Update: 7 January 2016
Koko the gorilla is again making headlines. She appears in a video calling on world leaders to take action on climate change. "Time hurry. Fix Earth! Help Earth! Hurry!" are among the words that Koko signs.
It might appear that Koko has mastered the ability to communicate a complex message using signs. But as the article below explains, she has been trained well to make certain sounds and gestures.
The video is a campaign message, so it is possible that she is copying the signs being asked of her, rather than sending us a message of her own.
Nonetheless, her unique skills are impressive and show that apes can learn some aspects of language.
In the gorilla world Koko is a bit of a celebrity. At least, to humans. She's known for her incredible sign language skills, learnt in her 40 years of living with humans.
She's a Western Lowland gorilla and started her training when she was one.
She blows "raspberries" with her tongue and was observed pretending to talk on the phone
If you've read the headlines, you could be forgiven for thinking that Koko was in the process of mastering the ability to talk. "The most famous gorilla is showing signs of earth speech" – wrote one influential website. "She is showing signs that she may be able to learn to talk" a newspaper wrote. You get the idea.
But is this true, is Koko really showing any such ability?
In short no. What Koko can in fact do, is manipulate her vocal chords to create an assortment of sounds. For example, she coughs on cue:
Well, I hear you say, that's not quite as exciting as a gorilla being able to talk. True, but it's still an interesting finding, one which - along with similar studies - is changing our idea of how speech evolved.
To understand why, I spoke with the man behind these new observations of Koko, Marcus Perlman of the University of Wisconsin-Madison, US.
Their grunts are not only meaningful, but can change over time
He sifted through 71 hours of footage of Koko and started noticing some "amazing vocal repertoires". His intention was to look at her gestures, not her vocal abilities, so he was surprised by what he discovered.
As well as her fake coughes, she also fakes sneezes, blows "raspberries" with her tongue and was observed pretending to talk on the phone.
These behaviours all require her to control her vocalisation and breathing. The observations are published in the journal Animal Cognition.
There has been a longstanding idea that all non-human primates, such as great apes such as chimpanzees and gorillas, were unable to control their vocal sounds at all.
It was thought their grunts were just automatic response to stimuli. It was also not believed possible for apes to learn new vocalisations.
These flexible sounds may have been the framework on which our language capacity was built
Because of that, the idea that "flexible vocal behaviour" was important to human speech was dismissed, says Perlman.
Instead, gestures were deemed more important and we have long known that apes can make distinct, meaningful gestures. The idea was that "maybe their gestures evolved into human language, and maybe the original language of our ancestors were more gesture-like," Perlman explains.
Koko, along with other studies, puts this idea to rest. For example, other research found that chimps changed the type of grunt they use to signal the word 'apple', to make it align with their new companions. This shows that their grunts are not only meaningful, but can change over time.
If apes have these vocal abilities, in addition to gestures, their flexible sounds may have been the framework on which our language capacity was built over the course of millions of years, says Perlman.
It's funny that there is so much excitement over the gorilla that coughs
This all points to one thing: the fact that apes are able to manipulate their vocal sounds suggests our common ancestor did too.
It's like a backwards puzzle, all other early-humans have gone extinct, so we can only look at living apes to infer how our extinct ancestors may have developed language abilities.
Koko, we must remember, grew up in unique circumstances and was immersed in human interaction from birth. Her repertoire of meaningful gestures is therefore unusually large.
What do other researchers think?
Joseph Devlin from University College London's department of experimental psychology, in the UK, also studies the evolution of language.
She exhibits conscious control of her breathing like we do
It's funny that there is so much excitement over the gorilla that coughs, he says. Still, though it sounds banal, "there is something cool here".
"Speech is impossible without cognitive control of breathing. So grunts, chuffs and the noises that other primates make might just be emotional vocalisations that occur automatically without conscious control.
"The fact that Koko can blow her nose or fake a cough when asked to demonstrates that she exhibits conscious control of her breathing like we do."
Language has many aspects to it. Koko's gestures and grunts may seem mundane but they represent crucial manipulations, the ability of which is important in everday speech.
Language in its full form may be unique to humans, but every species has traits which make them unique. As Darwin said, we differ from our closest relatives in degree, not kind.
And I have written before, many traits which we once believed were unique to humans are found in the animal kingdom.
"Perhaps what is unique to humans is that we may be the only species that has *all* of these abilities. But it is increasingly evidence that most, if not all, of the component abilities that make up language are also found in other species, and that’s pretty exciting."
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