An adolescent orangutan called Rocky could hold the key to understanding how speech evolved in early humans.
Rocky, who was eight at the time of the study, was able to copy the pitch and tone of vowel-like sounds made by researchers even though those sounds are not part of orangutan’s usual repertoire of calls. This discovery suggests orangutans have the ability to control their voices and that humans’ great ape ancestors may have been able to develop a precursor to human speech.
As speech is a learned behaviour, it was previously thought that language could not have originated from great apes since they were not known to be capable of producing new sounds. Rocky, currently a resident of Indianapolis Zoo in Indiana, USA, has single-handedly turned that assumption on its head.
Wookies and grumphs
To get to their findings, researchers from Durham University played a vocal imitation game with Rocky. A researcher made random sounds by varying the tone or pitch of her voice and Rocky was encouraged to mimic those sounds in return for a treat.
Researchers are calling the sounds that Rocky made “wookies” – a unique vocalisation among the usual orangutan vocal repertoire. Rocky adjusted his wookies to match the human demonstrator and was able to distinguish the difference between low and high pitched variants of the sound.
Rocky’s wookies were compared with the world’s largest available database of orangutan calls and researchers found wookies were indeed a entirely new vocalisation for orangutans. The results suggest non-human great apes are able to achieve levels of vocal control that is comparable to that in humans and can do so in real-time conversational situations.
Birds can grasp the basics of grammar
“Grumphs,” vocal calls produced by orangutans in the wild, were found to occupy the same frequency range as wookies, but they are made using the exhalation of air rather than inhalation, making them significantly distinct from wookies.
It had been presumed that great apes have no control over the sounds they make, but this study proves orangutans have the capacity to control their own voices, said the study’s lead researcher, Dr Adriano Lameira of Durham University.
“This indicates 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.
“It 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,” he said.
Orangutans share 97 per cent of their DNA with humans, making them one of our most closely related species. They have been known to use modified human sign language and make paintings and drawings in captivity.
The study, published in Scientific Reports, builds on Lamiera’s earlier work where he found that orangutans are also able to make vocals calls at the same rhythm and pace as human speech.