolved from the communication systems of the ancestral great apes,” Dr. Lameira said.
“Instead of learning new sounds, it has been presumed that sounds made by great apes are driven by arousal over which they have no control, but our research proves that orangutans have the potential capacity to control the action of their voices.”
“This indicates that the voice control shown by humans could derive from an evolutionary ancestor with similar voice control capacities as those found in orangutans and in all great apes more generally.”
“This opens up the potential for us to learn more about the vocal capacities of early hominids that lived before the split between the orangutan and human lineages to see how the vocal system evolved towards full-blown speech in humans.”
The findings were published this week in the journal Scientific Reports.
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A.R. Lameira et al. 2016. Vocal fold control beyond the species-specific repertoire in an orang-utan. Sci. Rep. 6, 30315; doi: 10.1038/srep30315
