Washington: Challenging the perception that humans are the only primates with the capacity for speech, new research has found that gorillas too can learn new vocal and breathing-related behaviours -- key requirements for human speech.
The study followed the behaviour of Koko the gorilla, best known for a lifelong study to teach her a silent form of communication, American Sign Language.
Koko has spent more than 40 years interacting with humans.
Marcus Perlman from University of Wisconsin-Madison in the US, and his collaborator sifted 71 hours of video of Koko interacting with humans and found repeated examples of Koko performing nine different, voluntary behaviours that required control over her vocalisation and breathing.
These were learned behaviours, not part of the typical gorilla repertoire.
Among other things, the researchers watched Koko blow her nose into a tissue, play wind instruments, and mimic phone conversations by chattering wordlessly into a telephone cradled between her ear and the crook of an elbow.
"She does not produce a pretty, periodic sound when she performs these behaviors, like we do when we speak," said Perlman.
"But she can control her larynx enough to produce a controlled grunting sound," Perlman noted.
Koko can also cough on command -- not particularly ground-breaking human behaviour, but impressive for a gorilla because it requires her to close off her larynx, the researchers found.
These behaviors are all learned, Perlman said, and the result of living with humans since Koko was just six months old.
"She shows the potential under the right environmental conditions for apes to develop quite a bit of flexible control over their vocal tract. It's not as fine as human control, but it is certainly control," Perlman said.
This suggests that some of the evolutionary groundwork for the human ability to speak was in place at least by the time of our last common ancestor with gorillas, estimated to be around 10 million years ago, noted the study published in the journal Animal Cognition.